is there a difference between 250k pot and "rolled off" 500k pot?

[twotimingpete]

explain

[wagdog]

Yes.

 

Consider this:

 

1 2 3

0 0 0

 

Where 1,2 and 3 are the lugs on the pot. 1 is the incoming ac signal from a pickup and 3 is ground, 2 goes out to the amp. Across that pot (1->3) you are seeing either 250k of resistance to ground or 500k - ALWAYS.

 

With the pot on 10, between 1 and 2 is 0k resistance and from 2->3 is 500k (or 250k). As you roll the pot down, the ratio changes, BUT, you always see the full resistance between 1 and 3 regardless - less resistance (i.e. 250k) means more highs are bled to ground - hence a 250k pot passes more highs to ground and lets the lows pass.

 

That's my understanding anyway... I could be wrong.

[GilmourD]

 

Yes. Consider this: 1 2 3 0 0 0 Where 1,2 and 3 are the lugs on the pot. 1 is the incoming ac signal from a pickup and 3 is ground, 2 goes out to the amp. Across that pot (1->3) you are seeing either 250k of resistance to ground or 500k - ALWAYS. With the pot on 10, between 1 and 2 is 0k resistance and from 2->3 is 500k (or 250k). As you roll the pot down, the ratio changes, BUT, you always see the full resistance between 1 and 3 regardless - less resistance (i.e. 250k) means more highs are bled to ground - hence a 250k pot passes more highs to ground and lets the lows pass. That's my understanding anyway... I could be wrong.

 

 

Yeah, pretty much.

 

It is different because a volume pot functions as a voltage divider. Wagdog explains it pretty well as far as what the pot is presenting to the circuit. I'd go into more detail about WHY it's different, but... I'm beat and I'm starting a new job in the morning, so off to bed I go. LOL

[ericwylde]

results are always different

specially for amp gain pots

a rolled off 1M (most common value) never sounds the same as a 500k or a 250k

a higher value is always more saturated and processed on the mids on heavily overdriven amps,

some brands compensate that by using low values or bleeding a small resistor to ground in parallel with the pot (that's a pretty efficient mod for most oversaturated amps)

[Armitage]

 

Different pot values and how they affect you!

 

Humbucker graph shown.

 

Humbuckers traditionally come with 500k volume and tone pots, with .022 caps. Single coils traditionally use 250k pots. Remember, pickups were voiced/made to run at these values, changing the value changes their intended tone, (good or bad is an opinion), as well as their output.

 

The top curve indicates virtually no load, the second curve down indicates a 1meg pot, the third down is a 500k pot, the fourth is a 250k pot and the bottom curve represents a 100k pot. As you can see, higher pots give you more output and raise the resonant peaks output. The resonant peak doesn't shift in frequency, but it does shift in amplitude. The resonant peak frequency of most HBs is usually around 5k to 7k. Gibson went to 300k pots in the early '80s to fatten up the tone of their guitars.

 

With tone controls (they react differently then volume pots because of the way they're wired in the circuit), a 250k pot is the same as turning your 500k tone pot down to it's resistive mid point (5 on a linear taper pot). Even on 10, a tone pot bleeds high end to ground, but pickups were designed in this circuit in mind, and some people think they sound cold and glassy without a tone pot in the circuit, some people can't tell a difference.

 

If you want to see what it's like to use different value pots, without pulling breakable knobs and changing out your pots, here's a temporary way just to see what it's like.

 

 

 

 

This is how you can hear what going from a 250k to 500k (or even 500k to 1 Meg) volume pot sounds like. Just disconnect the pickups input wire to the pot and put a 250k (or close 240k or 270k), (or to try 1 Meg, 500k or close), resistor in series. It'll sound the same, but you CAN'T turn the volume all the way off, remember this is just a test function. You can also try doing it to your tone pot as shown. Before going to the tone pot, insert a 250k resistor to go from 250k to 500k. If you like it, go buy the pots.

 

 

 

 

In many guitars with 250k tone pots, I've just left the resistor in permanently; you just can't turn it down as much as if you had used an actual 500k tone pot, but it helps keep some guitars brighter.

 

 

 

 

This is how you can hear what going from a 500k pot down to a 250k volume and tone pot sounds like. Just put a 500k (or close, e.g. 510k or 470k) resistor in parallel with the pots outer lugs. You can actually even leave it this way, the only difference will be the volume and tone pots taper (i.e. 10 will be 10, 0 will be 0, but it'll be half as loud at a different place on the knob).

 

You use audio pots, instead of linear, because the ear isn't linear with volume, and audio pots (also known as log pots) are designed to match the way you hear. Of course distortion and compression can mess that up...

 

P.S. if your "or close" value is slightly higher then the pot, the value will be slightly higher on 10 then the actual double, (or halved value) in these circuits. If lower, it'll be slightly lower.

 

 

Expensive pots sound the same as cheap pots as long as they're the correct value (the actual measured value, not the stated value). And changing brands of pots does NOTHING as long as they measure the same. Pots are not capacitive and are not reactive (certainly not in the audio range)... but pots that claim to be a certain value can be 20% off, and that makes a difference, so measure them. Especially if the ones you take out are 20% low and the ones going in are 20% high, you may very well hear that. Of course quality pots last longer, make less noise when you turn them... and can feel better... but the same exact measured value will sound identical... because it is.