[sdiy] protection circuit at audio output

[Mike]

From: "Antti Pitkämäki"

> Whoa, lotsa trouble from that stinky old chip ;)
>

I think this may have something to do with the grounding in the C64. I've
had similar faults with industrial equipment. One of the devices can 'float'
it's earth up to quite a high level, and then changing the connections can
introduce a large spike into the system.

IMHO, the most sure fire answer is an op-amp driving a transformer, (quite a
few people using some of the analogue modelling synths have added cheapo
TX's just to 'phatten' up the sound, -  people forget that a lot of the
'valve sound' is due to all that not-exactly-linear Iron and Copper). A
fully floating output will prevent most interaction - if it can damage a SID
on the other side of a TX, then your life is at risk!

This may be more of a USA problem too - in the UK and Germany we have far
tighter regulations on earthing, which may remove a lot of these problems.
Even so, I'm going to put a set of op-amp buffers into the MIDIbox SID I'm
building, and likewise with the FM module, it's too late to regret when
you're on stage and the lights are coming up....and the chips have expired

HTH

||\/||ike