Hum/Noise vs shielded cable or twisted wires in a Peavey Triumph 60

[stoneattic]

So I have a Peavey Triumph 60 that, with the help of the folks on this forum, I was able to get up and running a couple of years ago. I haven't used it much over the years, but recently went to use it and it was very noisy. It had been a while since I used it but I did remember it being noisy, but couldn't remember for sure HOW noisy. Searching online it appears other folks with this amp have observed it was noisy as well. To make matters worse I had done the diode/noise gate bypass mod and the EQ on the Crunch and Ultra channel mod with a switches to enable/disable on both.

Schematic can be found here: https://peavey.com/forum/viewtopic.php?t=32885

The diode/noise gate bypass mod jumpers over CR2.
The EQ mod keeps the Mid and Low EQs in the circuit when switched to the Crunch or Ultra channels by clipping the jumper between the junction of R11 and C62 and the relay.

So I substituted a 12AU7 for V2 and that helped the noise a good bit, but of course reduced the gain. I'm okay with the reduced gain because the gain on tap with the 12AX7 is ridiculous.
But there is a hum/noise when not playing that is there regardless of channel or if there is nothing plugged in, an instrument is plugged in or a grounded plug.

I'm not sure if the switches and wiring I added is causing the hum/noise. I found that if I move the wires from the EQ mod switch around the hum gets better or worse and if I tap it you can hear it in the speaker. The noise seems slightly worse in the bypass (non-stock) position). The diode mode wires do not seem affected by touching or moving. I've also noticed that finger/string noise seems much more noticeable on this amp than any of my others.

My questions/options are:
1 - live with the noise
2 - put shielded cables to the switches (and if I do this I believe I should ground only one end, but which end?)
3 - ?

Pic of the switch routing/wires attached. The wires are positioned in the best location to reduce the noise.

Any ideas, suggestions, etc?

[Chuck H]

Most of the noise is thermal hiss from series resistance and impressive gain levels. That amp has huge preamp clipping. On par with almost any modern uber gain amp. Hiss is a VERY typical byproduct. That's probably why the noise gate was added to the circuit in the first place. As some modern amps with similar gain levels do.

You could try to reduce series resistance in voltage dividers to a point where it doesn't impact gain. It would certainly be a PITA experimenting on a PCB amp like that and it would alter the sound such that other circuit mods may be necessary. There are some tubes that have low microphonics and a little less extreme top end. The Sovtek 12ax7WA comes to mind. Try to get selected tubes because they can be hummy/buzzy on their own sometimes, but a quiet one would probably help your issue without much change in overall tone. And consider fussing with the noise gate circuit. Maybe work out circuit values that don't cause objectionable problems that inspired you to bypass it. I never had a problem with mine so I'm not sure why you did that.

[daz]

I had one of those the first year they came out. Man did that thing have gain !!! I was still into pretty heavy OD back then (around 88) and that amp delivered like no other at the time. Thing wouldn't clean up with the guitar volume at all but back then i didn't care much

[Chuck H]

I had one of those the first year they came out. Man did that thing have gain !!! I was still into pretty heavy OD back then (around 88) and that amp delivered like no other at the time. Thing wouldn't clean up with the guitar volume at all but back then i didn't care much

Same story here. A real grinder. I also had a Rock Master preamp. Same as the Triumph but I could plug it into a Peavey Classic 60/60 rack mount power amp and run it into a pair of 2x12 cabs with an Alesis Quadraverb for stereo effects I used a simple momentary switch to operate the advance function on the Qverbs midi controller to manage about twenty presets. I played A LOT of gigs with that rig. Then I got tired of everything sounding generic and bought a beat up Marshall head (Rock Master and 60/60 as partial trade), which is when I started doing modifications. That was the beginning of the end I eventually went to old school floor pedals into the front end when a simple effects loop off the treble pot didn't work out and pawned the Qverb. Never looked back.

[stoneattic]

Thanks for the responses.

Maybe it is just the nature of the beast, but it is worse than any other amp I have. The Triumph might be the highest gain though, at least with the 12AX7 in V2.

I did the noise gate mods because others recommended it and I like to tweak. I put it in with a switch so that I could do an A/B comparison. Without the gate notes sustain better and drop off less abruptly. It actually seems a little like adding a mild compressor when bypassed. The difference is subtle though. You get a little better sustain and smoother note tail off in exchange for a little bit more noise.

The EQ mod was a big improvement. I would definitely recommend this mod.

I was just assuming that, especially based on the noise moving the EQ mod switch wires caused, there would be something like shielded cable to the switch that might help the noise. Although I'm not sure the proper way to ground the shield and if just standard instrument cable would work or if it should be 2 conductor with a separate shield..

I will try some other 12AX7s (I have tons laying around) to see if any help the noise.

One other thing I noticed is that the noise when not playing didn't change with volume or gain. It was just as noisy with the amp volume low as it was cranked.

[Chuck H]

One other thing I noticed is that the noise when not playing didn't change with volume or gain. It was just as noisy with the amp volume low as it was cranked.

Well that seems odd. That might be a bad connection. Of course we all expect a high gain amp turned up loud to hiss like a snake. But the hiss should be analogous to volume settings. If it's not I would say you almost certainly have an open ground connection in the signal chain.

EDIT: It occurs to me now, also, that you may have a silicootie that's gone noisy too. I can't remember if the amp uses a SS effects loop, but if it does that may be on the other side of the preamp volume controls so a noisy amplifier there feeds unabated into the power amp.

[daz]

I thought they'd be full of SS devices but looked at the schematic, albeit it rather quickly, and it appears to be pretty much purely tube including the loop ! Thats was quite surprising considering the modern tight gain tone. By the way, how the H did they get such a tight hi gain tone using all those 22uf cathode stages and .022uf couplers? I don't get how thats accomplished. One 22uf cathode in mine and it turns to useless fat mush even if i cut the coupler values in half or less.

[stoneattic]

Right, no ICs at all and the only silicon appears to be a transistor for LED and diodes. The bad ground makes sense and fits the really noticeable string/finger noise and possibly the noise when moving the EQ switch wire. Now the fun of trying to figure out where the bad ground is...

[stoneattic]

I finally got around to working on this again. I ended up removing the mod switches and leaving the EQ mod enabled, but undoing the gate mod. It is much quieter. Even quiet enough that I removed the 12AU7 and put the 12AX7 back in V2. It's still a little noisy, but much better and bearable. I plan on grabbing shielded wire and putting the switches back in if only to see how much of a difference it makes in noise.

My new dilemma is that the bias on the new tubes (Sovtek 6L6WXT+) is much lower (22-25mA) than the previous (RCA) tubes (32-33mA). So now I need to add a bias pot to it.