Safety issue ? -Phonic Power Pod 1062,mixer amp, from 2002

Most consumer-grade amps have two-prong plugs, so what are you going to earth it to? The ground in such an amp is always relative, often the CT on the power transformer itself or back end of the bridge rectifier, quite possibly floating a few volts away from earth ground. It must be rare enough to satisfy regulators that the mains transformer fails open circuit but shorted to the case.

If the unit has a three prong plug, I'd say give a ground strap a try if you're concerned... most power trannies are bolted onto a metal case, not wood, and the case is grounded in the case of a three prong plug. Ground loop noise problems would depend quite a lot on the grounding scheme used in the amp, i.e. whether or not power and signal grounds are appropriately isolated to minimize interference.

Dave

mains

plate

strap

The

on

in

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

mains

plate

strap

The

on

in

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Is there a capacitor strapped across the mains switch, or the input socket? That would account for the clout he got when touching the mains plug pins

Ron(UK)

earth

CT

circuit

if

not

Ground

used

metal

There is a .47uF , 330 V polycarbonate between neutral and live on the amp side of the mains switch which would self discharge through the transformer in mS but nothing else except a fuse.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Are you sure it`s on the transformer side of the switch?

Ron

amp

transformer

Mystery solved, yes that cap is on the mains cord side of the switch. So what class of electric shock do you call that, high impedance , DC , of little medical consequence in itself, but surprise effect could have indirect consequences.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

second attempt

amp

transformer

Mystery solved, yes that cap is on the mains cord side of the switch. So what class of electric shock do you call that, high impedance , DC , of little medical consequence in itself, but surprise effect could have indirect consequences.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

That's what I was thinking too but it shouldn't happen by touching the earth pin alone. Of course, likely he didn't just touch the one pin.

Graham

Do you seriously mean POLYCARBONATE ? They are UNSAFE for across the mains use because they have very poor pulse tolerance. It should be a safety X-type cap.

Graham

As suspected.

The IEC safety regs (60065) specify the maximum energy allowable for such filtering caps. I forget the clause and I don't fancy looking it up right now.

Graham

amp

use

cap.

X1 type, large yellow cased , I thought were polycarbonate but I stand corrected. I thought the critical factor was they had to be self-healing which could be from pulse or surge.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on