Peavey Classic VTX - Bypass Preamp but keep Phaser and reverb?

[greenroom2009]

Hi,

I picked up a Peavey Classic VTX in beautiful shape. Caps have been replaced, everything else original and really nice. However, the preamp sucks. Any OD pedal in front is fizzy, internal OD is fizzy. Bleh. The cleans are awesome and the phase is magical.

Now, when i plug my Joyo American 'preamp pedal' into the Power Amp in, it sounds great. Putting any OD in front of the Joyo is great. But I loose the Phaser and reverb.

Is there a way to move the Power Amp input to be before the Phaser and Reverb so they are still available? I don't care about channel switching or the EQ. I have looked at the schematic and I think I know where the right insertion point would be .. but I would rather hear from an expert.

I am comfortable with soldering and clipping, jumping parts on the PCB .. or adding another input jack if need be. I just need help understanding the circuit. I can provide the schematic if needed.

Thanks

[52 Bill]

Welcome to the place. Have you considered getting the amp to sound the way you want instead? There may or may not be a problem with the distortion channel that is making it sound bad to you.

Fixing the channel may be an easier solution than trying to modify it to do what you want to do.

[nickb]

How about using the preamp out as an Fx send and power amp in as an FX return with your Joyo pedal? Mind you that would put the OD after the phase and reverb which would not be so good.

I have a Heritage VTX - much the same preamp. I don't like it's OD much either. It might be tweakable but I've never bothered to look.

[rhubarb9999]

Welcome to the place. Have you considered getting the amp to sound the way you want instead? There may or may not be a problem with the distortion channel that is making it sound bad to you.

Fixing the channel may be an easier solution than trying to modify it to do what you want to do.

When using the clean channel or no gain on the crunch channel the amp sounds great. It still has the original power tubes but I also tried a set of brand new JJ tubes .. same result. I tried a Les Paul and a Tele.

The only abnormal sound is a bad crackle/distortion/crunch then the Reverb is turned up past 5 or so. Below that is fine. Anything involving an overdrive pedal or the crunch section with gain is very 'fizzy'. I cant seem to EQ it out. Using the 'American' pedal (a Fender preamp simulator) into the Power Amp in makes the amp sound like a Twin .. but without reverb or phase.

What should I be looking for to 'fix' the preamp section? I have read about changing the opamps .. i have some different ones on hand .. I could give it a go.

[rhubarb9999]

Hmmm ... that's actually an interesting idea.

Something like this ....

Front of Amp in ->Clean channel -> Preamp out ->Pedal board (Wah,OD,Chorus,Delay)-> Joyo American -> Power Amp in

The only downside is that the phase and reverb would be BEFORE the overdrive. Not ideal .. but it might work.

[nickb]

What should I be looking for to 'fix' the preamp section? I have read about changing the opamps .. i have some different ones on hand .. I could give it a go.

Changing the opamps will probably have little effect and I personally wouldn't bother with that. I find it interesting that you describe the OD as fizzy. I always thought it sounded a bit dark and unmusical somehow. Either ours are different and/or it's subjective.

Taking look at the OD stage I see it's basically diode clipper with the saturation control doing a sort of mix between clipped and clean. There is a bit of filtering around that stage that could be changed to perhaps loose some of the farty bottoms. Perhaps a bit of HF rolloff after the clipper might help too. I get the feeling that the budget would not stretch to any more opamps in the design so they crammed as much as they could into this stage.

Extra Info:
The cap C6 rolls of the low end and C3 does the high end (when the saturation is high). I would make them both about half the value but you may not want the hassle of yanking the PCB and experimenting. Nothing currently there to control the HF fizz after the clipper Maybe I'll give it a go next week once I've got past a few must do things.

Schematic:

[rhubarb9999]

With the help of the Peavey forum, I got exactly what I was looking for.

I lifted the positive side of C26 and hooked the output of the American pedal to it. PERFECT!

Dead quiet, lots of gain on tap. Reverb and phase work as they should. Switching works with an added bonus.

When I switch to the OD channel, the Post volume matches the Clean volume when at 10. So, if I set the volume on the American to be my solo volume on the Clean channel, then back the Post volume down to 7 or so and stay on the OD channel, I now have a Boost on the footswitch!

I removed the wire from the Preamp Out jack and jumped C26 to it for now. My plan is to put a switch and another jack in so the amp can run totally stock or in this new mode.

So basically I have a 50 watt Twin with boost and phase. The American also does a very convincing Tweed tone and takes pedals really well. They also make pedals that are really good versions of an AC30, Marshall, and Mesa. At $40 each .. can't go wrong.

Thanks for everyone's help!

[nickb]

With the help of the Peavey forum, I got exactly what I was looking for.

I lifted the positive side of C26 and hooked the output of the American pedal to it. PERFECT!

Dead quiet, lots of gain on tap. Reverb and phase work as they should. Switching works with an added bonus.

When I switch to the OD channel, the Post volume matches the Clean volume when at 10. So, if I set the volume on the American to be my solo volume on the Clean channel, then back the Post volume down to 7 or so and stay on the OD channel, I now have a Boost on the footswitch!

I removed the wire from the Preamp Out jack and jumped C26 to it for now. My plan is to put a switch and another jack in so the amp can run totally stock or in this new mode.

So basically I have a 50 watt Twin with boost and phase. The American also does a very convincing Tweed tone and takes pedals really well. They also make pedals that are really good versions of an AC30, Marshall, and Mesa. At $40 each .. can't go wrong.

Thanks for everyone's help!

Thx for letting us know +1