On Mar 18, 4:59*pm, Terry Casey wrote:
In message
on Fri, 18 Mar 2011 08:52:07 -0700 (PDT)
*Tabby wrote:



I have occasionally seen a volume pot carrying dc, but not wired up
correctly, ie arranged so that any slight poor connection produces a
lot of noise.

What do you mean by 'not wired up correctly'?

Carbon pots carrying DC are much more prone to be noisy.

The change from valves to transistors, with their lower impedance circuitry and
leaky electrolytic coupling capacitors, considerably increased the incidence of
noisy volume controls.

Some can be cleaned easily and give long service before more attention is
required, whereas, if the track is badly worn, relief, if any, is only
temporary, no matter what you use.

In such cases, the only remedy is replacement.

These can typically be silenced just by connceting the
unconnected pot end to the wiper ...

There shouldn't be an unconnected end! The pot will typically be connected
between signal and ground with the output being between the wiper and ground.

Carbon pots carrying DC are much more prone to be noisy.

The change from valves to transistors, with their lower impedance circuitry and
'leaky' electrolytic coupling capacitors, considerably increased the incidence
of noisy volume controls.

Some can be cleaned easily and give long service before more attention is
required, whereas, if the track is badly worn, relief, if any, is only
temporary, no matter what you use.

In such cases, the only remedy is replacement.

*... or if that cant be done fitting a fixed R to the wiper and ground or one
of the other terminals.

That will modify the 'law' of the pot and change the wiper position for most
settings. If the track is worn in the area that is most usually used (not
surprising!) moving the operating point to a relatively unused section can
work.

Fine as a diy work around but not worthwhile if a replacement is to hand as
that will give a better guarantee of a long term solution.


I wasnt quite clear was I. Sometimes the pot is wired such that if the
wiper goes oc, the output, which connects to the wiper, is o/c. Adding
a fixed R across the pot's output prevents this, ie from wiper to
ground end. It can be high enough value to have only a trivial effect
on the 'law' of the pot, which is a fairly trivial matter anyhow.


NT