Adding a 2nd Master volume to a Peavey VTM

[JustMike]

 I think it's pretty simple Can I just put it pre phase inverter?

http://dl.dropbox.com/u/20590817/peavey_vtm_60_120.pdf
 It looks like v3 is an fx loop buffer?
 What I'm trying to accomplish is have a post fx loop MV so I can plug in an external preamp.

[Jack1962]

are you wanting a level control for the FX loop or are you wanting another Master Volume ? for the FX Loop level control use a 1meg pot attached to pin 5(fx return) and pin 8(gnd) of J3

[JustMike]

 I want a master volume after the FX loop.

[jerrydyer]

I like those amps, interesting story behind those. Mike are you here in orange county CA and do you rent rehearsal space from Shaul at Backline?

[jerrydyer]

do you just need to attenuate there in general? what effects units? good ones have adjustable parameters inside there.  I see a spot another 1 meg pot could work (in theory)  lol   ..

[JustMike]

I like those amps, interesting story behind those. Mike are you here in orange county CA and do you rent rehearsal space from Shaul at Backline?

 No, I'm in Orange county FL! But I was in Hollywood Ca. back in '91 or so and I can't remember the name of the rehearsal space I was in, but lots of bands were there.
 So...about the Master volume..?.. It looks like this thing has a tube buffered fx loop after the master. Am I right?

[rzenc]

So...about the Master volume..?

I think you might be able to install a post PI master volume to it. Is this your idea?

Best Regards

R.

[Willabe]

I want a master volume after the FX loop.

              Brad     

[rzenc]

I want a master volume after the FX loop.

              Brad     

It's after 

Best Regards

R.

[Willabe]

It's after 

True.   

What I'm trying to accomplish is have a post fx loop MV so I can plug in an external preamp.

                  Brad     

[JustMike]

 Can it work between J3 & C13, after the presence control and before the PI?

[rzenc]

Can it work between J3 & C13, after the presence control and before the PI?

I think not...but that's my opinion.

It looks like this thing has a tube buffered fx loop after the master. Am I right?

I think not. See signal flow drawing below, so that you will understand how your amp preamp signal goes to your FX loop and returns from it. Also, FX loop is passive, not active buffered. A buffered FX loop would need a tube to drive (generally a CF design) the sending jack and receive the returning jack also into tube stage, which is not the case here...

IMHO, I'd do it by replacing R11 with 500KA pot so that your master volume would prior to a gain stage. It will also work for the amp pre as well (turn it full on and your amp will be back to stock specs).

Another option would be a post PI master volume, which would allow you to use V3 as a gain stage to drive the P.I. harder and generate more distortion. Your stand alone preamp should have a output level control, this way you can blend it's output and P.I. driving signal. Just replace R24 & R25 with a dual ganged 250KA pot. Turn it full on and your amp will be back to stock specs). Also search for LARMAR PPIMV for more instructions on how to do it right.

See drawings below...

Hope this helps,

Best Regards

R.
 

[JustMike]

Hmmm...it's obvious when you point it out that there is no buffering whatsoever for the fx loop. It's about as primitive as it gets, eh?
 I'm going with your first suggestion at R11 as my preamp has no master volume on ch. 2 and I love the way it sounds when it's cranked.

 Many Thanks.

[JustMike]

 I wired in a 500kA pot at R11 as suggested and I've got 2 issues. The sound is thin now and the pot is noisy when I rotate it.
 I wired it >input from J7 to pin 3 of pot, Output (wiper) to pin 2 of V3a and pin 1 of pot to gnd.
 Might it work better if I place it before C14 ( the coupling cap immediately after the fx return)?

[rzenc]

The sound is thin

Does it behaves like this even when you rotate to max?

and the pot is noisy when I rotate it.

Might be rusty. Spray potentiometer lubricant and give it some full turns back and forth.

Hope this helps.

Best Regards

R.

[JustMike]

 I moved it to the spot I mentioned above and it appears to be working the way it should. I think having it before the coupling cap is what made the noise disappear. Also sounds normal now ( no thin-ness).

[rzenc]

sounds normal now

Nice!

Best Regards

R.