Channel B has a Hiss

[Dante]

I usually just run two amps in mono, from a stereo FX unit. So, I haven't tried running the MP-2 in stereo for some time now.

Well, I did this morning and Channel B is hissing slightly. I can get it louder with the volume, but it's there. Kinda like a very low white noise....sounds like an amp cranked way up with nothing hooked to it.

It's not overly annoying until I stop playing....Any ideas?

[rnolan]

Hey Dante, I've found MP-2s can get a bit noisy (similar to what you describe) on the high gain settings.  You can try increasing the noise gate threshold, which I've had to do a little over time (i.e. what was just right when it was new(er) is now not quite enough. But I don't need to use the gate for voice 5 or less, only on the high gain (6 - 10).
Also (obviously) give the jacks a clean since nothings been plugged into it/them for a while.  With one of my studio MP-2s I was having one channel drop out (using cab sim outs).  Some of that issue ended up being gummy assignment buttons on mixer channels but also inserting the jack a few times also made a difference (hence it may just need a clean).  Also check if it's the same issue on the cab sim outs. They split off just after the Output level control so the input to the cab sim/emulator is the same signal that goes to the main outs (see page 4 of the MP-2 manual).

IIRC your MP-2 went over to MJMP at one stage for some work?  Did you get the noise mod done?  Only one of my MP-2s has had the noise mod, my original MP-2 (bought new way back when) is still fine.  I did one of the 2 studio units, and it was the one with the dropout issue.

Other things to check, depending how you have it patched, is fx loops (are you using the loops?).

So the signal goes stereo after the chorus (before that there is no A + B), since you only have the noise on the B channel, then it makes sense it's after the chorus (or possibly introduced by the chorus?), so next are the fx loops (if switched out should make no difference),  then tremolo (also if switched out...), then midi controlled stereo vol, but then 2 stereo pots, Room EQ and Output level.  Both you can clean (and I've had a scratchy Room EQ knob before, a few sweeps fixed it and it's probably not something you change that much, albeit quite handy (I've found) for different rooms/stages).

Another thought, have you tried switching the leads to make sure it's channel B and not the amp after it?

[Dante]

Thx Richard

It's not a speaker wire, I tried a few....its not the power amp, it's just the MP2. Studio outs and amp outs both do it, the speaker emulator has no effect on the hiss.

It's not a high gain voicing, because channel A is quiet, they would both be hissy if that was it. I was not using the FX loops. This morning, just to be sure, I plugged into the FX loops and I have a little buzz in the RETURN of LOOP A. Fiddling with the Line/Inst button seems to fix it, so there's an issue there I need to address...but it's not the hiss

I believe I had MJMP go thru my Classic, maybe it was my mp-2....I don't know

So, in summary, something in channel B of the MP-2 is making a little hiss.  If there is a little soldering I can do to fix it, I'm down. And, I need to address my Line/Inst switch while I'm in there

I will try to get a good recording of it

[MarshallJMP]

It was your classic.

Does the room EQ knob has an influence on the hiss?

[Dante]

@MJMP: The room EQ just changes the EQ, doesn't effect the amount of hiss

FX Loop Buzz:
I tried reflowing the solder on that switch, no go. All the contacts look fine, feel solid. The switch itself is a mess, I can get the buzz gone and make it show up again by wiggling the little white button side to side. I'm going to need a new switch, pic attached

[rnolan]

Hey Dante, I've had issues with those switches before, I managed to clean them a bit by spaying and pressing in and out multiple times.  Also the output pot comes after the Room EQ pot (on the schematic in the manual).  But if it's not that, and the loop is ok (or not used), makes me think maybe one channel of the chorus?

[MarshallJMP]

Just looked and the room EQ pot is after the volume pot. Maybe something on the satellite board?

[Dante]

I finally got around to cleaning out that switch. Guess what? It worked!

No more noises from the FX loop. Still have that hiss in channel B, but I'm not using that channel. I'm running mono on each side for my stereo rig.

[rnolan]

Hey Dante, great news .  But the channel B hiss shouldn't be there , I still wonder what's causing that .