[sdiy] SID output protection?

[grenert]

I think probably the greatest risk to a SID chip in an actual C64 is the
horrible power supply that originally came with the computers.
https://www.lemon64.com/forum/viewtopic.php?t=70345

Best,
J. P.


On Mon, Jul 28, 2025 at 9:44 AM Ben Stuyts via Synth-diy <
synth-diy at synth-diy.org> wrote:

> What is the mechanism that destroys the SID? Is it some transient voltage
> surge, or ESD? If so perhaps a few well placed TVS’s and/or Shottky diodes
> would help. (At output and power pins.)
>
> And take precautions for people connecting it to a phantom powered input...
>
> Ben
>
>
> > On 28 Jul 2025, at 17:36, Antti Pitkämäki via Synth-diy <
> synth-diy at synth-diy.org> wrote:
> >
> > Hi,
> >
> > I have an ongoing project of adding 3 additional SID sound chips to an
> old Commodore 128DCR computer for a total of 4 SIDs (I'm planning a C128DCR
> for this project instead of a C64 due to the 128DCR's additional space for
> modding). I've got the basic idea of how to implement it sorted out, but
> there is one crucial aspect I'm not yet sure how to implement properly: SID
> output protection.
> >
> > SIDs are known to break/fry easily. A situation where it often occurs is
> when the mixer connected to the computer is turned off while the computer
> is powered (the computer should be switched off before switching off the
> mixer). Another potential cause of SID death is (accidental) hot plugging
> equipment. So I think my SIDs would need some protective circuits at their
> output.
> >
> > As it is, there is a already a single transistor buffer (2SC1815) at the
> output of the SID in a stock C64/C128. However, apparently the transistor
> doesn't do a very good job at protecting the SID.
> >
> > I've found several suggestions for SID output protection: an
> optocoupler, a ground loop isolator, diodes that short overvoltage or an
> additional op-amp buffer.
> >
> > I'm quite sure the best advice I can find resides in SynthDIY, so... If
> you had a delicate audio chip such as the SID, how would you protect it's
> output to prevent damage to the chip caused by voltage spikes, overvoltage
> or other anomalies from auxiliary equipment? Would a more sophisticated
> buffer than just the original transistor be sufficient or do I need
> something else?
> >
> > Any help would be greatly appreciated!
> >
> > BTW in case anybody is interested, I can share information on how to add
> 3 additional SID chips to a Commodore 64/128. Schematic-wise it's really
> quite simple.
> >
> > Finally, some background on my project: I've made C64 music for years,
> and some time ago I found out that my favorite native C64 music "tracker"
> has a version that supports up to 4 SIDs for 12 channels of sound. So my
> dream is to mod a C64/128 for 4 SIDs so that each SID has a separate
> output. It would be like a mini synth studio. 12 channels with 4 outputs (3
> channels per output) would have great possibilities and it would be enough
> to make synth music outside the chipmusic context. And the learning curve
> would be close to zero since I know the tracker well. Also I like "closed
> musical systems", I mean doing music with a single device (although I'd of
> course add external mixing and effects).
> >
> > Regards,
> > Antti
> >
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