JCM 800 and attenuator grounding issue

[DDawson 202]

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.

 

[scozz]

That’s a strange issue.

So if you run everything in front, all is well, including the attenuator working properly?

 

[DDawson 202]

That’s a strange issue.

So if you run everything in front, all is well, including the attenuator working properly?

Yes. I checked to see if touching anything would make feedback etc. and it was fine.

If I had anything in the effects loop in the attenuator it would feedback if I touched anything.

 

[Dogs of Doom]

you need to tell us what attenuator you are using & what your signal chain is, how you're powering effects, etc.

 

[DDawson 202]

you need to tell us what attenuator you are using & what your signal chain is, how you're powering effects, etc.

Bad Cat Unleash V2

Effects are Danelectro Fab Tone into low input.

Effects loop: Danelectro Dan Echo, Empress Zoia, Maxon EQ, passive volume box.

All powered by a 1 Spot 9v.

 

[Gunner64]

That reamper is powered by wall voltage right? I would be checking my outlets/power strip for proper ground. Just because they have 3 prongs doesn't mean they have proper ground.


I've seen outlets changed to 3 prong just to eliminate the need for an adapter. Wrong but people do it.

 

[Dogs of Doom]

I'm not sure what the problem was here, but, worth looking at:

Badcat Unleash effects loop problem

I received my Unleash a few days ago and it's working very well save for one problem. When I have effects running through the loop (DD-3 and Hardwire RV-7), I get a weird feedback sounding high-pitched noise if I have my amp up above halfway, or if I am boosting the input of the amp. It's...

www.thegearpage.net

not an educated guess, by intuition tells me, that, if you are getting mild shocks, that it may well be low voltage, like your effect's power supply.

W/ your effects, otherwise, if they are all hooked up together, on that power supply, they work fine?

Sometimes, an effect will have reverse polarity, which will mean that the positive will take the ground route, for instance, the effects case, & negative output cable.

I see in that thread, that it is recommended to try all effects battery powered (if possible). I'd try that, but best bet is to check polarity of the pedals &/or eliminate them one-at-a-time & see if one is the culprit.

Other than that, there may be a fault w/ the Badcat it's self.

Try only hooking up the passive vol pedal. See if it still has that charge. If so, maybe try hooking up a multimeter to see what the charge is...

 

[Dogs of Doom]

That reamper is powered by wall voltage right? I would be checking my outlets for proper ground. Just because they have 3 prongs doesn't mean they have proper ground.

I've seen outlets changed to 3 prong just to eliminate the need for an adapter. Wrong but people do it.

I did that, but... my boxes were all grounded, so I hooked up ground to the box, on all of them...

 

[Old Punker]

to the forum @DDawson 202!

Is it a well known problem that you can't combine an attenuator with effects in the loop on a JCM 800?

No, not AFAIK. I have used my Power Station and effects loop with my SC20H no problem and know of others using older JCM800's without any issues.
IMO it sounds like you have a grounding issue, on either your JCM800 or on your Bad Cat.

I've already made sure there were no problems with the outlet I was plugged into...

IDK what you used to test your outlet, but to do it properly you need to use something like this (Electrical Receptacle Wall Plug AC Outlet Ground Tester)
...

If you have a voltmeter it would be beneficial to know the magnitude of the voltage difference across any two points where you received shocks.

First, I would check the integrity of the ground connection on your amp, and if that is okay then check the same on your attenuator. If you're unsure, take it to a tech. Sometimes ground connections can lose their integrity over time, or may not have been done right in the first place. This is assuming that your outlet tested okay with a proper tester.

If these all checked out and the problem persists, you may want to try using the Ground Lift switch on your Bad Cat to eliminate your feedback issue. I stress that you must first be sure that the grounds on your outlet, amp, and attenuator are all good before trying the lift. Please also read this brief note on ground lift

Ground Lift - inSync

In some situations, it may be useful or become necessary to defeat a signal’s path to... Read more »

www.sweetwater.com

as well as your attenuator manual first.

** I just noticed you said you have a 'passive volume box' in your loop. Why?
If you are talking about what I understand a passive volume box is, something like this?

Then there is no need for that if you are using an attenuator. These little volume boxes take a portion of your signal and shunt it directly to ground.

If you are using something like this then the first thing I would do is remove it from your rig altogether and check to see if your initial problem still exists.

I'm not an expert but I hope some of this may help. Let us know how it goes.

 

[DDawson 202]

Great info.

I used a basic wall outlet tester and it said there were no ground issues.

However ("Receptacle circuit testers have some limitations. They may indicate incorrect wiring, but cannot be relied upon to indicate correct wiring.")

For the last two weeks its been tonal bliss minus dealing with this grounding issue. I swore I wouldn't use the fx loop.

I will try the passive volume box in the effects loop only. That would make sense. I also want to mention that i was able to use all of the effects for about a half hour before it shocked me again and I just gave up. It shocked me when I switched patches on the ZOIA.

 

[DDawson 202]

to the forum @DDawson 202!

Is it a well known problem that you can't combine an attenuator with effects in the loop on a JCM 800?

No, not AFAIK. I have used my Power Station and effects loop with my SC20H no problem and know of others using older JCM800's without any issues.
IMO it sounds like you have a grounding issue, on either your JCM800 or on your Bad Cat.

I've already made sure there were no problems with the outlet I was plugged into...

IDK what you used to test your outlet, but to do it properly you need to use something like this (Electrical Receptacle Wall Plug AC Outlet Ground Tester)
...

If you have a voltmeter it would be beneficial to know the magnitude of the voltage difference across any two points where you received shocks.

First, I would check the integrity of the ground connection on your amp, and if that is okay then check the same on your attenuator. If you're unsure, take it to a tech. Sometimes ground connections can lose their integrity over time, or may not have been done right in the first place. This is assuming that your outlet tested okay with a proper tester.

If these all checked out and the problem persists, you may want to try using the Ground Lift switch on your Bad Cat to eliminate your feedback issue. I stress that you must first be sure that the grounds on your outlet, amp, and attenuator are all good before trying the lift. Please also read this brief note on ground lift
XXX
as well as your attenuator manual first.

** I just noticed you said you have a 'passive volume box' in your loop. Why?
If you are talking about what I understand a passive volume box is, something like this?

Then there is no need for that if you are using an attenuator. These little volume boxes take a portion of your signal and shunt it directly to ground.

If you are using something like this then the first thing I would do is remove it from your rig altogether and check to see if your initial problem still exists.

I'm not an expert but I hope some of this may help. Let us know how it goes.

THX,

Yes I used one of those (the wall checker)

I also used a vol box like that one. Just to fine tune the signal.

Both with and without.


As far as the Amp. I cannot verify as I have never had any problems I did once take it to the shop and they made no indication of a grounding problem.

I'm probably just returning the V2 because I'm not too into the technical side and can get very close to a similar tone just using pedals.

Thanks for the info. I was mainly wondering if anyone had a similar experience with this or a similar product and if it is worth holding on to based on that.

also I don't believe the V2 has a ground lift.

 

[Dogs of Doom]

Empress doesn't recommend the 1-spot:

Power Supply Compatibility Chart for Empress Effects Pedals

assets.empresseffects.com

(about ¾ the way down, all yellow, above the VooDoo in all red)

while it says it'll work, w/ that pedal, it says it's noisy...

 

[Old Punker]

Great info.

I used a basic wall outlet tester and it said there were no ground issues.

However ("Receptacle circuit testers have some limitations. They may indicate incorrect wiring, but cannot be relied upon to indicate correct wiring.")

For the last two weeks its been tonal bliss minus dealing with this grounding issue. I swore I wouldn't use the fx loop.

I will try the passive volume box in the effects loop only. That would make sense. I also want to mention that i was able to use all of the effects for about a half hour before it shocked me again and I just gave up. It shocked me when I switched patches on the ZOIA.

I'm not certain which above post you are replying to but just to clarify,

What I suggested was to remove the passive volume box from your rig altogether (sitting all alone in a drawer somewhere) and then test your amp and Bad cat together, while using the effects loop of the attenuator.

 

[DDawson 202]

I'm not certain which above post you are replying to but just to clarify,

What I suggested was to remove the passive volume box from your rig altogether (sitting all alone in a drawer somewhere) and then test your amp and Bad cat together, while using the effects loop of the attenuator.

Thanks, I was replying to the other post.

OK. So I tried what you said and took out the passive volume box. That led me to try different cables. What I noticed is that I only had feedback when the external cab was connected.

I believe it’s something with the external cab.

 

[DDawson 202]

The feedback loop goes away when I disconnect the external cabinet.

 

[Old Punker]

The feedback loop goes away when I disconnect the external cabinet.

Cool. No more shocks either?

Maybe there is a problem with the wiring of the external cab?

Another thing, make sure that you are using a speaker cable to connect the external cab, as opposed to an instrument cable. They look very similar and it's easy to get the two mixed up (I've done it).

 

[DDawson 202]

Cool. No more shocks either?

Maybe there is a problem with the wiring of the external cab?

Another thing, make sure that you are using a speaker cable to connect the external cab, as opposed to an instrument cable. They look very similar and it's easy to get the two mixed up (I've done it).

I’m not a professional but I managed to connect a ground wire (It is a shielded copper wire) from inside of the external cab (Speaker chassis) to the actual Amp chassis. It’s solid now just have to remember to disconnect it if I move the amp. I am using speaker cables not instrument cables. Thanks for the guidance. I guess it wasn’t as big of a problem as I thought. I am surprised that the cabinet wasn’t fully ground.

 

[Freddy G]

I’m not a professional but I managed to connect a ground wire (It is a shielded copper wire) from inside of the external cab (Speaker chassis) to the actual Amp chassis. It’s solid now just have to remember to disconnect it if I move the amp. I am using speaker cables not instrument cables. Thanks for the guidance. I guess it wasn’t as big of a problem as I thought. I am surprised that the cabinet wasn’t fully ground.

You shouldn't be surprised. Cabinets are never fully grounded. Or even a tiny bit grounded.

 

[DonaldBort]

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.

Have you considered using the FAS "Humbuster" cable design? You can make one yourself and give it a shot in an attempt to eliminate your ground loop. I've made and used a number of these in the past when a ground lift or hum wouldn't go away, here's a link to read up on it a bit more.

Humbuster - Fractal Audio Wiki

wiki.fractalaudio.com

 

[TheChris]

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.

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?