Questions about resistors, sound quality and 'mojo'

[tommycataus]

Hello all, apologies if this has been covered before, although I couldn't find anything definitive through searching.

1) Strictly for building simple effects (9V), have any of you noticed a perceivable difference in using carbon comp resistors over metal, whether it be to do with hiss or general tone?

2) I have noticed that, in some effects I have built and experimented with, the trimpots seem to introduce hiss whereas the use of a fixed carbon resistor eliminates this. Can anyone confirm whether this is just my imagination or not?

3) Is there any merit in using vintage carbon resistors in fuzz boxes and the like? I know that in amplifiers and other high voltage audio applications there is supposedly a difference in tone, however I don't know if the same can be said for a fuzz face clone, for example. I have seen some very nice looking gutshots that include germanium transistors, PIO caps and vintage resistors. I know that some swear by using vintage caps, but I don't know whether the resistors are just for aesthetic consistency.

Lastly, I know that a great proportion of this stuff is based on personal taste, however I am curious as to whether anyone has checked out these differences and formed an opinion based on their own experimentation. What do you think?

[Arcane Analog]

If you do not use mojo parts your pedal will sound normal.

[FiveseveN]

I don't know whether the resistors are just for aesthetic consistency.

"Tone" is aesthetic as well. If using some vintage component predictably produces some consistent change in performance, some will prefer it, some will not.
Lots of people have formed opinions but they rarely have anything to do with sound. Trouble is we can hear a lot less than we think we can.

[tommycataus]

Aha! I just found a telling article:

http://www.geofex.com/Article_Folders/carbon_comp/carboncomp.htm

Can't find anything about trimpots causing hiss though...

[bluebunny]

Can't find anything about trimpots causing hiss though...

I've read elsewhere that they can be noisy, if they're in the audio path.  In which case, good practice is to pull the trimmer (once "set") and replace with two fixed resistors.

[tommycataus]

Ah great, thanks Marc! So I take it as long as they are only being used for biasing etc. then using them will not cause any noticeable issues?

[R.G.]

Trimpots cause hiss for a few reasons; one is that they're deliberately cheap, so they're often made of carbon composition material, which has excess noise. Another is that they are pots, and their wipers may or may not make really good contact with the resistive strip. Intermittent, low-pressure contacts are prone to being noisy.

They will be less noisy at very low currents than at higher currents.

[tommycataus]

Brilliant information, thanks so much RG! I guess it's a trade off then between better quality and added tweakability.