POTS explanation

[Amateur]

Re: POTS explanation

I should probably update that pic to make it more clear. That second resistor and cap are used to simulate a tone control on "10", so that you can test the volume pot value in a "real" condition. In other words, you wouldn't necessarily want to experiment to find the perfect volume pot value, without having a tone control installed. Then again, you can just use a standard tone control.

Artie,

Here is what I'm thinking:

We usually don't know what the actually load the amp will present unless we go in and measure when it is in operation, and we usually don't crank the amp all the way up to "10", and also when we adjust some of the knobs in the amp, tha load may actually change. A constant load may not be the best way to find the sweet spot for the pickup-amp combination since the amp may also has its own sweet spot, and if I am using more than one pickup at a time, then the whole picture may be changed. I agree it is a simple way to estimate the sweet spot of one pickup. Can we figure out a way to find a simple way to determine the "sweet range" for the guitar-amp combination?

 

[DonLduk]

Re: POTS explanation

oops missed a cero there hehe

 

[octavedoctor]

Re: POTS explanation

Wow, that's a damn science! :burnout:

So, simply for humbuckers it's always 500k volume!
As for tone there is a possible variation from 250k to 1000k! Right?
And what about capacitors? How do they affect the sound?

Let's say I want to add some fatness to the E-B-G strings, what shall I do with tone pot and cap?

If you want to fatten up individual strings forget about the pots and the caps: changes to the circuitry will only have a global effect.

Adjusting pole pieces will have a small effect on the intensity of the response from individual strings but the only way of controlling the response of individual strings is to change the gauge. Fatter strings = less support for high end harmonics + more mass in the pickup field = fatter tone.

Think about the gauge of the string being like chucking a bigger rock in the pond. You get a bigger splash and the ripples travel further...

 

[octavedoctor]

Re: POTS explanation

For example the Fender Noiseless pickups use 1K ohm tone pots rather than the 250K ones

Er, are you sure about that? 1kohm is a really, really tiny resistance. that would not be compatible with the input impedance of most amps. Even EMG low-Z pickups use 25kohm pots...

the noiseless pickups are stacks and a stack can be parallel configured just like a 'bucker so that pots and amp "see" a lower impedance, but even then 100k would be about a practical limit.

 

[Artie]

Re: POTS explanation

Artie,

Here is what I'm thinking:

We usually don't know what the actually load the amp will present unless we go in and measure when it is in operation, and we usually don't crank the amp all the way up to "10", and also when we adjust some of the knobs in the amp, tha load may actually change. A constant load may not be the best way to find the sweet spot for the pickup-amp combination since the amp may also has its own sweet spot, and if I am using more than one pickup at a time, then the whole picture may be changed. I agree it is a simple way to estimate the sweet spot of one pickup. Can we figure out a way to find a simple way to determine the "sweet range" for the guitar-amp combination?

What you're saying is correct, however, at some point, for practical purposes, we have to draw the line somewhere. Most amps that I've seen are around 1 meg input impedance. (This is an area where Kent S. or Jeff Seal could better comment.) And, because of the way the input circuitry is designed, most of the settings won't affect that impedance. So, if you plug into your "main" amp, and adjust the pot, (using that technique), you're pretty good to go.

I should also add - that technique is probably better thought of as an "experiment" just so you can hear the difference that pot values have, rather than a pot selection method.

Artie

 

[LPCustom]

Re: POTS explanation

Er, are you sure about that? 1kohm is a really, really tiny resistance. that would not be compatible with the input impedance of most amps. Even EMG low-Z pickups use 25kohm pots...

the noiseless pickups are stacks and a stack can be parallel configured just like a 'bucker so that pots and amp "see" a lower impedance, but even then 100k would be about a practical limit.

Actually it's 1M ohms, not 1K. That was a typo. And "normal" Fender stuff is 250K ohms. Yer supposed to know what I meant... :smack: :foot:

Fender sends out new pots with their noiseless pickup sets because they do not use the standard pot ratings. They use 1M Ohm pots for the tone and a 500K Ohm pot for the volume. That's what came with mine. And I checked them with a multi-meter to be sure they were correct.

 

[Amateur]

Re: POTS explanation

I have 250k pots with nioseless pickups in my Fender Strat on both volume and tone controls. They sent then to me as a package when I re-fitted my guitar. I bought it right from Fender.

Ooops! Screwed up. Those are 1 Megs. I was looking at my other Strat.

 

[Amateur]

Re: POTS explanation

What you're saying is correct, however, at some point, for practical purposes, we have to draw the line somewhere. Most amps that I've seen are around 1 meg input impedance. (This is an area where Kent S. or Jeff Seal could better comment.) And, because of the way the input circuitry is designed, most of the settings won't affect that impedance. So, if you plug into your "main" amp, and adjust the pot, (using that technique), you're pretty good to go.

I should also add - that technique is probably better thought of as an "experiment" just so you can hear the difference that pot values have, rather than a pot selection method.

Artie

I was hoping we can get a range for the combination because I have 6 different amps and they may have different impedences.

 

[DonLduk]

Re: POTS explanation

Ok i fixed the .047uF capacitor and ran the simulation. It worked as a charm.

Here are the results.

The final circuit, you can see it here.

http://www.geocities.com/luiguibanez/SD/circuit.jpg

as you can see, ive modeled the pots with a pair of resistors, Rt1 and Rt2 for the Tone Pot and Rv1 and Rv2 for volume pot. The idea of this is to have the voltages from their middle points, and the modeling is right as long as Rx1 and Rx2 sum up for the total pot (say 250k, it'll be 250k + 1, but that one ohm is irelevant to me, just to modelate the pot at its extremes values). The AC generator is a rough approx. because im not keeping in mind the L, which I suppose its high and affects the circuit, so this is very rough, just to get the idea.

I ran an AC sweep from 60hz to 6khz.


so here are the sims:

500k pots, full volume, full tone
http://www.geocities.com/luiguibanez/SD/500k_tone_working.jpg

Here we see the result of the guitar we play most of us, you know full volume, tone pot that doesnt affect our highs. we can see the signal stays at 0.1mv lower than original for all frecuencies. there we arent blocking any high frequencies.


500k pots, full volume, reduced tone
http://www.geocities.com/luiguibanez/SD/500k_tone_normal.jpg

Here we can see the tone pot being effective. We see the signal reduces 1/3 of original in only from 60hz to 500 hz. which we can say, the higher frequencies are being "blocked out".



Now lets see whats the difference with using 250k pots for both volume and tone pots.


250k pots, full volume, full tone
http://www.geocities.com/luiguibanez/SD/250k_tone_working.jpg

We can see the filter acts with the same bandwith than with 500k, but the amplitude is reduced 0.2mv. that is, the guitar will have a lower volume...


250k pots, full volume, reduced tone
http://www.geocities.com/luiguibanez/SD/250k_tone_normal.jpg

this is hard to compare with the 500k pot, I dare to say they are equal. no if you use your tone pot cutting the most frequencies, it will be the same with if you use 500k or 250k pots.


Hope this helps people make their conclusions, and understand this thing a bit more.

 

[Artie]

Re: POTS explanation

Thats pretty cool. If I'm interpreting your conclusions properly, you're saying:

1. The difference between volume pots is simply output volume.

2. There is no difference in tone pots.

Again, if I'm reading that right, those conclusions don't jive with "real-world" results. I see two potential problems in your setup:

1. I think it is important to consider L in the output generator.

2. Rv1 and Rv2 should be replaced by a single resistor, with the measurment taken at the top. That is, the voltage measured at the output of Ro. The reason for that is, our concern with 250k or 500k pots is when both are at full volume, or "10". We want to see the affect of pickup "loading".

I'll expand on this more tonight. Gotta go to work.

Artie

 

[DonLduk]

Re: POTS explanation

hi artie. those arent the conclusions i got.
ill write up my own conclusions, but first, lets make a convention. all the test are at full volume, so we dont worry about it because when you lower the volume, our Vout is 0.

for the tone pot, lets call it tone pot "on" for when your tone is the original tone of the pickup, and tone pot "off "for when you move your tone and your pickup starts to lose highs and gain and you can play jazz, ok? hehe.

1) When at full volume and tone pot on, the only difference between 250k and 500k pots is that the volume of Vo reduced in 0.2mV. This, as we analyse this, causes volume drop with a 250k. This reduced amplitude also causes a change in the filter bandwidth, even though we cant see it right away because the graphs have a different scale for each simulation. If we graphs both sims on the same scale, we would see the 500kpot graphs 0.1mv higher than the 250kpot graph, hence, the cut will be at a higher frequency, hence, the 500k pot would be brighter than a 250k pot.

2) when you use full volume, and tone pot at full OFF, there is no difference between a 250k and a 500k.


about the setup, i'll replace the voltage generator with an L and a current generator in that same branch. I need a value for L though, if anyone knows an apprx.

and about the Rv1 and Rv2, if you see the Rv1 at 1ohm can be considered as cable, therefore you can "erase it" leaving only Rv2, and making the measurement Vo at the top, or as the voltage that drops at Rv2. and also Rv2 stays in paralel there, making a load...

let me know

 

[Artie]

Re: POTS explanation

Cool. That was a little more clear, and I agree now with #1 and #2 completely.

It would still be interesting to see the sim with an L component. I'm curious to see if the affect of a 250k vs 500k volume pot is purely high-frequency content. (It probably is. Just curious.)

Artie