Peavey amp

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Jmpj48
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Post by Jmpj48 »

1746CE14-9C38-4884-A241-EA2BC21F493A.png
. Could somebody tell me how the relay switching on this amp works. My problem is on the clean channel the tone stack works but on the gain channel the bass and mids are not working. The treble is working on the gain channel that’s crazy. So the relay is working it switches channels but not the tone stack. So on the gain it’s only letting the treble through.

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george giblet
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Post by george giblet »

See discussion below and patent as this now seems incorrect - in fact it's opposite.


Clean: SW1-A is open, SW1-B is to the right
In clean mode the LEVEL pot is disconnect the U1A provides the gain control.
The tone control operates normally.

Gain: SW-1A is closed (9 to 11), and SW-1B is to left
In gain mode the LEVEL pot is grounded allow U1B to provide high gain.
The components C5 & R7 largely bypass the tone control. The treble will still do something but it becomes more like a mid control. When the treble control is on minimum you might find the bass and mids have a small effect.

From what I can see the idea is the gain channel has a largely fixed voicing and the controls are used primarily for clean tone.
Last edited by george giblet on 30 Aug 2020, 23:22, edited 1 time in total.

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Jmpj48
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Post by Jmpj48 »

I don’t think I have ever seen a amp that the tone stack don’t work on the gain channel lol. I wonder if I could bypass the clean and get the tone stack to work on the gain channel. This is a peavey vss 20 head. Got it at a pawn shop I have never seen one before it was made in 1988. I read a few reviews on it before I bought it got bad reviews. But actually it sounds pretty good. And for 20 watts stereo it is loud. It’s got chorus on it to sounds good. Or it don’t have a fx loop on it I could put one on it were I could use a eq in the loop and leave the tone stack like it is.

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phatt
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Post by phatt »

I notice that R27 is 22k,, holy crap man that will just kill the ability of tone controls. The tone setup is HiZ but with 22k across the output your tone will be very restricted. :slap:
If it were me I would lift one end of R27 just to see/hear if it improves the tone controls ability.

It may have so much that the amp will oscillate at high gain but you will likely end up with a much stronger working signal level so you would not need so much gain anyway.
Just my 2 cents worth,, maybe give it try.
Phil.

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Post by soulsonic »

which amp is this? jeez
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Post by phatt »

@ Soulsonic
Says it's a vss 20 head

@ george giblet
Thanks Good explanation,, I was confused about the relays and the way they are drawn.

@Jmpj48
Unless I've missed something,,,If you want you can just lift one end of C5 and the tone should work on both Clean and Drive.
Phil.

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Post by Jmpj48 »

Ok I’ll try that thanks for the info

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Post by Jmpj48 »

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Post by Jmpj48 »

64F01278-6BBF-4293-810C-4BE4BF6F8B55.png
. If I wanted to add a fx loop were would I go about putting it. Would it go right after post volume and before power amp.

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Post by Jmpj48 »

I lifted one of r27 didn't like the sound didn't change the tone stack Soldered it back.Then i lifted c5 tone stack didn't change except the treble acted like a gain control. I soldered it back i guess i will add a fx loop to it were i can run a eq in the loop. Thanks for the help

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Post by george giblet »

I notice that R27 is 22k,, holy crap man that will just kill the ability of tone controls.
Well spotted. I don't get it.
I've seen the C5+R7 thing before on Peavey amps and variations on other amps but I don't remember the low R27 thing.
R27 is even a weird connection when SW1-B is to the left.

Looking at the second part of the schematic the switch to the right pulls down the diodes so you would think that is the gain mode.
What I said before doesn't seem correct now. It also looks like the output is shorted to the switched ground where R30 and C21 meet.

The schem doesn't look right.

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Post by Jmpj48 »

The only way I can get the bass and mids to work In gain mode is lower the treble pot all the way down to the left and it acts like a gain pot it’s add distortion. That’s crazy I never seen anything like this. The amp sounds good except for the bass and mids not working right.There is no balls to sound I guess u could say lol. I play metal music or 80’s metal. I looked at the manual it has a couple of examples how to set the amp for metal and it has the typical settings bass at 3 mids at 9 treble at 3. So I know the tone stack should work in gain mode. But it’s not maybe it something in the relay gone bad. Maybe I should order a new one. This looks like a bad design by peavey. Not adding a tone stack after the gain channel. Around 1989 they started to use the there bottom/body/edge active tone stack that sounded awesome. This amp is a very Weird design lol. I never even Heard of this amp before tell I seen it in a pawn shop. It was actually a mini stack it came with 2 single speaker cabs that way u can use the stereo chorus on it. By the way the chorus sounds really good on it. But it only has one knob on it to adjust the chorus instead of 2 controls that’s weird to lol.

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Post by Jmpj48 »

I might try to mod this into a bandit circuit. One channel only gain. I wish this was the trans Tube but I could mod it to the bandit solo series circuit its got ic in it. It has a active baxendall tone stack.

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Post by george giblet »

I haven't had a chance to look into this more deeply. The idea was to see what the manual said about the intended behaviour. Maybe it explains what it should do. From the manual, is the patent for the "Super Sat" circuit. It might explain some stuff. Normally values are given in the patent.

The old Bandit route is an option. In principle the Super Sat supposed to be an improvement over the old Bandit circuit.


Peavey VSS 20 Manual
https://assets.peavey.com/literature/ma ... 300892.pdf

Super Sat/Superdistortion patent
https://patentimages.storage.googleapis ... 811401.pdf

In the patent there's no 22k. Also the weird short I mentioned isn't their. The patent circiuit diagram makes more sense.
And there is a table of part values. In the patent, when the extra treble cap is connected the second gain stage is active. That also makes more sense.

The question is what's the circuit on the PCB? Does it match the patent or the PV schematic - which obviously has some errors.
Last edited by george giblet on 01 Sep 2020, 01:09, edited 1 time in total.

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Post by george giblet »

I found some schematics of supersat era Peavey's.

The two Audition schematics have the supersat-ish circuit but they don't have the switching or the 22k.

The Bandit 75 is the Band in the supersat era. It has the 22k.
(There is likely to be a Bandit 112 supersat after this model, I can't find the schematic)

The Special 112 is similar to the Bandit 75.


The Special 112 offers an additional Presence control which takes place of the fixed treble boost on the VSS 20 and the Bandit 75.
The other thing to note is Special 112 and Band 75 don't show the error where the output of the opamp near the 1M pot shorted to ground.
Both do have the 22k resistor.


Peavey Audition 20 (1984)
Supersat-ish but no switching
http://www.kobra.hr/Schematics/Peavey/P ... 0(20W).jpg

Peavey Audition 30 (1986)
Supersat-ish but no switching
http://www.kobra.hr/Schematics/Peavey/P ... n%2030.jpg

Bandit 75 Solo Series (1987-89)
Supersat w/switching
https://www.audioservicemanuals.com/p/p ... -schematic

Special 112 SM
Supersat w/switching + presence
https://elektrotanya.com/peavey_special ... nload.html

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Post by Jmpj48 »

Thanks for all the info good stuff

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Post by teemuk »

Consult the manual. It probably says tone controls are inoperational on gain channel (that's "feature" of several Peavey amps of the era, sometimes implemented to a "Thick" switch). Yes, as explained the tone stack is bypassed with signal path that swamps impedance of tone controls.

Later "Supersaturation" amplifiers began to feature channel-specific tone controls with the old passive stack for clean channel and 3-band active circuit for supersat.

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Post by Jmpj48 »

There is the block diagram from the manual no tone stack on gain channel goes straight to the chorus circuit. Why would they make a amp with no tone stack on the gain channel. And don’t even put a fx loop in it. Don’t make no since lol.
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Post by microbailey »

There’s no tonestack but as your block diagram shows the “thick” control which I’ve seen implemented as a pull switch usually gives a mid range boost. I thinks that’s the only EQ you get on the gain side.
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Post by teemuk »

Jmpj48 wrote: 31 Aug 2020, 17:20 Why would they make a amp with no tone stack on the gain channel. And don’t even put a fx loop in it.
It's one of the cheaper models so to reduce cost they cut down features. You get what you pay for.

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