Greetings,

I know there are a few here who are very well qualified with hifi (and
particularly amplifier) electronic design. Can you help?

I have an Alchemist Nexus amplifier which, when turned above a certain
volume, screeches loudly through the speaker output.

I believe that the amp is outputting DC - does that sound right?

I have removed two burnt out resistors - identical on each channel on the
PCB - and I had already replaced two 4 amp output fuses before testing
produced the results described and before I removed the burnt resistors.

Can anyone confirm my translation of the resistor colour codes (gathered
from an identical amp as those in the faulty amp were badly burnt):

1st digit: Brown: 1
2nd digit Black: 0
Multiplier: Black: 0
Quality: Brown: 1

I make this 10 ohms of a high-tolerance 1%/1000 hour anticipated failure?

I want to be certain as, while I am confident that my soldering skills are
up to the task (the components are not surface mount), I have not carried
out such a repair before without the aid of a manufacturer's service manual
before.

I have created a small rollover image at
http://www.alchemisthifi.info/fault/resistor.htm which allows you to compare
the damage on the bad amp with the good amp.

The manufacturer (Alchemist) is no longer in business and there are no
circuit diagrams about.

Beyond the resistor confirmation, any constructive advice you can offer
about my approach would be appreciated.

TIA.

JustMe wrote:

Greetings,

I know there are a few here who are very well qualified with hifi (and
particularly amplifier) electronic design. Can you help?

I have an Alchemist Nexus amplifier which, when turned above a certain
volume, screeches loudly through the speaker output.

I believe that the amp is outputting DC - does that sound right?

I have removed two burnt out resistors - identical on each channel on the
PCB - and I had already replaced two 4 amp output fuses before testing
produced the results described and before I removed the burnt resistors.

Can anyone confirm my translation of the resistor colour codes (gathered
from an identical amp as those in the faulty amp were badly burnt):

1st digit: Brown: 1
2nd digit Black: 0
Multiplier: Black: 0
Quality: Brown: 1

I make this 10 ohms of a high-tolerance 1%/1000 hour anticipated failure?

I want to be certain as, while I am confident that my soldering skills are
up to the task (the components are not surface mount), I have not carried
out such a repair before without the aid of a manufacturer's service
manual before.

I have created a small rollover image at
http://www.alchemisthifi.info/fault/resistor.htm which allows you to
compare the damage on the bad amp with the good amp.

The manufacturer (Alchemist) is no longer in business and there are no
circuit diagrams about.

Beyond the resistor confirmation, any constructive advice you can offer
about my approach would be appreciated.

TIA.

In all probability the burnt out resistor(s) are not the cause of the
problem but an effect of it. Resistors very rarely fail short circuit so
it is likely that whatever this resistor is connected to has actually
failed and taken out the resistor with it.

Ian
--
Ian Bell

"Ian Bell" wrote in message
...
JustMe wrote:

Greetings,

I know there are a few here who are very well qualified with hifi (and
particularly amplifier) electronic design. Can you help?

I have an Alchemist Nexus amplifier which, when turned above a certain
volume, screeches loudly through the speaker output.

I believe that the amp is outputting DC - does that sound right?

I have removed two burnt out resistors - identical on each channel on
the
PCB - and I had already replaced two 4 amp output fuses before testing
produced the results described and before I removed the burnt resistors.

Can anyone confirm my translation of the resistor colour codes (gathered
from an identical amp as those in the faulty amp were badly burnt):

1st digit: Brown: 1
2nd digit Black: 0
Multiplier: Black: 0
Quality: Brown: 1

I make this 10 ohms of a high-tolerance 1%/1000 hour anticipated
failure?

I want to be certain as, while I am confident that my soldering skills
are
up to the task (the components are not surface mount), I have not
carried
out such a repair before without the aid of a manufacturer's service
manual before.

I have created a small rollover image at
http://www.alchemisthifi.info/fault/resistor.htm which allows you to
compare the damage on the bad amp with the good amp.

The manufacturer (Alchemist) is no longer in business and there are no
circuit diagrams about.

Beyond the resistor confirmation, any constructive advice you can offer
about my approach would be appreciated.

TIA.

In all probability the burnt out resistor(s) are not the cause of the
problem but an effect of it. Resistors very rarely fail short circuit so
it is likely that whatever this resistor is connected to has actually
failed and taken out the resistor with it.

Ian

Yes, I wondered about that too but, with my limited knowledge, I've not been
able to identify any other faulty components - what else would cause an amp
to go DC in the manner described at the top? The o.p transistors all compare
well with those in the good amp, for instance.

Either way, they need replacing and so I thought I'd start there, even if I
have to replace them again, after.

Have I read the resistor's rating correctly?

JustMe wrote:

"Ian Bell" wrote in message
...
JustMe wrote:

Greetings,

I know there are a few here who are very well qualified with hifi (and
particularly amplifier) electronic design. Can you help?

I have an Alchemist Nexus amplifier which, when turned above a certain
volume, screeches loudly through the speaker output.

I believe that the amp is outputting DC - does that sound right?

I have removed two burnt out resistors - identical on each channel on
the
PCB - and I had already replaced two 4 amp output fuses before testing
produced the results described and before I removed the burnt
resistors.

Can anyone confirm my translation of the resistor colour codes
(gathered from an identical amp as those in the faulty amp were badly
burnt):

1st digit: Brown: 1
2nd digit Black: 0
Multiplier: Black: 0
Quality: Brown: 1

I make this 10 ohms of a high-tolerance 1%/1000 hour anticipated
failure?

I want to be certain as, while I am confident that my soldering skills
are
up to the task (the components are not surface mount), I have not
carried
out such a repair before without the aid of a manufacturer's service
manual before.

I have created a small rollover image at
http://www.alchemisthifi.info/fault/resistor.htm which allows you to
compare the damage on the bad amp with the good amp.

The manufacturer (Alchemist) is no longer in business and there are no
circuit diagrams about.

Beyond the resistor confirmation, any constructive advice you can offer
about my approach would be appreciated.

TIA.

In all probability the burnt out resistor(s) are not the cause of the
problem but an effect of it. Resistors very rarely fail short circuit so
it is likely that whatever this resistor is connected to has actually
failed and taken out the resistor with it.

Ian

Yes, I wondered about that too but, with my limited knowledge, I've not
been able to identify any other faulty components - what else would cause
an amp to go DC in the manner described at the top? The o.p transistors
all compare well with those in the good amp, for instance.

When you say compare well what do you mean? And when you say the amp outputs
dc, between what points do you measure this, what value do you read and how
does it compare with a good amp?

If the output trannys are OK then it may well be their drive circuit that is
giving the problem but you really need a circuit to get into this levele of
detail.


Either way, they need replacing and so I thought I'd start there, even if
I have to replace them again, after.

Have I read the resistor's rating correctly?

Looks like 10ohms 1% to me.

IAn

--
Ian Bell

Contact Chris Found at He designed a few alchemist
products and would certainly help if he can. He's a friendly chap (lives in
Fulham) Andy

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

"Andy Evans" wrote in message
...
Contact Chris Found at He designed a few alchemist
products and would certainly help if he can. He's a friendly chap (lives
in
Fulham) Andy

I believe the Nexus amp was designed by Glen Gayle - Chris designed their
digital products and the Product8 pre amp too. I could send it to Glen, but
I'd really like to try and sort it at home, if I can.

I believe the Nexus amp was designed by Glen Gayle - Chris designed their
digital products and the Product8 pre amp too. I could send it to Glen, but
I'd really like to try and sort it at home, if I can.

you can email Chris and he'll give you his phone number - he may be able to
tell you what to do over the phone. Andy

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

JustMe wrote:

Greetings,

I know there are a few here who are very well qualified with hifi (and
particularly amplifier) electronic design. Can you help?

I have an Alchemist Nexus amplifier which, when turned above a certain
volume, screeches loudly through the speaker output.

I believe that the amp is outputting DC - does that sound right?

No.


I have removed two burnt out resistors - identical on each channel on the
PCB - and I had already replaced two 4 amp output fuses before testing
produced the results described and before I removed the burnt resistors.

Can anyone confirm my translation of the resistor colour codes (gathered
from an identical amp as those in the faulty amp were badly burnt):

1st digit: Brown: 1
2nd digit Black: 0
Multiplier: Black: 0
Quality: Brown: 1

I make this 10 ohms of a high-tolerance 1%/1000 hour anticipated failure?

Resistors don't have " 1000 hour anticipated failure " bands !


I want to be certain as, while I am confident that my soldering skills are
up to the task (the components are not surface mount), I have not carried
out such a repair before without the aid of a manufacturer's service manual
before.

I have created a small rollover image at
http://www.alchemisthifi.info/fault/resistor.htm which allows you to compare
the damage on the bad amp with the good amp.

The manufacturer (Alchemist) is no longer in business and there are no
circuit diagrams about.

Beyond the resistor confirmation, any constructive advice you can offer
about my approach would be appreciated.

If you don't know how to troubleshoot - give up or give it to someone who does.


Graham

"Pooh Bear" wrote in message
...

JustMe wrote:

Greetings,

I know there are a few here who are very well qualified with hifi (and
particularly amplifier) electronic design. Can you help?

I have an Alchemist Nexus amplifier which, when turned above a certain
volume, screeches loudly through the speaker output.

I believe that the amp is outputting DC - does that sound right?

No.


I have removed two burnt out resistors - identical on each channel on
the
PCB - and I had already replaced two 4 amp output fuses before testing
produced the results described and before I removed the burnt resistors.

Can anyone confirm my translation of the resistor colour codes (gathered
from an identical amp as those in the faulty amp were badly burnt):

1st digit: Brown: 1
2nd digit Black: 0
Multiplier: Black: 0
Quality: Brown: 1

I make this 10 ohms of a high-tolerance 1%/1000 hour anticipated
failure?

Resistors don't have " 1000 hour anticipated failure " bands !

I believe that they have a failure rating which is a percentage after 1000
hours, hence 1% per 1000 hours - 1% anticipated failure after 1000 hours. Is
this wrong?

I want to be certain as, while I am confident that my soldering skills
are
up to the task (the components are not surface mount), I have not
carried
out such a repair before without the aid of a manufacturer's service
manual
before.

I have created a small rollover image at
http://www.alchemisthifi.info/fault/resistor.htm which allows you to
compare
the damage on the bad amp with the good amp.

The manufacturer (Alchemist) is no longer in business and there are no
circuit diagrams about.

Beyond the resistor confirmation, any constructive advice you can offer
about my approach would be appreciated.

If you don't know how to troubleshoot - give up or give it to someone who
does.

That's very helpful - I'll learn a lot like that - thanks.

Graham

JustMe wrote:

"Pooh Bear" wrote in message
...

Resistors don't have " 1000 hour anticipated failure " bands !

I believe that they have a failure rating which is a percentage after 1000
hours, hence 1% per 1000 hours - 1% anticipated failure after 1000 hours. Is
this wrong?

Yes

If you don't know how to troubleshoot - give up or give it to someone who
does.

That's very helpful - I'll learn a lot like that - thanks.

Just being practical - it's not something that's easy unless you already know a
lot about repairs in general.

There's more scope for combustion with power amps !


Graham.