1 meg pots

[stratobastard]

What's the deal with 1 meg pots?

what kind of sound difference does it make?
Does it have specific applications?
If anyone has any experience with them please let me know.

 

[JOLLY]

Re: 1 meg pots

This is about the best thing I've ever found to explain them:

http://www.torresengineering.com/how1and2megp.html

 

[Artie]

Re: 1 meg pots

To be honest, I don't think that thats a very good explanation of pot values. Here's why:

The important part of this info is that one side of the pot is connected to ground. Even with the volume on 10, the pickup is connected to ground via a resistor/value of the pot. Some of the pickup's signal is "short circuited" to ground and lost.

None of the pickups signal is "shorted to ground and lost." That implies that the best situation would be to have no resistance. Why would you want any of your signal "lost"? We know thats not correct.

The resitance of a pot is connected across the pickup, acting as a "load". Its how much work we want the little AC generator, (the pup), to do. Think of a V8 engine. It has a certain size flywheel on it to damp engine vibrations. If you have no flywheel at all, the engine would shake the car apart. Too heavy and the engine would be smooth, but acceleration would suffer.

Pickup load is similar. The lower the resistance, the greater the current through the pup coils. And the greater the current, the greater the "field" thats generated by the string vibration. Up to a limit. The pickup/string relationship has limits. The "trick" is to find that perfect balance between pickup loading, and subsequent signal damping. (The "flywheel" affect.)

As a general rule, 250k per coil is a good starting point. So, you use 500k for humbuckers. You can raise that value to 1 meg to "brighten" the pup, or lower it to 250k, (like for a JB), to smooth the pups highs a bit.

Experimentation is the key. And hearing what results others have had.

 

[stratobastard]

Re: 1 meg pots

Thanks guys

 

[JB_From_Hell]

Re: 1 meg pots

Good explanation Artie.

 

[stratobastard]

Re: 1 meg pots

Very good explanation, very easy to understand....

Thanks again!

 

[Kent S.]

Re: 1 meg pots

None of the pickups signal is "shorted to ground and lost." That implies that the best situation would be to have no resistance. Why would you want any of your signal "lost"? We know thats not correct.

That *is* correct, you do lose signal to ground thru that connection, if you do a voltage divider equation for the various source impedances involved you'd see that the source and the *load* form a voltage divider of their own, hence the higher Fc being attenuated in proportion (to ground). The best situation would be to have *no resistance*, as in infinite resistance (not zero resistance) between the signal and ground ... this is of course impossible, because the signal must terminate somewhere to complete the connection (hardwire a pup to the input of an amp, and it still gets loaded by the amp's input impedance) ... so you always lose some of your signal in regard to the full voltage of the upper frequencies (more specifically the frequencies with the highest source impedance).

Pickup load is similar. The lower the resistance, the greater the current through the pup coils. And the greater the current, the greater the "field" thats generated by the string vibration. Up to a limit. The pickup/string relationship has limits. .........

The current induced into the coil has nothing to do with the load, the resulting voltage that the coil outputs does, but not really noticeable in practice (you'd have to get the pot value equal to the pup's value {if you could even assume a single value ...which of course you can't} for it to drop the voltage to half ... although, yes ... the current would increase ... *if* the coil weren't producing it to begin with ... so it's not quite the same as a current being driven thru a changing resistance.
Anyway, again, the voltage of those higher impedanced frequencies get shunted off more to ground the lower the pot is valued.
If you were to reduce the value of the pot low enough, you'd start to not only damp the resonant peak fc, but cause a highend roll-off (similar to a tone control), get it even lower, and you can start reducing the maximum output voltage that the pup is capable of delivering.
So, yes a higher valued pot, will allow a bit truer tone from the pup. Higher will be brighter, and lower will be warmer, (also a bit more even in the mids) ... personal taste. I've used from 100k to 5Meg ... depends on what you are after ... one side note though, lower impedance pots tend to reduce the susceptance of hash and RFI better than higher valued pots ... I've seldom ever heard this to be a problem, but just as a side note ... they also have been reported to be a bit quieter in certain active circuits ... to much going on there to speculate though.
Anyway, I'm outta here .................

 

[Artie]

Re: 1 meg pots

What you're saying is, of course, correct. I think where we are at odds, is more a matter of semantics, than technical differences. My objection to the original authors explanation was simply in the use of the term "shorted to ground and lost". In electrical-ese, a "short" is generally an error condition, and signal "loss" is undesirable.

Finding the right pot value, and thus loading affect of a pup, is a balancing act. For example, a JB likes a 250k pot. A 1 Meg pot would likely make the pup shrill and harsh. So in this instance, we want a certain amount of the signal, "shorted, and lost".

I just didn't want folks, who are trying to understand the relationship between pot value and pup, to come to the conclusion that raising the pot value will regain "lost" signal.