Studio Pro Silver Stripe T-Dynamics Distortion

This forum is for talking about all kinds of Peavey guitar amplifiers.
Post Reply
Monkey_Relish
New Member
Posts: 3
Joined: Thu Jun 22, 2017 7:08 am

Studio Pro Silver Stripe T-Dynamics Distortion

Post by Monkey_Relish » Thu Jun 22, 2017 8:21 am

Hi all,

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 check out the clipping diode section.

Image

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. Clever Hartley.
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.

Image

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.

Now, I'm not Dr Electronics, I just know enough to be dangerous. I'm hoping someone WAY more knowledgeable than me can either tell me i'm an idiot, or i'm on the right track.

Monkey Relish

User avatar
Enzo
Member
Posts: 9535
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: Studio Pro Silver Stripe T-Dynamics Distortion

Post by Enzo » Thu Jun 22, 2017 10:43 am

I don't see those as clipping diodes, I see them as limiters, I could be wrong. But I don't know anyone who puts clipping diodes in a power amp.

U4 is a pair of buffers, I'd be hesitant to stuff diodes in the feedback loops there.

Your power amp starts way up at the powr amp in jack. (FX return)

I don't see any clipping diodes in the amp. I do see a cross coupled pair in the lead channel in the preamp, but those are noise reduction, not clipping diodes.

The T-dynamics is not a distortion control, it is a power control. There is a nice paper on Transtube, and the end paragraphs are about T-dynamics:
https://peavey.com/support/technotes/ha ... pter_3.pdf

Monkey_Relish
New Member
Posts: 3
Joined: Thu Jun 22, 2017 7:08 am

Re: Studio Pro Silver Stripe T-Dynamics Distortion

Post by Monkey_Relish » Thu Jun 22, 2017 7:52 pm

From the above link :- Chapter 3 TransTube® by Hartley Peavey
Chapter 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.
Now, my reading of that is what I described above. The T-Dynamics section is in the output stage, and the power amp section
is immediately after this stage. The T-Dynamics variably engages a clipping section. This is done by changing the gain on the input op-amp
to increase the signal so as the clipping operates at a lower volume, or decrease the signal so it clips at a higher volume.
The output op-amp is to maintain the same volume for any setting.

Kind of makes sense ?

Mr Relish

Post Reply