Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubenit on August 14, 2013, 08:57:20 am
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I've posted this once before but couldn't find my original post doing a "Search" so I'll post this again.
I am talking to someone who is interested in the idea of me building them a PreAmp that can be plugged straight into a PA system.
So, I like the D'Mars ODS clean & overdrive. And I like the FX onboard. My thinking is to build this with the hopes that it will work reasonably well into a solid state PA system. I certainly would anticipate a warmer sound with the tube then just plugging straight into pedals and the PA which is what the individual is currently doing.
My main questions are:
1) Would this work plugging into a PA system?
2) Would the output jack be the same as the input or FX jacks? (shortening)
3) I am presuming that with NO power tubes that running this preamp without
it being plugged into the PA or a speaker will not be a problem (compared
to running an amp without plugging into a speaker)
4) Would it be OK to just ignore nodes A and B and simply use nodes C and
D for the preamp setup? (In other words no problems with not using A and B
connected to anything, but have them there for filtering?)
With respect, Tubenit
I am also thinking that IF somewhere down the line this person wants an entire amp with power section and speaker that I could do what HBP and Timbo have done with an upstairs & downstairs chassis. I would use a separate PT & OT for a lower chassis and build an LTPI that is point to point and into a push/pull power section.
I'm thinking that instead of B+ umbilical cord, I could have a preamp head sitting on top of a speaker cab with a power amp. And the only umbiical cord would be the signal instead of voltages.
In fact, one could build this preamp and then build a power amp section using various tube types like GlennJeff has done. Have a power amp with the capability of EL84's or 6V6/6L6.
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Hi Jeff.
Plans looks interesting. I built some guitar preamps and they sounded remarkably well when pushing SS power amps.
About your questions:
1) Yes;
2) Not necessarily;
3) No problem that I can report at all. I tested them on the bench with no load attached to output expect scope probes and it did not catch fire, unlike amps when pushed without speaker cab/proper load;
4) I would keep the filtering and possibly add some capacitance to it. I believe you are also aiming for low noise power supply.
IMHO, I would employ a CF stage after your FX level instead of running it straight from the plate. 12AU7/12AT7/12BH7/ECC88 are triodes worth experimenting with CF and maybe some pentodes too.
I like your idea of preamp having it's own PT. As you said, later on you can build a poweramp to suit your friend's needs.
I attached an AC CF output stage that I used on one of the pres.
Let me know whether I can help you further.
Happy hunting!!
Best Regards
R.
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Rzenc,
Hey, THANKS so much for the information and help! I truly appreciate it and it's nice to hear from someone with actual experience trying to do this.
If you would explain the CF idea after the FX. It has a CF going into the FX almost exactly like the one you've drawn. All three of my amps have this FX on board and it seems to work flawlessly, IMO.
Is the CF needed there for going out to the SS power amp? Is that the reasoning behind it?
Thanks and with respect, Tubenit
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Is the CF needed there for going out to the SS power amp? Is that the reasoning behind ?
Check out input impedance on SS PA amps. Some have it ~10K. IMHO, you will be better providing about 10x less that, say ~1K to minimize inserction loss. That ckt should be around 600ohms Z.
Also, the lower out Z is supposed to handle noise around cable connection and 'shield' it against external interference.
Also, the last stage is a gain stage with high amp factor and output impedance around 40K. The CF would isolate it from PA input stage and help to better transfer the integrity of your processed guitar signal.
The main idea behind it is to buffer the preamp output stage. Thus helping to isolate from noises and improve signal transfer.
Edit: CF stages may introduce some compression effects too. Which may or not help.
Hope this helps!
Best Regards
R.
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You're saying to add a CF at the end of the FX signal chain, so that the CF is just prior to going into the ss PA system?
I agree with rzenc about using a cathode follower (or source follower as in your drawing). A solid state amplifier will likely have a low input impedance that will load your hi Z tube signal considerably.
Doing it this way will improve the tone into the PA? Is that correct?
I think the follower will have minimal impact on the tone.
Something else to consider... Rzenc is discussing sending your preamp signal to a POWER AMP. The signal level from your preamp will likely be a good match for a power amp input. But... Your preamp signal level will likely be much too hot to send to a mic input on a PA system. If that's the case, you will need a voltage divider at the output of your preamp. Maybe even use a switch at the output to select high level or low level. However, if your PA accepts line level inputs, no need.
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Steve,
Man, I always am grateful for your help! Thanks!
One thing that I was not thinking thru correctly was noting that the Power Amp and a PA system are not the same thing. I was erroneously not making the distinction that needed to be noted.
I am thinking that the FX level pot should function as the voltage divider that is needed prior to the PA system?
Assuming this guy wants this built, I'll definitely include the CF at the "end" of the FX prior to the PA.
Thanks and with respect, Tubenit
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I have an impedence adaptor but I think it's the "wrong" kind & would need more adaptors to make it work. It's lo-Z to hi-Z & I'm understanding that I want the opposite.
http://www.sweetwater.com/store/detail/LittleIMP/ (http://www.sweetwater.com/store/detail/LittleIMP/)
Tubenit
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cathode or MOSFET follower will drive the best and what you need with either is reduction in signal (line level) to the SS amp. you can do this with a Cc 10k-15K : 150/600 ohm transformer or a divider network. the source follower or cathode follower's output signal will likely be over 100Vpk - that'll kill most SS amp inputs. the advantage with the transformer approach is the line-side load can be configured balanced or un-balanced. you'll want to design so that the full volume output to the SS amp is around 2Vpk. it really helps to have an o-scope with this kind of work.
--pete
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Related thoughts - how long is the cable fun from the preamp to the power amp. If more than 10' you should consider a balanced line out. That would be a 3 conductor cable terminating in either TRS plugs, or XLR. Lundhal has schematics on its website for the things I mention in this post.
As Dummyload says impedance matching from the hi-impedance output of the preamp to the low-impedance (hi-Z) SS input is a concern. This can be addressed with a matching tranny inside the preamp to drive a balanced line-out. You may consider 2 lines out: one hi-impedance for a tube power amp, for which your CF schematic is fine; the other low-impedance to feed a SS amp or effects loop.
For the fx return, as rzenc says: impedance matching may again be a concern. A CF input is one alternative; also, see Merlin's book for a tube CF input circuit. "Designing Tube Preamps for Guitar & Bass". Another alternative for the fx return, again, is a matching transformer, this time from low to high impedance. You can build both TRS and/or XLR jacks into the preamp chassis - and maybe hi-lo impedance SW's - to dispense with the need for adapter plugs which may vanish when needed.
Impedance matching is a PITA. I feel your pain. I'm grappling with the same issues, having managed to avoid them for years.
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THANKS guys! I'll study your responses and help and figure out what is a reasonable risk approach and go from there.
Always appreciate the input and responses!
With respect, Tubenit
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Pete,
Thinking about what you said while mowing the yard. ............. :think1:
Any chance you can take my schematic and modify it to show the transformer placement. I'm thinking this might be between the CF and the FX level pot? I attached the SCH schematic to be changed to show your idea.
2nd question: Will this change the preamp tube tone?
3rd question: Any chance you already have a source for the trannie that you're mentioning? IF not, I can look for Hammond or Edcor.
4th question: Is it reasonable to build this first with out the transformer & then try it and IF it's not what is wanted then add the trannie?
With respect, Tubenit
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I attached an AC CF output stage that I used
Regarding the CF schematic, R101, the grid leak, should be connected to the grid of the Triode.
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This is a bit longwinded, sorry, just trying to clarify what others have already stated. Hope I don't create more confusion.
If your adapter is a transformer it may work OK wired the opposite way tubenit, just don't drive too much signal into it. Here is a schem, may need tweeking with regards to levels. Low Z to Hi Z / Line to Mic / Unbalanced or Balanced transformers are a very standard component at any electronics store that caters to audio guys. You get the quality that you pay for often. Your looking for 10 K (to 100 K) unbalanced Line to 600 Ohm balanced Line to drive a long cable run to a mixing desk or a typical balanced amp input.
If you use a CF or MOSFET follower this "Hammond 140QEX CHASSIS MOUNT" should do the job. (http://www.hammondmfg.com/pdf/140QEX.pdf (http://www.hammondmfg.com/pdf/140QEX.pdf)) but you may need to lower the value of the output pot a little or a lot.
Here is another possibility http://www.tubesandmore.com/products/P-T42TM022 (http://www.tubesandmore.com/products/P-T42TM022)
Two issues really:
1) providing the correct signal voltage for the actual input that he is plugging into. (Is he plugging into a MIC input - need very low signal. If plugging into LINE input need about 1/2 to 2 V peak signal.)
2) Preventing signal degradation if the signal is to be transmitted over a very long cable, a long cable looks like a capacitor to ground and will lose lots of high frequencies if not driven by a low impedance source, such as a CF or MOSFET FOLLOWER. Low impedance balanced cable also prevents HUM from being picked up over long cable runs.
You could also just use a resistive divider to get the right signal for your clients specific application but best to provide a more general solution in case his circumstances change. The potentiometer after the MOSFET follower should provide all the adjustment needed, a transformer adapter will take care of signal degradation and noise pickup (impedance matching).
The inclusion of a transformer also helps prevent strange ground loops between guitar amp, PA and microphone and provides a small increase to the electrical isolation between the various components of the "live gig" sound system thereby improving electrical safety to a small degree.
All the best.
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Any chance you can take my schematic and modify it to show the transformer placement. I'm thinking this might be between the CF and the FX level pot? I attached the SCH schematic to be changed to show your idea.
i attached a schematic of something RicharD and i built about 4 years ago. it's the output section of a bass preamp we built. ours had a NE555 one-shot delay timer coupled to a relay that is a mute feature to avoid power on/off thumps noise and other weirdness as the tubes warm up or fade out.
your plan seems like it will work. my only concern is the output level may be too high and could damage downstream equipment. you really should get an oscilloscope to aid with testing and confirmation this design. if the SS amp you're using doesn't have input over-volt protection you could easily fry it.
2nd question: Will this change the preamp tube tone?
probably. how much? unknown.
3rd question: Any chance you already have a source for the trannie that you're mentioning? IF not, I can look for Hammond or Edcor.
http://www.edcorusa.com/p/159/xsm10k-150 (http://www.edcorusa.com/p/159/xsm10k-150)
http://www.edcorusa.com/p/160/xsm10k-600 (http://www.edcorusa.com/p/160/xsm10k-600)
http://cinemag.biz/output/PDF/CM-2810.pdf (http://cinemag.biz/output/PDF/CM-2810.pdf)
http://www.ebay.com/itm/Altec-Peerless-Transformer-15095a-/190883089186 (http://www.ebay.com/itm/Altec-Peerless-Transformer-15095a-/190883089186)
the edcor's are a bargain i've heard and read good things about them but have no experience with the small signal stuff; of the two i'm most familiar with, the altec is best sounding overall; the cinemag is the most neutral sounding. we have tested the altec and cinemag in our bass pre-amp. we liked the altec best, but they are drying up, hence why we trialed the cinemag. the cinemag will run about $70.00/ea last time i priced them. hammond has some stuff. i've never bothered with it.
4th question: Is it reasonable to build this first with out the transformer & then try it and IF it's not what is wanted then add the trannie?
yes. good small signal transformers are costly.
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Pete,
Oh man, I hate revealing how ignorant I am about this stuff. :BangHead: :icon_biggrin:
I have had ZERO formal training in electronics. Not even one hour's worth in a classroom ever. I don't know if I've ever actually seen an oscilloscope in person? And would have no idea how to use it at all. Almost everything I've learned about electronics has been from this forum and reading some of Kevin O'Connor's stuff.
:dontknow:
Due to my lack of knowledge, I was thinking I could just build this thing, plug it into a PA system with a guitar cord and have it work just fine? I didn't realize that there would impedance issues and that it could actually "fry" something down stream.
So, in light of that, I want to explore options and try to come up with an idea that is suitable for my lack of knowledge & within my reach.
How about the idea of building this with the mosfet CF at the end of the active FX and then plugging into a "device" that then plugs into the solid state PA? That would allow me to have a tube preamp set up that could then also be plugged straight into an upstairs/downstairs arrangement using another chassis for an LTPI and tube power amp.
Would this device accomplish what is needed for the concerns you have expressed? IF you can bear with me a little longer, I sure would appreciate the help and advice.
http://www.musiciansfriend.com/pro-audio/motu-zbox-guitar-impedence-adapter (http://www.musiciansfriend.com/pro-audio/motu-zbox-guitar-impedence-adapter)
OR maybe this direct box:
http://www.musiciansfriend.com/pro-audio/whirlwind-imp-2-standard-direct-box (http://www.musiciansfriend.com/pro-audio/whirlwind-imp-2-standard-direct-box)
In other words, I'd like to be able to build the design with the schematic I posted (which I can do successfully), plug into some reasonably inexpensive device that addresses the impedance issue and then plug straight into the PA system.
With respect, Tubenit
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The more I am thinking about this ........... the more I am thinking I'd like some external device that is between the tube preamp and the solid state PA .
OK, I found an article "how to convert high Z microphone to low Z". I don't know if this would apply or not?
You don't need an Op-Amp, you don't need a transformer. A simple JFET like a J310 will work perfectly.
Use a 9V battery to power the JFET drain. Connect a resistor equal to the element impedance from gate to ground. Put a 270 ohm resistor from source to ground (battery negative and mike ground). Pick the audio off the source with a 1uF or so capacitor. Feed the mic into the gate via a .1uF cap.
You have an instant $1.00 conversion. I use this with D104's on my ICOMs and Yaesu's.
http://www.eham.net/ehamforum/smf/index.php?topic=26560.0 (http://www.eham.net/ehamforum/smf/index.php?topic=26560.0)
With respect, Tubenit
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tubenit,
Sorry we frightened you with "geek speak". In practice it should be very simple to accomplish, especially for someone of your experience.
How about, I go down to the audio shop tomorrow, pick up a transformer and wire it into my D'Mars and then send you some pics, schematics and photo's. I've got mixing desks and SS PA amps here to test it all and make sure it's peachy.
The jfet solution is for microphones which have a very small signal to start off with. You are needing to adapt a rather large signal in such a way that it will be adjustable for different situations. You basically have your FET there already, it's just a MOSFET, and with a few extra resistors around that output pot could be made to work fine under most circumstances. The transformer idea is "the more professional" solution. The chances of blowing something up downstream are zero if you start with the volume turned down and then work it up slowly.
All the best.
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How about, I go down to the audio shop tomorrow, pick up a transformer and wire it into my D'Mars and then send you some pics, schematics and photo's. I've got mixing desks and SS PA amps here to test it all and make sure it's peachy.
Wow! That is remarkably generous and kind of you! IF ......... you have time, convenience and some interest, that'd be great.
However, if you're reasonably confident that this approach will work and I'm over complicating it in my thinking and response, .......... then maybe just confirm what Pete has posted in the schematic with trannie? I'd hate for you to go to all that effort if the schematic is already answering the needed questions?
If that schematic will work as drawn, then I think maybe I'd be good with it.
If you'd alter the schematic in some fashion, then I'd be interested in hearing about it.
I probably will not start on this build for about a month from now, cause I want the player to come over and try my 3 amps out first & listen to his playing and response to what tone he is looking for.
You guys are great! I sure appreciate the help with this type of a challenge!
With respect, Tubenit
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Well,
Pete's schem looks like he's running the transformer from a normal high plate gain stage to give a lo z out and using a second cathode follower to give a hi z out. Sure it works fine but need to get his input on that.
I'm talking about running a transformer off of your last MOSFET follower, as per the diagrams I included, which also should work fine.
I did want a studio line out facility on my amp so I'll do it both ways and get back here with the outcome.
All the best.
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Whoops - it was Jensen that has the schematics for their trannies. Here's a tube driven, line level output circuit: http://www.jensen-transformers.com/datashts/10k611m.pdf (http://www.jensen-transformers.com/datashts/10k611m.pdf)
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GlennJeff and Jjasilli,
THANKS guys! Appreciate the help alot. Once I get a schematic clearly defined, I think I can figure out how to make this work OK.
With respect, Tubenit
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Whoops - it was Jensen that has the schematics for their trannies. Here's a tube driven, line level output circuit: http://www.jensen-transformers.com/datashts/10k611m.pdf (http://www.jensen-transformers.com/datashts/10k611m.pdf)
thanks, jj for that link. now we have an alternative to the cinemag and altec.
--pete
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...normal high plate gain stage to give a lo z out and using a second cathode follower to give a hi z out. Sure it works fine but need to get his input on that...
it's actually a plate follower. it works very well.
the hard work is already done. on our bass pre those two 12AU7 are fed by a bax-stack and what is basically the it's second channel of the ampeg SVT bass head with a minor tweak to the cut filter.
a later mod was to add a 1M level control to the plate follower; it replaced the 1M grid-leak/FB of VXb; it uses the wiper as the input. this mod allowed RicharD to adjust the level being fed to the mixing board independently of what's he's feeding the stage amp.
the schematic i posted is the output stages of our pre in the links below.
http://sotxampco.com/Images/KB02.jpg (http://sotxampco.com/Images/KB02.jpg)
http://sotxampco.com/Images/Kelsey-Board.jpg (http://sotxampco.com/Images/Kelsey-Board.jpg)
--pete
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It seems to me you could put a SPDT SW on the Jensen CF output: then one leg to the line driving tranny per the schematic; the other leg to a phone jack to connect to a tube power amp, like you usually do.
Also, you can put a ground lift SW in the XLR connection. This is a handy option that might eliminate hum in case of ground loops at the venue.
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in jj's plan you need to add a coupling cap between the wiper of 250K (FX out pot) and pin 7 of V4b.
--pete
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in the "pete" plan, delete the 250K pot and make it fixed resistor value experiment with 100K-1M. increase/decrease .033 coupling cap value accordingly.
--pete
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Funny thing is its cheaper to buy the whirlwind DI box that the jenson trans thats inside it.
Bill
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> I have an impedence adaptor but I think it's the "wrong" kind
You can turn it around.
BUT it is for MIKE level. Much lower Power than Line level. It will distort bass.
I'm not sure why there are two "return" jacks on your first drawing?
I'll assume V3a carries a strong guitar-level signal, suitable to go to an effects chain. Then V3b should have a gain of about 10, to bring 200mV up to 2V to drive a big power-amp's input.
This must be LOW impedance. It may face 10K or less. 2.8V into 10K is 3mA, so the tube doing this work should be flowing 6mA. A MOSFET may be convenient. Alternately use one of the small power pentodes (or triode-pentode {6BM8?}) and a Reverb Transformer so you have a Watt output which will drive any Line input or a speaker for the bedroom.
> something RicharD and i built
That's fine also.
There should also be a 10:1 divider to output 200mV into a PA board's line input (they can usually handle such a level; if the sound dude is a fool, he can take the "power amp" tap instead).
For total flexibility, you want to drop below 100mV and then feed a 7:1 transformer. That part you have will work but the connectors are wrong, pull the guts out.
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That part you have will work but the connectors are wrong, pull the guts out.
what part???
--pete
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Well, for first experiment, made it as simple as it gets, and it worked surprisingly well.
This was using a el cheapo 600 Ohm to 10kOhm audio matching transformer, $5 from the local audio hobby shop.
(SPECS http://www.altronics.com.au/index.asp?area=item&id=M0712 (http://www.altronics.com.au/index.asp?area=item&id=M0712) )
Needs a small filter cap across the primary of the transformer to roll off some high frequencies as it will be running into a PA, effectively a very large mid quality hi fi, no roll off like with a guitar speaker.
Bear in mind that FX return pot gives you a volume control.
Changing source resistor ( much smaller, WAG 10k Ohm, matching impedance of transformer primary) and coupling cap (bigger, like .47uF, Xc= 3k3 at 50 Hz) may be a way to optimise.
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By all means leave the source resistor as 100k, I tried it at 22k with 1uF bypass and got a lot more signal but it might have been a bit "compressed" and grittier.
It depends on how much signal you actually need for the final application. I was running this into a mixing desk, the desk has plenty of adjustment for 100k source resistor. You will need to increase the coupling cap to prevent bass roll off.
Your schematic looks great for adjusting treble roll off as well just need to tweek values till you get it right. Maybe 50k - 250k pot rather than 1 Meg, season with capacitor to taste (WAG .01uF).
Pete's idea of using a tube, well, tubes are always better. :laugh: Depends on real estate, cost considerations and other dull worldly constraints. I'll have a go at Pete's over the next day or so. I also have a somewhat better quality transformer to try out as well.
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tubenit,
What I'm seeing on Pete's schematic is different to your take on it (I think).
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What I'm seeing on Pete's schematic is different to your take on it (I think).
I don't know what that means? :dontknow:
Pete's idea of using a tube, well, tubes are always better.
OK, then let's work with Pete's plan. :icon_biggrin:
My main goal is to preserve the D'Mars OD clean, OD & FX tone. And then send it effectively into a PA system without losing the integrity of the tone.
in the "pete" plan, delete the 250K pot and make it fixed resistor value experiment with 100K-1M. increase/decrease .033 coupling cap value accordingly.
There is a point with the D'Mars that lowering the FX level below "4" begins to lose some of the tone I like.
So what I want and need to do is make it so I can keep that tone going into Pete's impedance topology.
So my main concern is that I want to keep the FX Level pot at around 100k and then use the 220k to drop some signal if needed? I'm concerned a 25ka pot for the FX level is going to mess with the tone in a way that I won't like.
Q1: Is that a reasonable plan?
Q2: Is the DPDT needed after the iso trannie? Can I just eliminate that?
Q3: Any drawing errors that I've done with Pete's impedance topology that you can see?
Q4: No ground is needed on the primary side of the iso trannie? Correct?
Thanks for the help guys!!! I'll be building this for someone else so I want to nail this down as close as possible to a reasonable DRAFT.
I've got both 12AU7 and 12AV7 tubes available for this.
With respect, Tubenit
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tubenit,
Q1.
It will be somewhat different as it's no longer driving a PI, you are the Tsar of Tweak however, so go with your plan.
Q2.
The DPDT is there for convenience and flexibility, but not absolutely necessary.
Q3 & Q4.
Go back to reply 14 and re examine DL's schems, I think you may have slipped up. The OT does need a ground. (As always I may be wrong). I believe his plan is two independent circuits, one for Balanced Send to Desk/PA (long cable run), and one for Hi Gain / Hi Z unbalanced send to stage amp / SS Power Amp (short cable run). They are kind of drawn around a central ground wire so it's a bit of an optical illusion.
ALSO, the MOSFET "MAY" or "MAY NOT" be needed if going with pete's (DL's) topology.
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GlennJeff,
THANKS for the response and clarification!
With respect, Tubenit
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OK, I want to toss out an alternative plan.
The unit will probably not be plugged into a tube power amp and only be used with a solid state PA.
I want to try to keep the FX level pot with a high enough value (100k-250k) to preserve tone. #1
Assuming that the signal eventually needs to be lowered ........... how about using a 100k into the iso trannie? #3
(in other words, I want to preserve the D' Mars OD tone going into the impedance topology & lower the gain coming out of the impedance topology instead of compromising the D'Mars OD tone.)
IF I use this approach then I can eliminate the mosfet CF and use the first triode of a 12AU7 for the CF at the end of the FX.
I am thinking I can use a simple spdt to switch between high and low Z? #2
I have now grounded the lower part of the iso trannie primary Is this correct now? # 4
I have also eliminated the dpdt into the lo-Z jack. #5
How about this alternative plan? Any comments, corrections, edits, errors ................. ???
Can you guys give a thumbs up with this being a reasonable plan with my objective to preserve the D'Mars OD tone as best I can into a ss PA system?
In other words, can you name each idea #1, #2, etc........ and OK or edit it when you give your response.
THANKS for the help!!
With respect, Tubenit
EDIT: Left schematic to explain questions but the schematic was NOT used
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Hope others with more experience can reply also but,
#0: I think you need to be clear about what exactly it is being plugged into, I'm assuming some MIXER DESK portion of a small club PA from your description.
#1 DL's plan will probably work OK with 250k input pot.
I guess what I was saying was "If it's different circuitry after the FX return then it may sound different, it may be an insignificant difference however."
#2 Couldn't say. (Will that CF alter your tone? You probably know that from experience).
The Hi-Z branch may need to be field tested (Looks good)?
#3 Should work OK
#4 Correct
#5 Not a problem if the unit is only plugged into one plug at any one time.
You are the one with the really sharp ears, maybe breadboard a few ideas and make a decision based on results.
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GlennJeff,
Excellent! Thanks for the replies on each of those items! Very helpful & encouraging to me.
I can always put a resistor across the 250ka FX level pot to lower the value if needed.
The CF does alter the tone but not necessarily in a bad way. Just different. I think it's a little more compressed?
Not exactly sure what type of unit it's going to be plugged into but will find out within a week or so.
After Pete (DL) looks at this, and hopefully gives similar "thumbs up" responses. I will presume it is a reasonable risk and will post a layout for it for others to see.
Ultimately, I will just have to build it, try it in "that" PA system and then tweak from there. I've always presumed that I will need or want to tweak something.
With respect, Tubenit
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Am out of town. But briefly for a level out control I think you can put a pot in place of the grid leak resistor on the input feed to the Jensen CF schematic. (That prior part of the circuit is not shown in that schematic.
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I still think that a pot before the transformer is not only superfluous, but may screw with impedance. The pot before the driving tube should be fine.
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I still think that a pot before the transformer is not only superfluous, but may screw with impedance. The pot before the driving tube should be fine.
Think I can get away with a 100k or 250k pot prior to the driving tube? Reason I ask this is because I lose an important piece of the D'Mars ODS tone when I dial a 250k pot down below around "4'?
So I was wanting to preserve the D'Mars tone as best as possible and then find another place to drop gain/volume levels.
IF I can get away with at least a 100k pot prior to the driving tube, then I don't mind losing the "superfluous" pot before the trannie.
with respect, Tubenit
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I mean the pot before the 12au7 tube that drives the fx loop
EDIT. GE data sheet for 12au7 shows typical circuits for a grid leak resistor from 100K to 500K. So you're fine.
Again, the issue with a pot before the edcor or Jensen tranny is that the resistance of the pot will be in parallel with the tubes internal plate resistance, the plate load resistor, and the primary winding of the tranny. OTOH the pot before the tube will control vol w/o introducing new issues.
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jjasilli,
THANKS that's useful info.
With respect, Tubenit
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Ok. A pot or fixed resistor before the edcor tranny was bothering me in regard to impedance matching the output of the 12au7 to primary of the edcor. That tube's plate resistance is about 8K in parallel with the plate resistor is about 7K, in parallel with the 100K shunt resistor is about 6K. This is feeding a 10K primary. This will work but probably cause frequency loss which I don't know how to calculate.
I don't understand the purpose of this resistor.
I'm guessing the Jensen schematic will give hi-fi results with no frequency loss. OTOH, using the Rule of Ten's in your schematic, a 100K plate resistor and no shunt resistor should keep you within about 20% of the edcor's primary impedance.
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I don't understand the purpose of this resistor.
Pete had it in his schematic, so I put it in. I am presuming that it's simply dropping some gain/volume?
I can always bypass it and compare.
with respect, Tubenit
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I think you need a low impedance source driving a high impedance load to prevent frequency loss / loading effects jj.
That circuit, as it is drawn, looks like it needs to be built so it can be assessed, and should get you pretty close to where you want to go.
I would build it like this, but I'm a bit strange. :icon_biggrin:
All the best.
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That's impedance bridging. But preferably the output impedance of the driving tube circuit is designed to match the input impedance of a tranny's primary coil.
I agree that tubenit's plan should work.
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Let's agree to agree that we are not necessarily disagreeing. :l2:
But preferably the output impedance of the driving tube circuit is designed to match the input impedance of a tranny's primary coil.
Yep.
6K source : 10k load - good enough for rock and roll.
Lose the 100K and up plate resistor if you like it a bit more spicy (7K : 10K).
All the best
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Guys,
I really truly appreciate the help! I will go back thru the thread and delete previous schematics that I posted.
This will be my prototype with the understanding that things will need to be tweaked. Pete suggested getting two of the Edcor trannies so that if the signal is too hot, I can change to a more suitable trannie.
Unless anyone sees any significant errors, I'll use this.
Many thanks to all of you!
With respect, Tubenit
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Per a previous post I too am grappling with these issues, and this thread is very helpful. My understanding is that the 12au7 's output is not supposed to have a load within the fx driving circuit, including the edcor tranny. Rather the load should be presented by the receiving device, in this case an SS power amp. Modern SS devices, at their input, want to see a source impedance of 200R - 2000R. The edcor tranny satisfies the source impedance requirement of the receiving device. But, again, the load on the fx output circuit in the preamp comes not from within, but from the outside device it is driving.
This is just like power tubes matched to the primary of the OT, driving a speaker load. The plate impedance of the power tube ideally is matched to the impedance of the OT primary. Though a load is needed, there is no load within that circuit. The load comes from the outside - from the device that is driven, in this case the speaker. The OT matches the output impedance of the power tube(s) to the input impedance of the speakers. We are all familiar with that.
Same thing applies to an fx driving circuit. So, the primary impedance of the edcor ideally should match the source impedance presented to it by the output circuitry of the 12au7 which I roughly estimated based on the GE data sheet and the resistor values in Tubenit's schematic.
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Before I pull down the previous experiment to build tubenit's cct 2 posts up, thought I would document this simple experiment with schematic and sound clip.
This goes from transformer out, into desk then digital recorder, so its a reasonable representation of what the preamp sounds like through good monitors. The PA will colour the sound differently.
https://soundcloud.com/tags/guitar%20amp%20test%20tone
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Great tone; well played too! I agree that a SS driver is a fine alternative, especially since the signal is going into SS equipment anyway.
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I can't seem to pull up the sound clip??
I get a page with all kinds of sound clips with 24 pages of sound clips in addition to that.
Can you repost the link or give a specific name to the sound clip?
I really would love to hear it!
Best regards, Tubenit
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Working my end ???
https://soundcloud.com/tags/guitar%20amp%20test%20tone
Takes 10 seconds to get going though.
Try this one maybe ?
https://soundcloud.com/glennjeff/dmarscln2loz
OH and that is a 20 metre cable run as well.
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Wow! That worked!
I like that tone ALOT! Very cool sound. That would work out fine for me.
IF (& you sure don't have to), you try that with the trannie behind the OD section also, I'd love to hear that sound clip.
AND .......... nice playing! Sounded really good to me.
THANKS so much! with respect, Tubenit
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Don't know which thread I'm supposed to be using but here is the D'Mars OD channel with a Hi to Lo transformer hanging off the valve cathode followers cathode coupling cap.
There is no problems with level, I had to use a divide by 10 cable to stop it overloading a line input (-10dbU Line in I think)
https://soundcloud.com/glennjeff/dmarsod1
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There is no problems with level, I had to use a divide by 10 cable to stop it overloading a line input (-10dbU Line in I think)
I don't know what this means?? :dontknow:
Thanks for posting the soundclip!
With respect, Tubenit
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tubenit,
There was so much signal coming out of the transformer that it was overloading the line input on my desk. I had to use a cable that I have laying around for occasions when there is just too much signal. This cable has resistive dividers built into the plugs (XLR) to reduce the signal by a factor of 10. Some other posters thought that there might not be enough signal, so I thought I'd make the opposite observation.
What do you think of the sound coming out of the distorted channel ?, did the clips give you the information you required?
All the best.
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There was so much signal coming out of the transformer that it was overloading the line input on my desk. I had to use a cable that I have laying around for occasions when there is just too much signal. This cable has resistive dividers built into the plugs (XLR) to reduce the signal by a factor of 10. Some other posters thought that there might not be enough signal, so I thought I'd make the opposite observation.
What do you think of the sound coming out of the distorted channel ?, did the clips give you the information you required?
OK, got it. Thank you for the clarity. I ordered both a 10k/600 and a 10k/150 trannie as suggested by Pete.
Given your explanation, perhaps the 10k/150 8.2/1 would be better at reducing the signal down to a manageable level? IF I am understanding this correctly?
I thought the first soundclip of just clean was excellent/superb! I thought this one with the distortion was really good but not as excellent. However, it could have simply been that particularly recording and playing? I liked the guitar playing on the first one better also.
:icon_biggrin:
THANKS so much for the help and info! I am starting to order parts on this and hopefully will being the build in the next 3 weeks or less.
With respect, Tubenit
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Yes, there are 2 factors to consider for the source and receiving devices: impedance, and voltage. Typically the source impedance will be bridged (not literally matched) to the input impedance of the receiving device. I continue to advocate for the 10K:600R tranny for prior reasons stated in both threads.
As to the output voltage of the source device (FX loop) - you're building the circuit. So you can control the output voltage by fine tuning the voltage going into the input (grid) of the 12au7 tube.
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Well, I hopefully will start building this in a few weeks and have it completed within a month out.
I ordered both trannies 10k/600 & 10k/150 and plan to try both.
My goal is to build it ........... tweak it .......... and then report back the good success with the design.
:think1:
We'll see if that happens or not? :icon_biggrin:
With respect, Tubenit
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OK, guys I start on this project this wkend! Got my parts from Doug and will build a board and hopefully punch out the blank chassis also.
Got a question. On the Edcor trannie ........... I don't know what to do with the CT on the input and output sides of the trannie?
Question 1:
Can someone help me out with that, please? If you could post a schem or drawing that would be helpful to me.
http://www.edcorusa.com/Content/Manuals/XSM10K-150.pdf (http://www.edcorusa.com/Content/Manuals/XSM10K-150.pdf)
My best guess is the CT on the output side hooks into the XLR jack in some manner?
Question 2:
Also ......... I am thinking this trannie should probably be mounted inside the chassis do to the exposed terminals on the trannie? On the other hand, I am thinking with shrink tubing that I could safely mount it on the outside of the chassis and cover the terminals on the trannie with several layers of shrink tubing?
Would the outside chassis approach with shrink tubing be reasonable?
With respect, Tubenit
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I don't know what to do with the CT on the input and output sides of the trannie?
The center taps are used if you are dealing with balanced inputs and/or balanced outputs. Your input is definitely unbalanced so just ignore the primary CT. And I'm guessing you're going to connect this unit to a PA unbalanced input using a standard guitar cable? If so, just ignore the secondary CT also. But if you want the common mode noise rejection advantages of balanced lines, then use a XLR jack and cable to connect to the PA. In this case, you would use the secondary CT.
If the transformer is small and fragile, I'd put it inside the chassis. I probably would not use heat shrink on the terminals but if I did, I'd only use one piece per terminal.
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if you want the common mode noise rejection advantages of balanced lines, then use a XLR jack and cable to connect to the PA. In this case, you would use the secondary CT.
Q1:
I am not sure how to "use the secondary CT". I am guessing that all three secondary wires will hook up to all three XLR connections? Is that correct?
Q2:
And that even with the XLR, I still will not use the primary CT. Is that correct?
As always, I truly appreciate the help. I am somewhat enthused about seeing if this idea will really work and sound good.
With respect, Tubenit
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Just google "how to wire an xlr jack" and you'll find plenty of simple diagrams for balanced operation or unbalanced operation. Here's a good link...
http://sommercable.com/2__produkte/2__130_support/340_belegungsplaene/belegungsplaene/nf_kabel.htm (http://sommercable.com/2__produkte/2__130_support/340_belegungsplaene/belegungsplaene/nf_kabel.htm)
I am guessing that all three secondary wires will hook up to all three XLR connections?
That's correct. The secondary CT would connect to the shield which should be pin 1 on an XLR jack. Then each end of the secondary would connect to pins 2 and 3 of the XLR jack.
And that even with the XLR, I still will not use the primary CT. Is that correct?
That's correct.
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Steve,
Thank you, my friend! I appreciate the help. I'll look up the XLR wiring and figure it out. I'm looking forward to this experiment and challenge.
Hopefully, within the next 3 wks or so, I can report back how this sounds thru a PA system?!
With respect, Tubenit
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Sorry, are you sure that is the correct way to hook up the output transformer? I believe pins 5 and 8 on the secondary should be left "floating" for a truly balanced output. The center tap is not used in this configuration, rather ground, or pin 1, should connect directly to the chassis.
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Sorry, are you sure that is the correct way to hook up the output transformer? I believe pins 5 and 8 on the secondary should be left "floating" for a truly balanced output. The center tap is not used in this configuration, rather ground, or pin 1, should connect directly to the chassis.
On second thought I believe you are correct. Thanks.
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May be someone has interest to give a look to this Jensen schematics
http://www.jensen-transformers.com/as/as021.pdf (http://www.jensen-transformers.com/as/as021.pdf)
http://www.jensen-transformers.com/as/as096.pdf (http://www.jensen-transformers.com/as/as096.pdf)
from this page
http://www.jensen-transformers.com/apps_sc.html (http://www.jensen-transformers.com/apps_sc.html)
and the attached schematic from Merlin
K
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Gentlemen,
THANKS for all the information! I don't understand all of it, but from what I gather ............... I think this would be the way to hook up
the Edcor trannie to the XLR jack?
Q1: Does that look like the correct wiring? (if not can you revise the schematic for the correct wiring, please?)
Q2: Does this look like a reasonable approach? ( I added the V4a since so many illustrations had something similar. Again, I am
trying to preserve the D'Mars ODS clean, OD & FX as close to original as I can).
With respect, Tubenit
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Hi Jeff
as you use an XLR and a you have a transformer with a CT
why did you choose to don't use a balanced output ?
A balanced output has his advantages and is used in professional units
Franco
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as you use an XLR and a you have a transformer with a CT
why did you choose to don't use a balanced output ?
A balanced output has his advantages and is used in professional units
I simply don't understand how to hook up the wiring? And I don't know what a "balanced" or "unbalanced" ouput is? :dontknow:
I have no preference. What would be actually helpful to me if someone could draw me a schematic for my Edcor and XLR? I can understand a schematic, but I have limits to understanding the information that has been posted.
With respect, Tubenit
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There seems to be some mixed ideas about using the CT in a balanced XLR circuit, so I'll yield to the Jensen method. Pin 8 of the transformer should connect to pin 3 (not pin 1) of the XLR.
You don't have to use XLRs. A standard 1/4" phone jack works well too unless you have a very long cable run from your unit to the PA.
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Steve,
That is what I needed!!! :worthy1: :worthy1: THANK you!!
I am going to go with that XLR wiring and use the added V4a unless you direct me differently.
:icon_biggrin:
I appreciate that people are trying to help by providing information, but I don't understand significant portions of the info and at this juncture, I just needed a simple drawing to go from.
With respect and gratitude, Jeff
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I'm sorry Jeff I didn't understood you at 100%
if you want to read a bit about balanced audio and convenience to use it
http://en.wikipedia.org/wiki/Balanced_audio (http://en.wikipedia.org/wiki/Balanced_audio)
Franco
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Hey, no need to apologize at all.
I should apologize for not being smart enough to understand what you were sharing! And I do appreciate the info. While I may not understand all of it ............. I do continue to learn more. THANKS!
:thumbsup:
I'll read about the balanced lines.
Best regards, Jeff
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I do continue to learn more from you Jeff :wink:
Franco
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Got the board populated. Used Hoffman board and turrets.
Got the chassis blank punched out sanded and lacquered.
with respect, Tubenit
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Agree: 99.44% of the time the CT should be ignored, even for "balanced" wiring.
HARD-Balanced (CT to ground) is sometimes preferable when working directly under a high-power transmitter. (Many old-old radio microphones were hard-grounded.)
In any other audio situation, let the winding "float" (no connection to ground). It will self-balance to suit the situation. It will also work if you (or the sound-dude) grounds one side for an unbalanced connection. (With hard-ground on CT, a ground on another lead shorts-out the signal.)
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Agree: 99.44% of the time the CT should be ignored, even for "balanced" wiring.
With a small toggle switch, you can add a ground lift to the XLR pin #1. This is handy in a recording situation to remove a ground loop hum, and perhaps less useful in a house PA mixing board situation, but still, its easy to add. usually pin #1 is a 1Kohm Resistor to ground with a parallel .01uf cap, and the ground lift switch closes/opens pin #1 to ground. In a "ground lift" position (i.e. switch is open) you've got a 1K and .01 cap to ground. This shunts any RFI on the cable's shield to ground, but eliminates a ground loop with the device at the other end of the cable. Simple, and potentially very handy.
Also, on some 600CT transformers, the OT's output leads can be switched/strapped for 150,300, or 600ohm, depending on how the CT is provided: some transformers separate the CT into two discrete wires, others, use a single CT tap wire. for an example of the former, google the wiring for a UTC A24. Mostly this applies to mike level inputs, and not so much house mixers, but in a recording studio, changing the ohm output from 600 to 150 can significantly change the frequency response ... it depends on the device you plug into, and what the input Z of that device happens to be.
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Guys,
It works as the last schematic I posted reflects. Initial impression is that it sounds good to me. I only had a time for a super quick plug and play without taking any time to adjust anything. So far, I am pretty happy with it.
Will post some decent sound clips later. This was done by just plugging into an EmU Tracker which goes into a computer soundcard. Everything was on "5" except the volume which was "4" and the FX return which was "2".
http://www.soundclick.com/player/single_player.cfm?songid=12498845&q=hi&newref=1 (http://www.soundclick.com/player/single_player.cfm?songid=12498845&q=hi&newref=1)
Regarding the chassis layout. I built it so it could be converted into a complete amp at a later time IF wanted.
With respect, Tubenit
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OK, here is a demo of snippets from 3 different "1-take" soundclips showing the D'Mars PreAmp into my E-MU Tracker into the computer soundcard.
This PreAmp will go into a solid state PA system.
Only effects were slight EQ and delay in the mix except for 1:15-1:30 where I tried a Zenith Drive pedal out.
http://www.soundclick.com/player/single_player.cfm?songid=12500662&q=hi&newref=1 (http://www.soundclick.com/player/single_player.cfm?songid=12500662&q=hi&newref=1)
With respect, Tubenit
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I got the D'Mars PreAmp up and running and recorded it into an E-MU tracker device into a sound card.
Seems like it would clip fairly easily (into the red) both in the E-MU tracker and in the Mixcraft recording program. For exampe, I had to record on "3-4" range out of 100 recording volume in the Mixcraft.
Any thoughts whether this would be a similar experience with a solid state PA system? I am thinking there may be significant differences in how this sounds in a solid state PA vs. the computer sound card?
I am wondering IF I should use the 10k/150 trannie instead of the 10k/600 trannie? Which would you suggest as a first try into a solid state PA system. The 10k/600 is in there currently.
With respect, Tubenit
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Think to the CF that is preceding the transformer as an FX Loop circuit
and insert a pot (not a big one, say 10k-25k) as to tame the signal from the tube to the transformer
---
See the last schematic on this tread
http://www.el34world.com/Forum/index.php?topic=13120.0 (http://www.el34world.com/Forum/index.php?topic=13120.0)
---
You can also try to connect the cap preceding the transformer to the node between the 1.8k and the 27k resistors
K
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Franco,
Those are very good ideas! And I will try the pot first ( and then the other) and report back. May be a few days before I can get to it.
THANKS! With respect, Tubenit
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Sounds great!
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That sounds REALLY GOOD Jeff. (Think I might have to re tweak my D'Mars OD section seriously.)
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Thanks for the encouragement, guys! The PreAmp worked but sounded somewhat sterile and clipped too easily when trying to record.
I tried Franco's suggestion with the pot right before the matching transformer. It worked !!!!
Ironically, I first soldered in a 25k but it lost so much volume that I added a resistor to ground and kept increasing that resistor to ground
until it sounded like the "right" volume.
I ended up with a 1MA trim pot there with a 150k going into the trim pot. The trim pot there made a difference in the warmth and sustain of the PreAmp. I am thinking that what it ended up doing was to limit the clipping in the signal while allowing me to increase the FX level.
Anyhow, I have more warmth and sustain and it sounds closer to the real D'Mars PreAmp. I also removed the bright cap on the volume pot too.
I will try one more tweak on the OD to get it a little smoother and more overdriven after work today and then post another schematic.
I feel pretty encouraged by the progress!
With respect, Tubenit
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I will post a new sound clip (hopefully) within the next 4-5 days after I finish tweaking this and learning a new recording program.
What I will do is have one sound clip with 3 sections. And anyone that wants to respond can rate each section A, B & C on a scale of 1-10 with 10 being a true full tube amp tone.
(ex: if someone thought it sort of sounded close but isn't really a full tube amp type tone, then they might give a "7". IF they thought it was a true tube amp then they can give a "10")
Without knowing what is what, it could help in giving an unbiased review of the viability of this experiment/project?
After getting some responses, I'll give the results of which section is what.
I think it will be interesting to see how close I can get the tone of the preamp to a full tube amp tone? Hopefully people will give me some honest feedback on it. IF it's not getting close to a convincing tube amp tone, I would want to know that (& also if it is close).
With respect, Tubenit
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Tubenit Wrote: "I think it will be interesting to see how close I can get the tone of the preamp to a full tube amp tone?"
Careful there Skywalker, The Darkside may be calling you...
Silverfox.
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Careful there Skywalker, The Darkside may be calling you...
:l2: :l2: :laugh:
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Guys, I would truly love your feedback. I've tried working on the D'Mars PreAmp to tweak it as close as I can get to the sound of a full tube amp with the speaker mic'd.
There are 3 parts A, B & C. Each part is about a minute long.
IF you are willing to help participate in rating the success or failure or this project, just give feedback here on the soundclip thread:
http://www.el34world.com/Forum/index.php?topic=16065.new#new (http://www.el34world.com/Forum/index.php?topic=16065.new#new)
Thanks & with respect, Tubenit
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Hi Jeff
waiting for an answer from my son
I've remembered this italian project that may be of some interest to you
http://www.aresaudio.com/speaker-emulator.html (http://www.aresaudio.com/speaker-emulator.html)
(http://www.aresaudio.com/files/TubeSCHEMATIC.jpg)
Ciao
Franco
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Thanks Franco!
Is that entire schematic the speaker emulator ............... or is a portion of that schematic the speaker emulator?
In other words, IF I was going to add a speaker emulator to this project, would I be adding a portion of that schematic or the
entire schematic?
Thanks. With respect, Tubenit
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The schematic is complete
at the link I posted you can read further and find PCB Layout
here a sample of the original
http://www.aresaudio.com/files/Audio-originale.mp3 (http://www.aresaudio.com/files/Audio-originale.mp3)
and here the emulated signal
http://www.aresaudio.com/files/Demo-Emulato.mp3 (http://www.aresaudio.com/files/Demo-Emulato.mp3)
I've read about this project some time ago in a forum, but now didn't remember if is to be used between guitar and preamp or in one other way
Franco
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OK, thanks Franco!
Here is the updated schematic.
with respect, Tubenit
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Hi Jeff
my son has listen the sample, he say that is difficult to give a response because what are you looking for
is something you can notice better when you play instead of when you listen
he say also that the best thing to do is to search to reach the most agreeable sound at your taste
there are many factor influencing the listen experience, however he say that at his taste
he feel the first part as more "electric", he like more and feel as more natural the second and the third part of the sample
From my part I ended to say that the part that I appreciate more is the third part but this is only my opinion and you know my ear situation
Franco
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PreAmp idea is scrapped!
I am dubbing this a noble effort with mediocre at best results ....................... :sad2:
Honestly, I had fun with this experiment but there was NO "wow factor" for me other then "wow, it actually makes sound". :l2:
Project is labeled a quasi-failure!
Thanks for the input guys, sorry it didn't work out!
With respect, Tubenit
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EH NO ! Jeff :sad:
Adesso ci spieghi cosa è successo :dontknow:
After getting some responses, I'll give the results of which section is what
Now we are waiting
Despite of all, all the three section of the sample has a pleasent sound
only one was better from the other
Ciao
Franco
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Results are in the sound clip section of the forum :icon_biggrin:
With respect, Tubenit
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Wow Jeff,
I find your conclusion rather puzzling.
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It worked. It sounded decent enough just not great to my ears. I was hoping for an "oh wow!" factor that it didn't have.
May try an isolation speaker cab route instead. Which may be a better solution for the guy in the long run anyway?
THANKS for your help on the project! The chassis was laid out in a way that is making converting it to a full D'Mars ODS with 6V6's really easy.
Best regards, Tubenit
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You know how life has those unexpected turns ............................. icon_biggrin
Turns out that making an isolation speaker box isn't going to work because of storage space in the closet that would've been used.
So, .................. the guy DOES want to try it thru the PA system.
I converted it back into a PreAmp ............. HOWEVER, I took the sound off the plate of the second triode in the FX. I did this because IF this gets converted into a full amp with a line out, that is where I would take it from.
So, ............ IF you would like to hear the new sound clip and offer some input whether the tone is improved at all, I would appreciate it.
http://www.el34world.com/Forum/index.php?topic=16065.0 (http://www.el34world.com/Forum/index.php?topic=16065.0)
Thanks, Tubenit
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I think you're at least 80% there. I suspect it would be good to feed your existing preamp circuit > PI > Push-Pull preamp tube (Double triode) set to clip > speaker emulator circuit > FX out.
The mini "power amp" section + speaker emulator would complete the full tube amp sound. Actually the PI and PP section could be contained in one triple triode. It's important that the the preamp tubes & PI generate harmonic distortion, while the PP tubes are set to clip.
You could use an after-market speaker emulator box, even now with the existing preamp.
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preamp circuit > PI > Push-Pull preamp tube (Double triode) set to clip
Are you talking about something like an LTPI going into a 12AU7 used as a power tube? Sort of a "firefly" idea.
Then into a speaker emulator with OUT a speaker connected to the amp?
And is there such a thing as a speaker emulator where the amp does NOT have to be plugged into a speaker. That's the thing .......... reportedly, there can't be an amp with speaker on stage ("zero volume stage")
THANK you for the direction and help! It is appreciated!
With respect, Tubenit
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Are you talking about something like an LTPI going into a 12AU7 used as a power tube? Sort of a "firefly" idea. Then into a speaker emulator with OUT a speaker connected to the amp?
Yes! Exactly.
And is there such a thing as a speaker emulator where the amp does NOT have to be plugged into a speaker.
Yes. See, e.g.: https://www.google.com/webhp?source=search_app#q=speaker+emulator (https://www.google.com/webhp?source=search_app#q=speaker+emulator)
Also there are DIY speaker emulator circuits. I believe the Aiken & Duncan sites have emulator / attenuator circuits.
With respect, Tubenit
[/quote]
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I asked and the speaker emulator I previously posted is to be connected at the end of the circuit
not between guitar and amp input as I wrongly supposed
Complete Project
http://www.aresaudio.com/speaker-emulator.html (http://www.aresaudio.com/speaker-emulator.html)
Schematic
(http://www.aresaudio.com/files/TubeSCHEMATIC.jpg)
K
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suggest using a plate follower to drive the x-former. take the HI-Z out from a cathode or source follower. in my limited experience, that configuration sounded best overall.
--pete
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Ciao Pete
I agree with you
but the project was planned, developed, build and tested with that architecture :dontknow: :dontknow:
there are also samples to hear the results, you can find it in a my previous post :dontknow: :dontknow:
you can listen and give your response
Franco
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Ciao Pete
I agree with you
but the project was planned, developed, build and tested with that architecture :dontknow: :dontknow:
there are also samples to hear the results, you can find it in a my previous post :dontknow: :dontknow:
you can listen and give your response
Franco
http://www.el34world.com/Forum/index.php?topic=15921.50 (http://www.el34world.com/Forum/index.php?topic=15921.50)
if in that link is what jeff built then it's a CF driving the x-former... not a plate follower.
--pete
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Ciao Pete
Jeff has build his preamp with balanced output preceding the balance output transformer with a CF
that, as far as I can know, is the architecture that can give the best performance
Given the above, I don't know why the choice of guy who planned the speaker emulator
(something that seems Jeff may be interested)
( http://www.aresaudio.com/speaker-emulator.html (http://www.aresaudio.com/speaker-emulator.html) )
was to use an anode follower instead of a CF
I wasn't saying that Jeff used the anode follower architecture
(I hope I've understand what you were saying in the previous post)
Franco
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The last sound clip was directly off the plate of return triode of the FX loop.
The reason that was done is that I am thinking of finishing the amp out as a complete combo amp. See attached schematic.
However, now after reading about the Hughes and Kettner Red Box ............. I am rethinking my approach?
I am thinking about using a dummy load 100w/8ohm resistor instead of the speaker and running into the Red Box speaker emulator.
http://www.parts-express.com/pe/showdetl.cfm?partnumber=019-020 (http://www.parts-express.com/pe/showdetl.cfm?partnumber=019-020)
Thoughts????? Think this would work and be a safe idea with no damage to the OT?
With respect, Tubenit
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I don't think a dummy load will damage the OT
only you must consider that if the player like the sound of the amp crunched
he will tend to use it at max power, this, of course, will shorten the life of the final tubes
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Something like the Herzog Champ
(http://www.tdpri.com/forum/attachments/shock-brothers-diy-amps/89317d1310247347t-champ-herzog-power-supply-fog-herzog-schematic-power-supply-footswitch-jpg)
(http://www.tdpri.com/forum/attachments/shock-brothers-diy-amps/89318d1310247364t-champ-herzog-power-supply-fog-herzog-schematic-without-power-supply-footswitch-jpg)
Franco
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tubenit,
I don't think you can asses anything without actually plugging into the PA. You are trying to tell the future, as in weird voodoo / astrology / stock market analysis.
Leave your options open so that you have a "piece of test equipment" that can be experimented with in the PA.
You have a couple of transformers, you could have one off a plate, one off a cathode and try the dummy load/speaker emulation as well. You won't know until you give it a go, so keep your options open for the time being, this is R & D.
Bear in mind that the PA is a set of speakers, thus speaker emulation may be overkill. I don't believe that trying to get that exact "guitar amp" sound out of the front of a PA is necessarily an appropriate design objective. Get a great sounding tube based guitar preamp that works into a PA may be a more appropriate way of looking at it (or not).
Personally, I'm a bit averse to having a heat generating dummy, like "fire paranoia" or "peak oil awareness" or whatever.
Having a "Firefly" as a distortion section seems to me like a good experiment also, something I have been thinking about for a while.
I'm really looking forward to your report on the experience you and your "client" have with a PA system.
I think the last couple of recordings you have provided had a "as good as it gets engineering" sound about them.
All the best.
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Glenn,
Did you see the size of the dummy load resistor and the picture of it? Looks pretty hefty to me at "6-1/2" L x 1-9/16" W x 3/4" H". With the amp using 6K6's, it should only be about a 7-8 watt amp with a 100w dummy load. I am thinking that would not be a problem?
I am definitely keeping options open. I will build a complete amp (head). And then I can try the PreAmp still using a Red Box speaker emulator with the PreAmp ........ and/OR try the load resistor and a line out into the Red Box.
Both are options I am exploring. And as of now, I am scheduled to try it in the PA system a week from today so that gives me some time to experiment more at home first.
I can easily get a small box and mount the matching transformer in it with a pot into the bottom of a small combo cab to have a PreAmp out design. It could mount in the bottom of a small combo cab much like a reverb pan. So that is do-able and I know how it sounds.
IF I end up with the PreAmp, then using a PPIMV would suffice to keep the speaker silent.
AND .......... I had already researched and drawn up a D'Mars with a push/pull 6SN7 power amp design. Much like the firefly power amp but using a 6SN7 instead of the 12AU7 idea. I've heard some sound clips of a 6SN7 push/pull Trainwreck design and think it sounds really excellent.
With respect, Tubenit
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As an FYI ............. Reviews of 100w dummyload resistor.
JUST bought a Carvin Vintage 16 all tube amp, and the church I play at decided to go direct, with headphones. This allows me to connect the speaker output to a Behringer Ultra G GI-100 (active direct box with speaker simulation) and this 8-ohm load to get the sweet overdriven tube sound totally direct, no live sound. MUCH cheaper than powersoak/loadbox combinations. Did not overheat, worked great. Solid construction, fits nicely in gig bag or back of amp.
I have used this with a standard amplifier to run in mono and with guitar amps. Functions beautifully. With guitar amps, you can put a DI in between this and the power amp and have your own silent recording rig.
And a response regarding the idea from another amp builder:
Been using load boxes for years and years. It will work. Haven't used a Redbox but it should work as you expect. I run big Marshalls on loads then those are channelized to a line mixer where effects are added then to a stereo power amp that drives 4x12 cabs.
You are doing something a little different than that, but yeah it works fine.
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I agree that a full-blown amp with "normal" instead of Firefly power tubes is an alternative. The trade-off seems to be weight / more general usage. At under 20 watts, the iron, and the total weight of the amp could still come-in at about 16 pounds -- not too bad. But still heavier than than a Firefly needs to be. 6GW8's have triodes built-in for the PI to save space & heater requirements.
So I think there's 3 ways to go: a) Full-size: full amp going to the SS Public Assembly (PA) amp, or mixing board, after the power tubes; b) Mini size: Firefly platform for less weight; c) Micro-size: Compactron tubes in a basic Firefly platform.
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Just a quick update. Decided I would build a dummyload box for this amp.
With respect, Tubenit
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I've used the RedBox solution into the board with that 8R/100W Resistor from Parts Express as a dummy load. This was for venues where it seemed using any speaker was "too loud". I thought the results were acceptable, but of course would prefer to mic a guitar speaker if possible.
I will say if you go this route, research the speaker emulator options. I've had my Red Box since the early 90's. When A/B'ed with a buddy's newer model in a studio setting, my older one definitely sounded better than his newer one. He said that seemed to be the prevailing opinion on the interwebs.
Edit:
The older version of the Red Box I have is the "Mk II". I found a picture I took of it with the load resistor and its super deluxe mount. Feel free to borrow my design for the resistor mount. :icon_biggrin:
http://oi55.tinypic.com/fbg494.jpg (http://oi55.tinypic.com/fbg494.jpg)
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Boots,
Been a while since I've seen you post. Nice to hear from you! THANK you for the information!
I bought a Red Box Mk III for $45 which is also an older model so I am hoping it will work well for me.
Regarding the resistor mounting. Remarkable creative craftsmanship! Excellent focus on the details of the design with super clean layout.
I'd get that patented ASAP. (BTW, I love "simple")
:thumbsup: :thumbsup: :icon_biggrin:
Thanks, Tubenit
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Got the D'Mars ODS built and have tried it with both 6V6's and 6K6's. It sounds amazingly good to me!
Waiting on the dummy load resistor, Red Box and foot switch ............ all which have reportedly been shipped.
More later .......................
Tubenit
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OK, the Red Box speaker emulator arrived .................
AND ........... the dummy load resistor arrived.
To my great surprise the O-ring contacts on the dummy load resistor will NOT take solder. I even tried sanding them to etch them but it did not work.
Do you guys think this would be OK to use a speaker jack to wire to aluminum O-rings and then bolt them together?
Do you see any issues taking that approach? I don't want to risk damaging the OT and power tubes.
With respect, Tubenit
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A good tight connection is a good tight connection :smiley: Those bolts will be much tighter than the plug in your speaker jack, I'd think.
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It may be sensible to view the 100w resistor as a 100w heatsink. So if you're using a 40w iron to try to solder to it, well...
You could try to get a bigger iron, like the kind plumbers use. But it would be a shame to buy something for a likely single-use.
So it seems reasonable to bolt the contacts together. Use at least a keps nut (the kind with a captive star washer) and consider an additional lock washer as well. You want to bolt this stuff done tight so it is unlikely to every come loose without your prior intent. :icon_biggrin:
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HBP,
Thanks my friend! I appreciate the help and comments! Will approach it that way for sure.
Ironically, I talked with my son today who is an EE that does research and design .................. where he works, they use these dummy load resistors all the time and often with bolts like you're suggesting.
Best regards and respect, Tubenit
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The suggested system will act fine
if you want a more "professional" look you can use wire to wire crimp connectors
this way is a good thing to have the wires of the resistor and of the jack of the same diameter
(http://ecx.images-amazon.com/images/I/41wHgPHEXCL._SL500_AA300_PIcountsize-15,TopRight,0,0_AA300_SH20_.jpg)
(https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcQ-51P4ruCcg_WgWSZQcRJz6mBrsD4MQIrPSZERpYhGg_m80MQT)
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with this kind of connector you can use wires of different diameter
(http://www.3m.com/product/images/Crimp-Sleeve-Connector-300.jpg)
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this in a "no-crimp" connector with a screw
(http://media-cloud.bestshopping.com/images/more/cabla/big400/4f12deee0fdba51b0158c19ad69fffab-ipwmc40.png)
Ciao
Franco
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OK, I promised an honest review of this project. This is my honest personal assessment.
Using my favorite tube amp as an "A+" reference point, I'd give this somewhere between a B to B+ and definitely falling short of an A-.
I do prefer an amp somewhat pushed and hanging right on the edge of overdrive so when you dig in, it definitely has sweet harmonics and overdrives and you pick more lightly and it cleans up. This system will NOT allow you to "hang on that edge" so it's not eligible for anything in the "A" range, IMO.
Does it capture the warmth and touch sensitivity of a tube amp. My answer is yes.
Using 6K6GT tubes with 307 volts on the plates ................. the 100w dummy resistor does NOT even get warm. In fact, it remained cool to the touch even after almost 2 hrs of playing. The 6K6GT tube are probably around 7-8 watts. My conclusion here is the dummy load resistor should be very safe for the amp & now allows the amp to be run withOUT a speaker and using a line out into the speaker emulator.
The speaker emulator surprised me in how well it worked and sounded thru the PA system. It did indeed sound very similar (not same) as a mic'd speaker. The H&K Red Box MK III has a Fenderish combo tone and a Marshallish 4X12 stack tone. I'm not real impressed with the 4X12 tone and found it too compressed. The "combo" tone is reasonably convincing & honestly exceeded my expectations. I think it's possible that someone could think it was a mic'd speaker if they could not A/B it with an actual mic'd speaker? I think I could tell an A/B difference but haven't tried that?
The amp (floor level noise) was very quiet at idle even when being played thru the PA system at volumes much louder then what would be used normally . I was concerned about typical "tube" hiss but it's looking to be a non-issue at this point.
Regarding the amp itself........ I think it has a very warm lush tone and got similar feedback from several band players. The clean/OD footswitch worked flawlessly and will be very useful. The guy I built it for was commenting about relying more on the amps tube OD and less on pedal OD. He was using a LesPaul and the pickups are hot enough that the Normal/Mid-boost switch is fairly useless for the Les Paul but could possibly be a big help for a strat or tele to fatten the tone.
Because the amp has a built in tube FX loop, it will allow the delay pedal to be used after the preamp instead of before the preamp. The Hardwire delay pedal added too much noise in front of the preamp but in the FX loop after the preamp, it was reasonably quiet. It still can remain on his pedal board and be plugged into the FX loop.
This will be used for a few weeks before a final opinion is settled on. Total cost is around $450 for the complete amp, dual footswitch, used H&K Red Box III, and dummy load resistor. A figured wood cab would add maybe $75 in cost for materials pushing the DIY total to $525.
Downside of the system ........................
I like the FX loop dialed in at "5-7" send and "5" level. I think there is a "sweet spot" tonally there. The FX worked best in the PA system settings dialed in at "3" send and "3" level which I think lessens the sweet tone somewhat. Maybe the real sound guy can compensate this in the PA system and allow the levels to be at my preferred settings? I don't know if the amp can be dialed in to hang right on that edge of overdrive to clean?
IF a month or so out, opinions about using this system changes or something emerges as a glitch in the system, I will come back and let everyone know. Otherwise, this will probably stand as"the" review.
IF nothing goes off course, I do think this is a reasonable approach for someone who may prefer a tube amp but still needs a "zero volume" stage. With a 100w dummy load resistor and an H&K speaker emulator, I think amps that are maybe 25 watts or less could be good candidates for this approach.
With respect, 10thtx
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Many Thanks for the review
Franco
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1 minute sound clip test for the amp and speaker emulator. No speaker connected. This is the dummy load with a line out into the
Hughes & Kettner Red Box Mk III speaker emulator. I added too much compression into the rhythm part but the sample gives you an idea of how the Red Box speaker emulator sounds.
http://www.soundclick.com/player/single_player.cfm?songid=12527023&q=hi&newref=1 (http://www.soundclick.com/player/single_player.cfm?songid=12527023&q=hi&newref=1)
With respect, Tubenit
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Sounds like a tube amp to me!
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Sheer coincidence-
I was sitting here practicing when I read your thread and clicked on the link for the sample.
Lets just say, I was using a tone shaping network prior to the input for a Kustom Defender that I modded to a 3 control Tone stack.
. The Kustom Defender is an EL84 base 10 watt amp. I was plugged into a 4x12 cabinet and had the Defender slightly over driven; It sounded almost exactly like your amp
Your amp sounds like a tube amp and allegedly like an emulated Bogner Ecstasy on the Red channel with slight gain.
Silverfox.