In article , Sala
Massimo
wrote:
Hi

I am the happy owner of one A1 amplifier, bought in 1991. It is 20 Watt
class A amplifier, build around MOSFET.

In the last months the A1 started to malfunction, the volume knob works
very bad: when I turn the knob I hear strange noise ("shhh shhh" as
there is sand inside the knob, and also some "crack") and the volume
output isn't in accordance with the knob position.

I took the unit to repair, but they said me they cannot because they
haven't the potentiometer.

I ask you: 1) is really the pot the culprit ?

From what you describe I'd say that the pot has become damaged by d.c.
applied through its wiper (variable connection). The symptoms of
'whooshing' sounds when rotated and some cracks are classic signs of this
damage. The cause may be something like a capacitor in series with the pot
leaking d.c. and thus degrading the pot. Hence you'd need to replace the
relevant capacitor(s) as well as the pot to avoid any new volume control
rapidly getting the same problem.

In some cases, cleaning the pot and replacing the capacitors may cause the
problem to go away even if you go on using the old pot. However applying
cleaner to some of the better Alps pots can be problematic, so a new pot
makes sense if available.


2) where can I found one (or two) spare parts? It is a Alps 0071 50KAX2
(I cannot measure the value because it is soldered).

Sounds like a"50K" = 50kOhm pot. I'd guess "AX" means "A-law" (semi log,
for a volume pot), and the "2" means stereo. However I don't have the
relevant data to hand, so this is a guess. Sounds about right, though.

Finding individual Alps pots can be awkward at times. The people I used to
buy from went out of business! :-/ I don't currently know who will sell
their better ones in small quantities to individuals.

I don't recognise the part number sufficiently. However have a look at the
Maplin website/catalogue. You may find that something in their ranges will
do the job. Failing that, below... :-)


4) which are Musical Fidelity address, Emai and phone?

See Alec's reply. :-) MF can probably source a pot and fix your amp for
you.

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html