Grateful Dead Music Forum

I've been dealing with an odd noise issue for some time. Happens with my modded Twin or SMS connected to the Mc2100 or connected to the QSCPLX, though not as pronounced with the QSCPLX as the MC2100. Happens if guitar/cord is connected or not.

It's not a hum, but more of a deep hiss. Sounds like a water fall or white noise and increases as the volume is turned up and is gone when either power amps volume is at zero.
Also, both power amps are dead silent with the volumes cranked when no preamp is connected to them. I've tried all possible eliminations (different cords, different venues etc) with no results.

The only other thing I can think of is it's something going on in the preamps.
The odd thing is that when using the Twin as a combo on it's own, there is no power amp noise. Pretty quiet.

Any insight would be helpful. Thanks!

I had the same problem- I have the sms preamp- it turned out to be one of the tubes- replaced the tube - and no noise! hope its as easy as that. peace

Thanks for the input, but I have tried tubes with no results. I will try again and see.

tommybo wrote:I had the same problem- I have the sms preamp- it turned out to be one of the tubes- replaced the tube - and no noise! hope its as easy as that. peace

Wow, tommybo! That is exactly what the problem was. I purchased new tubes when I did the work on the Twin, so I didn't think it could be tubes. I should have known better. That means a tube is bad in my SMS also.

Thanks again, brother! Made my day

i'm glad it was an easy fix- I always freak out when something fails or breaks and I always think the worst- then I take a deep breath and then logic kicks in - so glad you can fix it- rock on ! peace brother..............