Hi again, Yes, the bridge was perhaps a littlelow on margin, but I was
thinking along similar lines. Just because it powers up and works does not
mean its OK.

Now I know its easy to convince oneself that you can hear something, but
this morning on turning it on, I think I heard the hum reduce a lot slower
than it used to do.
So, I'm thinking, a capacitor which is slightly leaky might still be in the
circuit. No other work was done other than fit a new bridge, so I'm
thinking, it might be wise to get the guy to change out the caps as well, or
measure what the supply drain is off load.

Its one of those old chicken and egg things. As far as picking up stuff, no
it certanly was not apt to do this, but the earth seems connected OK from
the lead, and I'm not into any of Russes mains leads either!

There are, I'm told some smaller capacitors scattered around, but they
surely would bbe much higher voltage devices. The new bridge is slightly
bigger than its predessor, and thus there is more wire connecting it to the
pcb.
As I say, I can more or less tell what is there, but my sight precludes me
investigating personally.
I'm desperately trying to remember the maker. Starts with an E I think.

Brian

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"Jim Lesurf" wrote in message
...
In article , Serge Auckland
wrote:

"Brian Gaff" wrote in message
m...
My subwoofer picks up. Mobile phones, radar pulses, clicks and bangs
on the mains and occasionally short wave radio.


The very short speaker wires from amp to speaker in the box appear to
be the culprits for the higher frequencies, and the input leads the
way in for the rest, except The mains borne crap.

It has a three core mains lead of the iec variety, but its only been
doing these things since it had a new bridge rectifier fitted a while
back. I am suspicious that some capacitors may have been damaged when
the bridge went down, but I'd have thought this would just result in
hum.

The amp is built on pcbs maounted on the heatsink which effectively
forms the back of the cabinet beside the port.

Any ideas?

Brian

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I'll preface this by saying that it's hard to diagnose at long distance,
but by your description I would look at the following first:-

Assuming a conventional power supply, not switch-mode, 1) Any mains
filtering before the mains transformer may have been damaged by
excessive current due to the rectifier failure 2) Any high frequency
filtering i.e. small capacitors across the rectifier and/or smoothing
capacitors may have been damaged by excessive voltage due to rectifier
failure. 3) Check also the main reservoir capacitors as they too may
have been damaged, but I agree that hum is the more likely result of
damage there.

I'd agree with the above comments. However I am also wondering why
anything
related to the PSU would then cause the amp to become sensitive to things
on its signal input leads. Who changed the diodes, and what else did they
do? I also wonder *why* the "bridge went down".

Slainte,

Jim

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