"Eeyore" wrote in message
...
I'm helping to sort out a piece of alleged studio recording gear that was
somewhat thrown together by a bunch of useless idiots whose company has
now
ceased trading. It's a quasi 'replica' of some historic equipment that
once
belonged to Air Studios in Monserrat.

The latest joy (of many!) is pickup from the PSU. I was concerned about
these
spikes (see pics) that the mic amp delights in reproducing. I've never
seen
anything as bad as this before but I don't use mic transformers myself and
this
unit does, which appears to be a problem.

The ac line frequency rectifiers are 1N5404s. I simply tacked 0.1uF across
them
to see if it helped at all but it didn't. I have some UF4004s I could use
instead of them (their 1 A rating is fine in this application) but I'm
open to
other advice.

The top trace is the output of the mic amp on max gain (70dB).
The bottom trace is the ripple voltage on the (half wave) rectified
positive
supply (only on 2nd pic).

I can't figure why the spikes seem to be displaced but it's that rotten
TDS210
again and I have next to zero faith in it. Sorry about the pic quality
btw, I
didn't take them.


Graham


Hard to see with the picture quality but do you have full wave? (Xfrmr
secondaries may be out of balance.)
Try 1nf across the Xfrmr secondaries as well. John Larkins suggestions as to
rectifier selection is on the money.