400K pots?

S

SF audio

New member
So I wired in a couple of 750K resistors to the pots in my explorer (500K pots) to bring it down to 300k. Wow, THAT is the sound of those classic riffs we all know. The Burstbuckers sounds rather pedestrian with the 500K pots IMO, but taking them down to 300K makes them bite and respond better, rather than being wide open and bland.

So I was thinking on my other guitars with 500K pots...what about 400K? First of all, what size resistor would I need for that, and has any one experimented with 400K pots? At what intervals would you notice a change in sound, every 50 or 100K? This is kinda nerdy stuff but it seems you can really affect the sound (and response) with pot resistance.
 
Re: 400K pots?

Did you actually measure the 500k pots you have??

There are plenty of nominally 500k pots that measure in the low 400s range as stock. So maybe see what you have already and measure from there.
 
Re: 400K pots?

SF audio said:
So I was thinking on my other guitars with 500K pots...what about 400K? First of all, what size resistor would I need for that, and has any one experimented with 400K pots? At what intervals would you notice a change in sound, every 50 or 100K? This is kinda nerdy stuff but it seems you can really affect the sound (and response) with pot resistance.
Click to expand...

1) you'd need a parallel 2M resistor to obtain 400k from a perfect 500k pot. Keep in mind that parallel resistance affects the taper of a pot.

2) About the "has anyone experimented with 400k pots": What AlexR said. I've played plenty of guitars with supposed 500k pots measuring values like 420k, 403k and so on. Consequence: if you want 400k controls, many regular pots will get you there.

3) If you want to know what lowered resistance does, just lower your tone control: a tone pot mostly lowers the resistive load during most of its curve. The tone cap starts to really alter the main resonant peak at really low settings : below 1/3 in many cases; it means that above 1/3 and up to 10/10, the action of the tone pot is mostly resistive (which doesn't mean that a cap can't be heard with the tone pot full up: just that its influence is extremely subtle).

5) Schematically, a change of 100k in the resistive load = a change of 1dB in the resonant peak. 1dB is supposed to be the threshold of perception under which any change becomes hardly noticeable, if any (once again, empirical reality might be a bit more complicated; I'm just talking about theory here).

Enjoy anyway: there's many things to do with added LRC loads coupled to passive transducers. :-)
 
Re: 400K pots?

Changing the resistance on the volume isn't the same as turning the tone knob. Resistance dampens the full signal. Capacitance cuts frequencies above the point determined by the cap value. Also what difference does it make if he lowers the resistance with a pot that meters around 500k plus a resistor in parallel or if he happens to find a pot that's way out of spec?
 
Re: 400K pots?

Clint 55 said:
Changing the resistance on the volume isn't the same as turning the tone knob. Resistance dampens the full signal. Capacitance cuts frequencies above the point determined by the cap value. Also what difference does it make if he lowers the resistance with a pot that meters around 500k plus a resistor in parallel or if he happens to find a pot that's way out of spec?
Click to expand...

Here is emulated the response of a (linear) tone pot from 0 to 10, while the volume stays full up and when a resistor is wired in parallel:

PotTaperParallelResistor.jpg

Now, here is emulated the same thing without parallel resistor: I've just lowered the virtual value of the tone pot in order to achieve the same overall resistive load:

PotTaperLowResistanceControl.jpg

What these pictures illustrate:

-the resistance of the pots considered separately doesn't matter as long as all pots are full up. If the overall resistive load stays identical, the resonant peak will remain at the same frequency and output level once all control full up (-6,24dB @ 5400hz in my sims). IOW, a 250k volume and a 500k tone pot would give the same resonant peak with all pots full up than a 500k volume and a 250k tone... but also than a 500k volume with a linear 500k tone lowered @ 50%;

-the action of a tone cap on the main resonant peak (in red) isn't obvious before the tone pot settings get really low;

-a parallel resistor changes the taper of the tone control: except @ 0/10 and 10/10, the frequential curves aren't at the same place nor have the same shape with or without parallel resistor.

EDIT - I've searched a link useful to share. The best that I've found for the moment is this one with its "linear pot" and "tapered pot" calculators, FWIW: https://www.diystompboxes.com/analogalchemy/emh/emh.html
If I find something else interesting, I'll post it too.


Please, note that...

-this answer doesn't exclude a thousand of nuances. We all know that schematical theory is just that: schematized (so, for example, there's a subtle sensorial difference between 250k volume + 500k tone and 500k volume + 250k tone, because the tone pot is not a brick wall).

-I post mere simulations because 5Spice asks me a few seconds of work only. But if necessary and if time permits, I'll share actual measurements done with real pickups and illustrating the same thing.

-The goal of this answer is not to argue. Just trying to clarify the logics behind my previous statements. Thx in advance to read it accordingly. :-)
 
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Re: 400K pots?

I can confirm that many supposed 500k pots can measure as low as 400k. I can also confirm that if I compared a 500k pot with one that measured 400k, but the time I got everything back together after switching them out, I don't know if I'd hear it as a big change.
 
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