AMB Laboratories DIY Audio

[gh0st_inthe_machine]

thanks cobretti, my tester is labelled 3 lights = normal.

Earth to neutral is actually measuring between 1 and 4 VAC depending on the outlet, so I'm guessing all is not entirely well. I think I'll call a sparky.

In the meantime, I'll make a temporary earthing for the b22. This would be much easier to do in the PSU case (connect o22's gnd to the case) rather then in the b22 case, this feels like it's equivalent to me... ?

[cobretti]

thanks cobretti, my tester is labelled 3 lights = normal.

Earth to neutral is actually measuring between 1 and 4 VAC depending on the outlet, so I'm guessing all is not entirely well. I think I'll call a sparky.

In the meantime, I'll make a temporary earthing for the b22. This would be much easier to do in the PSU case (connect o22's gnd to the case) rather then in the b22 case, this feels like it's equivalent to me... ?

It depends how much stuff and "what" is plugged to the outlet at the moment you do measurement. My outlets measure between 0.2 - 0.3VAC. GFCI are lower, around 10's of mV. If you have 4volts, I think it's too much. You should try to measure in lowZ if possible. You may have loose wire somewhere, hope it's not on the service drop or the transformer itself.

[gh0st_inthe_machine]

All of my 13-amp outlets go through a GFCI (RCD in UK-speak) in the consumer unit. Anyhow, I'll get the whole system checked over by an electrician, I'll post the findings in case it's useful to someone.

[gh0st_inthe_machine]

out of interest amb, when you said it was expected to have an AC potential between earth and the o22 rails (but that 100v was excessive) what would you consider a normal range, considering I'm 240v mains?

[amb]

Since the two potentials are really in different universes (sharing no common reference), I guess it could be anything; but my gut feel is that it should be minimal, not enough to give you a shock, whatever that means.

[gh0st_inthe_machine]

OK, update time.

Firstly, I noticed that swapping the primary connections around does make a difference, despite the theory that the ac polarity shouldn't matter. The difference is not small either - around 110VAC between transformer ground and ac earth with the live and neutral reversed, and 30-40VAC with it the right way around. Perhaps this has to do with the insulation inside the transformer, I've no idea. In any case, this helped bring the figure down.

I got an electrician to check the house over and everything was fine, negligible voltage between neutral and earth, and while there were a few similar issues elsewhere in the house (tingling metal casework on an appliance and light switch) these turned out to be separate and unrelated, and I've resolved both since.

So with 40VAC on the b22 case and no concerns about the mains, I tried connecting the o22 grounds to ac earth in the PSU chassis (each via it's own loop breaker) and [touch wood] this has been successful: no buzz on the case and no audible noise during use - it's as dead silent as it was before.

Hopefully that puts this to bed!