New Build TB OVERDRIVE

[TIMBO]

Hi guy's, I had a lot of fun and success with my last build and its made me want to do a real version of the BTO. I had a spare OT (1750K) that my be OK for a pair of 6L6s,these i had in my spare parts box.

The original amp has a FUZZ circuit in it and had an unusual sound so i have kept it,i always like a REVERB and also had a spare long tank so that is in as well.

Now Tubenit came alone with his OD this and OD that, this got me thinking the original had two spare half triodes and well now this will have an OD as well.

AGAIN, Tubenit came along with his active loop.The passive loop is something i have in all my builds and the salesman that T is i think an active loop would be BUTE.

SOMEONE STOP ME, Can't have all great things without getting out of the chair so i'm going to throw in a couple of relays/footswitch.

SOOOOOOOOOOOOOOO much going on 
Might need to delete a few things :-

The Tone pot in the OD, does this have a any effect on the OD in terms the actual overdrive, can the amps treble/bass controls do the tonal effect??
Can the active loop send level be fixed at a set level and the pot mounted on the circuit board as a set and forget,does it need to be adjusted often???
The pot used as the FX level, T said that it worked great as a MASTER VOL, I have had great success with the PPIMV and was going to use it in this build. Could this FX level replace the PPIMV as a master vol???
I have had a switch that in other build that allows FIX and CATHODE biasing will the FIX bias work with this PPIMV??
Can anyone see any problems adding an OD to this circuit,as i not sure what effect it might create.

Anyway, a few questions before i start drilling.Thanks
 
 

[tubenit]

The Tone pot in the OD, does this have a any effect on the OD in terms the actual overdrive, can the amps treble/bass controls do the tonal effect??

The OD tone pot is VERY important to me tone wise and I use it more than clean tone controls (which I tend to set and forget). It does effect the OD in that when dialed in right, you get some really nice harmonics. I think it helps sustain some frequencies also?  

Can the active loop send level be fixed at a set level and the pot mounted on the circuit board as a set and forget,does it need to be adjusted often???

Yes, the send can be fixed or done as an internal trim pot. I almost never adjust mine on the D'Lator & on the TBM w/FX .......... the FX send pot is next to a tube socket and not very convenient to change & I use it more as a "set and forget" trimmer.

The pot used as the FX level, T said that it worked great as a MASTER VOL, I have had great success with the PPIMV and was going to use it in this build. Could this FX level replace the PPIMV as a master vol???

My opinion is yes.  When I have the D'Lator in the D'Mars ODS circuit,  I use the FX level to adjust volume more than the PPIMV.  On the TBM, there is no PPIMV and I just use the FX level pot.  It works great, IMO!

I have had a switch that in other build that allows FIX and CATHODE biasing will the FIX bias work with this PPIMV??

I am not sure of the answer on this one?  I think the PPIMV only works with cathode biased, but I could be dead wrong on that?

I think is a cool amp design!  IF you draw up a SCH layout, would you please share it?  Looking forward to hearing more about your build.
With respect, Tubenit

[sluckey]

I have had a switch that in other build that allows FIX and CATHODE biasing will the FIX bias work with this PPIMV??

yes

[tubenit]

I have had a switch that in other build that allows FIX and CATHODE biasing will the FIX bias work with this PPIMV??
yes

Yep, I was dead wrong (again)! 

Sluckey, 

I am SO glad that you are around to help us out! I genuinely appreciate your seeing in our(my) blindspots and keeping us (me) on track!  Thanks, my friend!

Your very generous with your help and time! So many of my builds would've remained problematic without your knowledge and generousity.

With respect, Tubenit

[TIMBO]

Hi guy's, Ive had to do a scale drawing to see if it would fit into the chassis i have (17.5"x10"x3") its going to be tight but i think i was able to keep runs short and direct. I started a SCH layout but it would not fit onto one page and was hard to follow.Thanks

[tubenit]

You impress me!  That's pretty interesting and I think would be worth the experiment.

Get Geezer's input, please before you start.  He and I communicate "off the forum" some, & I think he might have something useful to you in the way of an opinion and/or advice on this type of layout and design.

Geezer's got the most "can do" attitude I know about experimenting and his innovation is remarkable.  I'd PM him for some feedback and maybe invite him to post on this thread if he is open to it.

I'm rooting for you!  THANKS so much for sharing your innovative ideas!

With respect, Tubenit

[Willabe]

Sluckey, 

I am SO glad that you are around to help us out! I genuinely appreciate your seeing in our(my) blindspots and keeping us (me) on track!  Thanks, my friend!

Your very generous with your help and time! So many of my builds would've remained problematic without your knowledge and generousity.

With respect, Tubenit

Well said.


              Brad     

[TIMBO]

OK, I think i've got the layout nailed. 

[tubenit]

Thanks for sharing your layout/s!

Out of curiousity, ............ have you done relays on the regular turret board before?  I am wondering how that would work out?  I have a category that perhaps that would be a really nice way of doing them?

with respect, Tubenit

[TIMBO]

Hey Tubenit, I think that your idea of separate relay boards IS the best idea, but the fact that i am really crambed for space has left me no real option but to mount them on to circuit board. I mounted on the relay on the circuit board of the jubilee build and was a pain to do any changes to.

This time i have sockets that makes the relay removeable and turrets at the side (like yours)that will make it easy to swap wires if neccessary.

I have asked the question before about the relay giving off any interference to other components and most have said that they are OK.
Again mounting on the circuit board has kept every thing short.

I believe that simple is best, but it is hard not to go overboard when so many of you guys come up with such great ideas and as we all know when building these oneoff is that it is only when we have finished we find what it sounds like.

Thanks 

[tubenit]

Timbo,

Honestly, your idea may prove to be the better?  I truly don't know?  Maybe having them on the board will leave it will lesser wires crossing overhead the relay from the boards to the pots.

With respect, Tubenit

[Geezer]

Here's a pic of a board I recently built with 8x relays built right onto the board, along with the DC power supply/voltage regulator.

It works perfectly and makes the most of the space I had to squeeze a TON of circuit into the available space.

So, don't be afraid to mount the relays on the board......mine switch silently.

[Tone Junkie]

Damn Geezer thats a lot of switching. Looks cool, whatcha buuilding inquiering minds want to know.
Bill                                                   

[jojokeo]

I have had a switch that in other build that allows FIX and CATHODE biasing will the FIX bias work with this PPIMV??

yes

For fixed bias PPIMV do you not need the resistors & caps after the wipers going towards the 220k resistors w/ the neg bias voltage as in schematic below???

[TIMBO]

I'll second that, leaves my two relays for dead.

While we are on the relay subject, the relays i have don't have the + marked on them,so i will assume that it can be wired any way and a diode won't be required   Thanks  

[TIMBO]

Thanks jojo, I was hoping that i can eliminate the PPIMV and use the FX level as my master, so i will wire in the active loop and see how it performs and i can add the PPIMV later if required.Thanks

[jojokeo]

I have the same deal w/ an amp that can be switched from cathode to fixed bias but has Master Volume only as a pre phase inverter or after the tone stack. Same sort of thing as the FX level I would think? But I wouldn't mind changing this to a "real" PPIMV if possible?

*Need Sluckey's help on this "universal" PPIMV schematic if it can be done or not?

[sluckey]

*Need Sluckey's help on this "universal" PPIMV schematic if it can be done or not?

Are you referring to the Mission Amps schematic you posted? If so, yes, that MV will work well with a fixed bias amp.

Or, you can eliminate a couple caps and resistors by using the MV in the schematic Timbo posted in the first message in this thread.

[sluckey]

relays i have don't have the + marked on them,so i will assume that it can be wired any way and a diode won't be required 

Yes, you can wire the coil either way.

The diode is not required for proper operation of the relay regardless of whether the coil has a polarity marking. The purpose of that diode is to kill the voltage spike that occurs whenever the relay coil (actually an inductor) is de-energized (switched off). This spike is actually the CEMF generated by the inductor in it's attempt to oppose any change in current thru the inductor (basic inductor properties). This voltage spike will cause a "pop" in the amplifier. Using the reverse connected diode across the dc coil will short out this voltage spike, effectively eliminating or reducing the audible pop.

I highly recommend using a despiking diode on any dc relay used in an amplifier circuit. The industry standard diode used in low voltage dc relays is the fast acting (and cheap) 1N4148.

[jojokeo]

Or, you can eliminate a couple caps and resistors by using the MV in the schematic Timbo posted in the first message in this thread.

So then this type of Master Volume control is wired up the same for BOTH fixed and cathode biased amps?

[sluckey]

Well there's one difference. The bottom of the MV pots connect to ground for a cathode biased amp, but the bottom of the MV pots connects to bias for a fixed bias amp. Other than that difference, the circuits are the same.

[TIMBO]

All good info, thanks guy's.

[SILVERGUN]

Here's a pic of a board I recently built with 8x relays built right onto the board, along with the DC power supply/voltage regulator.

Geezer, are you utilizing a special wiring scheme for the power supply to those relays?.....I think I see that one "blocking" diode appears to be serving 2 relay sockets...?

[Geezer]

The relays are activated in pairs (4 foot switch unit) so each pair is like a DP4T switch. And yes, I used 1x diode for each pair.

G

[jojokeo]

Well there's one difference. The bottom of the MV pots connect to ground for a cathode biased amp, but the bottom of the MV pots connects to bias for a fixed bias amp. Other than that difference, the circuits are the same.

Does anyone have the two drawings of a PPIMV for comparrison: one for cathode bias and one for fixed bias to see & look at the differences and which can be printed out? TIA, Keo

[sluckey]

This is cut from Timbo's circuit in his original post. In the cathode biased version, the pots are connected to ground. In the fixed bias version the pots are connected to the negative bias (which is AC ground due to the bias filter cap).

[jojokeo]

Many thanks!!!!

Was there any reason for two caps coming off the pots as shown in the Mission Amps schematic for the fixed bias version?

Also, with an amp that has both the PPIMV and VVR - does having the PPIMV allow a cleaner tone to output tubes (because there's a signal adjustment to lower here) when the VVR is turned down? Because with VVR turned down the pi & output tubes can easily be overdriven, therefore you'd be able to lessen the signal hitting the tubes in the lower B+ condition. This would allow better "lower vol" clean-ish tones from a 50watt amp lets say.

[sluckey]

Was there any reason for two caps coming off the pots as shown in the Mission Amps schematic for the fixed bias version?

Yes. The caps isolate the MV from the bias circuit, preventing the MV from changing the bias to the output tubes. That would happen since Bruce's circuit connects the MV pots to ground, therefore the MV would provide a current path for the bias voltage which will create a voltage divider that changes the bias to the tubes. This problem does not exist if you connect the MV pots to the bias voltage rather than ground, eliminating the need for the extra isolation/blocking caps.

This would allow better "lower vol" clean-ish tones from a 50watt amp lets say.

I don't have any hands on VVR experience, but getting a low volume clean tone from a big amp has never been a problem. Just turn the volume down. I believe VVR is all about getting a low volume "dirty" sound from a big amp.

[jojokeo]

Thanks sluckey, I see the difference now. Doesn't this seem to be everyone's favorite master volume of the day? I think I have a cross-line on an amp, others have the pre-ppi, and only VVR on others, but don't think I have this one installed on anything? I've read varying opinions on it where tubenit didn't like on his 56T and other amps a year or two ago but seems to have changed his mind lately? Also, geezer had this combined w/ VVR, then when the VVR burnt out for some reason - he didn't mind and left it out in favor of only using the PPIMV. Then I've read others that like the verisitility of having both VVR and PPIMV to dial in the sound and level they feel is optimum.

[Geezer]

Those all have limitations and loss of good tone when turned down.

I have settled on the 2x triode buffered effects loop (dumble type with send/return/recovery controls) as the best, using the return and recovery pots to limit the volume with the least negative effect.

Ymmv, G

[jojokeo]

Thanks geezer, so then you're basically only using a pre-ppi as a master volume then or rather the now famous "PELMV" (post effects loop mater vol). ;)

[TIMBO]

Now we are getting somewhere, I too are a fan of the PPIMV more so than the VVR (cost and sound) but they both loose a bit when turned down. So if the LOOP LEVEL (as a master with no FXs plugged in) can maintain the sound/tone at any level this can only be a good thing.Can any one give me a YES on this??

BUT will it perform the same with an FX pluggud in??   Thanks

[Geezer]

I only use mine with effects in the loop. I find that the extra triodes/buffers add something that I like to the tone. So to me, it's something a bit more than just a pre-phase inverter master volume.

G

[TIMBO]

Hi guy's, I been thinking about using the LOOP LEVEL as a MASTER VOLUME and think it best to position it as on "sheet 2" and DELETE the PPIMV. BUTTTTTT, If it does not perform as i would like a MASTER VOLUME too, i would be unable to reposition it as on "Sheet 1" (the PPIMV can be added if neccessary at any time)

Can anyone throw any ideas my way. Thanks  

[TIMBO]

Back again, My next problem is TRANSFORMERS, Their position and orientation.

I have arranged then this way for ease of wiring but i'm not sure how they will effect the tubes. I think that the PREAMP tubes will be least effected this way  Thanks

[TIMBO]

Hi guy's, Finally was able to drill some holes, thought i had it all good BUT  (can you spot the GOOF) thank god for ALUMINIUM and the guys at the sheet metal shop.

[SILVERGUN]

(can you spot the GOOF)

Do you mean you weren't trying to merge those 2 tubes together for a little transconductance mojo??

This was the part of my last build that really surprised me......I couldn't believe it took me 78 hours to get my chassis laid out and cut/drilled........I agree

[TIMBO]

Hi guy's,got the main PSU sorted and getting 420v@ the standby. The bias voltage supply is tap off the main PSU with a bit tweaking i'm getting a good range from 0 to -55v,but i'm thinking that being able to dial it down to 0v may not be a good thing ( IDIOT factor).Thanks

[sluckey]

i'm thinking that being able to dial it down to 0v may not be a good thing

I agree.

[tubenit]

Hey man, I am rooting for you!  Really looking forward to hearing how this build turns out. THANKS for sharing your ideas. I love the gutsy innovation.

With respect, Tubenit

[jazbo8]

Slightly OT, what hookup wires are you using in the build? I went through the trouble of running shielded cables for many low level signal path in my TOS build but just read somewhere that solid-core hookup wire should provide a quicker, open sound (hi-fi speak)...

Jaz

[TIMBO]

Hi jaz, Funny you should ask, I actually use cable that you would use for TRAILER lights. I can get 7 core cable that has green, brown,red,black,white,yellow and blue, each are multi strand @ 0.64mm/22ga.The concern with using this wire is that the insulation was not rated for high voltages. I have since found that here in Australia most electricial wires are clad in V-90 PVC insulation that is rated @ 700v so this was good news to me and at a couple of bucks a meter, its pretty cheep. 

I much prefer to use the multi strand cable just makes it a bit easier to get into tight places and i don't think that it makes much of a difference to the sound/tone of an amp.

The topic has come up before about that colour codes in valve amps are not set in stone but i find different colour wire makes it easier to troubleshoot/trace and having seven wires is perfect for valve (9 pin) sockets :-

PIN 1 - RED
PIN 2 - WHITE
PIN 3 - BLACK
PIN 4 - GREEN
PIN 5 - WHITE (when using with 12.6v supply)
PIN 6 - BROWN
PIN 7 - YELLOW
PIN 8 - BLUE
PIN 9 - GREEN
GROUNDS - BLACK
Other component connection is what ever bits i have laying around,some like to use YELLOW but just makes it hard to trace.

Hope this helps.

[jazbo8]

That's a good tip for color-coding the wires, I can see how it can help with tracing signal and troubleshooting.

Thanks,
Jaz

[TIMBO]

Hey jaz, You can't have enough SHEILDED cable for the TOS and it is way better to run shielded in the signal path. Hope the TOS build is going well, they are a fantastic amp.

[jazbo8]

The TOS was my most ambitious build to date, it sounded dreadful (hard to believe I know) until I swap out the OPT, now it's my favorite! I am sure it can be improved upon further with some tube-rolling, parts tweaking... anyway I'd like to enjoy playing it for awhile, before messing with it - which is not always a good thing...

BTW, I think it is a good idea to get +-20% on the bias control, but you definitely do not want to get close to 0... Looking forward to hearing some clips on your new build.

Jaz

[TIMBO]

Hi guy's, Rehashed the bias circuit as per the fender circuit from sluckey's info and getting a better range of -29v to -58v. Thanks

[TIMBO]

Hi guy's, Got the boards together and so far alls coming together nicely.

[sluckey]

Quite an ambitious project. And nicely done too.

[Willabe]

Quite an ambitious project. And nicely done too.

Yep, very nice Timbo!


              Brad     

[tubenit]

Very impressive!  THANKS for continuing to share about it.

with respect, Tubenit