[sdiy] SID output protection?

[Ben Stuyts]

> On 30 Jul 2025, at 17:34, Ingo Debus via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> That link doesn’t work for me. Is that probably a link to a file on your own computer?
> However, I googled the file name of that pdf and found this one:
> https://www.c64.cz/data2/download/x12/122790/MOS6581_Alternative_output_V2_0.pdf
> Is it this one? This circuit looks a bit strange. Why didn’t they just connect the negative power supply terminal of the opamp to ground? What are the two 18k resistors good for?

Probably tried to give it a +/- 6V power supply in a very bad way…

> Also, the 500R/220pF lowpass has a cutoff frequency in the MHz range. The 10k/1000pF lowpass of the original circuit has a cutoff frequency of about 16 kHz. Maybe this is the reason for the „additional treble“?

I think my own -3 dB point is already lower than 16 kHz. :-)

> I still don’t see why an opamp buffer should protect the SID’s output better than the original emitter follower circuit. Can anyone explain?

Maybe more stuff between the output jack and the SID.

But I don’t get it. It’s 2025, not 1980. Why don’t they add some decent transient protection? Put some TVS’s on there against ESD and transients, and include the buffer op-amp. Put a 1k output resistor on it, like Oren already mentioned. Somebody is bound to put +48V on that output from a wrongly configured input channel on the mixer.

Ben

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20250730/5be7388a/attachment.htm>