In article ,
tony sayer wrote:
In article , Dave Plowman (News)
scribeth thus
This time, a BBC AM8/16. Basically, a BBC modified Quad 405 to drive
the LS5/8. Has a crossover added to the input to the amps.

One of the two produces a pretty loud squawk on switching off. Not a
fault as such, as plenty early BBC ones in service did the same. But
the BBC did seem to find a cure. The pair I had were ok.

Sadly, the three circuits I've got for the crossover are all the same.

I've only got the one amp here, so can't just look for any differences.

I can post a link to the crossover circuit if it helps. It gets its
power from the + side of the Quad PS and regulates that down to 30
volts.


Are you saying that one channel squawks whist the other doesn't?.

It seems to be both channels (LF & HF) on the one amp.

If this was a problem overall with the 405 I bet QUAD would have done a
mod for it even in the balanced input splitter/driver board

I don't think it's anything to do with the Quad part.

Very much expect its a duff cap or caps somewhere well worth changing at
the age thats likely to be..

Thing is I well remember new ones doing it at work, when they first came
out. My pair here didn't, but then now no longer have AM8s.

This amp I'm looking at seems to have a later crossover, by my BBC
schematics. But I dunno how many versions there were. And measures just
fine. There are very few electrolytics on this PCB and to change all the
caps on spec would be a very difficult job since many are very odd values.

--
*Why is the word abbreviation so long? *

Dave Plowman London SW
To e-mail, change noise into sound.