Re: Preamp causes hum even when off

On Feb 29, 4:00 pm, t...@xxxxxxxxxxx wrote:

Thanks for the tip about the screwdriver.  If you don't object, I
would like to post that in the diyaudio thread (including proper
credit to you, of course).

How about this - you pass the tip and take credit if it works. If it
does not, blame me. It is a very old poor-man's signal tracer trick
from even before my time.

To be brutally honest with you, from what I see as to craftsmanship, I
would start over with that kit, working from the crimp-connectors
back. I would also lean towards twisted pairs ILO shielded cable,
leave one end unconnected, typically the one at the volume-control
side. I would also make sure that the board is "above ground" at its
chassis screws - use plastic screws or proper insulators if necessary.
Square off the ground connections - run them as close to the chassis
as possible to the ground point, not wildly overland as they appear
now. Try to eschew multiple grounds - jump from shield-to-shield
*then* to ground, keeping the jumpers as short as possible. As it is
now, your shield grounds appear to go from the input side to the
volume control to the board to the output side. That is an awfully
long way and ample opportunity for problems to occur. Better you
connect the shields to ground at the common ground, and run either a
twisted pair or disconnect the ground at the VC both directions.

I have to guess that all this has been suggested already?

Peter Wieck
Wyncote, PA
.

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