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Thread: Which pots for P90's?

  1. #1
    Member ILRGuitars's Avatar
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    Which pots for P90's?

    Hi guys, I need some help with my ES330 tribute. I have P90's installed with B500k tone pots and .22 caps. The pots are cheap Chinese ones. The problem is that the tone pots on both pickups don't really change the tone until the pot is almost fully rolled back ( '0' position ). I have tried both modern and vintage wiring styles too.

    Question is: Is it a pot, wiring or cap problem? What are the possible solutions?

    Your infinite knowledge and suggestions are appreciated.

  2. #2
    Overlord of Music Dedman's Avatar
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    try an A type pot instead. Audio taper should give a more gradual control. I use A's for both volume and tone although the kits come with B's for tone.
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    Overlord of Music Simon Barden's Avatar
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    What value capacitors are you using? You normally want 0.022uF for P90s. Also, the cheap kit ones may be way out of tolerance.

  4. #4
    Member ILRGuitars's Avatar
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    I'm using .022's for the caps. Thinking it could be the cheap pots but I will try an 'A' pot too. Thanks guys

  5. #5
    Overlord of Music WeirdBits's Avatar
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    A pots would get my vote too, in most situations.

    Just out of interest, how do you have your tone pots wired? That is, the connections on the actual tone pot itself, not which lug it links to on the volume pot.
    Scott.

  6. #6
    Overlord of Music Simon Barden's Avatar
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    Audio pots will give you a quicker response to turning the tone control than a linear pot. I had this the wrong way round in my head until recently.

    I've just measured the resistance of a CTS 550k Audio pot (from BareKnuckle) and here it is, shown alongside a theoretical linear pot slope.

    Click image for larger version. 

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    With the knob on 10, you get the maximum resistance (which limits the effect of the tone capacitor on the pickup circuit). As you turn down the knob, the resistance of the pot decreases and so more of the high frequencies pass to ground via the tone capacitor. (It doesn't matter if the capacitor or the pot is first, as they are connected in series and the result is the same).

    With the knob on 5, with the linear pot, you've got 50% of the pot resistance between the signal and the capacitor. But with the audio taper pot and the knob on 5, you've only got about 10% of the pot resistance left, so a lot more high and mid frequencies will be sent off to ground at that position. (That percentage will vary depending on the actual log slope used, but it is very unlikely to be more than 20%).

    So an audio pot used for tone will act quickly, then have a lot less affect in the last half of its travel. A linear pot will have a slower effect on the tone when turning down. Again I only realised this recently, and I'm sure I've stated the opposite in some of my post replies, for which I apologise.

  7. #7
    GAStronomist wazkelly's Avatar
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    For those folks who actually properly use a tone pot, and I am not one of them, then linear might make sense.

    I'm with Dedman in using audio's for everything as you can interchange and have spares without getting hung up about not having the right one on hand if something fails.

    This is a link to an interesting forum thread on the topic of 500k vs 250k when used with P90's...
    https://www.seymourduncan.com/forum/...s-250k-or-500k

    Might need a bit of trial and error but starting with 2 x 500k on a semi hollow body could work as they can sometimes sound a bit dull compared to solid body.
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  8. #8
    Overlord of Music Simon Barden's Avatar
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    I read some of that forum. I liked the chap who said that he could hear the difference in cap values with his no-load pot turned all the way up - like when the cap is out of circuit. What planet do these guys come from?

    The fact is that there are a wide variety of sounds available from P90 pickups depending on the magnets used and the level of winding. Alnico II with slightly under-wound coils are going to be very clear and bright and may benefit from using one or two 300k or 250k pots. Others with powerful ceramics and a high number of windings need all the brightness they can get. Others in the middle, with Alnico Vs and a traditional 8k-9k-ish winding, will probably be fine with 500k pots for most people, but on some guitars (depending on teh construction and woods) might sound a bit bright for some. It probably depends if you're rock/blues or jazz orientated with your P90s.

    I finally got round to changing over the pickups in my '93 Hamer USA archtop (it's rather like a DC Gibson). The neck was rather muffled and the bridge was a mid-heavy hammer. They were made by Seymour Duncan for Hamer at a time when DS didn't offer P90s in their range. I started out by changing the neck pickup for an IronGear P90. This sounded great on it's own, but the bridge was now dull and overly powerful in comparison. Also, the two pickups, despite both having core+braid leads, were out of phase in the both-on position.

    I looked at the old neck pickup and saw it had really thick ceramic magnets fitted. I then remembered that I has a used Gibson P100 (hum cancelling version) pickup that I'd bought but never fitted, and had a look at its magnets. Thinner and probably Alnico V. SO I took both pickups apart, and just by trying to push the magnet pairs together, the Alnico V was a lot less powerful than the Ceramic SD set.

    So I though that I'd have a go at replacing the magnets in the SD bridge pickup with the Alnico ones (hoping that this would reduce the output and add more clarity, and swap the polarity around to get the 'both on' sound back in phase.

    This was easy enough to do (backplate held on by two screws), but although I'd corrected the phase issue, the pickup was still brutally powerful and mid-heavy. So I ditched the pickup and put another IronGear one in, and now it sounds great.

    I've only just got round to measuring the SD pickup DCRs, and found out that they are 11.9k neck and 14.8k bridge. Compared to the vintage 9k-ish values, these are severely overwound. No wonder that along with the ceramic magnets, they were very powerful pups! Someone mentioned they were fitting a BareKnuckle 'Pig 90 (Alnico V) to their guitar, and I calculated that the bridge pickup 21.5k DCR resistance in 45AWG wire was equivalent to about half that if 42AWG wire had been used, so equal to around 11.8k. The SDs used 42AWG wire, and very powerful ceramic magnets, and with that bridge pickup at 14.9k would have stomped all over the BK 'Pig for output. Great for all-out distortion, but not much else.

  9. #9
    Member ILRGuitars's Avatar
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    Quote Originally Posted by WeirdBits View Post
    A pots would get my vote too, in most situations.

    Just out of interest, how do you have your tone pots wired? That is, the connections on the actual tone pot itself, not which lug it links to on the volume pot.
    I've tried a number of ways to wire the tone pots; modern and 50's wiring, but the problem is still the same.

  10. #10
    Member ILRGuitars's Avatar
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    Simon, I think you have nailed it. I'm going for the 'A' pots and I will let you guys know how it works.

    It's certainly a subject for discussion, eh?

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