Buzz in 1987x

[pj1967]

Hi all,

I've got a 2008 Marshall 1987x reissue (with FX loop) that has an annoying buzz-like oscillation going on. It's very prominent when playng lower notes, particularly low A (low E string, 5th fret), but tends to disappear when playing higher notes (12th fret or higher). I've swapped pre-amp and power tubes (actually this was the first thing I did), and even switched out the 50uF+50uF filter caps (Rubys replaced with F&T). But, the problem persisted.

So, using the FX loop, I isolated it to the preamp section. Nearest I can tell, it seems more prominent in the Normal channel than the High Treble channel. Also, the annoying buzz occurs when the FX loop is bypassed, so I can't point the finger at the FX loop circuit.

Any ideas?

THX,

PJ

[pj1967]

So, after much hair pulling, hand wringing, and threats of tossing it out the window, I finally found the problem. And, it's embarrasing...the attentuator. When I bought the 1987x used, it came with a 16ohm Hotplate. Now, I rarely, if ever, get to fully crank my amps without an attenuator 'cause I'm married with little kids (wife stays home)...'nough said.

But, the other day, I had the rare opportunity to run the amp through the cab with no attentuator and lo and behold, no buzzing! Stupid me. I even tried this Hotplate with my Metro JTM 45/100 (George put together for me, thank you, George...it's a beauty BTW!), and made the poor amp sound like crap, too. With my high gain JCM800s and even JVM it wasn't as bad...I suspect the buzzing was swamped out...but still not very pleasing. Time to take apart an attenuator...maybe I'll let my 5 year old do it.

So, go tell all your friends what a stupid idget PJ is.

--PJ