tube PreAmp & FX into SS power PA

[Glennjeff]

Wow Jeff,

I find your conclusion rather puzzling.

[tubenit]

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

[tubenit]

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
 
Thanks,  Tubenit

[jjasilli]

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.

[tubenit]

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

[jjasilli]

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

Also there are DIY speaker emulator circuits.  I believe the Aiken & Duncan sites have emulator / attenuator circuits. 


With respect, Tubenit
[/quote]

[kagliostro]

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

Schematic


K

[DummyLoad]

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

[kagliostro]

Ciao Pete

I agree with you

but the project was planned, developed, build and tested with that architecture   

there are also samples to hear the results, you can find it in a my previous post 

you can listen and give your response

Franco

[DummyLoad]

Ciao Pete

I agree with you

but the project was planned, developed, build and tested with that architecture   

there are also samples to hear the results, you can find it in a my previous post 

you can listen and give your response

Franco

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

[kagliostro]

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 )

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

[tubenit]

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

Thoughts?????     Think this would work and be a safe idea with no damage to the OT?

With respect, Tubenit

[kagliostro]

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

---

Something like the Herzog Champ





Franco

[Glennjeff]

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.

[tubenit]

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

[tubenit]

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. 

[jjasilli]

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. 

[tubenit]

Just a quick update.  Decided I would build a dummyload box for this amp.

With respect, Tubenit

[Boots Deville]

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. 

http://oi55.tinypic.com/fbg494.jpg

[tubenit]

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")
 

Thanks, Tubenit

[tubenit]

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

[tubenit]

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

[John]

A good tight connection is a good tight connection Those bolts will be much tighter than the plug in your speaker jack, I'd think.

[HotBluePlates]

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. 

[tubenit]

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

[kagliostro]

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





---

with this kind of connector you can use wires of different diameter



---

this in a "no-crimp" connector with a screw



Ciao

Franco

[tubenit]

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

[kagliostro]

Many Thanks for the review

Franco

[tubenit]

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

With respect, Tubenit

[jjasilli]

Sounds like a tube amp to me!

[silverfox]

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.