Audiolab 8000A getting hot

[big jim]

Hi can anyone advise me my amp gets hot at idle is this normal.



many thanks. jim

[Mooly]

You need to measure and confirm the output stage is drawing the correct quiescent current.
You'll have to come up with a service manual for that info... but for a class b (or ab) amp running at say 100ma the answer is no, it should not be "hot".

Circuit shown listed here for free,
Free Manuals User / Service / Schematics for Download | HiFi Engine

haven't time to look now

[big jim]

Hi thanks mooly ive checked the bias current its about 90ma
also checked the output stage for oscillation but seems ok.


thanks. jim

[chlorofille]

If possible, try and measure what the exact temperature is. I have thin skin on my fingers so I find 43 Deg celcius hot to the touch =)

[Andy5112405]

I've got the Audiolab 8000A Service manual in soft copy (scanned) if you are interested. Would be better to send on CD as files are quite big.

The 8000A evolved in its production run so you may need to use a bit of artistic license.

[Andy5112405]

Bias is factory set by selecting R809 - R812. Bias should be 100mA. You have measured 90mA which is fine just aging of components.

Are you allowing sufficient room for cooling. You should have at least 150mm all the way around it, sides and top.

60 Degrees C is HOT for a Class AB amplifier, however, 40 Degrees above ambient is acceptable. During the winter some guys like to crank the heating up to 25 Degrees, this will make electronics run hotter, especially if the unit can't radiate the heat through being too confined.

[Mooly]

Another thought, is the DC offset OK ?

Sounds like it is all OK though.

[big jim]

Hi thanks all ive checked every thing and the amplifer works perfectly beleive it or not i have owned this amplifier for over 15 years but only just recently ive noticed that it runs very hot when using headphones and for this type of amplifier it surprised me.


regards jim

[Andy5112405]

It's unlikely to be anything to do with using headphones as the main power amp is still used, the headphone socket is across the speakers with a 390R resistor in series with it. Even short circuit headphones wouldn't cause it to overheat.

Could possibly be just dust build-up. Computers often fail when the fins of the heatsinks become clogged with "human".

[Mooly]

If the output stage current is OK and stable i.e. doesn't drift upward in value (you say it is OK) and the mains voltage is correct (is it adjustable, not set for 220 and used on 240 ) then it's all normal.

There is no doubt... that's it

If it's hotter than it should, then it's because the heat can not get away, not because of any circuit problem.