Q: where to put "low noise" components? and noise issues

[km-r]

i dont get many metal film resistors here and i want to put some in my dr boogey.
so id like to place metal film resistors in critical places to minimize the hiss... i cant have all replaced into metal films.
where are these critical places[this question does not only apply to the DB]?
and what capacitors can be considered "low noise?"

[Joe Hart]

I would say the critical places are in the signal path (don't waste them if they aren't going to have any effect) and early on in the signal path (because any noise early on with just get multiplied as it goes to output). But I'm sure others here have more specific details about this.
-Joe Hart

[petemoore]

i dont get many metal film resistors here and i want to put some in my dr boogey.
so id like to place metal film resistors in critical places to minimize the hiss... i cant have all replaced into metal films.
Big resistors create more thermal noise.
where are these critical places[this question does not only apply to the DB]?
and what capacitors can be considered "low noise?"
  Input. Mainly true of anything which amplifies.
  If you hook a wire to your speaker, you'll notice it doesn't respond at all to noise [juse your thumb to put a voltage across the speakers cable-plug. Try the same trick at an input and notice what a difference signal multiplication makes...no noise on the output end, easy noise detection on the input.

[Ben N]

Two articles for your persusal (should be in the Wiki):
http://geofex.com/Article_Folders/carbon_comp/carboncomp.htm
http://www.aikenamps.com/ResistorNoise.htm.

The Geofex article is more on where carbon might add something, so it is more useful as a guide assuming that you will use metal film everywhere but. The Aiken article gives you the technical poop on how and where resistors add noise. Although the article is geared to amps, it should still be helpful in the stompbox context, especially for gain-type units.

[R.G.]

i cant have all replaced into metal films. where are these critical places?

Since noise is multiplied by all the gain that comes after it in the signal chain, noise is most critical in the front end of any amplifier. If you have a limited amount of low noise resistors and transistors, use them in the very first stage first. The higher the gain of the device, the more this is critical. It's only in gain-of-one applications where noise in all stages has equal contributions.

and what capacitors can be considered "low noise?"

All of them except leaky electrolytics. Ideal capacitors (and inductors) generate no noise whatsoever. It's only the resistor imperfections that make thermal noise. Leaky electrolytics have a lot of noise, but this is a degenerate case, not something you design.

[Ice-9]

Would it also be wise to use low noise resistors in the voltage divider circuit as if there is noise on the rails this might find its way into the signal. I'm probs wrong, just thinking out loud again.

[R.G.]

You are correct in concept; however, as a practical matter a bias string is usually shunted to ground by capacitors, which help attenuate the thermal noise the resistors make.