R.G. Keen is an electronics guru
of monumental proportions. He posts regularly on Ampage and other DIY
guitar sites, and is a font of constant information. Go to his
site at geofex.com and you will
find an enormous amount of info about guitar effects and tube amps, as
well as dozens of projects to build.
Here is a thread I
pulled from Ampage by R.G. about the differences between the various
resistor and capacitor types, and their effect on tone:
Subject: resistors and caps
I've read that metal resistors have less hiss then carbon ones, but
that carbon ones have vintage Mojo.
Also there are many different caps, some which should sound great for
audio, some very bad...
What is the real deal here? Or does anyone know a webpage where I can
read about this stuff. I read one once but I forgot the url...
thanks!
From: R.G.
Subject: Re: resistors and caps
I guess I really should have done the carbon composition resistor FAQ.
Carbon composition resistors are composed of a cylindrical space filled
with carbon granules. They have excess noise above the minimum that a
pure resistance of the same value would have. Sometimes much more.
Metal film and wirewound resistors have noise levels very close to the
minimum that any resistor can have for a given value, so from strictly
noise considerations, they're more optimal that carbon comp, although
they may have other characteristics that are a handicap in some
situations, principally at high voltage or high power.
Carbon comp resistors have a relatively high voltage coefficent of
resistance. That means that the resistance changes with the voltage
across them, so the same resistor has a lower resistance at low
voltages/currents than it does with high voltages/currents. While all
resistors have something like this, carbon comp stands out for having a
particularly large one compared to the other commonly available ones.
In this context, "high" means around 100V and up. In tube amps, this
can mean that carbon composition resistors have a measurable second
harmonic distortion, hence the reputation for sweeter sound.
At low voltages the effect is usually too small to measure. Your 9V (or
12V, or +/- 15V) effect will not show the good distortion, only the
noise. There is no vintage mojo, only the high voltage resistance
change, or the occasional one that has *bad* point contact and
rectification effects.
As to caps, I reproduce an earlier post I did on this. I guess I should
just post this stuff every week or two.
=================================================
The hifi guys are more nuts on this subject, but I'll give you in a
capsule the more-or-less accepted rules of thumb. I do hate to see the
hifi tweako mystique infiltrating the musical and effects arena...
sigh...
For tonal qualities, caps are largely chosen by their dielectric
absorption.
The semi-accepted order is:
teflon - thought to sound ultimately clear, use for circuit boards too
polystyrene - ditto
polycarbonate - ditto minus a hair
polypropylene - ditto, plus available in uF sizes
polyester (mylar) - Ok if you can't get something better, not a lot
worse than the
other plastic films, and much better than those lower in the list
NPO ceramic - only available in tiny sizes
aluminum electrolytic - the accepted standard for uF and up sizes
simply on $ and size
paper - obsolete, can't get them anymore; thought to be "tweedy" or
some such nonsense, by the tubies
other ceramic types - thought to sound "grainy"
tantalum - unreliable and thought to sound grainy
Above teflon is vacuum then air, which are impractical for all normal
circuits. There exist other exotica, like glass dielectric capacitors
for special purposes.
There are capacitance size and voltage limits, obviously. 100uF
polystyrene caps don't exist, while aluminum is barely working up a
sweat at 100uF. Likewise, there are no 1000V aluminums, but 1Kv
ceramics are easy and cheap. Also the construction of the capacitor,
whether stacked, rolled, folded, extended tab, etc., etc., can have
real effects (as distinguished from silliness like cryogenic stress
relief or water jacketing).
I personally have staged a couple of capacitor shootouts, and haven't
yet found someone who could tell simply by listening whether they were
hearing music through a polypropylene versus ceramic, although I don't
doubt that someone might be able to.
"Best sounding in FX" is not something you can nail down, as you will
find that each person may perceive "better" and "best" as meaning
something different. I'd be willing to make a significant bet with you
that I could set up a test where I changed only the capacitor and you
would not be able to do more than 50% +/- 2% correct telling the caps
apart by sound alone.
IMHO you would be wasting your money chasing down and buying super
premium caps for effects. Use mylar and aluminum, get it working, and
when it's going good, substitute out for some super-premium stuff until
you satisfy your curiosity. On the other hand, don't just use the
high-value ceramic caps for audio coupling (even though many highly
sought after vintage effects did exactly this).
There are people who disagree with me strenuously, even violently.
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R.G.