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

[René Schmitz]

On 18.01.2020 11:59, Neil Johnson wrote:
> Brian wrote:
>> Personally, I would not assume that a series resistor was intended as “protection.”
> 
> Indeed not, unless you're using fusible resistors.

It is merely a last resort. Ideally there should be a fuse in the supply 
that (hopefully) trips before the resistor burns out. But this is not 
always a given.

>> 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.
> 
> Bypass/decoupling capacitors have a very different role to play than a
> series low-pass filter.  For one thing the values of decoupling caps
> tend to be much smaller: a 22R series resistor and a 100nF decoupling
> capacitor have a -3dB point around 72kHz - way above audio and no help
> to combat falling PSRR.

If the resistor is a single one common to all chips, located at the 
power entry to the module, then you need to add all the bypass capacity. 
In that case there needs to be one larger bypass of say 22 - 100u 
electrolytic per module, and a 100n near each chip. This arrangement is 
more effective down to the range where the opamps PSRR can take over.

Best,
  René

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