JCM 800 and attenuator grounding issue

[tonefinder]

Hey dude- is the same 1-spot powering both in-front fx AND those in the loop? Because this caused huge problems for me with my attenuator's fx loop.

Now I have a fancy, isolated power supply. But initially, using 2 separate 1-spots also solved the problem for me (one for in-front pedals, one for those in the loop).

 

[DDawson 202]

Tes

I wasn't aware of an attenuator that needed power... Having effects AFTER the power section seems odd too. Is this because you don't have a loop on the amp?

The other thing is - what is the impedience of the loop on that thing? This is a pet-peeve of mine. Pedals - which are -20 - go in FRONT of amps. Loops that are line-level (-10) should only see RACK effects. Sure, you can put pedals in a loop, but then you're introducing a mismatch... Noise, and is that possibly the 'ground loop' you speak of?

The amp I have has no effects loop built in. I use delay effects and digital effects in the loop if I can. Less distortion on the effects or none for that matter. All in all it’s a nice addition to tweak the sound. The problem I was happening resulted in actual shocks and noisy fb if I touch anything and actually still continues. It goes away completely if I unhook the external cab.

 

[Old Punker]

Hey dude- is the same 1-spot powering both in-front fx AND those in the loop? Because this caused huge problems for me with my attenuator's fx loop.

Now I have a fancy, isolated power supply. But initially, using 2 separate 1-spots also solved the problem for me (one for in-front pedals, one for those in the loop).

Come to think of it, I also had issues back when I used a 1-spot for pedals both in front of my amp + pedals in (attenuator) loop. I also went out and bought an isolated power supply (the kind used for pedal boards) and never had a problem since.

 

[Old Punker]

Tes

The amp I have has no effects loop built in. I use delay effects and digital effects in the loop if I can. Less distortion on the effects or none for that matter. All in all it’s a nice addition to tweak the sound. The problem I was happening resulted in actual shocks and noisy fb if I touch anything and actually still continues. It goes away completely if I unhook the external cab.

Did someone else modify your cab (change speaker or wiring)?

 

[BigAl]

Try this at the effects loop on the attenuator. They're 2 isolation transformers in a box (one for send and one for return).

https://www.amazon.com/dp/B00BARTW3I?psc=1&ref=ppx_yo2ov_dt_b_product_details

 

[DDawson 202]

Did someone else modify your cab (change speaker or wiring)?

No, I dont believe so. What’s wacky is the wire that the speaker is connected to is connected with tabs and not soldered to the speaker. Not messing with it for the time being. It might not be making enough contact?

 

[DDawson 202]

Try this at the effects loop on the attenuator. They're 2 isolation transformers in a box (one for send and one for return).

https://www.amazon.com/dp/B00BARTW3I?psc=1&ref=ppx_yo2ov_dt_b_product_details

Need to get one of these.

 

[Dogs of Doom]

Need to get one of these.

I think that's purely for line level, not speaker...

 

[Trapland]

First time posting,

I am dealing with an attenuator problem with my 1982 JCM 800 4010 combo.

Normally it sounds awesome no problems. I recently acquired a really nice attenuator (not mentioning brand).

This attenuator has a built in effects loop that was was part of the decision to purchase it in the first place.

Hooked everything up correctly and was experimenting with different ways of adding effects. I realized that unless I ran the effects only through the front of the amp was the only way to avoid mild shocks when touching the pedals or the speaker cable plugs.

I've already made sure there were no problems with the outlet I was plugged into and made sure everything was on the same power strip. I tried using separate outlets as well.

I first noticed the problems when I used the effects loop. Essentially using the effects loop is a no-go. As well this thing has a headphone jack. I can't imagine the safety hazard there.

Is it a well known problem that you can't combine an attenuator with effects in the loop on a JCM 800? I'm sick of experimenting after being mildly shocked several times. Do I need a power conditioner? Is there something I can add to the effects chain that will eliminate ground loops?

Please help.

It doesn't sound like you got a very "nice" attenuator at all.
Attenuators do ONE thing. They attenuate the high power of a speaker output before it gets to its load (speaker).

A real attenuator CANNOT have an effects loop. Anyone who says it can does not know what they have. Effects loops are added AFTER the power amp by dumping all of the power amp high power into a dummy load, taking a low level sample then reamplifying that signal with your effects to another amplifier (usually a solid state one).

This is NOT an attenuator, but is a reamper. Ground loop issues when trying to reamplify another amp post power amp are incredibly common.

Nothing is wrong with your jcm800. If you have shocks with a grounded amp and your dummyload/re-amper but not without its the re-amper. Return it and get a real reactive attenuator like Ironman, Marshall, or Weber. It will sound better and you won't be dumbing down your sound and awesome amp playing it thru a crappy solid state re-amplifier.

Is it a Bad Cat? Lol.

 

[mickeydg5]

@DDawson 202
I have to ask, did you use speaker cables from both amplifier to BadCat and from BadCat to the speaker cabinet?

 

[Norfolk Martin]

I wasn't aware of an attenuator that needed power... Having effects AFTER the power section seems odd too. Is this because you don't have a loop on the amp?

I took a look at the Bad Cat Unleash V2. its not an "attenuator" in the classic sense It attenuates the speaker output of the amp back down to line level, sends that to an effects loop , and the has an internal ( presumably class D) amp that pushes the signal back to speaker level after the FX loop . I assume the idea is that ( unlike a loop internal to the amp) you can push the power tubes on your amp into distortion, the put effects on the resulting sound. Precisely why anyone would need do this escapes me , unless their amp has no FX loop, and it's not possible to fit one. As its internal amp is 100w , possibly it's intended the you plug something like a 5w or 10 combo into it and get a full 100w op for stage volume?

But if your stage amp is already 100w, it seem like a lot of trouble for not much gain.