Peavey’s Secret

[Jacob]

Prior to building my own amps (recently) I almost exclusively used Peavey “Classic” series amps. My first tube amp (about 10 years ago) was a Classic 50 head which I paired with a Vox 2x12 cabinet.

Since then, I’ve also acquired the Classic 30 and Classic 20 (Mini Head)

It wasn’t until I started building/became more familiar with actual classic amps, that I realized how impressive the amount of Clean Headroom/Volume the Peavey Classic amps have for EL84s, especially the Classic 20 mini head (2xEL84s)

I was wondering if anyone here could educate me on how they achieve this?

I have the current version of the AC15, and it definitely has enough clean headroom for me. But by comparison, the Classic 20 just seems to have WAY more despite having the same tube setup.

It also seems that the Peavey can take Boost/Drive pedals much more easily without compressing/caving in compared to an AC15.
But the Vox definitely has a more compelling/responsive/touch sensitive tone going straight in compared to the Peavey.

I’m guessing this is a trade off?

Anyway, just hoping there might be something to learn here about circuit design.

Are there elements of the Peavey Classic circuits that are good practices for maximizing clean headroom/volume?

Would a handwired version of these circuits give it more soul/vibe?

Or is that the trade off?

I’d love to learn something here!

Thanks!
Jake

[jim]

You ask a very open ended question.  But you have built amps and studied schematics.   Its also the reason why we must have a different amp for every musical obsession.   Your AC15 has a pentode pre-amp tube--not a dual triode like the Peavey or Fender.  It is very sensitive to being pushed and quickly turns to mush with pedals. Plug in direct and you have clean if you tickle the strings and bite if you stab.Also the Vox has no negative feedback and is more free running.  The Peavey and Fender feed a small voltage from a speaker tap to an earlier stage that cancels out some distortion making them behave. There is not much difference between an exact factory circuit board replica of a classic hand built circuit.   Point to point is simply easier to service and modify.  The list could go on and on.....Jim

[Jacob]

You ask a very open ended question.  But you have built amps and studied schematics.   Its also the reason why we must have a different amp for every musical obsession.   Your AC15 has a pentode pre-amp tube--not a dual triode like the Peavey or Fender.  It is very sensitive to being pushed and quickly turns to mush with pedals. Plug in direct and you have clean if you tickle the strings and bite if you stab.Also the Vox has no negative feedback and is more free running.  The Peavey and Fender feed a small voltage from a speaker tap to an earlier stage that cancels out some distortion making them behave. There is not much difference between an exact factory circuit board replica of a classic hand built circuit.   Point to point is simply easier to service and modify.  The list could go on and on.....Jim

Pentode preamp tube? Do you mean an EF86? I have the current production AC15, which uses 12ax7s.

So if comparing this with the Classic 20, which has an identical tube lineup, do you think the difference in clean headroom is only that the Peavey has a Negative Feedback circuit?

And yes, an open ended question. Hoping to learn as much as possible.

[tubenit]

Print off both schematics and set them side by side and start looking at the differences in topology, voltages and component values.  Mark or write down the differences on one of the schematics.  For example, the Vox has .1 post phase invertor coupling caps and the Peavey has .047.   There are lots of differences to be noted.


With respect, Tubenit

[Jacob]

Print off both schematics and set them side by side and start looking at the differences in topology, voltages and component values.  Mark or write down the differences on one of the schematics.  For example, the Vox has .1 post phase invertor coupling caps and the Peavey has .047.   There are lots of differences to be noted.


With respect, Tubenit

Thanks Tubenit! I will definitely do that.

Are there any key areas in the amp where higher/lower voltages/values affect the headroom more so than others?
Or is it a cumulative approach across the entire circuit?

Can a few key changes in a few key places change the headroom characteristics of an amp significantly?

Or do all values in all locations need to be chosen with that goal in mind the whole way through?

Hoping this will help me know what to look for when comparing the schematics

[SILVERGUN]

I’d love to learn something here!

These 2 videos are a great visual representation of what happens in a gain stage. I found these to be helpful and I got lucky because they were produced during a time when I was trying to piece some knowledge together. Hopefully you'll get something from them.

Understanding the Tube Amp: Biasing the Triode on Vimeo

Understanding the Tube Amp: The Triode Revised on Vimeo

[brewdude]

I think it can be said that, generally speaking, higher voltages are cleaner with more headroom.  However, operating conditions (bias) can greatly influence the clean/dirty/headroom/compression.

[Jacob]

I’d love to learn something here!

These 2 videos are a great visual representation of what happens in a gain stage. I found these to be helpful and I got lucky because they were produced during a time when I was trying to piece some knowledge together. Hopefully you'll get something from them.

Understanding the Tube Amp: Biasing the Triode on Vimeo

Understanding the Tube Amp: The Triode Revised on Vimeo

Thank you! I will check these out ASAP!

[Jacob]

I think it can be said that, generally speaking, higher voltages are cleaner with more headroom.  However, operating conditions (bias) can greatly influence the clean/dirty/headroom/compression.

Thank you! I thought that might be the case, but wasn’t sure