[sdiy] protection circuit at audio output

[Antti PitkXmXki]

>From: Michael Buchstaller <buchi at allnet.de>

Yes, I'm planning to take the audio out of the C64's DIN connector.

> >I also wonder if it's
> >that transistor that people have fried instead of the SID. Of course 
>fried
> >transistor also means no sound, but replacing the transistor must be a 
>lot
> >cheaper than replacing the SID!
>
>Usually, the transistor is not so easy to kill.

These are texts/messages that got me concerned:

>From the Prophet64 manual:

"Caution! SIDs have been observed failing after being connected to mixing 
devices when mixer power has been turned off. Whether this is due to back 
current or any other spikes on the connection is not known. User is adviced 
to first carefully remove the audio connection to the SID before external 
unit is turned off."

>From the Prophet64 forum:

"I've read that you can build some sort of protective circuits for the audio 
ins and outs on the SID (C64 audio plug) to prevent them from being fried 
when connecting cables. Has anyone got a clue of what to use? Schematics?
So far I have only managed to ruin one SID when I connected it to my mixer. 
Don't know what I did wrong, luckily it was an old 6581 revision 1 or 2 and 
not one of my 8580 babies.. Just don't want it to happen again."

"it was probably killed by some tiny power spike. There's a warning in the 
"getting started" manual about turning the mixer off while the C64 is 
connected, maybe that's what you did wrong. I'd love a protection circuit, 
until then I'll just use the TV headphones output."

I guess I'll simply build a suitable cable (without protection circuitry) 
for connecting my C64(s) to a mixer or my stereo system so I can finally 
hear the sound properly, but I sure wonder what went wrong in those cases 
that I quoted! The transistor or the SID or what?

Thanks again for the answers,
Antti P.

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