Correct Pot Value
From mgarvi–(at)–anix.com Wed Nov 8 15:41:24 CST 1995
In
>A friend of mine just bought Barden pickups for his Strat. The pickups
I’d tend to go with what Barden says. He knows the optimal values
> What does the difference in pot values give you ?
Not a dumb question at all, Tom. Here’s what I know:
All pickups are inductors by nature (as are all big coils of wire).
Not so.
Ironically, if you put too much resistance in SERIES with the guitar’s
The treble loss caused by series resistance is actually a complex
Conversely, players that prefer brighter rhythm sounds may benefit
In any case, you can see that it’s usually best to strike a balance
For single coils, usually 250k is enough. For humbuckers, which
You can try some experiments pretty easily. Put a 500k pot in. Turn
Paralleling your 500k volume pot with the 470k resistor simulates
—————————————————————–
I saved the ugly math for the end. Impedance is like a resistance
X = 2 * pi * L
where X is reactance in ohms and L is inductance in Henrys.
A typical humbucker may be around 7.5 Henrys or so.
5000hz * 3.14159 * 7.5hy = 235500 ohms.
Remember that the objective in choosing the correct pot is not in
5khz may seem like a low limit for treble frequencies, but most
Strat pickups have a lower inductance, and therefore will not
Also be aware that pots can commonly be found in two ‘tapers’:
I hope that helps a bit.
Regards,
From fto–(at)–etcom.com Wed Nov 8 15:41:55 CST 1995
In article <47q3dt$7p--(at)--anix2.panix.com> mgarvi–(at)–anix.com (Mark Garvin) writes:
As usual, a very informative post. Thanks Mark.
>I saved the ugly math for the end. Impedance is like a resistance
>X = 2 * pi * L
You’ve been up too late . . . that should be X = 2 * pi * f * L,
>where X is reactance in ohms and L is inductance in Henrys.
>A typical humbucker may be around 7.5 Henrys or so.
7.5 henrys? That seems really huge. Not that I’ve actually measured
>This means that at 5khz the pickup’s reactance will be around 235k ohms.
>5000hz * 3.14159 * 7.5hy = 235500 ohms.
Another typo, you left out the “2″ on the left side but got the right
>Remember that the objective in choosing the correct pot is not in
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From: mgarvi–(at)–anix.com (Mark Garvin)
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Subject: Re: Pot Question
Date: 8 Nov 1995 06:14:05 -0500
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>are the double-rail type, a humbucker which fits in the same space as a
>conventional Strat pickup. Barden has advised using 250k pots; local
>music stores advise using 500k pots Which will give optimum signal
>strength and tone?
for his own pickups.
>Excuse me if this seems like a dumb question, but I promised I’d post
>this for him, as we can’t seem to get a good answer from anyone we know.
>Thanks in advance for your response.
This means that they have a higher impedance (like resistance) at
higher frequencies. If you ‘load them down’ with a lower resistance,
then sometimes you’ll lose some signal…mostly treble. So considering
this, you might think you should use as high a value pot as possible.
output, you can also diminish treble. This happens as a higher
resistance volume control is being turned down. For example, if you’ve
backed the guitar’s volume control down by 1/10th, you’ll have 25k
in series with the guitar output if you are using a 250k pot. With
a 500k pot, you’ll have 50k in series.
interaction with cable capacitance, etc. and some players use it
to their advantage. Turning the guitar down automatically changes
to a mellower rhythm tone.
>from putting a small value capacitor from the center terminal of
the guitar’s volume over to the right terminal (as viewed from
the bottom of the pot). This will allow more highs thru as the
pot is backed down. You could try a .001 cap for a start. I’m
just guessing at the value. I don’t do this on my own guitars,
so I don’t really have a personal preference.
between high ‘paralleled’ resistance (the volume pot turned up full)
and low ‘series’ resistance (as the pot is being turned down).
have higher inductance, 500k is more appropriate.
the guitar volume up all the way. Get a 470k or 510k resistor from
Radio Shack or wherever –low wattage is fine. Unscrew the sleeve
>from the 1/4″ plug going into your guitar. As you are playing, have
someone hold the resistor across the two connections and see if you
can tell the difference.
changing to a 250k pot.
which varies with frequency. Inductors are lower impedance at
low frequencies, etc. The effective resistance (called ‘reactance’)
at a given freq. is:
This means that at 5khz the pickup’s reactance will be around 235k ohms.
*matching* the reactance, but in staying about twice as high (ancient
Hippy wisdom). So in this case, a 500k pot is appropriate.
guitar speakers start to roll off around there anyway. So guitar
amps in general don’t respond much above say…7khz. If they did,
you probably wouldn’t like it.
require as high value pot.
log and linear. The log pots may be better for guitar, since
the volume increases smoothly as the pot is rotated. But I know
players who like the faster increase provided by a linear taper pot.
Mark Garvin
Composer/Design Engineer
New York City
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From: fto–(at)–etcom.com (Tom May)
Subject: Re: Pot Question
In-Reply-To: mgarvi–(at)–anix.com’s message of 8 Nov 1995 06:14:05 -0500
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>which varies with frequency. Inductors are lower impedance at
>low frequencies, etc. The effective resistance (called ‘reactance’)
>at a given freq. is:
where f is the frequency in Hz. ^^^
the inductance of any pickups (just resistance), but I’m just
wondering where you got that number. I guess pickups do have quite a
few turns.
answer anyway. I wish I could do that. I’m not dissing you, I just
wanted to point that out for anybody who was following along and got
confuzed.
>*matching* the reactance, but in staying about twice as high (ancient
>Hippy wisdom).
–
Tom.
