JVM Problems (Soundclip)

[Matt Smith]

Hey Guys--
My beloved JVM has started acting up.
My first thought was obviously a tube issue, though the noise is inconsistent and intermittent. There's no visible arcing or weirdness in the tubes, and it seems to make the noise on any channel. I haven't gotten the new tubes to swap out yet, so what's your opinion based on this clip? Tube issue or something more serious? It's just a minute or so of me playing a couple of Queensryche riffs.

JVM Soundclip

Thanks!

 

[zakky]

sounds like a preamp tube has gone bad.....

 

[ArthurD]

Or bad solder... Or even cable.
I had a similar problem when connected a bad cable to the cab. Be sure its a speaker cable and its good.

 

[GuitarHack]

Matt, it does sound like a preamp tube (possibly). Even before the replacements arrive, swap the pre-tubes around and see if a difference is heard.

On a side note, even with the noise, your tone is awesome. I always used your amp/cab tests as a RAW reference tone and didn't get close in comparison. Damn dude, you know how to mic a Cab.

 

[Matt Smith]

Haha, thanks man, I appreciate it. And thanks guys for your ideas.

I should have mentioned that I tried different instrument cables, speaker cables, guitars and cabs before anything, and all that stuff is fine. Today I swapped out each of the preamp tubes one by one with a good one, and that made no difference, so it doesn't seem to be the problem. One thing of note is that the noise sounds "reverby" to me...even though I don't have the reverb on (except on the clean channel), the noise sounds like it's going through the reverb tank or something. Bizarre. Others have suggested it may be a bad pot or capacitor. I guess I'll have to take it to a tech. Thanks everyone for your help and ideas--I really appreciate it.

Matt

 

[GuitarHack]

Sorry Matt, sounded a little like a preamp tube had gone microphonic and was picking up the vibrations from the Powertubes and causing the Reverb-y (feedback)type effect. I had a similar thing on my first Revolution.

 

[greyskull]

Could be a pre-amp Valve, but it could also be a dieing resistor.
I had a similar thing in my JMP when it was acting up

 

[sprack]

Play out through the effects loop. That'll narrow it to pre vs power amp tubes.

Edit: Looked at the the schematic. V9a could still be suspect. But at least its down to that one tube and the power section.