Pot questions

[killpop99]

1). When a potentiometer is turned up all the way (guitar on 10), the entire resistance of the pot is sent to ground correct?

2). If the first question is true, why then do 250k pots make pickups sound darker than 500k or 1m pots?

3). When the pot is turned all the way down (guitar on 0) on a 500k pot, it places 500k of resistance on the signal (thereby cutting it off), right?

[Billy Batz]

On 10 the pot is basically no more thn a 500k or 250k or whatever, resistor to ground from the signal. As you turn it down it adds more resistance between the 'input' lug and the 'output' lug/wiper, and less resistance between the output and ground until the 'output' and ground are directly connected. Thats why you get no sound. People mistakenly say its because you have the full 500k in series with the signal but thats not true. You can put a 1M in series and although it will reduce the signal a lot, and make it muddy as all hell, you still get plenty of signal without a the ground reference side.

A resistance to ground has an impedance effect somewhat like a series resistance. Its frequency specific and higher impedances attenuate treble more easily then lows. That effect also comes into play when you roll back the volume. You put more resistance between the 'input' and 'output' lug which attenuates highs moreso then lows and thats why you often put a bright cap in place there so it doesnt get muddy when you lower the volume for a cleaner tone.

The tone pot figures into this as well.

[killpop99]

I was asking because I was considering using a 50k pot as my negative feedback resistor. (I might try to get a triple ganged pot that was discussed in another thread) This is because of the ppimv. I just figured the guitar pots would be a good way to ask these questions, they have been bothering me for awhile. Thanks

So I would take a 50k pot, run a wire from the 8ohm tap (or whatever tap) to one outer lug of the pot, and then just run another wire from the middle lug to the presence pot. And I don't need a ground reference right?

[killpop99]

I guess a better question would be: When I use a pot with NO ground reference, if that pot is on 10 (up all the way), then there is no resistance at all to the signal, and when it is turned to 0 (down all the way), there is 50k of resistance (on a 50k pot)?

[fillmore nyc]

1). When a potentiometer is turned up all the way (guitar on 10), the entire resistance of the pot is sent to ground correct?

2). If the first question is true, why then do 250k pots make pickups sound darker than 500k or 1m pots?

3). When the pot is turned all the way down (guitar on 0) on a 500k pot, it places 500k of resistance on the signal (thereby cutting it off), right?

When a 250k pot is on "10", it sounds a little darker than a 500k, or a 1meg pot cause there is less resistance for some signal to get to ground thru the pot wiper.
(Meaning, on a 250k pot, there is only 250,000 ohms of resistance keeping signal from the pup's from going to ground. On a 1meg pot, there is 1,000,000 ohms of resistance holding back signal from reaching ground).

When a pot is on "0" (off) the signal from the pup's is fully sent to ground thru the "arms" inside the pot along the resistance path.
(The arms are the little gizmo's that slide around the pots resistance path, and the central arm connected to the middle lug of the pot).

When the pot is midway thru the sweep (on "5"), part of the signal is being sent thru the resistance path inside the pot to ground, thereby cutting back the volume.

Any electrical current always trys to seek ground, which is why different pot resistances will sound brighter or darker when the pot is on "10".

The resistance of the pot is always in play when using a pot at anything other than fully off.

[killpop99]

Thanks

[Billy Batz]

I guess a better question would be: When I use a pot with NO ground reference, if that pot is on 10 (up all the way), then there is no resistance at all to the signal, and when it is turned to 0 (down all the way), there is 50k of resistance (on a 50k pot)?

It isnt that static. It depends on how you hook up a pot. You can have a pot so that when its on 10 there is the full resistance or no resistance.

Its called a rheostat. You only use the center wiper lug and one of the side lugs. Whish side lug you use will determine whether you get 0 or full resistance on 10.

A NFB control or 'focus' as some people call it, is useful. I use it in my 12 series type amp. I have a 100k pot with a 10k fixed resistor so the lowest it will go is 10k. You probably want a fixed resistor of some value. At some point the NFB gets too high and sounds bad.

That triple ganged pot isnt a bad idea I just dont think youll find one. If anyone would have one mouser would. But I think youll have to stick with a dual ganged master and a separate NFB control. it may be better to do it that way anyway because even if you could find a triple gang at 250k (you can use a parallel resistance across the NFB pot to get its value to where you want it, just parallel the pot to a fixed NFB resistor of the right value) theres no guarantee the NFB will 'track' down evenly with the MV to give you the right amount at any given spot. A separate NFB control would.

[killpop99]

I guess a better question would be: When I use a pot with NO ground reference, if that pot is on 10 (up all the way), then there is no resistance at all to the signal, and when it is turned to 0 (down all the way), there is 50k of resistance (on a 50k pot)?

It isnt that static. It depends on how you hook up a pot. You can have a pot so that when its on 10 there is the full resistance or no resistance.

Its called a rheostat. You only use the center wiper lug and one of the side lugs. Whish side lug you use will determine whether you get 0 or full resistance on 10.

A NFB control or 'focus' as some people call it, is useful. I use it in my 12 series type amp. I have a 100k pot with a 10k fixed resistor. You probably want a fixed resistor of some value. At some point the NFB gets too high and sounds bad.

That triple ganged pot isnt a bad idea I just dont think youll find one. If anyone would have one mouser would. But I think youll have to stick with a dual ganged master and a separate NFB control. it may be better to do it that way anyway because even if you could find a triple gang at 250k (you can use a parallel resistance across the NFB pot to get its value to where you want it, just parallel the pot to a fixed NFB resistor of the right value) theres no guarantee the NFB will 'track' down evenly with the MV to give you the right amount at any given spot. A separate NFB control would.

So you use a nfb control? How do you like it? I think I might be heading to radioshack soon!

[Billy Batz]

Its useful. I marked off the position for 47k. Most of the time I will leave it there. If I want the amp to be a bit tighter or brighter Ill turn it down a bit and if I want it a bit smokier or gainier Ill turn it up a bit. All depends how Im running the presence and how much drive Im going for but I tend to leave it around that mark and rarely have it up or down full.

[killpop99]

well I went ahead and did it, I used a 50k pot (I got an alpha one from radio shack and had to shave off most of that long ass post), I really like it, I used a numbered barrel knob so I can get a good idea where it is, Its interesting to hear the effect of nfb. The low volume tones (-3) are much better now. I suppose this thread should be moved to the mods section?