Question for Artie and others about POTS...

[Lewguitar]

I'm thinking of installing a switch to put a 500K resistor in parallel with a 500K pot on a guitar with both humbucker and single coil pickups to make the pot sound like a 250K pot when I'm using the single coils. How does this affect the taper of the pot? Any negatives? Thanks, Lew

 

[Artie]

Re: Question for Artie and others about POTS...

Hey Lew; as far as I can tell, the only thing that will happen, is you might get a slight shift in the taper. For instance, an audio taper pot set halfway, should give you about 90% volume. That may move to around 87% - 88%.

Shouldn't be a problem.

Now - one caveat; I did this one time on my guitar, and got some oddball behavior. I was getting full volume at around 7 - 8 on the volume control, then the volume started to lower again as I went to 10. Since it didn't work, I just removed it, and never really got around to analyzing why.

You may have to just "try" it, and see what happens. Or maybe Kent S. or Robert will pop-in. Sorry not to be able to be more specific.

 

[Lewguitar]

Re: Question for Artie and others about POTS...

Thanks! I'm going to put a neck humbucker in my James Burton Tele and use 500K pots. I'd like the tone pot to a push/pull that would do the 500K resistor trick to both pots. Thanks again! Lew

 

[Kent S.]

Re: Question for Artie and others about POTS...

Hey Lew; as far as I can tell, the only thing that will happen, is you might get a slight shift in the taper. For instance, an audio taper pot set halfway, should give you about 90% volume. That may move to around 87% - 88%.

Well, it sounds like you've had less sleep than I have Artie ... :laugh2
An audio taper pot turned down to 7.5 will be half the voltage at 10 ( -6dB referenced to voltage); turned halfway down to 5 it will be 1/10 the voltage at 10 (-20dB voltage reference);turned halfway down again to 2.5 will be half that voltage (another -6db, for a total of -26dB). The perceived effects of course depend on whether the instrument is played clean or effected by compression of some type (overdrive/distortion).

Shouldn't be a problem.

Now - one caveat; I did this one time on my guitar, and got some oddball behavior. I was getting full volume at around 7 - 8 on the volume control, then the volume started to lower again as I went to 10. Since it didn't work, I just removed it, and never really got around to analyzing why.

The taper shouldn't be affected at all, as all you are doing is loading the signal line. ***Now if you run the resistor as a tapering resistor (between wiper and either the CW lug or the CCW lug that's a different story, as that affects the taper of the pot, and the load on the pup changes according to the actual position of the pot***. That's *part* of what Barlo was doing.
The only thing that will happen in adding the resistor that Lew speaks of it here, is that the amplitutde of the pup(s)' resonant peak will be dampened,
translation ... it will warm the pups up some. I knew this already, but ran a simulation anyway using a DMZ PAF model, the taper stayed the exact same into a 1Meg termination impedance (i.e.the *hi* input on a BF Fender amp).
Now, I still think that there is a much better way to do this, but it does cause a slight character change ... which Lew may not want (I like it, but he may want his pups to stay a bit *truer* to their tone ... just warm up a bit), so in that case this would be a better way to go.

 

[Kent S.]

Re: Question for Artie and others about POTS...

.....Lew, another thing here is, that it depends *how* that resistor is connected if it's connected to the wiper (or to the CW lug WITH the wiper tied to it), or if it's connected to the CW lug but not tied to the wiper {it will be connected to the CCW lug of the tone pot of course). If it's tied to the wiper it will remain a constant path to ground (500k) paralleled with whatever the resistance of the tone pot. If it is not tied to the wiper the resistance will be the CCW:W of the tone pot paralleled with the resistance of the CW:W in series with the resistance of the 500K resistor (or close to it as a 500k may be hard to find). Simply put, here is a comparison resistances between CCW:W {standard tone knob function ... variable resistor} of a *real 250k-A pot* , a Faux- 250k (R tied to W ... *R-sourced*), Faux- 250k
( R not tied to W ... *R-unsourced*) as related to the pots position and the percenatge of total resistance to the full total resistance,(Tr) 250k value.

Position:..250k-A Pot...Faux 250k(sourced)...Faux 250k(unsourced)
10..........250k............250k.......................250k
9............205k............225k.......................242k
8............160k............195k.......................218k
7............115k............158k.......................177k
6.............70k.............109k.......................120k
5.............25k...............46k........................48k
4.............20k...............37k........................38k
3.............15k...............28k........................29k
2.............10k...............19k........................20k
1..............5k.................9.8k.......................9.9k
0..............0...................0...........................0

% of Total Resistance (250k) Per Position ( %:Tr ):
Position:...250k-A Pot....Faux 250k(sourced)...Faux 250k(unsourced)
10..........100%.............100%......................100%
9.............82%...............90%........................97%
8.............64%...............78%........................87%
7.............46%...............63%........................71%
6.............28%...............44%........................48%
5.............10%...............18%........................19%
4..............8%................15%(14.8%).............16%(15.4%)
3..............6%................11%(11.2%).............12%(11.6%)
2..............4%.................8%(7.69%)...............7.8%(7.84%)
1..............2%.................3.9%(3.92%)............4%(3.96%)
0..............0%.................0%..........................0%

....You'll note that some of the numbers had to be ... err... statistically rounded in order for them not to be rounded to the same value, real values shown in parentheses. The spread rounding allows a bit better comparison of the true nature of the effect upon the resistive taper.

 

[Lewguitar]

Re: Question for Artie and others about POTS...

I was thinking of connecting it to the unused terminal of the tone pot...but from your other post I got the impression that it wouldn't change the 500K tone pot to a 250K....but that connecting a 500K resistor to ground to the same terminal on the volume pot, would work to make it 250K!

I don't know if I'll really do this anyway...if the Jerry Donahue Tele Lead pickup sounds a little brighter with 500K pots that might be a good thing.

Lew

 

[Artie]

Re: Question for Artie and others about POTS...

S% of Total Resistance (250k) Per Position ( %:Tr ):
Position:...250k-A Pot....Faux 250k(sourced)...Faux 250k(unsourced)
10..........100%.............100%......................100%
9.............82%...............90%........................97%
8.............64%...............78%........................87%
7.............46%...............63%........................71%
6.............28%...............44%........................48%
5.............10%...............18%........................19%
4..............8%................15%(14.8%).............16%(15.4%)
3..............6%................11%(11.2%).............12%(11.6%)
2..............4%.................8%(7.69%)...............7.8%(7.84%)
1..............2%.................3.9%(3.92%)............4%(3.96%)
0..............0%.................0%..........................0%

....You'll note that some of the numbers had to be ... err... statistically rounded in order for them not to be rounded to the same value, real values shown in parentheses. The spread rounding allows a bit better comparison of the true nature of the effect upon the resistive taper.

You're such a "stats" whore! :laugh2:

 

[Lewguitar]

Re: Question for Artie and others about POTS...

You're such a "stats" whore! :laugh2:

My brother's like that! Kent, do you know Bruce Collins from Mission Amps? You'd like him. http://www.missionamps.com

I'm a real trial and error guy...I just swap resistors and caps until I get the sound I want. Kinda like adjusting tone controls...only with a soldering tool!

My head starts to spin when it comes to math...just have no gift for it. Tho I know it can really save some time.

It's all intuitive, the way I do things.

Lew

 

[Kent S.]

Re: Question for Artie and others about POTS...

I was thinking of connecting it to the unused terminal of the tone pot...but from your other post I got the impression that it wouldn't change the 500K tone pot to a 250K....but that connecting a 500K resistor to ground to the same terminal on the volume pot, would work to make it 250K!

I don't know if I'll really do this anyway...if the Jerry Donahue Tele Lead pickup sounds a little brighter with 500K pots that might be a good thing.

Lew

It won't effect the taper of the volume control, just run it from the signal (CW lug of pot in standard wiring ... ie. pup not wired to wiper) to ground and it will load down the pup, and warm things up.
It will however effect the taper of the tone pot though, and depending how it's hooked.
See the volume pot is still hooked as a voltage divider, and unless you add the resistor between the CW:W or W:CCW lugs it won't effect the taper (or vary the load back and forth with the position of the pot), but it will load the pups ... like a 250k pot would ...
The reason for it effecting the tone pot like it does is that the tone pot is wired as a variable resistor. The short version Lew is this ...
Volume knob with ...
*A*) a resistor added between CW:W ... yes the taper is effected (and
the load in different positions);
*B*) a resistor added between W:CCW ... yes taper is effected (and load
varies);
*C*) a resistor added between CW to CCW (hot to ground) ... taper is not
effected, signal is loaded down (like a 250k in this case).
Tone knob with ...
*A*) a resistor added between CW:W ... yes taper is effected (loading
doesn't become an issue with tone controls);
*B*) a resistor added between W:CCW ... yes taper is effected (that would
be a 250k tone pot at 10, but the taper would change the lower it
went, the highs wouldn't roll of as fast as a true 250k-A pot);
*C*) a resistor added between CW:CCW lug ... yes the taper would change
(again a 250k at 10, the highs would roll off a bit slower still than *C*)

 

[Kent S.]

Re: Question for Artie and others about POTS...

You're such a "stats" whore! :laugh2:

Nah man, more like Data Mogul ... :laugh2:

 

[Kent S.]

Re: Question for Artie and others about POTS...

My brother's like that! Kent, do you know Bruce Collins from Mission Amps? You'd like him. http://www.missionamps.com

No, I sure don't, I consider myself in good company though with both of you though ... I'll have to e-mail 'em when I get some time. :cool3:

I'm a real trial and error guy...I just swap resistors and caps until I get the sound I want. Kinda like adjusting tone controls...only with a soldering tool!


My head starts to spin when it comes to math...just have no gift for it. Tho I know it can really save some time.

It's all intuitive, the way I do things.

Lew

Sometimes you have to do it that way, especially if you are intering new territory of some kind, and aren't sure of the practical range of something.
Building from a known base then often becomes the best method, and then analyzing the results. I do many intuitive things as well, and I most certainly see the value of a pragmatic and tactile approach ... the two go together, and always have as far as I have known ... but enough philosophical bent ... Happy tweaking Lew!

 

[Artie]

Re: Question for Artie and others about POTS...

Its funny . . . the subtle difference a little chunk of carbon in the signal chain can make . . .

Well . . . more carbon, til the "talent" takes hold . . . :smack:

 

[Lewguitar]

Re: Question for Artie and others about POTS...

Big Thanks to Artie and Kent:

THANKS!

Lew