peavey ltd 400 shocking the player

[georage]

Hi. Can anyone help with this problem? A guy asked me to fix his amp because it shocked him through the guitar strings. I was even able to get it to shock me and it was a little buzz about like a bee sting. The way I got it to shock me was by flipping the polarity switch to one position and then lifting the equipment ground. Then i was able to read 120v to mains ground. I measured the current from the chassis to ground with my amp clamp and it read zero and simply grounding the chassis was enough to clear the voltage, but it would still deliver a tiny shock.
My question is, how is this possible and can i make it stop? I replaced the two .022uf caps on the primary of the transformer with y type caps and that did not help. any insight would be helpful.

[Helmholtz]

Did you measure safety ground resistance from chassis to mains plug?
Sometimes the ground pin becomes loose and disconnected.

[g1]

What exactly do you mean by 'lift the equipment ground', do you mean the 3rd prong of the AC plug?
If you had to do that and he did not, I expect he does not have proper 3 prong wiring in his house. Then a slight shock will be possible with amps that have a polarity switch with cap to chassis.
Removing the cap circled in red should eliminate the problem.

[georage]

yes, I lifted the equipment(safety) ground by using a 3 to 2 prong plug adapter. I can only assume that his house outlets are ungrounded. I will check the cord though, thats a good point. so, I should get rid of the type vl cap and keep the type evl cap? That makes sense. I really dont know what that vl cap does honestly.

[Jon Snell]

For safety sake, take out the 0.022uF DEATH cap!
All equipment with a three prong mains lead MUST be plugged into an earthed mains supply and the DEATH cap is of no use.

Pretty basic stuff really.

[Greg Robinson]

For safety sake, take out the 0.022uF DEATH cap!
All equipment with a three prong mains lead MUST be plugged into an earthed mains supply and the DEATH cap is of no use.

Pretty basic stuff really.

Echoing the above advice.

I'd also probably premptively replace the "type EVL" with a modern class X rated cap, and consider replacing/rewiring the 3 way power switch for modern standard polarized wiring, with the fuses always on the live/active side.

[georage]

ok. Thats what im going to do. Thank you guys very much.

[g1]

All equipment with a three prong mains lead MUST be plugged into an earthed mains supply and the DEATH cap is of no use.

Pretty basic stuff really.

Depends what you mean by 'death' cap as there is no official definition. Safety rated caps in that position (line to ground) are still used in modern designs so they can serve some purpose. And if equipment with 3 prong AC were only ever connected to properly earthed outlets, the death cap could never cause a problem (line breaker would just blow).

Sure I agree we should remove them in most old guitar amps, but I'm not going to remove one in a modern amp that has no polarity switch.
Sorry to nit-pick, but the terminology and incomplete descriptions about 'death caps' in widespread use online could be improved upon, in my opinion.

[Jon Snell]

I would have thought the name is obvious.
If the capacitor that connects the live to the earth goes short circuit, you will have a live chassis.
If it is leaky you will get possibly dangerous voltages on the chassis.
That is why it is called a death cap; because it can cause fatalities and in fact has done in the past, when faulty.

Its real purpose and definition, was to produce an HF short circuit back to the mains supply helping to reduce interference. (Similar to the now used class Y capacitor in your iPhone/Androis charger ... get a slight tingle from that some times? most people do).

In countries that have 110volt mains suppllies, is can be just uncomfortable when it fails but elsewhere we have 240volts and that is a real problem.
Imagine being on stage, old amp has a faulty RF filter capacitor, (to give it its correct description), guitar is live. Guitarist has decent shoes on so insulated from ground and happens to be a singer as well. Lips touch the microphone, the microphone is earthed and the strings are live.

Doesn't take a rocket scientist to work out where the power goes, does it.

A portable appliance, (amplifier in this case), will not pass a safety electrical test without a bonded earth.

Hope that clarifies why they are and have always been dangerous.

[g1]

I would have thought the name is obvious.
If the capacitor that connects the live to the earth goes short circuit, you will have a live chassis.
If it is leaky you will get possibly dangerous voltages on the chassis.

Not if the chassis is earthed, and there are no issues with the house wiring. Earthed chassis can't have voltage on it.
Problems with 'death caps' require multiple failures, first the cap itself, then the earthing of the chassis.
Removing them 'just because', rather than replacing with proper safety rated 'class Y' cap is still ignoring why they are used (and approved) in modern equipment, which is for noise and EMI issues. Many of the EMI filters built into modern IEC receptacles have them.
Yes, I remove them in old stuff when installing 3 conductor upgrade power cords. No, I do not remove proper approved 'line to earth' caps in modern equipment, which still qualify as 'death caps' by the internet definition (line to ground).
Again, this is just my rant about the misconceptions around the term 'death cap'. It is multiple failures that cause any issues, not the circuit position of the cap. There is nothing inherently dangerous about a line to ground cap if properly done, which is why approved designs can still include them.

[georage]

So. I initially thought that the shock came from a faulty death cap and i replaced the old caps with new safety caps y rated. I should have used a x cap on the line to line, and i will, but the old caps were not faulty. They were not shorted and the new caps did the same thing. they let me get a little shock when the chassis was ungrounded and the polarity was switched to live chassis. Every new appliance that i've seen has y and x caps in the power supply and thats why i thought that changing them would solve the shocking issue. I can remove the line to chassis capacitor but im not really sure if that will cause issues with emi noise. noise is better than getting shocked, but I deffer to the experts here because im not sure that there isnt another capacitor that will shock the player as well. I dont see one in the schematic but im not an engineer. Im an electrician. I know from being an electrician that you cant stop people from plugging things in backwards or breaking the ground off or plugging in to mis-wired outlets. Im still on board with removing the death cap and leaving the polarity switch....and maybe i can label the switch so the player can choose wisely which polarity he wants. safety is my main concern and i will have to inspect the wiring closely to make sure the chassis is solidly bonded to the equipment ground(safety ground). I did after all test and discover that if the chassis is earth grounded that the high voltage disappears and is safe to touch. btw if you would like to know, i did the test by switching to live chassis and then "lifting" the ground with a 3 to 2 prong adapter and then probing from chassis to equipment ground on my grounded bench outlet. I then connected a jumper to chassis and equipment ground and clamped that jumper with an amp clamp to read how much current was going to ground and then, when it appeared safe i held one finger between the chassis and that jumper so that the current could only travel through the tip of my finger to ground and not my body. its important not to touch the chassis with one hand and the ground with the other hand...or lips to guitar strings...strings to bare feet etc.

[Greg Robinson]

First off - Y-class caps are rated for both line-to-ground AND line-to-line usage, so can be used in place of X-class caps. X-class caps are only rated for line-to-line use, so cannot be used in place of Y-class.

Second, the "death cap" - line to ground and polarity switch are an artefact of North American transition from ungrounded, non-polarized outlets, to the modern grounded, polarized outlets. The line to ground cap was NOT for EMI purposes, but to maintain AC grounding on the chassis with ungrounded outlets. It can be safely omitted. With modern North American wiring being both grounded and polarized, you'd also be better off removing/rewiring the power switch for modern convention with the line/active fused. The amp SHOULD NOT be used ungrounded or with the polarity reversed - again, this was just an artefact of old North American wiring standards, and is NOT safe, it was simply the best compromise for the time. With the primary wiring updated to modern wiring standards and the chassis grounded, the "death cap" - with a properly rated Y-class cap, will again become safe (but is not required).

Musicians, especially gigging ones, are best to carry with them an outlet tester to make sure that outlets are properly earthed and do not have line/return swapped. It's simply not safe to use ungrounded outlets.

[georage]

Hey Guys. I removed the death cap and replaced the x-capacitor and recapped the ltd400 and it works great. Now, without the death cap installed, I get 21 volts and 64 volts AC on the chassis to ground depending on which position the polarity switch is in.

[Helmholtz]

Now, without the death cap installed, I get 21 volts and 64 volts AC on the chassis to ground depending on which position the polarity switch is in.

Means the amp is not safety grounded and thus not safe.
There must zero Ohm between chassis and ground.
With chassis connected to ground there can't be a voltage between.

[georage]

I was just testing out the amp with and without the safety ground and on either polarity by plugging a guitar cable in and touching the tip to get a hum noise. I noticed that when the amp is grounded the hum sounds normal and it sounds the same on both polarities. However when the ground is lifted and it either polarity, when i touch the tip of the guitar cord the amp pops extremely loud and the hum is extremely loud and the dim bulb lights up like the amp is pulling abut 100 watts. the amp will normally light up the dimbulb if it is played extremely loud. Im not sure that removing the y capacitor didnt cause another kind of problem.