Bypass Capacitors, Tone Capacitors and Guitar Tone:
Refers to how the frequency profile on a guitar is controlled
There two different types of capacitors in a guitar, the tone cap and the bypass cap.
The tone cap, attached to the tone pot, sends highs to ground and are typically from
a standard .022uf, it can vary from 330pf to .1uf. The treble bypass capacitor
attaches to the volume pot between the input and the output. Thes are much smaller caps,
from 100pf to 2200pf depending on how much of the highs you want to retain when the volume is
turned down. Typically, 1000pf (or .001uf) run in parallel with a 150k resistor allows you to
turn down the volume without losing the highs. These are treble bleed or bypass circuits.
For those who want a flat profile, which helps effects pedals and rackmount units do their
job much better across the guitar register frequencies from low to high, they should use
a tone cap grounding out the tone control of only 100 picofarad, which is enough to keep ultrasonics
off of the signal, which is only hiss noise if it can be heard, and tends to damage electronics.
A blues sound would use a tone capacitor slightly larger than the standard, such as a .033uf ceramic type.
Such guitar tech setups aim to achieve a less bright, fuzzier sound than rock guitar, and would therefore
likely add a germanium diode to, before a 150,000 ohm resistor, to enhance even harmonics which can
be said to propagate better in a slightly unbalanced wave distorted signal. This of course assumes
that it will be necessary to add some kind of distortion effect device into the signal path anyway.
Because the volume/treble capacitor is always in the signal path and the tone capacitor is not
they tend to bring more money and be made of things like silver foil, copper foil, papaer in oil
silver mica, molded mica, and teflon or metalized polypropylene and polystyrene (MKP or MKS).
The only known so-called disadvantage to using low cost ceramics is that they can become microphonic.
However, some guitar players see that as an advantage because it picks up the resonance of the wood
of their guitar and they say that the wood type and shape can be heard to influence the sound character.
Of course, there is some debate about the hypfest that results in such fine distinctions in some circles.
The debates tend to center on whether new old stock is worthy of consideration and if there is any
measureable difference in the sound response. On the latter question at least, it has been shown that
any capacitor material will give the same roll-off in the profile. However, the case of a capacitor does
flex slightly, giving credence to the arguement that differences in package design may in fact influence
the dynamic behaviors of a capacitor under conditions of high stress. I would assume that this would be
most likely near the maximum voltage rating of the capacitor, any almost all small capacitors exceep the
voltage that they are likely to see from a single coil pickup, about 5 volts, by a factor of 10 or more.
Actually a .022uf capacitor imposes a seriously downward curving device-like profile at the entire upper
end of the sound spectrum and should be considered to be a target if you want to engineer signal distortion
effects. It certainly makes it difficult to later make the overall sound of a live band into a ruler flat
profile, even if one uses the latest and setup intensive digital signal compensation processors. It defeats
square wave intended distortion signals for stomp boxes with limited equalization capabilities as well.
No study has ever shown that materials a capacitor are made from have effects on sound quality.
Most small capacitor materials available are non-polar. As explained, a polar capacitors
in these small signal small capacitance and high impedance circuits may provide the best tone, that is,
if it were possible to buy a polar capacitor such as a Tantalum or Niobium in the 330pf to .033uf range.
Wet Tantalum capacitors get a bad review on the internet, yet their prices hold up far above others.
In my opinion, comparative tones in various capacitors is caused by variation in ripple current capacity.
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