problem with audiolab 8000a

davidgale

Member
2008-01-24 11:32 am
i have an old (mid 80s) audiolab 8000a integrated amplifier. a few days back i was listening to some music and somehow one of the wires from one of the speakers fell out. i switched off the amplifier and connected the missing wire to the speaker. i turned the amplifier on but there was no sound out of the speakers and the 'overload' diode was lit on (but there is sound coming from headphones if i connect them). i brought the amp to local technician who has repaired this amp several times before and he can't resolve the problem. he says that all transistors are ok.
any clues?
 

ashok

Member
2002-06-06 4:43 am
3RS
Does it have an output relay ? If so the relay or its drive circuit could be faulty.
The headphone output usually is connected to the output of the amp through a resistor and would not work if the amp is dead.

Funnily I worked a lot with my friends Audiolab 8000A but I've forgotten the finer details .......:hot: .... signs of old age ?
I had some pics of the innards . Must search it out.
There is also a generic circuit diagram on this forum. Did you find it ?
Cheers
 

davidgale

Member
2008-01-24 11:32 am
i just phoned the technician. he says that the relay is working ok. the reason why there is no output to the speakers is that there is some slight current on on one of the channels and relay is not switching on speaker output. but he cannot track down where does this current arise from.
 

ashok

Member
2002-06-06 4:43 am
3RS
I don't know what 'some current' means.
The protection circuit looks for a dc voltage at the output ( which can damage your speaker ). It will then prevent the relay from turning on if it finds a dc offset.
You can check the output of the two channels on the board before the relay and determine if you have a large dc offset.
If so , some component on that channel is bust. Shouldn't be too hard to find out. I'll send you a copy of the circuit diagram that I have.

I'm out of town and will be back only tomorrow , so there will be a delay.
Cheers.
 
davidgale you are not alone. I have been asked to look at an AUDIOLAB 8000A with a similar problem. No output from the speakers but ok from the headphones, You will also find that the preamp still works.
A quick investigation has shown that the protection circuit on one of the channels has some burnt resistors and 1 capacitor is also blown. I have not investigated further but the transistors seem ok on both outputs. I will try and have a good look but I think the trick is to identify what else blew with the protection circuit.

I have looked at a few threads with similar problems but no straightforward solutions are forthcoming nowadays on here. I think we have too many diy experts who seem to always deviate from what the initial problem/ fault is. Most threads seem to trail off into never ending design philosophy discussions.
 
AUDIOLAB 8000A FIXED

Davidgale I hope you fixed your amp.

I have finally fixed my audiolab 8000A without too much work in the end. I just had to be patient as the problem was not obvious. The protection circuit had fried components which i replaced. I still had not solved the problem as I was getting no output and the two 470R resistors in the protection circuit were heating up very badly. The problem was still in the power amp section. All the transistors tested fine but just check for another short component on the side that fried the protection circuit. Mine is up and running and the cost was next to nothing as no transistor in the power amp needed replacing despite the protection circuit components being completely fried. Patience pays