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