[sdiy] Module power - regulated or filtered (passively)?

[rsdio at audiobanshee.com]

First of all, thanks for the many great comments in this thread.

On Jan 7, 2020, at 9:42 PM, Pete Hartman <pete.hartman at gmail.com> wrote:
> On Tue, Jan 7, 2020 at 10:16 PM Quincas Moreira <quincas at gmail.com> wrote:
>> Yes, Yusynth and MFOS modules for example use such protection, and I can vouch that it does work, as I've burned a few myself when starting out due to inverted opamps. The 10R burned before anything else could be damaged on the boards. Erica Synths uses resetable fuses for the same purpose and it's a better solution since you don't then have to replace the fuse, it just interrupts the flow when excessive current is drawn, but doesn't burn out.
> 
> "Usually".  I've seen it done :-D   By others in this particular case.  The board was in such bad shape by the time I saw it, I have no idea what they did to melt the PTC fuse.

Personally, I would not assume that a series resistor was intended as “protection.” Since all integrated circuits should have a bypass capacitor, then a series resistor in front of that is going to create an RC filter. I would assume that the RC filter was intended, and the “protection” was merely a partial side-effect.

I don’t doubt that such resistors sometimes burn out under adverse conditions, but since they’re not manufactured as fuses then it’s not really safe to rely on them burning out before the other components. Chances are, when power is abused, something will burn out, but there don’t seem to be any guarantees that the series resistors will be the ones, and certainly not the only ones.


> The problem I have with the 10R solution is that if it's a VCO and it draws any significant current *and* uses the rails for reference (which a lot of those using this method seem to do), it can lead to an unstable VCO.  It doesn't take much to be audible, and I have encountered this with "real" designs in the DIY space.
> 
> Pete

Any time a reference is needed, I would not use resistors. I might be open to skipping the regulators, if possible, but I’d certainly use an accurate reference - one that is active, not passive. Eurorack just doesn’t seem to be the kind of environment where designs can get by with using the rails for reference. Again, I don’t doubt that such circuits appear in the DIY space.

Brian