Thanks for the reply.
Yes, there's a whole lot going on there that I would need to understand first.
I will definitely leave it alone, No point messing up what is a surprisingly good amp.

Mr Relish

OK, there is a fair bit going on there. So, the "Hard Clipping" diodes I circled aren't there for clipping ? Or is this happening before the middle two op amps ?

I probably should just leave it alone and go play with pedal circuits LOL.

Mr Relish

Hi all, first time poster.

I recently picked up a Peavey Studio Pro 112 "Silver Stripe". Basically an Express without the T-Dynamics pot and a crappier speaker.
Now, as I can't leave anything alone, I emailed Peavey for the schematic so I could add the T-Dynamics pot.
The T-Dynamics circuit is the same as a Bandit, Silver Stripe and Red Stripe are mostly identical.
Adding the T-Dynamics pot is relatively easy.



Here's how I think the T-Dynamics section works.

This is the distortion section controlled by the T-Dynamics pot. U5A and U5B are the pre and post gain sections.
The T-Dynamics is a dual gang 10KA/10KC pot. Log 10k and reverse log 10k.
With the pot at 100%, the pre gain is at minimum, and the post gain is at maximum. This requires more signal into this stage before clipping occurs.
With the pot at 20%, the pre gain is at maximum, and the post gain is at minimum. This requires less signal into this stage before clipping occurs.
The output signal from the post gain stage is the same for any pot position.
The studio Pro has no T-Dynamics pot. It is the same circuit board with no pot, but set for 100% with a jumper

Now, the parallel op-amps U4A and U4B, I think that U4B passes the positive part of the waveform, and U4A the negative part. Not 100% sure here.

From a link ENZO pointed me towards on the PEAVEY forum :-

QuoteChapter 3 TransTube® by Hartley Peavey
Most people ASSUME that our TDynamics control is nothing more than "master volume"... WRONG!
The T-Dynamics variably engages a clipping circuit in the output stage that effectively lowers the power amp's headroom,
thus emulating a lower powered amp.
When the T-Dynamics control is turned down, it is not just acting as a volume control for the amp,
it actually decreases the available voltage swing just as a smaller/less powerful amplifier would do
while retaining all the vital TransTube overload characteristics that so effectively emulates a tube amp's sound and feel.

So, if the T-Dynamics section is effectively a variable clipping circuit, it could be modified to change the "Tube Breakup" sound this circuit is meant to emulate.



So, I circled what I think are the hard clipping diodes in red (CR32, 34, 44 & 46).
As for diode mods to change the distortion characteristics, these could be changed for Germanium diodes, two for each 1N4148.
Or, for assymetrical clipping, differing amount of diodes for each, say bridging CR46.

Or, the circuit could be changed to soft clipping, like a tube screamer. Removing the hard clipping diodes, and adding the diodes in blue.
I THINK they are shown the right way.

Am I reading this circuit right ?

Monkey Relish