Edu-ma-cate me on tone pots and volume pots

[Magic Twanger]

Hi gang,

I see many of the different models have different values for their respective tone pots. What do these different values actually mean tonally?


I've heard that there are volume pots as well - that retain their highs or bass as you turn down as well - which ones are these?
Such as:
500k pots on the Axis;
250k on the Morse, Silo and SUB1 plus a capacitor on the tone;
25k on the Luke etc....

In a nutshell, higher value pots on the volume or tone mean what?

...and this capacitor business....?????

Thanks,
Magic

 

[Chad]

I've heard that there are volume pots as well - that retain their highs or bass as you turn down as well - which ones are these?

A capacitor allows higher frequencies to pass through, so a cap between a middle and outer lug of a volume pot will send the higher frequenies that the cap allows straight to the output.

In a nutshell, higher value pots on the volume or tone mean what?

A higher value pot has more resistance to ground therefore it allows a brighter sound. So a 500k will generally sound brigher than a 250K.

...and this capacitor business....?????

A cap can be used as mentioned above. Also, a cap is used in a tone control to allow it to function. A cap HAS to be used in a tone control or it isn't a tone control. In the tone control the cap is sent to ground. As you turn the pot control up it is resisting the frequencies that are being sent to ground by the cap, so the sound is brighter. As you turn the control down, there is less resistance to the frequencies being sent to ground so the sound is darker.

 

[Chad]

It also worth noting that on a guitar with both a volume and tone control if both pots are 500K and are turned up to 10, this results in a sound similar to what you would get on a guitar with a single 250K volume pot (and no tone control). In other words, the two controls interact.

 

[beej]

Right on the cap business!

It also worth noting that on a guitar with both a volume and tone control if both pots are 500K and are turned up to 10, this results in a sound similar to what you would get on a guitar with a single 250K volume pot (and no tone control). In other words, the two controls interact.

Not exactly. The pickups see the load of the pots REGARDLESS of their setting. This is because the middle lug of the pot is varied while the resistance from the outside lugs stays constant.

The pickups, your cord, etc., it's all one big LCR (inductance, capacitance, resistance) circuit. Each component has an effect on the output frequencies of your pickups. Add too much capacitance (e.g. by using a long cord) and you alter the "resonant peak" of the pickups, and shift the resulting frequencies downward. In effect, this causes you to swallow the highs and dull the sound a bit.

Same thing with resistance: in general, the more resistance on the pickups, the brighter the sound will be as you shift the resonant frequency peak of the pickups upward. This is why single coil pickups (which are brighter than humbuckers) need less resistance in the controls (usually 250k pots) whereas humbuckers like to see more resistance (usually 500k controls) to brighten then up.

Resistance seen by the pickups is a combination of the total resistance in the circuit. Normally you just worry about the pots. When you add identical resistors in series, the total resistance is half of each pot. (It's 1/Rtotal = 1/R1 + 1/R2). So two 500k pots results in 250k seen by the pickups.

You can also vary the inductance of the pickup which widens the frequency peak. Bill Lawrence sells a "Q Filter" that you can use to do this. It will take a midrangey humbucker and add more highs and lows to the ouput, for more of a single coil sound.

Lastly: the 25k pickup on the Luke is because the EMG pickups are Active and not passive like a regular guitar. Different thing entirely.

 

[beej]

A while back I did a long rant on pickups, series/parallel wiring etc. Nerded out for a bit. Good for a read if you want more info:


http://www.ernieball.com/forums/showthread.php?t=11146

 

[Chad]

And where exactly did I say that it won't affect the entire pot sweep?

 

[beej]

You said "if both pots are 500K and are turned up to 10" then you'd get a sound similar to "a single 250K volume pot".

I was pointing out that it doesn't matter if the pots are turned up or not. Simply having them in the circuit loads the pickups.

The bit about the middle lug was to clarify how the pots affected the output, while still providing load.

 

[Chad]

That was merely an example as I felt readers could more easily relate to an example that deals with the full value of the pots. Other examples with lower pot settings get harder to understand especially if dealing with log pots. Further, I would assume that the reader would understand this example meant with the 250K volume pot on 10 as well. So how about this...

It also worth noting that on a guitar with both a volume and tone control if both pots are 500K and are turned up to 10, this results in a sound similar to what you would get on a guitar with a single 250K volume pot (and no tone control) also turned up to 10. In other words, the two controls interact.

 

[beej]

Hey- Chad, man this was meant in good spirits. We're all on the same team here- talking guitar and having fun.

That's cool. Just thought maybe you or the other readers didn't realize that the setting the pot is dialed in to doesn't matter as far as the tonal change on the guitar is concerned.

 

[Chad]

beej: Yep, all in good fun. Sometimes these tech talks can seem a little rigid even if not intended.

I do have some questions and am going to go against what I said and try to complicate this:

If a guitar has 500K volume and tone *linear* pots and both settings are on 5, would that be similar in sound to a guitar with a single 250K volume *linear* pot set on 5?

Or on the guitar with the tone pot, would the frequencies that aren't being sent to ground through the cap in the tone pot be a little more apparent? It's hard to word what I'm trying to say there...I hope that makes sense.

 

[beej]

Cool, cool. Sometimes I can sound a little smarmy when I'm nerding out.

If a guitar has 500K volume and tone *linear* pots and both settings are on 5, would that be similar in sound to a guitar with a single 250K volume *linear* pot set on 5?

I see your point. Clearly they sound different, though that's due more to the filtered highs from the tone control rather than the reduced loading.

So yes, if you want to compare apples to apples you have to talk about the pots up. When I talk about this stuff, I try and separate out the effect of the tone control's filtering from the effect of adding resistance to a pickup.

 

[Magic Twanger]

Hi guys,

Thanks for the extremely informative posts.

I know that the tech talk can get boring for some - but since I'm new to all the tech stuff - I personally really enjoy hearing all the details of how, why and because, etc... - it all helps me to learn.

So - I DO appredciate all the fine details.

beej, I will read that thread you provided when I get a chance...

Thanks again!!!

Magic

 

[fogman]

You guys lost me at "Hi Gang!"
I feel like I'm at a computer programming convention!
Cool information, I'll need to let this sink in for a few days, then read it again!

 

[tommyindelaware]

http://www.stewmac.com/cgi-bin/haze...G=3&s1=Free_info_sheets&item=freeinfo/fi.html

http://www.stewmac.com/cgi-bin/haze...G=5&s1=Free_info_sheets&item=freeinfo/fi.html

next chapter will be on no load pots.
& there may be a pop quiz.......so study good....unless u wanna end up in summer school.....

 

[jongitarz]

WTF is happening with our collective skin? It seems to be getting thin. Lighten up and enjoy the ride as BP would say.

 

[Eilif]

If a guitar with a 500k tone pot is wailing alone in a forest but there is no one to hear it, does that mean it makes no sound?

What is the sound of a one-handed 250k tone pot clapping?

 

[beej]

 

[Mick]

You guys lost me at "Hi Gang!"
I feel like I'm at a computer programming convention!
Cool information, I'll need to let this sink in for a few days, then read it again!

Only interesting if you own a MM guitar

 

[Spudmurphy]

I've gone to pot reading this !

I just go to my buddy and say "My pot is gone, got a replacement?"
- yeah thats £**.

If I want to know more I'll PM Beej.
Sssheesh and I thought taxation was complex!!!