Capacitor Test: Polyester Film vs. Paper-in-Oil (PIO) in Guitar Tone Circuit


Does capacitor kind (paper-in-oil -- PIO, polyester film, ceramic) matter in guitar tone circuits? If so, how much? A short test, downloadable samples, and my opinion below.

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33 thoughts on “Capacitor Test: Polyester Film vs. Paper-in-Oil (PIO) in Guitar Tone Circuit

  1. On the subject of lower value caps did you know that tone caps are always in circuit and drain off tone from your pickups even when you dial in full treble?

    Even on the best of guitars the effect can be REALLY noticeable and can be made worse by the stock value of the cheap tone caps usually fitted by manufacturers. The higher the cap value the greater the drain, and together with the tone and volume pots presents an appreciable “load” on the top range of your the pickups – the cap literally drags down your tone!

    One solution is a complete rewire with “no load” pots – but the caps still present a problem & tonal range may be limited.

    There are many guitarists who will have nothing else but 0.01uf caps fitted – and its worth a few quid to get a decent quality cap (paper in oil/PETP/Orange drop) as the stock caps often dry out or fail. This may explain why guitarists don’t use their tone controls at all. They complain that their tone control is dull and lifeless. This may be because of the “loading” issue, or the cheap stock caps that guitar manufacturers fit have dried out and are sapping tone even more, or their pickups are a little weak

    Any way round the result is the same – their guitar lacks sparkle. And whenever they use the tone control, the sound they get is unusable and the taper of the tone control (the way it reacts as you turn it down) is useless to them. I’m sure many of you have experienced the last problem; when closing your tone control, all changes occur between 10 and 8, and from 8 all the way to 0 there is no usable tone – it’s just dull.

    Choosing a quality cap e.g Paper in Oil (PIO) cap will give a HUGE improvement, and this cap value (0.01uf) makes the guitar a whole lot brighter and more harmonically rich. Personally I prefer to buy a cap with a test certificate from someone like Monstertone on ebay uk. With the tone setting on full treble, the 0.01uf caps present a lighter “load” on the pickups and help restore the top end losses that can occur.

  2. I did my last test for this matter and my last guitar set-up for the tone was:
    > 2x PIO 10nF,
    > 1x ceramic 10nF
    > a 500k no-load push-pull potentiometer for the purposes of choose between single PIO 10nF or PIO 20nF by parallel it on push down the knob. And the “no-load” is for by passing all capacitor from the guitar if the knob is set full to the right (it is like guitar with no knob other than volume knob).

    The test is also had same conclusion that the PIO gives the better tone (at least for me).

    Why can I say this? Because I tried replace one of the 10nF PIO with one 10nF ceramic, so the comparison is between:
    > Paralleled: 10nF PIO + 10nF PIO.
    > Paralleled: 10nF PIO + 10nF ceramic.

    The result was PIO + PIO better than PIO + ceramic. The sound of PIO + ceramic was like, for me, not a guitar should sound.

    In this setup it is really much more easy to notice that PIO still better guitar tone capacitor than the stock capacitor. Why this is happened? Don’t forget, capacity of the capacitor not the only one parameter in capacitor. There is ESR for example. The ESR of ceramic capacitor is the lowest among the other capacitor. And by paralleling the two types of the capacitor, the total ESR like turned down to lower than already lowest of that ceramic type.

    By the book of electronics, it is always said that lower the ESR the better. But in this matter it is not always that way.

  3. Yeah not a great test but the correct result ?
    Why are PIO caps soooo good?
    Not my words but sums it up well
    “They form a special magical reaction with the oxygen free cables, the special wooden box the amplifier is in, and various other superstitions only audiophools can see. These things aren’t meant for ordinary muggles who have to do electronics by applying physics and maths.”
    Here are some better tests
    Same result though! the construction makes no difference, ony the value does?
    Scotty had it right ” You canny change the laws of physics”

  4. Guys. I have lost count of the number oc times that my oscilloscope shows no difference between a stereo pair of preamps, but my ears hear night and day. 100 times out of 100, my ears are right. Some things have turned out to be BS, no doubt. PIO caps are not of them. BTW, I lecture in psychology research methods and philosophy of science, so spare me the usual. If you can’t hear thd benefit of PIO over stock caps, your stock cap was great, or, more likely, the other components/configuration are masking yhe impact. Or you’re not as discriminating as you publically assert yourself to be. Every year, there’s a ‘study’ showing that there’s no difference between $5 and $50 wine. Why? The testers are inexperienced. P.S. solid core wire in cotton also rules, also in preamps/EQs. Peace.

    1. The only real question in this (or any other) particular situation is: do you hear a difference, and are you satisfied that it is significant? Just like with wine.

  5. Hoax. Typical vintage mojo baloney. There may be subtle differences but in the end its all personal choice. Its like asking which is a better color red or blue?

  6. I have seen lots and lots of comparisons on the web including
    * switching setups so you can switch between caps of same/different values and strumming a chord
    * using a recording from a guitar and passing it through different caps (OMG I couldn’t believe that one)
    * fitting one cap – playing, then fitting another and claiming that they can/cannot hear a difference

    Most techniques are unconsciously flawed. A recording will not behave like a pickup. It will not have the same impedance or response as a pickup and won’t behave as one – conceptually flawed and pointless I’m afraid! Nor can YouTube quality sound recording pick up the sonic difference. A transistor amp will not behave like a tube amp input and you cant just strum a single chord on a PIO cap setup (particularly one that hasn’t been through the burn in process) and pick up the difference on a frequency analyser. And I defy anyone (unless they had a dud cap originally- and that happens quite frequently ) to remember what their guitar sounded like an hour ago. Audio memory is notoriously short. All flawed methods!

    Most people don’t know what to listen for – expecting a difference in the amount of bass/treble and expecting that to be the tone difference. Not so – that’s really to do with cap value and tone pot setting .

    With a decent cap fitted the strings sound and “ring” differently and with PIO or Paper in Wax caps the guitar will sound, feel and behave in a different way. No amount of oscilloscope or frequency analyser watching will evidence that. Unscientific? Not at all! How can a machine designed for a different purpose pick it up the way a guitar feels and resonates. Its just not the right measurement tool to use. I wonder if an Oscilloscope can detect the difference between a classic Gibson Les Paul and a copy? All of these tests claim to be definitive, but sadly have no sound scientific basis (no pun intended).

    There is a tool which will do the job- the human ear! And extensive playing reveals a wealth of difference with a decent cap fitted. I have fitted PIO and Paper in Wax caps to guitars and its like bringing the guitar to life. Sometimes it is because a cheap cap has dried out, or has a different ESR (equivalent Series Resistance- look it up) or is just generally a bit of a dud and behaving more like a resistor- but whatever the reason many cheap caps simply SAP TONE. After all they only cost 0.5pence wholesale!

    But if you want to alter your tone response then high quality components will simply sound better. I like the KY409 Russians or KBG PIOs or MBM Paper in Wax caps – all will be an improvement for a few pounds/dollars and should last a lifetime if you buy ones that are tested. These old caps come from the 70s and 80s and do dry out – so its important to buy ones that have passed a quality control test. I like the fact that MONSTERTONE on test all their PIO and Paper in Wax caps – gives me more confidence that they will work.

    I wouldn’t pay hundreds for some esoteric cap- and if you are happy with your stock cap then hey fine by me stick with it- but spending a few pounds on something which DOES produce a noticeable and audible improvement seems like a wise investment on an instrument which will have cost a lot to buy in the first place.

  7. Regarding testing technique, it’s not rocket science. One simply needs to isolate the variable being studied, accounting for all confounding variables, i.e. not change more than one variable at any one time. Here, I’ve done exactly that – the only variable changed was the cap type. If you need to go to greater lengths to prove something in tone business, usually that something is simply not worth it.

    In the end, youtube recordings, and mp3s and all sorts of less-than-ideal mediums are what people are going to listen to your guitar on – regardless, I have provided high-quality samples of the test.

    No amount of oscilloscope or frequency analyser watching will evidence that.

    Then it is virtually non-existent.

    I wonder if an Oscilloscope can detect the difference between a classic Gibson Les Paul and a copy?

    Can the human ear? Time and time again, people can’t tell a Gibson Les Paul from an Epiphone LP in a blind test. Oh, you need to actually hold the guitar and look at it to tell? Then you’re activating all your biases, and you’ll hear what you want to hear.

    In the end, as long as no serious cash changes hands for a mere capacitor, it’s all up to each guitarists. And even then, if paying too much for a cap makes someone happy, so be it. My test simply shows that under normal conditions, the difference is so minute as to be insignificant for all practical purposes.

  8. I agree that tests should avoid potential bias. But in the end a judgement made by ear can be the only definitive test. And that means that the evaluator must be able of discerning the differences and be willing to admit it. One mans ‘subtle’ difference in tone may be a regarded as huge by another simply because the difference they hear is enough to substantiate that opinion.

    Oscilloscopes can only show voltage levels- they are not a suitable tool for evaluating the tonal and even timbral changes that are introduced. Likewise frequency analysers are far to crude to detect the changes. Its not that they are not there or can’t be heard – but you won’t detect them with the wrong tool.

    So back to the recordings- there are appreciable differences between the recordings which evidences that caps do sound different. Is it worth a few pounds or $ for a quality cap- up to the individual to make the choice. But guitar manufacturers skimp on these components and I for one prefer to spend a bit more than 0.5p for a component which will give me confidence that I will not be compromising my instrument. I have changed out too many dud chucklet caps over the years to trust them. This is a case of you get what you pay for with a quality cap.

  9. I’m actually not a guitar player nor do I have guitar tube amps but I have many many vintage tube hifi amps and being a music lover and audiophile purist I may be speaking from a different perspective.
    At initial listening of the two caps,one may not hear a difference in the brief chords that were played however,I heard a difference in that the k40y pio caps had a better shimmer on the strings and it displayed more midrange body.. I knew what I was listening for but most here are probably playing it thru your PC,Mac,or I pad..I took my Music server and hooked it up to my tube DAC and then into the Mac Mc275 driving a pair of NewForm Research ribbon speakers and right away the differences were much more pronounced..The K40y caps were cleaner with more body and the shimmer was more pronounced…Where paper in oil caps really excel are inside the feedback loop and believe it or not,my Mac Mc275 had all 160P Spragues and 4 bumblebee caps which I changed them out to all K40Y-9s just because they were newer but they sounded pretty close.. I did use a couple film and tin foil caps in the mix and mixing different types of caps is where you can get a really nice sound because the amp extracts the best attributes in each cap.

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