the tone cap myth...

[David King]

Mark Hammer,
I think you are confusing "microphonic" in the pickup-feedback sense with microphonic -exhibiting piezo crystal-like behavior. Ceramic caps fall into the latter category. You hear noises when you tap on them.

[Steve A.]

But I do not think we are agreed on what the tone loading effect (tone pot on 10) is the result of. I claim it is the resistance of the pot that is making the effect with the cap acting as a low impedance path to ground. This effect is then the same as the loading that a volume pot does. But so far, no one with any electronics experience has agreed with this explanation, or said that it is wrong because....

Mike:

With a pot and a cap the result is an RC network, which is a filter- so that some of the high frequencies are bled to ground. With just a pot you have a percentage of all frequencies bled to ground.

You can hear the effect of the RC network if you switch from a 0.015uF tone cap to a 0.022uF tone cap and finally to a 0.047uF, with the tone pot kept at the same setting. It's almost like a wah wah pedal...

A capacitor has other properties besides capacitance and Salvarsan here spelled that out: ESR (equivalent series resistance), et al. It is all of the other properties that give each brand and model of cap their own individual sound and/or characteristics in a circuit.

While the skeptical side of me would be quick to pooh-pooh this thread, the other side of me that is fond of saying "Context is everything" is pleased by what I've been able to learn here.

Heh, heh, heh- you said "pooh-pooh".

Steve Ahola

[SK66]

Once upon a time I was curious about this so I did some testing.
Here are the results
Note: the link towards the end of article is broken.

[Mike Sulzer]

Mike:

With just a pot you have a percentage of all frequencies bled to ground.



A capacitor has other properties besides capacitance and Salvarsan here spelled that out: ESR (equivalent series resistance), et al.

It is well known that a small value for the volume pot decrease the treble, and so turning down the tone pot does also. Your statement about what a pot can do is correct when the circuit is resistive only. A pickup has resistance, inductance, and capacitance. As a result it has a low Q resonant peak that is loaded down by any additional resistance across it, causing a loss of treble since the resonance is at a frequency perceived as "brightness".

ESR, etc.: if the tone pot is on ten, its resistance dominates over any from the capacitor.

[hasserl]

Once upon a time I was curious about this so I did some testing.
Here are the results
Note: the link towards the end of article is broken.

That's what I'm talkin about! Actual empirical evidence, not subjective anecdotes. Thanks for posting that Steve, good job. And it shows what I pretty much expected, there may be some differences, but they are very slight and could be impossible to identify in a blind test. Other things, such as the type and thickness of your pick, or palming the pick and using just your fingers, will have much more of an effect than cap type. And once placed in the context of a band with other instruments the minimal differences would become completely concealed making them meaningless.

[j. pierce]

Mark Hammer,
I think you are confusing "microphonic" in the pickup-feedback sense with microphonic -exhibiting piezo crystal-like behavior. Ceramic caps fall into the latter category. You hear noises when you tap on them.

A cohort of mine had a Russian Big Muff which started making noises over time when hit the switch. I opened it up and nothing appeared out of the ordinary when I tested it.

Until I bumped one of the ceramic caps. (and other than the electrolytics, they were all ceramic) It pinged. They all pinged. I've heard ceramic caps make noise before, but this was ridicules. Had you used them in a guitar, they would have required you to stand absolutely still. It was like an electronic thumb piano. I have a bag of those caps somewhere (replaced them all) thinking someday I might a weird electronic instrument with them...

[Steve A.]

... ESR, etc.: if the tone pot is on ten, its resistance dominates over any from the capacitor.

I would agree with you if the tone pot and the tone cap were wired up in parallel, but with them in series the pot determines the amount of signal passing through the tone cap to ground. The tone pot is wired up as a variable resistor.

And yes there are capacitances inherent within the pickup and the shielded cable but they are several levels of magnitude less than the capacitance of a 0.022uF tone cap.
It would be like comparing apples and apple seeds...

Steve Ahola

[soundmasterg]

I came across this and thought it might be useful for those who wanted more info about capacitors and their differences and applications.

Greg

http://www.analogrules.com/capacitors.html

[Steve A.]

I came across this and thought it might be useful for those who wanted more info about capacitors and their differences and applications.

Greg

http://www.analogrules.com/capacitors.html

Greg:

Great article! I think I might steal it and put it on my site...

Not exactly aimed at guitars and guitar amps- I was not that impressed when I tried some polystyrene caps in the pF range (the leads were very thin and brittle). So I pretty much stick to polyester and polypropylene for the bigger coupling/tone caps, and ceramic and mica for the smaller pF caps. Just using a decent quality 630v polyester cap instead of a stock guitar tone cap is usually a big improvement- and only costs maybe 50 cents or a dollar...

Thanks for posting the link!

Steve Ahola

[Mike Sulzer]

I would agree with you if the tone pot and the tone cap were wired up in parallel, but with them in series the pot determines the amount of signal passing through the tone cap to ground. The tone pot is wired up as a variable resistor.

And yes there are capacitances inherent within the pickup and the shielded cable but they are several levels of magnitude less than the capacitance of a 0.022uF tone cap.
It would be like comparing apples and apple seeds...

Steve Ahola

Maybe I am not getting what you are saying, but if the tone pot is on 10, then any ESR in the cap is very small compared to the resistance of the tone pot, and thus the ESR is not significant.

[Steve A.]

Maybe I am not getting what you are saying, but if the tone pot is on 10, then any ESR in the cap is very small compared to the resistance of the tone pot, and thus the ESR is not significant.

I agree with that statement- I don't think that ESR alone is very critical in tone cap applications. Perhaps my perception of ESR is wrong but I thought that it explained how the Vox AC-30 tone stack with a 50pF treble cap is not, say, 5 times brighter than a Marshall tone stack with a 250pF treble cap. Intuition tells me that a 50pF treble cap would be too harsh and bright for at least my own tastes. In practise it isn't that much brighter and I thought it had to do with the comparative ESR values of the 250pF vs 50pF caps: the 50pF cap passes through a lot less audio signal than a 250pF cap, which allows for a larger portion of the signal to come from the bass and mid caps.

But I did bring up ESR because it is one of the "other" parameters of a cap that help determine how it sounds in an audio circuit. And in power supplies how it filters the voltage. Truth is, I usually forget the names of the rest of the parameters but they are just as important- if not more important than the ESR.

All of that technical stuff is great but what I care about is the sound and response it gives to my guitars. If it works I'm all in favor of it...

Steve Ahola

[Joe Gwinn]

I came across this and thought it might be useful for those who wanted more info about capacitors and their differences and applications.

http://www.analogrules.com/capacitors.html

Well written article, and it appears to be completely correct technically. Too bad he didn't cover paper capacitors.

[salvarsan]

Too bad he didn't cover paper capacitors.

Thanks for arousing my curiosity.

They're interesting and you can find a few early patents on them. The obvious benefits are that they are inexpensive. Most tables list paper dielectric constant around 2.0, wax paper is similar but moisture resistant. These caps would be larger than similar film capacitors (excepting teflon, of course).

A company still provides mil spec paper/foil caps:
http://www.dearbornelectronics.com/pdf/HSecscr.pdf

Their selection guide suggests that the paper-polyester hybrid dielectrics are better.

-drh

[RedHouse]

there are alot of guitar players who thinks caps have NO effect on anything, I was one of them ...

Yeah Baby!, I'm glad you're hearing the light (so-to-speak, pun intended)

Next step ...believe in the wood, then you will be complete.

[SteikBacon]

Damn, now I need to order more caps too hear this for myself...