Power Filtering components, if only using batteries?

[chptunes]

Hey folks.. Question:

If I only intend to use batteries to power my effect, do I still need to install Power Filtering components?  For example, R4 and C4 in this Mini-Booster schematic.. are these components serving any purpose if the power source is a 9v battery?


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Thanks in advance.. -Corey

[R.G.]

It's a good idea to put them in anyway, if not critical.

Filtering caps lower the apparent high frequency impedance of the power supply to the circuit. This matters to some circuits more than others. A good, low impedance power supply is nearly  never a bad thing.

Batteries start out with a low internal impedance, but this gets higher as the battery is used. The filtering cap keeps the high frequency impedance that the circuit sees low even with the battery getting higher.

[chptunes]

Thank you, sir.   

-Corey

[Electron Tornado]

R.G., you should really write a book about power supplies. I learn more from reading your posts than I do from the books I've read.

[PRR]

> write a book about power supplies

It would never be finished.

Fer example, in *this* circuit, power supply impedance is not critical. (The top FET is wired for high impedance, PS impedance need not be real low.)

OTOH, old batteries sometimes get "noisy". You hear individual zinc-atoms die. (Or is it gas-bubbles or dirty contacts?) *This* circuit has little power supply rejection. Half the batt-crap will appear on the output.

So yeah. You can sometimes get-away with omitting a cap in battery-only duty. But the brain-pain or extended testing to be sure it stays happy in ALL cases is more than one R & C is worth.

[chptunes]

Good input PRR.. Thank you.

-Corey

[jogina111]

I think you can socket them for some tone coloration..I do this for some ODs I've built..

[Electron Tornado]

> write a book about power supplies

It would never be finished.

I'm not sure why would you say that.

A book wouldn't have to be the be-all, end-all of power supply books for every application. What you and R.G. are able to do (I learn a lot from your posts as well) is to connect the theory with the practical, and add some insights some of us may not have heard of or considered. That is a very important element that many books out there often lack. Most people here are hobbiests - with a desire to learn more.