"Don Pearce" wrote



Mmmmm... that hum is 100Hz, not 50, so it pretty certainly comes from
the power supply rails, not stuff like ground loops. Do you have a
spare fat electrolytic you could hang across power supply in parallel
with the one already there? See if that kills, or at least reduces,
the level.


OK, that's interesting and would be good if I *don't* have any ground loops.
No I ain't got any spare electrolytics, but I can damn soon rectify*** that!
(I actually managed to use up all the components - I've come a long way from
me motorcycle-fettling days when I always ended up with a jamjar full of
'leftovers' for each bike..... :-)

Interesting thing is that, now that I've got it on the computer, I 'scoped
it**:

http://www.apah69.dsl.pipex.com/keith_g/show/humpic.jpg

The different traces swap places exactly when I switch the leads over, so
summat's up. (Buggered if I know what tho' - I'm not much cop at scopes
either!)

Which reminds me I haven't had an answer yet to an earlier question - that
top trace will slowly slide down the screen over a period of time. Anybody
got any idea what causes that?


**You sods are turning me into a bloody techie!!

***techie pun?

:-)