JCM 800 Fault??

SidNewton

One for ICBM and the amp buffs.....

Just got back from band practice  where my JCM 800 50 watt head started to make some unpleasant sounds which resembled a redneck making love to a pig.

I use the low input then use pedals for drive. A Fulltone OCD or Boss DS1 gives me my crunch rhythm and an Ibanez TS808/Mad Professor delay gives me my lead sound. I use a Bright Onion looper to switch between the 2 sounds. The OCD and DS1gave no problems but it squealed like a pig when switching to the lead sound.

So tried the singers guitar, same thing. Took the pedal board out of the equation and plugged straight into the high output and experienced similar noise. It's worse the closer you get to the amp. It most definitely doesn't sound like feedback. Please tell me it's a simple dodgy preamp valve that's causing the problem. It's currently valved with JJ's throughout and in all fairness didn't sound at it's best today.

ICBM

If it's worse when you're close to the amp it sounds like either microphonic or electromagnetic feedback.

What guitars did you try?

Was your phone in your trouser pocket right behind the guitar pickups?

SidNewton

Phone wasn't in my pocket. My guitar is a Fender Tele with Bare Knuckle pickups an the singers is some sort of ESP/Les paul with humbuckers, one of the cheaper ones I think.

When I was further from the amp it was doing it when I took my hands of the strings/bridge and only with the Tubescreamer/delay combination. Due to the confines of the room I'm never more than a 5-6 from the amp. as I said it's a horrible piercing sound.

ICBM

Sounds like electromagnetic feedback. That happens when you get the pickups too close to the amp's output transformer, with enough gain. Touching the strings adds a bit of capacitance which could help stop it up to a point.

Not easy to stop entirely if you're using enough volume and gain, without rolling off much treble somewhere. Try turning the presence down, and maybe the treble up a bit if it gets too dull. Or possibly the other way round, depending on exactly which frequency it's at...

SidNewton

Thanks fella, I will give that a try next time I use the amp. I'll let you know how it goes.

SidNewton

Tried the above suggestions yesterday and they helped a little.
The Tele I'm using has Bare Knuckle Flat Pole 50's in them which are quite hot. Would switching to a stacked humbucker help lessen the problem further?

Phil_aka_Pip

I'm nowhere near the expert that @ICBM is, but IMO his phrase "close to the amp" is highly significant. Were you playing with your bum right back against the amp due to lack of space? Is this the first time you've been in a cramped space? (won't be the last)

SidNewton

Phil_aka_Pip said:

I'm nowhere near the expert that @ICBM is, but IMO his phrase "close to the amp" is highly significant. Were you playing with your bum right back against the amp due to lack of space? Is this the first time you've been in a cramped space? (won't be the last)

Not that close to the amp, maybe  5ft away.