the tone cap myth...

[Mike Sulzer]

Mike:



I base my statements on electronic principles;
Steve Ahola

You have given some examples of a capacitor across a pickup with no resistor in series. Why? We are discussing what happens when the tone pot is on 10. The guitar tone control is a pot and capacitor connected in series across the pickup. [This is different from an RC network used as a low pass filter in which the input is connected to the R and the output is taken across the C.] When the pot is on zero the capacitor is directly across the pickup. It lowers the resonant frequency. When the pot is on 10, its large resistance in series with the capacitor prevents the much lower impedance of the C from having an effect.

[SK66]

I think some of the arguing here is based upon a misunderstanding.

Mike Sulzer is talking about a RC tone circuit using a "NO-LOAD" tone pot.
They are not "common", but they are available or you can make your own. When set at "10" there is no electrical connection to the wiper leg. That WILL remove a tone cap from the system if wired correctly.

[Possum]

...

Thats not my understanding of what he's saying. I understood him to say that the value of the tone cap has no effect on the guitar's tone when the pot is all the way open (maximum treble). I don't think anyone was talking about 1 megohm tone pots if thats what you mean. I started this thread saying that it IS true that the value of your tone cap directly effects the tone of your pickups when you're NOT using the tone pot to darken the pickup. My audio recording proves that is true, in changing from a .047 to a .022, easily heard. Why would we even be talking about a no load tone pot, I've never heard of anyone using anything like that, a new one on me :-)

[Mike Sulzer]

Thats not my understanding of what he's saying. I understood him to say that the value of the tone cap has no effect on the guitar's tone when the pot is all the way open (maximum treble). I don't think anyone was talking about 1 megohm tone pots if thats what you mean. I started this thread saying that it IS true that the value of your tone cap directly effects the tone of your pickups when you're NOT using the tone pot to darken the pickup. My audio recording proves that is true, in changing from a .047 to a .022, easily heard. Why would we even be talking about a no load tone pot, I've never heard of anyone using anything like that, a new one on me :-)

Steve, Possum

Possum has understood me correctly. I do mean that a 500K pot (on 10, full resistance) isolates the pickup from the capacitor. In previous posts, I have shown the difference in impedance in this case is too small to measure, and that calculations show that it is extremely small. But Possum, you have lost all credibility. In the last couple of days you have argued against test results by claiming that a Gibson pickup was a shrill foreign copy. You have incorrectly claimed that cathode bias would hide the difference between capacitors. You have stated incorrectly that a BJ uses cathode bias. I have listened to your sound clips. The "before" has an edgy distortion that is easy to hear. I do not believe that it comes from a capacitor with the tone pot in series on 10.

[SK66]

Steve, I am getting tired of writing the same thing over and over again: It is not the capacitor that is causing the effect when you go to a no load tone pot; it is the resistor (pot).

It's right there. I don't know if it was obviously stated earlier on in the discussion.

No, not a 1Meg pot. Fender started the "no-load" pot thing (I think).
When set at 10 there is no electrical connection to the wiper. They are avail in 250, 500, and maybe other values. And you can always make your own. Depending upon how it's wired it can remove just the cap, or the entire RC network. It can also be used to remove the load of the potentiometer in the vol control. You can effectively have a "straight out" signal with everything set to "10" if you use all no load pots.

[Mike Sulzer]

It's right there. I don't know if it was obviously stated earlier on in the discussion.

No, not a 1Meg pot. Fender started the "no-load" pot thing (I think).
When set at 10 there is no electrical connection to the wiper. They are avail in 250, 500, and maybe other values. And you can always make your own. Depending upon how it's wired it can remove just the cap, or the entire RC network. It can also be used to remove the load of the potentiometer in the vol control. You can effectively have a "straight out" signal with everything set to "10" if you use all no load pots.

Steve, what I meant in the quote just above is this: when you have a no load tone pot, and you turn from the highest resistance setting to "off the track", that is no connection, the change in the sound that you hear is from disconnecting the resistance. It has nothing to do with the capacitance because the resistance is much larger than the magnitude of the capacitive impedance at the resonant peak.

[SK66]

Steve, Possum

Possum has understood me correctly. I do mean that a 500K pot (on 10, full resistance) isolates the pickup from the capacitor.

Well then, I disagree.
Since the cap is always wired in series (actually it can be wired in parallel, but not common) it is always "there". Theoretically, it probably "shouldn't" have any effect as the resistance is a much greater factor, but in application it does. Not enough that I get concerned about it, and I'm not going to be getting involved with how my clients wire up their guitars.

**Note to all:
If you are concerned with which type of caps, you should also check into the different ways of installing the tone control wiring. The original way versus current (for LP types). ...look up "50's mod". Also look into the independent wiring mod.
Also how the volume contol(s) are wired as the method should ideally be different for master vs dual volume controls.
These can all make more difference than what "type" of cap you are using.

[Possum]

...

Listen to the audio clips I posted, all this arguing about theory is bullshit, you can plainly hear the differenece in my audio clips, you can plainly see the change in SK's frequency analyzer charts, if you insist these mean nothing when confronted with the real world then I'm sorry there's no credability in that, book formulas and esoterics don't sell pickups. I make my living making pickups and I listen to guitars everyday and all day long, if something works I use it, if it doesn't work I discard it. This WORKS. When I sell this set of pickups I will insist the player use a .022uf set of tone caps if they want the same tones I am getting. This is turning into a pointless argument here, we've already presented real world proof....END OF THREAD

[EtLa]

Disappearing Tone Control

They are not "common", but they are available or you can make your own. When set at "10" there is no electrical connection to the wiper leg. That WILL remove a tone cap from the system if wired correctly.

Yes and it's easy to make, when I need more sparkle from a guitar I modify my tone pots (no load) as shown here.
The site doesn't exist anymore but I found it on webarchive
http://web.archive.org/web/200503040...nity-tone.html

[Mike Sulzer]

Well then, I disagree.
Since the cap is always wired in series (actually it can be wired in parallel, but not common) it is always "there". Theoretically, it probably "shouldn't" have any effect as the resistance is a much greater factor, but in application it does. Not enough that I get concerned about it, and I'm not going to be getting involved with how my clients wire up their guitars.

If something that, as you say, "shouldn't" have an effect, but does nonetheless, then there is something to investigate. Resolving such things often requires careful work. We have heard listening tests with different results described. I think double blind testing would be required.

[Mike Sulzer]

Listen to the audio clips I posted, all this arguing about theory is bullshit, you can plainly hear the differenece in my audio clips, you can plainly see the change in SK's frequency analyzer charts, if you insist these mean nothing when confronted with the real world then I'm sorry there's no credability in that, book formulas and esoterics don't sell pickups. I make my living making pickups and I listen to guitars everyday and all day long, if something works I use it, if it doesn't work I discard it. This WORKS. When I sell this set of pickups I will insist the player use a .022uf set of tone caps if they want the same tones I am getting. This is turning into a pointless argument here, we've already presented real world proof....END OF THREAD

As I said, I did listen to your clips. The difference is plain. That does not mean it is the result of what you say its. Just as you did not believe other results presented above, why should I believe yours? You have not presented the real world proof that you think you have.

[David Schwab]

Steve, I am getting tired of writing the same thing over and over again: It is not the capacitor that is causing the effect when you go to a no load tone pot; it is the resistor (pot). Any resistor connected across the pickup with typical values causes a loss of treble. The capacitor acts as a short circuit in this case at the relevant frequencies so that the resistor is in effect connected across the pot. I have written this several times; you have not responded as if you have understood. Do you see what I mean? If not, can you tell me how I can better make this point?

Mike, how is the cap a short circuit when the pot is on ten, but not a short circuit when the pot is on zero, or even five?

The tone control effectively works like a frequency selective volume control. When you turn it down, you shunt the frequencies above where the cap is acting.

When you have the tone control on ten you have the resistance of the control between the cap and ground. So you are decreasing the effect of the cap by that amount. Larger value pots sound brighter. But it's not exactly the same effect as a volume control, which is loading the pickups, and attenuating all the frequencies, not just the highs. That's not counting the loading effect on the pickup's frequency response of course. Passive tone controls still work with active pickups after all.

So when the tone control is on ten, there still is some highs being bled off, which the a load control eliminates.

Implying that it's only the pot would mean that when on ten the attenuation is at a different frequency than when the control is at zero, since it removes the cap from the equation, and I don't buy that. If you wire up an on-off-on switch, so you have two different cap values (say a .1 and a 0.02) and the center removes the cap, I'm sure you will hear a subtle difference when the control is on ten, and you switch the switch.

The cap isn't just lowering the resonant frequency, it's shunting higher frequencies to ground.

I understand what you are saying, but the point is moot anyway, since you can't have a variable tone control without a pot.

If I understand Possum's original post (and I admit I haven't read every post here) he heard a difference between not only two different types of caps, but two different values. It was the difference in values that caused this, not the cap type. Even with the control on ten, the value of the cap makes a difference. I doubt he would have heard a difference swapping two .02 caps for example, unless the value of one was way off spec.

[David Schwab]

So what exactly are the "relevant frequencies" and who is it that determines that they are relevant? A 0.022uF cap across a pickup (with no resistor) will bleed off many/most of the high frequencies. Change that to a 0.015uF cap (once again with no resistor) and it sounds a bit like a wah pedal kicked to the back position.

Also the higher the impedance of the pickup, the more effect the tone control has. You can hear this if you have your tone turned down and switch a humbucker to parallel. The cutoff frequency rises.

EMG pickups come with .1 tone caps, because they have a lower output impedance. And even then the .1 cap has less of an effect than it would on a high impedance pickup.

As I said in my last post... just wire up a switch to change cap values, and keep the control on 10. You will of course hear a difference between caps. I've done this in the past, and also had two tone controls on a bass, each one with a different cap value.

Two interesting controls are the Fender TBX, which effectively removes the control from the circuit via a 1M resistance, and the "grease bucket" which eliminates the resonant peak (or "bass boost" as they call it) the control produces when you turn it down.

I'm not sure why you would want to do that, but I guess they thought it was a good idea. I think that little boost is the best part of having your tone on zero!

[Mike Sulzer]

Mike, how is the cap a short circuit when the pot is on ten, but not a short circuit when the pot is on zero, or even five?

That is a very good question, and the answer is this: Whether or not an impedance acts like a short depends on the value of the other impedances in the circuit. A coupling capacitor is a good example. Its value is selected so that it does not attenuate any frequencies in the range of interest significantly. So it is like a short circuit to those AC frequencies, but it blocks dc (infinite impedance). Suppose you have an amp stage with 10 times lower input impedance than another one. Then the coupling capacitor must be 10 times bigger (10 times lower impedance as a function of frequency) for it to have the same low frequency cutoff.

So if we have a 500K tone pot on 10, we have 500K in series with a capacitor with 2 or 3 K impedance magnitude at 3KHz. The capacitor "bleeds to ground" by having an impedance that decreases with frequency. But it cannot do that if there is a much larger impedance in series. The change in impedance with frequency of the series combination is negligible in the 3 KHz range. The series combination acts like a resistor.

When you turn the pot towards zero, the series resistance drops, and if you go far enough, the resistance is less than the impedance of the cap over a wide range of frequencies. The C is no longer acting like a short with respect to the R. Then the series combination acts much more like a capacitor than a resistor.

Does this make sense? I am happy to discuss it further if you like.

Mike

[soundmasterg]

That is a very good question, and the answer is this: Whether or not an impedance acts like a short depends on the value of the other impedances in the circuit. A coupling capacitor is a good example. Its value is selected so that it does not attenuate any frequencies in the range of interest significantly. So it is like a short circuit to those AC frequencies, but it blocks dc (infinite impedance). Suppose you have an amp stage with 10 times lower input impedance than another one. Then the coupling capacitor must be 10 times bigger (10 times lower impedance as a function of frequency) for it to have the same low frequency cutoff.

So if we have a 500K tone pot on 10, we have 500K in series with a capacitor with 2 or 3 K impedance magnitude at 3KHz. The capacitor "bleeds to ground" by having an impedance that decreases with frequency. But it cannot do that if there is a much larger impedance in series. The change in impedance with frequency of the series combination is negligible in the 3 KHz range. The series combination acts like a resistor.

When you turn the pot towards zero, the series resistance drops, and if you go far enough, the resistance is less than the impedance of the cap over a wide range of frequencies. The C is no longer acting like a short with respect to the R. Then the series combination acts much more like a capacitor than a resistor.

Does this make sense? I am happy to discuss it further if you like.

Mike

Mike,

I'm not discounting what you are saying here, but it seems like you are ignoring the fact that others can hear a difference between the different cap values when the pot is on 10, despite that the numbers say it shouldn't happen? Don't get caught up in the age old trap that a lot of engineers get caught in where they assume the math and numbers and test equipment explains everything. There are things related to sound that we can't measure and don't completely understand, and this is probably one of them.

I got some flak a couple years ago on another board because I changed a cathode bypass cap on the first stage in a Sunn 200S to a 300uf, and said there was a difference between that and the stock 250uf. By the numbers there should not be, but the effect that cap had on the sound of the amp was that the bottom end was just a little bit smoother and more present, and I liked it so I stuck with it. One person in particular was using all sorts of numbers and equations to prove I was wrong, but I could hear a difference, and so could others. The numbers still said there should not be a difference, but mostly everyone agreed that there was, though some could not hear a difference in their own tests. Since we all hear differently, that isn't surprising to me.

Of course when Possum went from one value cap to another, there will be a difference in the effect and sound of the tone control. I believe that even on 10 there will be a difference, though slight, because I've heard it myself in experiments on my own guitars, most recently with a guitar that has 3 different types of Seymour Duncan humbuckers. I switched from .022uf caps to .047uf caps on each pickup, with a 500k tone pot for each and noticed a difference each time with each pot on 10.

Greg