[sdiy] SID output protection?

[grant musictechnologiesgroup.com]

Excuse my heresy, but with the SID chips being so valuable, ... are any of the many clones (I think "workalikes" is probably a more suitable term) worthwhile? And do they come with any buffering or protection?

GB

------ Original Message ------
From "Ben Stuyts via Synth-diy" <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>>
To "Antti Pitkämäki" <antti.s.pitkamaki at gmail.com<mailto:antti.s.pitkamaki at gmail.com>>
Cc "SDIY" <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>>
Date 7/30/2025 3:32:21 PM
Subject Re: [sdiy] SID output protection?

Hi Antti,

On 30 Jul 2025, at 21:20, Antti Pitkämäki via Synth-diy <synth-diy at synth-diy.org> wrote:

So it seems I can just leave the original 10k/1000pF lowpass filter there for not-too-trebly-sound and forget about the original transistor buffer, going instead for the opamp buffer with protective diodes and the output resistor.

Yes, please do. The op-amp buffer costs next to nothing, compared to the rare and expensive SID chips.

Thanks for all the help and links, I'll go through the information contained in them and let's see if I manage to come up with decent solution. I know it's not difficult, this is just not my field of expertise :P

BTW, here is another SID output protection circuit:

https://csdb.dk/release/?id=150177

It is based on diodes without any active parts.

The series-diode D1 doesn’t make much sense either. It could influence the sound (not sure about the output voltage levels involved), but it is definitely a non-linear device. In my opinion, it would make more sense to connect the D1 between the top of D2 (anode) and +12V (cathode). That way, anything over +12 V is shunted to the 12V rail.

And then loose the zener. Do not use zeners for this. Use a decent TVS (and check its datasheet where it actually starts clipping). The 12 V zener isn’t much of a protection. It is:
a) slow
b) not really 12 V (look up the data sheet)

In all, I would ignore that circuit.

If you settle on a circuit, feel free to post the schematic here for a go-over. There are lots of experienced designers here with solid opinions.

Ben

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