Modify a 500k pot with a resistor so it works like a 250k pot?
Joey Goldstein
Can this be done?
--
Regards:
Joey Goldstein
Guitarist/Jazz Recording Artist/Teacher
Home Page: http://webhome.idirect.com/~joegold
Email: <joegold AT idirect DOT com>
g-mane
> Can this be done?
Yes, use a 220ká resistor. Put it right across the in&out lugs of the
500ká pot.
-G
--
do the usual to reply
Sooty
g-mane wrote:
>
> In article <3A422C7E...@nowhere.net>, joegoldATidirectDOTcom wrote:
>
> > Can this be done?
>
> Yes, use a 220kı resistor. Put it right across the in&out lugs of the
> 500kı pot.
> -G
You need a 500k resistor, if you want 250k total.
(2 500k in parallel give you 250k).
You won't retain the same taper as the 500k pot had, though.
Joey Goldstein
I don't know why you guys think this works but in my experience it does not.
I'm pretty sure from the people I've discussed this with that the answer
to the question in the subject of this thread is no. You would need to
somehow change the resistance value bewteen hot and ground when the pot
is wide open. That means you'd need access to the resistor material
inside the pot. Placing a resistor across the two hot lugs does nothing
about the resitance between hot and ground.
Thanks anyways though.
Giri Iyengar
>
> In article <3A422C7E...@nowhere.net>, joegoldATidirectDOTcom wrote:
>
> > Can this be done?
>
> 500k? pot.
"220k?," "500k?"....
Is this, like, Valley girl talk?
..Giri
Superczar
joegoldATidirectDOTcom wrote:
> Sooty wrote:
> > You need a 500k resistor, if you want 250k total.
> > (2 500k in parallel give you 250k).
> >
> > You won't retain the same taper as the 500k pot had, though.
>
> I don't know why you guys think this works but in my experience it
does not.
>
> I'm pretty sure from the people I've discussed this with that the
answer
> to the question in the subject of this thread is no. You would need to
> somehow change the resistance value bewteen hot and ground when the
pot
> is wide open. That means you'd need access to the resistor material
> inside the pot. Placing a resistor across the two hot lugs does
nothing
> about the resitance between hot and ground.
Unless something bizarre is eluding me, seems to me that Sooty's got it
right. With the pot turned down, you'd have the max of 250k, when dimed
it'd be shorted. This much is pretty fundamental. I also agree that the
taper would probably be skewed somewhat too.
What result did you actually get from your experience?
--
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Scott Hinman
>
> I don't know why you guys think this works but in my experience it does not.
You've misunderstood.
Believe me. Sooty knows his stuff. (He does all the work on my amps 'n stuff
.. but sometimes he doesn't 'splain things so good .. do you, Sooty <g>)
Here, maybe this will help.
500k
|-^^^^^^^-|
| 500k |
hot ---|-^^^|^^^-|---- gnd
|
|
wiper
The lower 500k is the internal resistance of the pot.
You put another 500k across that, giving you a total
of 250k between hot and gnd. The resistance between hot and
wiper now varies as follows, where 1 means the wiper is all
the way to the hot side, and 0 means its all the way to the gnd
side. This assumes starting with a linear taper pot.
Wiper position Resistance between hot and wiper.
1 0
0.9 45.5 k
0.8 83.3 k
0.7 115.4 k
0.6 142.8 k
0.5 166.7 k
0.4 187.5 k
0.3 205.9 k
0.2 222.2 k
0.1 236.8 k
0 250.0 k
Now this may not be the kind of taper you want, but it works.
> Placing a resistor across the two hot lugs does nothing
> about the resitance between hot and ground.
You mean between hot and wiper? No, that doesn't work.
You want the resistor across the outer terminals of the pot.
(Sooty's prolly gonna tell me I messed up the calculation :( ).
Cheers,
Scott H.
Dan Stanley
"Scott Hinman" <ashi...@chem.ucalgary.ca> wrote in message
news:3A427987...@chem.ucalgary.ca...
I put a 220kiloohm resistor across "in" and "out" ( hot and wiper, I guess
you sramt guys call it) on all my Fenderzoids volume controls. Why do I do
this? I dunno, I saw it on some variant of the high freq bleed mod people
are always doing to Strats and stuff. I think it has an effect on the taper,
too...anyway, I like it, I do it, I will continue to do it.
Tell Sooty I said hello.
Dan
Scott Hinman
Scott Hinman wrote:
The resistance between hot and
> wiper now varies as follows, where 1 means the wiper is all
> the way to the hot side, and 0 means its all the way to the gnd
> side. This assumes starting with a linear taper pot.
>
> Wiper position Resistance between hot and wiper.
> 1 0
> 0.9 45.5 k
> 0.8 83.3 k
> 0.7 115.4 k
> 0.6 142.8 k
> 0.5 166.7 k
> 0.4 187.5 k
> 0.3 205.9 k
> 0.2 222.2 k
> 0.1 236.8 k
> 0 250.0 k
>
> Now this may not be the kind of taper you want, but it works.
Ooops. Those numbers assume the wiper is connected to ground.
(i.e. using it as a variable resistor).
If you've got the wiper feeding a high impedance input, the resistance
between hot and wiper doesn't change. But it doesn't matter in that
case,
since the total resistance between hot and ground is still now 250 k,
and that's the load presented to whatever your hot is. It still
functions fine as a voltage divider. Does that make sense?
(And I said sometimes *Sooty* doesn't 'splain things good.
He's gonna charge me double next time he works on my amp :( )
What are you trying to do, anyway? Is it the ouput impedance
provided by your pot you're worried about? Like you're using
the wiper to feed a low impedance input or something?
Cheers,
Scott H.
Joey Goldstein
Ah, between the two outer lugs eh?
First off, this is for modifying a 500k audio taper volume pot (i.e.
leftmost lug shorted to ground) so that my single coil pickups think it
is a 250k pot when the pot is wide open. If it works, the plan is to rig
a switch for A/B-ing between a 500k vol pot and a 250k vol pot.
I thought that having anything wired across the two outer lugs, when the
leftmost lug is going to ground, would just short everything out to
ground. Perhaps not. So we're really talking about a resistor wired to
the rightmost outer lug and ground then. Correct?
The reason I've been confused by some of the posts is that in the normal
wiring of a treble pass circuit the cap + resistor is wired across the
center lug and the rightmost lug, i.e. between the 5 way switch hot out
and the jack's hot lug. This circuit merely prevents highs from going to
ground as the volume pot is turned down. It does not change the
resistance of the pot and is completely bypassed when the pot is cranked.
Thanks I'll look into this a bit more. A 500k resistor you say?
Scott Hinman
Scott Hinman wrote:
> > side. This assumes starting with a linear taper pot.
> >
> > Wiper position Resistance between hot and wiper.
> > 1 0
> > 0.9 45.5 k
> > 0.8 83.3 k
> > 0.7 115.4 k
> > 0.6 142.8 k
> > 0.5 166.7 k
> > 0.4 187.5 k
> > 0.3 205.9 k
> > 0.2 222.2 k
> > 0.1 236.8 k
> > 0 250.0 k
> >
> > Now this may not be the kind of taper you want, but it works.
>
> Ooops. Those numbers assume the wiper is connected to ground.
> (i.e. using it as a variable resistor).
> If you've got the wiper feeding a high impedance input, the resistance
> between hot and wiper doesn't change.
Good grief. Sooty phoned me! I DID screw up. The resistance still
changes, just differently, since now you're not shorting out
part of the internal pot resistance. (Sorry for all the confusion).
Here:
Wiper ohms between wiper and pot
1.0 0
0.9 47500
0.8 90000
0.7 127500
0.6 160000
0.5 187500
0.4 210000
0.3 227500
0.2 240000
0.1 247500
0 250000
Cheers,
Scott (who's giving up) H.
Scott Hinman
Dan Stanley wrote:
>
> I put a 220kiloohm resistor across "in" and "out" ( hot and wiper, I guess
> you sramt guys call it) on all my Fenderzoids volume controls. Why do I do
> this? I dunno, I saw it on some variant of the high freq bleed mod people
> are always doing to Strats and stuff. I think it has an effect on the taper,
Yah, it'll affect taper. Don't know how thats going affect frequencies, though.
Garvin will be along shortly.
> Tell Sooty I said hello.
Will do. We're meeting for a beer tonight, anyway.
Cheers,
Scott H.
Scott Hinman
Joey Goldstein wrote:
>
> I thought that having anything wired across the two outer lugs, when the
> leftmost lug is going to ground, would just short everything out to
> ground. Perhaps not. So we're really talking about a resistor wired to
> the rightmost outer lug and ground then. Correct?
Yes. Across the two outermost lugs.
>
> Thanks I'll look into this a bit more. A 500k resistor you say?
Yes. Can't hurt to try it. But you may like the taper you're left with.
Cheers,
Scott H.
cjt&trefoil
DPST switch on the back, and wire it so that the wipers and hots are
connected pairwise through the switch, with the grounds permanently
connected together. With the switch(es) closed, the combination will be
250K; open, either section will be 500K.
JMHO.
Joey Goldstein
cjt&trefoil wrote:
>
> To closely approximate a 250/500 K pot, get a dual 500K pot with a push/pull
> DPST switch on the back, and wire it so that the wipers and hots are
> connected pairwise through the switch, with the grounds permanently
> connected together. With the switch(es) closed, the combination will be
> 250K; open, either section will be 500K.
Hmm. Interesting. It'd have to be a push/pull rather than a push/push
switch so I'd know what position it was in. Thanks for the idea.
Chris Meissen
wrote:
>g-mane wrote:
[ .... ]
>> Yes, use a 220k? resistor. Put it right across the in&out lugs of the
>> 500k? pot.
>
>"220k?," "500k?"....
>
>Is this, like, Valley girl talk?
>
>..Giri
Close. Electronics Techie talk.
The basic unit of electrical resistance is called an "ohm." A single
ohm of resistance has very little effect on anything. Most often,
resistors are rated as having much more resistance, in the hundreds,
thousands, ten-thousands, hundred-thousands, and millions of ohms. The
technical prefixes used to shorten those terms are based on Greek
numbers. "kilo-" = 1 thousand ohms, "mega-"= 1 million ohms. They
are abbreviated as simply "k" or "m" and properly termed kohm and mohm
but in general usage this is shortened to simply the "k" or "m". They
should also be capitalized if one is going to be strictly correct but
this is also usually skipped. Thus, a 220k resistor is one that has
two hundred and twenty thousand ohms of resistance.
In our next lesson, we'll cover "volts." P-)
Andrew P. Mullhaupt
"Chris Meissen" <Im_...@inameSPAMTRAP.com> wrote in message
news:921c28$h1k$0...@63.162.246.191...
> On Thu, 21 Dec 2000 14:43:40 -0500, Giri Iyengar <giye...@ford.com>
> wrote:
>
> >g-mane wrote:
> [ .... ]
> >> Yes, use a 220k? resistor. Put it right across the in&out lugs of the
> >> 500k? pot.
> >
> >"220k?," "500k?"....
> >
> >Is this, like, Valley girl talk?
> >
> >..Giri
>
> Close. Electronics Techie talk.
Giri is pulling the collective leg. He's an engineer.
Later,
Andrew Mullhaupt
Joey Goldstein
Joey Goldstein wrote:
>
> Can this be done?
I dunno what I'm doing wrong but I've tried all of your suggestions and
here's what I found:
(with 500k audio taper pot : "leftmost" lug soldered to ground, center
lug soldered to hot on jack, "righmost" lug soldered to 5 way selector
switch) (I have a switch rigged to insert resistor or defeat resistor
for A/B comparisons)
1. 220k resistor across the center lug and the "rightmost" lug.
Result: no audible difference when pot is wide open but taper of pot as
volume is reduced becomes unusable. Same results with other resistor
values too (470k, 300k).
2. 470k (I don't have a 500k handy) resistor across "rightmost" lug and ground.
Result: Output reduced by about 80%. Muddy sound. Same result with 300k
resistor. (Same result with these resistor values across center lug and ground.)
3. 220k resistor across "rightmost" lug and ground.
Result: Too subtle to tell if anything worthwhile is happening. (Same
result with this resistor value across center lug and ground.) Would a
250k resistor work better and give the result I want?
Am I not following your suggestions correctly?
Do you all not understand what it is that I am tring to do?
Let me explain again.
A 250k pot has the effect of reducing the extreme high frequency content
of the signal coming from a single coil pickup. Using a 500k pot allows
these frequecies to pass resulting in a sound that has too much treble
aethetically speaking. Using a 250k pot on a humbucking pickup makes it
a little bit too muddy sounding. Since some of my guitars mix single
coil and humbucking pickups I would like to be able switch back and
forth between a single volume pot that behaves like a 500k pot or like a
250k pot at the flip of a switch.
I appreciate eveyone's input but am I doing something wrong or are these
suggestions just not right? Is there something I'm not getting?
Joey Goldstein
neurotic because I just rigged up one of my guitars with an A/B switch
going back and forth bewteen a 250k pot and a 500k pot and I can hardly
hear any difference anyways. There IS a difference there but it is real
subtle. Just a feeling.
I've been using 500k pots on these guitars mostly up until now and I
always thought the single coil sounds were suffering. A little too
brite, too brittle. Then I played a show this week with a 250k vol pot
and really liked my single coils sounds for the first time but i felt
like my humbucking sounds were squashed. Maybe it's all in my head.
Maybe #3 below is really the same effect as having the two different
values of pot? I give up.
Mark Garvin
>Y'know I may just be out of my mind or at least just a real serious
>neurotic because I just rigged up one of my guitars with an A/B switch
>going back and forth bewteen a 250k pot and a 500k pot and I can hardly
>hear any difference anyways. There IS a difference there but it is real
>subtle. Just a feeling.
The A/B switch is the only practical way to check that.
>I've been using 500k pots on these guitars mostly up until now and I
>always thought the single coil sounds were suffering. A little too
>brite, too brittle. Then I played a show this week with a 250k vol pot
>and really liked my single coils sounds for the first time but i felt
>like my humbucking sounds were squashed. Maybe it's all in my head.
Some bucker guitars use 300k. Close enough to 250k. Still, I'd
personally use 500k on a guitar that mixes both buckers and singles.
IMO, there has been too much made of the 'correct' value for controls.
It all depends on what you want to hear.
A couple comments on your previous posts:
>1. 220k resistor across the center lug and the "rightmost" lug.
>Result: no audible difference when pot is wide open but taper of pot as
>volume is reduced becomes unusable. Same results with other resistor
>values too (470k, 300k).
Following relates to this config only:
There are different types of audio tapers. Some have about 1/3
resistance at 1/2 rotation. Others have 1/10 resistance at 1/2.
My guess is that yours is the 1/3 variety. If you swapped in a
1/10 version, then it would tolerate bridging these two terminals
with a resistor. It would also cause the volume to come up more
slowly than a '1/3 type' pot when that resistor was not in circuit.
Depends if you can deal with that slower volume rise at the lower
part of the rotation.
Next two addressed together:
>2. 470k (I don't have a 500k handy) resistor across "rightmost" lug and ground.
>Result: Output reduced by about 80%. Muddy sound. Same result with 300k
>resistor. (Same result with these resistor values across center lug and ground.)
>3. 220k resistor across "rightmost" lug and ground.
>Result: Too subtle to tell if anything worthwhile is happening. (Same
>result with this resistor value across center lug and ground.) Would a
>250k resistor work better and give the result I want?
Something seems wrong here. If you're bridging a hot terminal
to ground, a 220k resistor will load down (remove) highs more
than a 470k.
Check the resistor values:
220k = Red Red Yel
470k = Yel Vio Yel
Maybe you got a 47k (Yel Vio Orange) by mistake?
>Am I not following your suggestions correctly?
>Do you all not understand what it is that I am tring to do?
Many in this thread do. Sooty is a freeeekin' geetar genious,
you know.
>Let me explain again.
>A 250k pot has the effect of reducing the extreme high frequency content
>of the signal coming from a single coil pickup. Using a 500k pot allows
>these frequecies to pass resulting in a sound that has too much treble
>aethetically speaking. Using a 250k pot on a humbucking pickup makes it
>a little bit too muddy sounding. Since some of my guitars mix single
>coil and humbucking pickups I would like to be able switch back and
>forth between a single volume pot that behaves like a 500k pot or like a
>250k pot at the flip of a switch.
Here's a possibility:
Use your existing 500k pot.
Hook a 470k across the hot and ground terminals of each strat pickup,
right AT the pickup (well, you know, where it gets to the switch).
When you switch in the strat pickups, the 470k will automatically
be paralleled with the volume control.
When you switch in the bucker, the 470k's will not be in circuit.
The one side effect is that when both strat pickups are on, there will
be three 500k's in parallel, which is lower than the normal 250k.
This can be corrected with a circuit variation that makes use of your
5-way switch, but you'd have to rewire the tone controls/5-way.
Try the circuit first and see if it works.
MGarvin
Joey Goldstein
The sound I got was more of a reduction in volume, about 80%. There were
less highs too but that is not what I noticed so much.
> Check the resistor values:
> 220k = Red Red Yel
> 470k = Yel Vio Yel
>
> Maybe you got a 47k (Yel Vio Orange) by mistake?
Hmm. That's possible. I buy these things a little funky electronics
surplus store. IO've never been able to read the colored bands. Whatever
is labeled in their bins is what I buy.
The colors on my 470k resistor are more like:
Orange Purple Brown Gold.
The 220k is:
Pink+Brown Pink+Brown Black Orange DarkOrange
Thanks Mark but I've tried that already and the results were the same as
#3.
I'm just going to play this guitar with the A/B switching between the 2
actual pots for a while and see if all this tinkering is worth it
anyways. I might just stick with the pot switching in the end or go back
to simply using one of the 2 values on a master pot.
> MGarvin
So the general consensus is that a 470k or a 500k resistor across the
"rightmost" lug and the "leftmost" lug (which is ground) should give me
what I want? Correct?
Mark Garvin
>Mark Garvin wrote:
>> Check the resistor values:
>> 220k = Red Red Yel
>> 470k = Yel Vio Yel
>>
>> Maybe you got a 47k (Yel Vio Orange) by mistake?
>Hmm. That's possible. I buy these things a little funky electronics
>surplus store. IO've never been able to read the colored bands. Whatever
>is labeled in their bins is what I buy.
>The colors on my 470k resistor are more like:
>Orange Purple Brown Gold.
>The 220k is:
>Pink+Brown Pink+Brown Black Orange DarkOrange
Tough to tell what those actually are without seeing them
(pink+brown isn't standard color <g>).
You could borrow an ohmmeter.
>> Here's a possibility:
>>
>> Use your existing 500k pot.
>> Hook a 470k across the hot and ground terminals of each strat pickup,
>> right AT the pickup (well, you know, where it gets to the switch).
>>
>> When you switch in the strat pickups, the 470k will automatically
>> be paralleled with the volume control.
>>
>> When you switch in the bucker, the 470k's will not be in circuit.
>Thanks Mark but I've tried that already and the results were the same as
>#3.
#3 (as I understood your description) will load down the strat AND
the bucker with 250k.
The circuit above places a 250k resistance across the strat pickups.
500k across the bucker. I thought that was the objective.
>So the general consensus is that a 470k or a 500k resistor across the
>"rightmost" lug and the "leftmost" lug (which is ground) should give me
>what I want? Correct?
That was #3, right? If so, see above.
MGarvin
Joey Goldstein
Should be. Unless these are not really 470k resistors.
> >So the general consensus is that a 470k or a 500k resistor across the
> >"rightmost" lug and the "leftmost" lug (which is ground) should give me
> >what I want? Correct?
>
> That was #3, right? If so, see above.
>
> MGarvin
--
Mark Garvin
>> Mark Garvin wrote:
>> >Joey Goldstein <nos...@nowhere.net> writes:
>> >> Mark Garvin wrote:
>> >> Check the resistor values:
>> >> 220k = Red Red Yel
>> >> 470k = Yel Vio Yel
>> >>
>> >> Maybe you got a 47k (Yel Vio Orange) by mistake?
>>
>> >The colors on my 470k resistor are more like:
>> >Orange Purple Brown Gold.
>> >The 220k is:
>> >Pink+Brown Pink+Brown Black Orange DarkOrange
>>
>> Tough to tell what those actually are without seeing them
>> (pink+brown isn't standard color <g>).
>> You could borrow an ohmmeter.
>> The circuit above [snipped] places a 250k resistance across
>> the strat pickups. 500k across the bucker. I thought that
>> was the objective.
>Should be. Unless these are not really 470k resistors.
From your description (serious volume loss), there's a good
chance they aren't.
The most critical band is the 3rd one. That's the number of
zeros at the end of the resistance. Yellow is four (zeros),
so yel-vio-yel = 470000 = 470k. If the 3rd band is really
orange (47000) or brown (470), that would account for what
you described.
I think pH was correct. Get thyself to Radio Shack. Resistors
are cheap. Sometimes nice to have an ohmmeter in the gig bag
as well for testing cables, etc.
Keep in mind that if you just bridge the 500k volume control
with a 470k, the bucker will also be loaded w 250k.
MGarvin
PS: A long 250k pot thread and no "Bright as shit!" in-jokes
from the rmmg regulars? What's wrong with you guys?
Joey Goldstein
Mark Garvin wrote:
>
> >
> The most critical band is the 3rd one. That's the number of
> zeros at the end of the resistance. Yellow is four (zeros),
> so yel-vio-yel = 470000 = 470k. If the 3rd band is really
> orange (47000) or brown (470), that would account for what
> you described.
I found this web page that clears things up a bit:
http://members.tripod.com/~schematics/resistor.htm
Yes, I'll probably buy some of my parts at Radio Shack from now on.
Not A Speck Of Cereal
[...]
[] PS: A long 250k pot thread and no "Bright as shit!" in-jokes
[] from the rmmg regulars? What's wrong with you guys?
Our people are on holiday, so we're taking it easy.
----
There is perhaps no phenomenon which contains so much
destructive feeling as moral indignation, which permits
envy or hate to be acted out under the guise of virtue.
-- Erich Fromm
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[These opinions are personal views only and only my personal views]