On Wed, 26 Aug 2009 09:16:10 +0100, "Arfa Daily"
put finger to keyboard and composed:


"Sylvia Else" wrote in message
. ..
The sustaining pedal on my Yamaha electronic piano is become rather flaky.
Sometimes it doesn't sustain when pressed.

So I disassembled the piano enough to get at the mechanism, (removed 12
screws, and 6 bolts), and was rather surprised to see that the business
end consists of a potentiometre.

I'm not really surprised that it's failing. In fact, the surprise is that
it's lasted so long. When a piano is played, the sustaining pedal is in
constant use. I can't help feeling potentiometres were never designed with
that kind of use in mind.

The design seems rather primitive.

Sylvia.

It's not unusual to find pots in such applications, and there are types
which are specifically designed to have very long mechanical lives. Using a
pot keeps the circuitry simple. As an alternative, many guitar effects
pedals use an optical arrangement instead, where a shaded or shaped
'shutter' mechanically connected to the pedal, passes between an LED and a
phototransistor or diode, the varying DC resistance of the device caused as
a result of this, serving as the equivalent of the varying resistance of
your pot.

Arfa

IIRC, I have two Yamaha service manuals, one for a piano (CP10) and
one for an organ (Electone). I believe the organ uses a noiseless
"optical pot", but I'll have to check the piano. Both instruments are
probably around 20-30 years old.

- Franc Zabkar
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