[sdiy] protection circuit at audio output

[Loscha]

The commonly held belief, vaguely supported by an interview with Bob
Yannes  was that the protection for the output stage of the SID was
one of the many unfinished parts of the project that would have been
done correctly, had Commodore stuck to their originally quoted time
frame for the development of the SID and other chips he and his team
were working on.

-Ed

On 1/5/07, Antti Pitkämäki <anpitkam at hotmail.com> wrote:
> Hi,
>
> I'm sorry for this neverending story, but I got the following report from a
> C64 forum:
>
> "I fried SID by connecting high power amplifier to c64's audio output. both
> were powered on. surely SID went down , because inserting another one brang
> sound again.
>
> looks like you have to turn off at least one of devices to have SID safe
> when connecting the stuff (I usually turn off the amplifier(s) - and this
> way I haven't broken anything so far) , but preferably both.
>
> usually I also power down C64 first and then amplifier - it's a kind of
> habit actually.
>
> so - these are not rumours , those are just facts. that circuity is actually
> protecting but it seems it doesn't protect in all cases ;-) . that broken
> SID could only make clicks coming from volume changes onwards (yes , it can
> still play digis)."
>
> But also:
>
> "I've been using a SID connected to my stereo amplifier for years so far and
> I've never fried any SID. Maybe I've just been lucky. A general rule is to
> never plug/unplug stuff when devices are powered on. I always turn on my C64
> and amplifier toghether with the same switch. "
>
> So I guess I'll think about that opamp-thing and also the isolation
> transformer. One fairly interesting idea is to put two diodes in series from
> signal to ground and two diodes from ground to signal at the output (with a
> series resistor) so that anything over +/- 1.4 volts would go to ground
> instead of the SID...
>
> Or maybe the danger is not in turning off mixer/amplifier (if the C64 is
> turned off), but plugging/unplugging the cable when the C64 and mixer are
> turned on...
>
> Whoa, lotsa trouble from that stinky old chip ;)
>
> Antti P.
>
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