Jim Root Terror malfunction

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Coma
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Jim Root Terror malfunction

Post by Coma » Wed Apr 17, 2019 6:36 am

I picked up a used JR Terror the other day and there something wonky with it.
It works fine as long as it has a pedal - any pedal - in the loop. Pedal doesn't even have to be turned on, it just has to be there.
Plug straight into front of amp with the loop empty and theres a loud, reverby hiss coming from the amp, volume drops massively and tone gets very thin.
Bridging the FX loop with just a patch cable doesn't help.

Les Paul Lover
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Re: Jim Root Terror malfunction

Post by Les Paul Lover » Fri Apr 19, 2019 7:36 am

Weird.

It's great that you can isolate the issue to the FX loop, but there isn't anything you can fix yourself there.

You will need to find a tech.
Ant

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Jondog
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Re: Jim Root Terror malfunction

Post by Jondog » Fri Apr 19, 2019 12:07 pm

Does it work with just a true-bypass pedal in bypass mode in the loop?
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Coma
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Re: Jim Root Terror malfunction

Post by Coma » Fri Apr 19, 2019 8:52 pm

Jondog wrote:
Fri Apr 19, 2019 12:07 pm
Does it work with just a true-bypass pedal in bypass mode in the loop?
It does. Also works with a buffered. I've tried one TB, one buffered and even one TS clone (which I don't know if it's BB or TB).

Even then, there isn't much high end in the amp. It works alright in standard tuning, but low tuned guitars sound like muffled garbage. I've never owned an orange before, so I've no idea if that's a fault or just the nature of the beast.

I've tried it through an attenuator with speaker speaker IR and it remains muddy and muddled. And the same noise phenomenon occurs with the loop empty.

For reference, that's running it with the treble cranked, through a 4x12 V30 loaded cab (both with a real speaker cab and with IR).

I've tried plugging straight into FX loop return. That works, no noise. Volume knob doesn't affect level, which is odd, I always thought that power amp level is what the volume knob is for? Shows what I know.

Jondog
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Re: Jim Root Terror malfunction

Post by Jondog » Fri Apr 19, 2019 11:08 pm

Volume knob is before the effects loop. Some amps have them before the phase inverter which drives the power tubes, some have them after the phase inverter. Dual channel amps like the Rockerverb usually have them before so each channel can have its own volume level. The Jim Root Terror is based off the Rockerverb which has a pre phase-inverter volume so they likely stuck with that design.
Do you have spare tubes to try? I would put another 12AT7 in the loop to see if anything changes. Could be beyond that, power tubes/preamp. If I have a used amp thats acting up, I like to re-tube or replace one tube at a time to pin-point. I always have spares so I can troubleshoot that first. Weak muddy sound is a characteristic of a bad tube(s).
Your true bypass pedal likely has resistors on the input/output jacks which alters the input/output impedance of the pedal or amp stage output/input impedance even in bypass mode. Builders put them there to eliminate popping noises. I suspect that impedance change is allowing signal to pass from a bad tube.
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Coma
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Re: Jim Root Terror malfunction

Post by Coma » Sat Apr 20, 2019 12:11 am

Have no spare tubes, never needed them. But I guess I'd start with swapping the at7 and then move on to the el84s.

Coma
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Re: Jim Root Terror malfunction

Post by Coma » Mon Apr 22, 2019 4:51 pm

Might've sussed it out thanks to a friend today, coud be a faulty switching jack in the FX return loop. Opened the amp up and ALL jacks in the whole thing looked dirty and nasty. Will be replacing all of them as well as both output tubes. Maybe one preamp tube as well, as it does reproduce some clicking when hitting it with that odd chopstick test.

I'm not sure the muffled sound will be fixed, though. I've sat through every demo I could find on youtube, and while some of them seem to get more range out of the treble dial, most metal oriented ones seem to run it cranked and even then the amp is pretty dark sounding. Wish I had another amp to compare it to.

Coma
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Re: Jim Root Terror malfunction

Post by Coma » Sat May 04, 2019 2:23 pm

Ok, since there's nothing more frustrating than googling for solutions to a problem, finding a thread on the same topic and OP never reporting on the solution, I figured I'll file a report (yes, I know, I'm a Saint. Jesus ain't got sh*t on me).

FX loop had dirty jacks that prevented them from switching. Sprayed with contact cleaner and that sorted out the noise and signal loss.

V1 tube was microphonic. Swapped that as well as V2 for Tung-sols and swapped power tubes for TAD el84-STR.

Amp is still dark, but now there's quite a bit more high end on tap. It's not perma-muffled anymore. Seem to have lost a bit of gain as well, though.

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