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 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!


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

ciao, Massimo
Italy

Troubleshooting: amplifier Musical Fidelity A1
 

"Sala Massimo" wrote in message m...
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 ?


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!


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

ciao, Massimo
Italy

Hi you will find that the codes on the output transistors are usually week numbers, the types are A1N and A1P which are NPN and PNP devices the number after that is the year/week number e.g. week 20 of 1990 or week 34 of 1990. The devices we have in stock here at work have similar codes on, you may find that Musical Fidelity can supply a replacement Alps Pot for your unit but I seem to remember you have to run a bunch of wires from the tags to the pcb.

Musical Fidelity
15/16 Olympic Trading Estate
Fulton Road
Wembley
HA9 0TF
Tel UK 0208 900 2866

Cheers
Alec

Troubleshooting: amplifier Musical Fidelity A1
 

"Sala Massimo" wrote in message m...
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 ?


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!


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

ciao, Massimo
Italy

Hi you will find that the codes on the output transistors are usually week numbers, the types are A1N and A1P which are NPN and PNP devices the number after that is the year/week number e.g. week 20 of 1990 or week 34 of 1990. The devices we have in stock here at work have similar codes on, you may find that Musical Fidelity can supply a replacement Alps Pot for your unit but I seem to remember you have to run a bunch of wires from the tags to the pcb.

Musical Fidelity
15/16 Olympic Trading Estate
Fulton Road
Wembley
HA9 0TF
Tel UK 0208 900 2866

Cheers
Alec

Troubleshooting: amplifier Musical Fidelity A1
 

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

Troubleshooting: amplifier Musical Fidelity A1
 

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

Troubleshooting: amplifier Musical Fidelity A1
 

"Lintone Audio" wrote in message
...
"Sala Massimo" wrote in message
m...
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 ?


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!


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

ciao, Massimo
Italy

Hi you will find that the codes on the output transistors are usually week
numbers, the types are A1N and A1P which are NPN and PNP devices the number
after that is the year/week number e.g. week 20 of 1990 or week 34 of 1990.
The devices we have in stock here at work have similar codes on, you may
find that Musical Fidelity can supply a replacement Alps Pot for your unit
but I seem to remember you have to run a bunch of wires from the tags to the
pcb.

Musical Fidelity
15/16 Olympic Trading Estate
Fulton Road
Wembley
HA9 0TF
Tel UK 0208 900 2866

Cheers
Alec


Also worth checking RS if you're going to fit yourself, as they do supply
ALPS pots (and there's useful spec on the product pages) and this does seem
the most likely cause of the fault you describe. MF will be able to advise
the value of the replacement even if they can't supply it.

Troubleshooting: amplifier Musical Fidelity A1
 

"Lintone Audio" wrote in message
...
"Sala Massimo" wrote in message
m...
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 ?


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!


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

ciao, Massimo
Italy

Hi you will find that the codes on the output transistors are usually week
numbers, the types are A1N and A1P which are NPN and PNP devices the number
after that is the year/week number e.g. week 20 of 1990 or week 34 of 1990.
The devices we have in stock here at work have similar codes on, you may
find that Musical Fidelity can supply a replacement Alps Pot for your unit
but I seem to remember you have to run a bunch of wires from the tags to the
pcb.

Musical Fidelity
15/16 Olympic Trading Estate
Fulton Road
Wembley
HA9 0TF
Tel UK 0208 900 2866

Cheers
Alec


Also worth checking RS if you're going to fit yourself, as they do supply
ALPS pots (and there's useful spec on the product pages) and this does seem
the most likely cause of the fault you describe. MF will be able to advise
the value of the replacement even if they can't supply it.

Troubleshooting: amplifier Musical Fidelity A1
 

"Jim Lesurf" wrote in message
...
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.

Nope, all bipolar, except for a couple of TL084 op-amps ;-)



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.

Jim's right - it seems to be a stock fault with these. But there's no
capacitors to check in this instance - my feeling is that it's a design
problem.

Please feel free to have a look at my homepage - you'll find lots of info
there, including schematics. It's currently the first result on a Google
search for "Musical Fidelity A1" ;-)



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).

Farnell stock the Alps "Blue Velvet" pot - don't know the part number off
the top of my head, but it's easy enough to find. 50K Log is what you need.

Cheers,

Mark
--
http://www.mhennessy.f9.co.uk/

Troubleshooting: amplifier Musical Fidelity A1
 

"Jim Lesurf" wrote in message
...
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.

Nope, all bipolar, except for a couple of TL084 op-amps ;-)



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.

Jim's right - it seems to be a stock fault with these. But there's no
capacitors to check in this instance - my feeling is that it's a design
problem.

Please feel free to have a look at my homepage - you'll find lots of info
there, including schematics. It's currently the first result on a Google
search for "Musical Fidelity A1" ;-)



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).

Farnell stock the Alps "Blue Velvet" pot - don't know the part number off
the top of my head, but it's easy enough to find. 50K Log is what you need.

Cheers,

Mark
--
http://www.mhennessy.f9.co.uk/

Troubleshooting: amplifier Musical Fidelity A1
 

In article , Mark Hennessy
wrote:
"Jim Lesurf" wrote in message
...


Jim's right - it seems to be a stock fault with these. But there's no
capacitors to check in this instance - my feeling is that it's a design
problem.

Ah. You mean they just allow d.c. bias to flow though the wipers?

IIRC this is 'relatively safe' with one polarity, but cruds up the wiper
and track with the other polarity. Sort of 'mini electroplating in the
home'. :-)

Please feel free to have a look at my homepage - you'll find lots of
info there, including schematics. It's currently the first result on a
Google search for "Musical Fidelity A1" ;-)

I'll have a look as well. I am after data on older MF items as well as
other UK makers. :-)


Farnell stock the Alps "Blue Velvet" pot - don't know the part number
off the top of my head, but it's easy enough to find. 50K Log is what
you need.

Cheers,

Mark -- http://www.mhennessy.f9.co.uk/

Thanks from me for letting me know the above. I should probably have known
already, but had forgotten! Do they also do the 40mm (big) detent pots? I
now only have a couple of these and my old suppler went out of business a
few years ago. They are very useful in controls as they allow controlled
re-settable, well-calibrated levels to be dialled up very easily.

Slainte,

Jim

--
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