500k volume pot vs 250k volume pot

[UCSDBoy]

Hi guys,

I've been wondering something. Obviously a potentiometer is a variable resistor and that means a 500k ohm pot can be turned down to give only 250k ohm resistance. When it's wired up as a voltage divider in a guitar circuit however, does the same effect still apply? I've heard that going from 250k pot to 500k pot would change the resonant peak of the attached pickups. However, can I simply turn down the volume knob to replicate what I would have had w/a 250k volume pot? Or is the resonant peak affected in a permanent way? My thinking is if the differences are simply something I can adjust then putting 500k knobs on an HSS Strat might not be so bad after all.

Thanks!

[AlexR]

No, as a volume you are simply turning down the volume once you get away from full. The tone is simply a linear filter so in that case 250k is 250k no matter whether that occurs at 10 or 6 on the dial.
A lesser volume pot value will have the same signal potential at 10 as the 500k.......albeit with the slightly different resonant peak - meaning the larger value pot will be brighter.

The question here about HSS is always a tough one. I mean you could try a 500k tone pot on the bridge slot to help with brightness. The tone circuit is also 'on' all the time. So 10 on a pot doesn't mean the pot is out of the circuit.....unless you go for a no-load tone pot. So maybe thats another way of getting some extra bite out of the bridge humbucker - as you can dial in a fully removed tone circuit as well as having the option of it in.

[GuitarStv]

Alex has it. Turning a 500k tone pot to 250k will sound exactly the same as a 250k tone pot being in the circuit. But volume pots are different. The large value volume pot is always brighter, even when turned down.

With an HSS setup and a 5 way switch, you should be able to wire in a 500k resistor to electrically drop the 500k volume pot down to 250k for the single coils, but leaving it full strength for the humbucker. This way all the pickups see the values they want and sound good.

[freefrog]

If I can help to precise what's going on...

Lowering a volume pot rises the resistance between pickups and output, while it diminishes the resistance from output to ground. It changes the curve. I mean that a 250k putting 125k between pickups and output + 125k between output and ground is not the same than a 500k putting twice 250k in these respective positions.

So, a 500k vol makes a passive pickup brighter when it's full up but potentially darker with half its value in each direction.

This effect can be partly corrected by a "treble bleed" capacitor. One rarely thinks to use a resistor from pickups to center lug (output) instead of the cap but it would change the curve as well, albeit not in the same way than a capacitor.

FWIW, I share below a botched 5spice sim showing the curves of a 250k volume vs a 500k volume from 10/10 to 1/10. The 500k puts the resonant peak over the roof when full up (reason why the pickup is brighter) but no more at "half way"...

I've lab measurements showing the same things somewhere in my archives but not enough time to search right now. Thx for your understanding.

HTH. :-)

[solspirit]

If I can help to precise what's going on...

Lowering a volume pot rises the resistance between pickups and output, while it diminishes the resistance from output to ground. It changes the curve. I mean that a 250k putting 125k between pickups and output + 125k between output and ground is not the same than a 500k putting twice 250k in these respective positions.

So, a 500k vol makes a passive pickup brighter when it's full up but potentially darker with half its value in each direction.

This effect can be partly corrected by a "treble bleed" capacitor. One rarely thinks to use a resistor from pickups to center lug (output) instead of the cap but it would change the curve as well, albeit not in the same way than a capacitor.

FWIW, I share below a botched 5spice sim showing the curves of a 250k volume vs a 500k volume from 10/10 to 1/10. The 500k puts the resonant peak over the roof when full up (reason why the pickup is brighter) but no more at "half way"...

I've lab measurements showing the same things somewhere in my archives but not enough time to search right now. Thx for your understanding.

HTH. :-)

Exactlý thís, 500 k vol & I would even go so far as to use 1 meģ tóne pots.

[solspirit]

Make sure you do the correct treble bleed though

[UCSDBoy]

Thank you everyone for all of your great answers! Based on what was said above, if I did use a 500k volume pot and had brighter single coils than normal - could I correct for that just by turning down the tone knob, or would the tone still be significantly different that what it would be with all 250ks? Thanks!

[jeremy]

there would be a difference between the two methods

[freefrog]

Thank you everyone for all of your great answers! Based on what was said above, if I did use a 500k volume pot and had brighter single coils than normal - could I correct for that just by turning down the tone knob, or would the tone still be significantly different that what it would be with all 250ks? Thanks!

Two 250k pots in parallel create a resistive load of 125k.

To obtain the same resistive load from a 500k volume pot and a 250k tone pot (or a 500k one, it doesn't matter), one needs the tone pot to be set at a tiny wee bit more than 166k.

If the tone pot is a linear 250k, it should measure 166k when set @ 66%... If it's a linear 500k tone control, it should measure 166k when set @ 33%.

Wether is due to 2x250k in parallel OR to a 500k volume control + a tone pot set @ 166k, an overall resistive load of 125k should give the same amplitude to the resonant peak, for a very, very similar tone in both cases.

Now, "similar" doesn't mean "identical" and that's where I agree with Jeremy : the capacitor linking a tone pot to ground doesn't affect the resonant peak but it might interfere with the harmonics, according to the value selected.

Paradoxically, very low value caps (like a 2.2nF instead of the usual 22nF) might have a more noticeable effect in this situation.

This phenomenon is easy to check with alligator clips - and ever more obvious if one pair the tone control to an inductor instead or in supplement of a capacitor...

Also and for the record: the great Bill Lawrence (RIP) used 500k pots + added parallel resistors to customize the overall resistive load if needed. It's simpler than having to lower a tone pot each time the pickups switch is manipulated and it's easy to mount. The only downside is that it won't correct the taper of a 500k volume control.

HTH.

[UCSDBoy]

Ty guys. I think I'm going to go with a 250k master volume, a 250k tone pot for the neck and mid, and a 500k tone pot for the JB. I've always heard that the JB does pretty well with 250k pots so I'm going to give it a try.

[eclecticsynergy]

My experience has been that the JB generally seems to like a 250K volume, especially in Fender scale guitars.

[Chistopher]

I generally use whichever pot of the correct taper I have on hand and if it sounds bad I switch to the other if I think it will help.