the tone cap myth...

[Shep]

I've attached a graph of capacitor / Dissipation / Frequency / Type / for comment. It's not ideal as the frequency starts far too high for guitar but it's food for thought.

[JGundry]

thanks, anyone else feel free to chime in if you find anything wrong with it- I am testing with the tone pot all the way up on 10 and all the way down- maybe i need to try different pickups with different frequency response and output and try different values for the pots- I can think of several things to try- I am not doing double blind at this point- I am just trying to hear some repeatable or noticeable difference and rule out the player as much as possible. If I can get any kind of difference at all I will go over to doing some double blind tests but right now I aint gettin nuttun.
It may be a while before I can go back to it- just trying to come up with an honest answer when people ask me about caps.

The problem with the test is that these are all metalized polyester caps with the possible exception of the Sprague but it looks like that one is a polyester cap also. They are all the same type of caps just in different brands. In this scenario the differences are going to be extremely subtle. You need a test rig with with a ceramic cap a PIO cap and a Polyester cap, a Polypropylene cap and a Polystyrene cap.

I have noticed with effect pedals that a signal sweep is not an adequate test of the differences in caps. The percussive nature of a guitar signal is way difference from a signal sweep.

[David Schwab]

I have noticed with effect pedals that a signal sweep is not an adequate test of the differences in caps. The percussive nature of a guitar signal is way difference from a signal sweep.

Transients! Does slew rate apply to caps?

This reminds me of the time I bought a new GK-800RB bass amp. It's a bi-amped rig, and the high frequency amp sounded somewhat dirty to me. Because it was new I brought it back to the store, and they brought it to their repair shop, which is a very reputable place. They said they didn't see a problem. So I spoke to the owner of the shop and he was sweeping a signal through the amp and looking at the output on a 'scope. I told him to plug a bass into it and try it, and right away he said "oh yeah! Now I hear it!"

So in the end there was a bad part in the amp, but it didn't show up until you hit it with something other than a static signal.

[Mike Sulzer]

Transients! Does slew rate apply to caps?

Caps are what limit the slew rate in amps. Slew rate happens because the compensation cap in the first stage of (for example) an op amp sets the highest frequency at which this stage can drive the second stage to full output. This happens because when a capacitor is driven by a constant sinusoidal current, the voltage across it decreases with frequency. You need the cap to make the amp stable. With better design and fabrication, this frequency has gone up for the newer amps.

[Joe Gwinn]

Caps are what limit the slew rate in amps. Slew rate happens because the compensation cap in the first stage of (for example) an op amp sets the highest frequency at which this stage can drive the second stage to full output. This happens because when a capacitor is driven by a constant sinusoidal current, the voltage across it decreases with frequency. You need the cap to make the amp stable. With better design and fabrication, this frequency has gone up for the newer amps.

Another way to say it is that the slew rate is limited by the combination of capacitor value and the current-sourcing capability of the amplifier stage that's trying to change the voltage across that capacitor. If the signal has features where the required voltage change per second exceeds that available from the capacitor-cum-drive-stage, slew-rate limiting will occur, because the available current just isn't enough.

The larger the capacitor and/or the smaller the max current, the lower the allowed slew rate.

[jason lollar]

"The problem with the test is that these are all metalized polyester caps with the possible exception of the Sprague but it looks like that one is a polyester cap also."
Well you have to look at why is the test being done- part of the test is to prove or disprove wether you can hear a difference in brands of capacitors in
a typical guitar circuit so that is a valid thing to test. all caps were matched
and checked for leakage. all caps were in the poly family but they all have noticeably different tone in certain amplifier circuits due to several reasons I dont know a whole lot about this but i have observed it.
the initial testing was done on a super reverb with the treble on around 8 or 9.
Why test for this? Because every other customer asks what brand sounds best and you see so much of this topic talked about on the net and in magazines- guys charging big $ for "musical caps"

so i dont see using the same type of cap as a problem with the test
its actually the whole point of the test

I also selected the types of caps to what I had availible in different manufacturers and that i could match within a percent and didnt leak.
If you look at the Xicon used- its different than an orange drop in ways. you would definately hear a difference between these caps used in many locations in a tube amp.

Also i am looking for a difference most people will be able to hear , just being able to hear a difference at this point would be great- hearing a difference that sounds better or worse to the average person would be the ultimate result.
Also I am using a variety of guitar cords- high quality and no effects in between of course- just an amp and a cord set at your average cleanish tone.
Later on I will try some ceramics and some silver mica.

[JGundry]

I have done this same listening test with amps and effects. I think the tonal differences within the same type of capacitor stack up in an amplifier circuit but with just one cap on a guitar the differences within the same type of caps is real subtle if you are talking caps of the same type. One thing to factor in is voltage rating for the cap. The voltage rating seems to effect the tone and the leakage tolerance changes with the voltage rating as well. For polyester film in a guitar 400V Mallory M-150's sound as good as any other polyester film cap to me. The major tonal differences seem to be between PIO, ceramic and polyester.

I think in a guitar the tonal differences between caps show up a bit more with a distorted guitar tone. The differences are hard to quantify. One cap may sound and feel sort of rubbery whereas a ceramic cap may have a harsher spikey feel when you pick a note.

[Shep]

Another thought ... has anyone measured their caps at the low voltage that they are operating at in situ ? I wonder if the paper/oil caps have an electro potential due to their more chemical nature that means they are less effective.

[Ghandi]

I also have the singlecoil.com caps and ordered some of this for 0,52€ as well:

MP3-Y2 22N :: WIMA, Funk-Entstörkondensator, Klasse Y2

http://www.reichelt.de/?;ACTION=3;LA...a16150c538ae94

they are identical inside/out and tone wise!!!

the caps i ordered from singlecoil.com where painted with some cheap black paint that I could easily pell off, under the cap it said MP3-Y2 22N!

the bumblee bee caps were made as pio up untill the end of 1959 and then changed to... guess what? look at the wima caps!
after 1960 sprague switched the cosmetics from bumble bee's colour code to the p160 black beauty's.

so this is also a difference to the 59' les paul using pio's and the 60' using paper/metal caps and sounding a bit brighter not only because of the thinner neck!

I also got some old russian K42Y-2 pio caps that sound exacly like the old pio bumble caps!


If somebody of you is interested in some of the caps, write me a line...

peace, love and bananas
ghandi

[Joe Gwinn]

One thing to factor in is voltage rating for the cap. The voltage rating seems to affect the tone and the leakage tolerance changes with the voltage rating as well. For polyester film in a guitar 400V Mallory M-150's sound as good as any other polyester film cap to me. The major tonal differences seem to be between PIO, ceramic and polyester.

This is not impossible.

Voltage does matter, although with film caps the effect is slight. Specifically, the capacitance of all capacitor types varies with voltage, but very slightly for polyester et al. What matters most is dielectric type; construction is of secondary importance (unless voltages are large enough to cause palpable electrostatic forces and motion of plates). From memory, I would expect ceramic to be the worst, with oiled or waxed paper in the middle, and polymer film to be the best (lowest variation of capacitance with voltage).

However, to see such effects in film capacitors requires voltages close to the max allowed, and a one volt signal on a 50 volt capacitor isn't going to exercise it too heavily.

Afterthought: Another thing that varies with dielectric thickness (and thus voltage rating) is soakage, which is an issue at low (woofer) frequencies.

But it's worth an A-B test, given the ease of making such a test.

[Ghandi]

I also have the singlecoil.com caps and ordered some of this for 0,52€ as well:

MP3-Y2 22N :: WIMA, Funk-Entstörkondensator, Klasse Y2

http://www.reichelt.de/?;ACTION=3;LA...a16150c538ae94

they are identical inside/out and tone wise!!!

the caps i ordered from singlecoil.com where painted with some cheap black paint that I could easily pell off, under the cap it said MP3-Y2 22N!

the bumblee bee caps were made as pio up untill the end of 1959 and then changed to... guess what? mylar!
after 1960 sprague switched the cosmetics from bumble bee's colour code to the p160 black beauty's.

so this is also a difference to the 59' les paul using pio's and the 60' using mylar caps and sounding a bit brighter not only because of the thinner neck!

I also got some old russian K42Y-2 pio caps that sound exacly like the old pio bumble caps!


If somebody of you is interested in some of the caps, write me a line...

peace, love and bananas
ghandi

[Diablo]

I also have the singlecoil.com caps and ordered some of this for 0,52€ as well:

MP3-Y2 22N :: WIMA, Funk-Entstörkondensator, Klasse Y2

http://www.reichelt.de/?;ACTION=3;LA...a16150c538ae94

they are identical inside/out and tone wise!!!

the caps i ordered from singlecoil.com where painted with some cheap black paint that I could easily pell off, under the cap it said MP3-Y2 22N!

the bumblee bee caps were made as pio up untill the end of 1959 and then changed to... guess what? look at the wima caps!
after 1960 sprague switched the cosmetics from bumble bee's colour code to the p160 black beauty's.

so this is also a difference to the 59' les paul using pio's and the 60' using paper/metal caps and sounding a bit brighter not only because of the thinner neck!

I also got some old russian K42Y-2 pio caps that sound exacly like the old pio bumble caps!


If somebody of you is interested in some of the caps, write me a line...

peace, love and bananas
ghandi

Those Sprague black beauties in your photo are mylar film and aluminum foil. I know for sure because I sacrificed one to science and cut it open. I'm using the same caps in my tweed bassman 5F6A.

[Ghandi]

yeah,
I also have some old '59 pio bumblebee caps that sounded exactly like the green russian pio's...

here two pics of the different bee's for comparison:

[EtLa]

For what it's worth, no measurement prior to the test.
YouTube - Guitar Tone Capacitors, part 1: Evaluating Material Types

[freefrog]

FWIW:

Having seen so many "vintage PIO caps" sold on the Net, I've decided to question the myth by myself ("myself" being a self-taught hobbyist, FYI).

I've unsoldered three caps in an old French radio (from 1959). These caps are like the last one pictured on this page: Condensateurs anciens

Their capacitance has increased with time: I've measured 29 to 31n instead of the 20n mentioned in orange on their glass tubes...

With these values in mind, I expected these old things to sound darker than the tone caps currently mounted in my LP (a couple of 22n "low ESR" ceramic tiny squares). Once the old PIO's soldered instead, here is what I've discovered:

-the behaviour of my tones pots had changed. At 6/10, for example, the resonant peak is not tamed in the same way than before. It sounds "rounder" and smoother but with an extended frequency response, more even and "natural";

-at 0/10, the sound is much clearer than previously, with much less volume drop;

-any position of my tone pots is now useable and creates a subtle variation that I wasn't noticing at all with the previous caps. There's also a "vocal" creamy quality that I had never heard before;

-at 10/10, the sound is actually brighter and more open than before.

Please, note that...

-I've changed only the tone caps, and nothing else : no other mod in my settings nor in my guitar, amp and testing gear;

-I've double checked my feelings with a frequency analyzer: the "new old cap" appear to modify the Q of my pickups (!)...Their frequency response diminishes more progressively beyond the resonant frequency whatever is the position of the pot, in such a way that I notice a relative "bonus" of 3db at 20khz.

Could someone explain me this strange experience? Why do PIO caps behave so differently when used as tone caps? Thx!