Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

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dicianne
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Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Sat Jun 19, 2021 10:18 pm

When I select the clean channel, I'm getting a fizzle/crackling sound on both the balanced out and main ts out, but not on the clean send, and common send outputs. It's not heard if I play soft, but anything just a tad louder it distorts. But not on the common send and clean send. Those sound fine. The crackle is just on the main outs (xlr/ts 1v rms)
The output on both clean send and common send is louder than on the main outs. The main outs sound about %20 lower than common/clean send, and crackle easily. Akin to how a distortion pedal with very low battery sounds like.
Any ideas what's wrong with it?

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Enzo
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by Enzo » Sun Jun 20, 2021 7:29 pm

Well first, your signal has to go through a zillion jacks on that model, no matter what channel ypou use. SO first thing I'd do would be to clean the cutout contacts on every jack.

You tested things like common send, but I see no report on testing the common return for example. Play through the common return and see if it is affected.

Those whole main outputs run through V4a and V4b, SO at least sub a different 12AX7 into V4.

dicianne
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Sun Jun 20, 2021 10:34 pm

Let me see if I understood you correctly. Plug my guitar straight into the return of the clean and common channels. Or just loop the clean/common send into the return socket. ?

I replaced all tubes already, just because it came with the original peavey branded tubes. I thought replacing all tubes would fix that crackle problem since they're over 30yrs old. Although I think I either put a 12au7 or 12at7 in v4 socket. I should recheck that.

Unrelated question maybe, but is it a good idea switching the 12xa7 tubes with any other 9pin tube? which tubes should I avoid. I more or less know which are for audio, and which look like they're are for other applications. I'm intrigued by how long plate tubes would sound like in this device. Is this safe. What should I watch out for?

Since I'm already playing a whacamole game with this unit, replacing old components at a time and whatnot, should I replace every component adjacent to the v4 socket? Any other component failure in that area that could result in this unpleasant distortion in the clean channel.?

Thanks for reading

dicianne
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Mon Jun 21, 2021 12:28 am

Ok just tested the return on both clean and common by pluggin in my guitar on those jacks. No distortion that I could hear. And that's with the volume all the way up. I do hear the occasional crackle that's normal when overloading an interface's input if I strum the guitar loud enough. But is not on the same constant level that I would hear if I plug in through either low or high gain input on the front while playing normal.

I also plugged in straight into my mixer to rule out the audio interface. And I'm getting the exact same distortion on the clean channel. The distortion already happens at notch 4 on the clean gain level knob, past that and it distorts. and not in a pleasant way
Last edited by dicianne on Thu Jun 24, 2021 3:05 am, edited 1 time in total.

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Enzo
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by Enzo » Mon Jun 21, 2021 2:15 am

I don't know what parts are near the socket, some parts of the V4 CIRCUIT can be on other circuit boards even.

You should definitely use 12AX7 in all sockets, at least until the problems are sorted out. You can experiment with any of the 12A?7 family, but V4 wouldn't be my choice for that. It is not an overdrive tube, it serves as a return boost for the common return and the other half is a cathode follower to drive the main output.

Have we cleaned the cutout contacts on the jacks yet?

dicianne
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Mon Jun 21, 2021 5:39 am

Have we cleaned the cutout contacts on the jacks yet?
I haven't cleaned them yet. I'm waiting for a deoxit can in the mail, and then I'll clean them up
I also swapped the tube in v4 with a 12ax7 and the issue still remains.

There's one odd thing I noticed about my preamp compared to others I've seen online. Mine has a weird configuration of 2 capacitor piggybacking on each other that i haven't seen on any other rockmaster preamp on the web. Is this normal? I want to make sure this isn't a mod from the previous owner

Thanks
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dicianne
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Thu Jun 24, 2021 2:55 am

Ok cleaning the output sockets made no difference. What next?
And what's that double cap configuration?. I'm spent a few hours looking at picture of this preamp model online. And not one single rockmaster preamp's insides has it. Is it a mod?
Could I use it as is? Just using the send outs? I'm not getting anywhere with this unit. I'm no electrical engineer and I don't feel remotely qualified to diagnose what's wrong with it. Even with people's help

dicianne
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Thu Jun 24, 2021 3:12 am

Now that I hear it closely the nasty distortion is present even in the distortion channels. The send outs, output a smooth, even, distorted signal. The main outs output the signal, with what sounds like a periodic modulated beating signal on top, and the crackle does seep in occasionally.

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Enzo
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by Enzo » Thu Jun 24, 2021 10:55 am

The dual cap is just two caps in parallel. In my experience, when I see this, I look at the schematic and see a 22uf 450v cap. I suspect someone went to replace it and did not have a 22uf cap, so they put two 10uf caps in parallel to make 20uf (close enough). It is also possible someone used this technique to make that cap larger, thinking it might reduce hum. In either case, I see nothing unusual about it.

If the common send sounds OK, that only leaves the V4 circuit and the ribbon cable over to the tube and back. That is all there is between the common send and the main outs. We could have cracked solder, or a noisy resistor, or a failing ribbon connection, or some other basic issue.

dicianne
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Thu Jun 24, 2021 10:08 pm

Ok. I'll take the pcb out and inspect traces between the v4 circuit and main outs, and test components in the path as well. Although I only know how to test caps and resistors. That's the limit of my "expertise" in the matter. I'm definitely changing that parallel cap, and adding the missing orange cap that should be next to it. I want this unit to look as stock as possible
Thanks for the help thus far

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Enzo
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by Enzo » Fri Jun 25, 2021 11:36 am

Doesn't your unit have a green disc cap where that orange one goes? If it is the same value, I see no reason to change it.

dicianne
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Sat Jun 26, 2021 1:28 am

Doesn't your unit have a green disc cap where that orange one goes?
Nope. There's just a bare wire there. I'll include more pics later. I'm taking the pcb out of the chassis
Thanks

dicianne
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Sat Jun 26, 2021 7:53 am

This looks worse than I thought. This is the v4 circuit. It looks like someone traced some of the circuit path with solder. There's some more of that on the main pcb as well near or around the main outs.
After putting it back together now I get crackle even on the clean send out. :/
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dicianne
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Wed Jun 30, 2021 11:59 pm

I re-soldered every connection point on the tubes pcb and it's gone back to how it was before. I figured I might've accidentally fractured the soldering points when I flexed the gray cables and as a consequence I was getting the same kind of distortion on the send and common outs. I'm still dealing with distortion on the xlr and ts main outs. There's one point on the pcb that looks heavily rusted and I'm wondering if this could be culprit for this distortion.
Last edited by dicianne on Thu Jul 01, 2021 1:00 am, edited 1 time in total.

dicianne
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Re: Peavey rockmaster preamp. Clean channel sounds distorted on main outs, but not on clean send

Post by dicianne » Thu Jul 01, 2021 12:58 am

pictures incoming..
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