Troubleshooting: amplifier Musical Fidelity A1
 

Hi

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

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).

3) by the way, do you know which are the exact final transistors?
I found on newsgroups many codes:
original: A1 N8915 and A1 P8919
poor quality? 2N3442 and 2N5876
good ? Motorola MJ15003 & MJ15004

My unit (model A1 X) has these transistors:
A1N9020 A1N9034
A1P9022 A1P9018
I don't understand why are there four different codes instead of two exact
couples!

ciao, Massimo
Italy

Troubleshooting: amplifier Musical Fidelity A1
 

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

Pricy, huh? :))

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.

Sounds like bad contacts in that knob...

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

I guess that isn't just a simple pot, more like a shunt... Musical Fidelity
is high-class audiophile company, so I guess they use high-quality shunts
for volume knobs...

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).

Don't know... You could contact Musical Fidelity and ask them to help you
find the right service-shop where you can repair your unit... Or simply find
some service shop from some audiophile genious... Local audiophile stores
are best thing to start... :)

ciao, Massimo
Italy

Oh, neighbour! :)))) Greetings from Fiume, Croatia... ;)


--
"Sravnjens li bananau crtu ?" upita Milosevica podjebava cizmao zmice.
"Nisam ja nikog bombardiro !" rece cizma gladi "Ja samo stolo njise humanitaranm !" By runf

Damir Lukic,
a member of hr.comp.hardver FAQ-team