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Capacitor Test


I decided to do some testing to determine if the TYPE of capacitor makes any difference when utilized as a tone capacitor in an electric guitar. To do this I used several capacitors wired to a switch and installed the switch in place of the tone capacitor in my LP junior type With P-90 pickups... caps were all rated at .047uf, ceramic tested at .044, the Polyester at .044, and the Paper In Oil at .045. After installation on the switch the assembly tested at ceramic .04475, Polyester .04551, and Paper in Oil at .04678. I tested many of each type and these were the closest matched, all were within tolerance but the polyester and Paper in oil were the most consistent. (The % of error was about the same for all other values tested (.022, .01, .03.) I was planing on doing the same tests with diferent values)

.047uf Capacitors

this first section is with the guitar tone control set to "10"

Ceramic Disk capacitor

Polyester Film

Paper in Oil

Ceramic (blue) over Polyester film

Paper in oil (blue) over Polyester

paper in oil (blue) over ceramic (I had to redo the paper in oil sample for this image which is why

it's slightly different than the original sample)

Based upon these images I'd say the Paper and OIl and the Polyester are pretty well matched but the ceramic seems to have a loss in the 67HZ area (it NEVER went higher than the image shown)


Tone control set to "0"

Ceramic Disk

Polyester Film

Paper In Oil

Ceramic disk(blue) over PIO

Polyester Film(blue) over Ceramic Disk

Polyester Film(blue) over PIO

Based upon these images I'd say the PIO and polyester film were very close. The ceramic disk retained a little more high end, and the PIO a minimum more lows at about 92hz. By simple images I'd say the ceramic disk would be the "worse" choice. with the other two being interchangeable.

Based upon listening tests I was able to discern VERY VERY MINOR differences. The Polyester seemed slightly smoother in the upper range, and the paper and oil slightly fuller/smoother in the middle/ upper middleleaving at tad more high edge. I tested this by playing thru a fixed sequence of chords while my son flipped the selector between positions at regular intervals. At reduced settings it seemed the ceramic cap sounded a little brittle in this test. The paper in oil seemed to react just a touch different in that when rolling off highs it affected a slightly wider range. However, there is NO WAY I would be able to discern these differences under any other conditions. They were so minor that I often had to compare between two caps several times to be sure I was hearing it. The heavyness of the picking stroke made much more difference than the cap type. From the pickiest standards, I'd say the Paper in oil may be more suited to for a smooth humbucker tone where you want a smooth top end when rolling off the tone, it seems to cut back a wider range all at once smoothly, where the polyester seemed to have sharper deliniation of where it cut frequencies, but does it smoothly. The polyester would be my nit picky choice for singlecoils. All things considered(price, availiability, size, and character) I'd choose decent quality polyester film. While I did not encounter it with this set of caps, ceramic disks and low quality polyester film caps can be somewhat microphonic I suppose that could be a good thing, just as a slightly microphonic pickup can be a good thing, but for reliabiliyt/consistency I'd say avoid them..... I WOULD NOT base my decision on character alone as it is VERY hard to discern. (I have excellent hearing and I get it tested annually).....I can also say the test reaffirmed my dislike for caps this large on the tone control....

I was also going to run them thru an oscilloscope, but I found this article discussing the hysterisis of different capacitor types with scope images. The author seems to know more about this stuff than I do, so I'll not bother... It should be noted that the discussion primarily considers capacitors "IN" the signal chain. Tone caps in a guitar are not "IN" the signal chain in that the audible sound does not pass thru the capacitor in order to be heard.

And one final note, this lab stuff is entirely out of my realm. Part of the reason I didn't do the scope test (besides finding something that seems to be "already done") is I don't know what I was "looking for", I couldn't get my sound card to function as a tone generator and sampler at the same time, and I didn't want to go thru the hassle of taking digital pics of an actual scope (sense it was "already done")