[sdiy] protection circuit at audio output

[Antti PitkXmXki]

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.

_________________________________________________________________
FREE pop-up blocking with the new MSN Toolbar - get it now! 
http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/