tingling metal around the house

patient_zer0 · Jan 31, 2012

Hi Guys,

First time poster and all that, wonder if anyone's got any ideas.

There's a metal light switch in the house which I've always noticed gives a buzzing sensation to the back of my finger, although I've never thought much of it until I was recently working on building an audio amplifier which has a mains to +/- 30VDC PSU housed in one chassis, and the amplifer in another, connected via an umbilical carrying -30VDC, G, +30VDC. The PSU chassis is connected to earth (but it's local ground is not), and the amp chassis isn't connected to earth, rather, that's connected to the PSU's ground.

Same thing as with the light switch - the amp chassis buzzes against my finger. Otherwise it all works fine. I've tried in sockets throughout the house, always the same.

Could this be caused by a mains issue? I've run one of those basic three-light socket testers to check that live neutral and ground are where they should be, and I get the 'normal' condition reported back.

I checked the light switch's potential to ac earth (via a nearby socket), which turns out to be @180VAC.

Is this indicative of a fault that wants fixing?!

GLENNSPARK · Jan 31, 2012

sounds to me like theres a voltage sitting on it.....poor insulation and no CPC to the circuit....

Octopus · Jan 31, 2012

Get a sparky in to do some basic tests. Shouldn't cost much and then you'll know what you're dealing with.

GLENNSPARK · Jan 31, 2012

i may have jumped the gun a bit earlier..i have a habit of not always reading posts fully before replying....but as i said..theres a voltage sitting on exposed metalwork by the sounds of it which is finding its way around via the CPC of final circuits...but really..as Murdoch has said....need to get an electrician to test here ....find out where the breakdown in insulation is..........

Marvo · Jan 31, 2012

If you're getting a tingling from parts all around the house it's indicative of two separate problems. You have an insulation issue causing earth leakage and an inadequate earth.

I'm all for helping people to help themselves but this can become a dangerous situation and you need specialised test equipment to prove and trace the problems. Assuming your installation doesn't look like some in this thread, an hour's labour for an experienced electrician should get you the testing and a plan/quote for remedial works.

patient_zer0 · Jan 31, 2012

thanks for the reply - I'll definitely get an electrician in to check it over

Rockingit · Jan 31, 2012

If you post your rough location you might find one of us on here can help you out - make sure you know who you're getting is worth the paying!

Andy 7671 · Jan 31, 2012

Cool, now you are on the way to becoming safe, can I ask why DC on an amplifier Power supply..?

Ive heard of it for turntables..Linn Sondek and the like, gives a more..linear..? is that the word..? speed of the platter.

For amplifiers I am intrigued.

patient_zer0 · Jan 31, 2012

I'm more of an implementer than an electronic engineer, try this

The amp actually has two dual-rail 30v power supplies, one for each channel, and two amps per channel (one positive, the other inverted) to drive a balanced signal, that is to say, instead of powering the positive side and connecting each speaker through to a common ground, each side is driven actively. The idea is, any noise picked up on one side is equally picked up on the other, so the voltage differential seen by the load is unaffected.

If anyone is in mid-northants, that's where I am.

Knobhead · Jan 31, 2012

Try reversing the connections on your base speakers. It sounds horrendous.
But the reasons for dual supplies is deeper rooted. A good amplifier will be a mirror or shielded design to give good reproduction.
Rotel were one of the first companies to adopt the mirror design. I’d love a separate amps per channel set up but can’t afford them. To be honest, do I need them.

View attachment 10421 View attachment 10420
My son and I have 5 Rotel amps between us. One of them older than he is (he’s 26 now).

patient_zer0 · Feb 1, 2012

dual supplies (aka dual mono) is certainly a purist issue - no possible contamination of common grounds or cross talk all the way back to the mains.

Balanced designs (requiring, of course, balanced XLR sources - we're not talking about using transformers to go from single-ended RCA input to balanced output) have some notable advantages (double the slew rate, lower noise driving long cable runs) and some disadvantages (higher output impedance). Like all the finer audiophile considerations, it's a matter of taste.

I've tried to make this amp a 'no compromise' build, so went balanced. Things are much cheaper in the DIY arena for high end audio if you put in the hours, I'd say you can generally get double the performance-per-£ against commercial products if you do it right, and some satisfaction to boot.