Blend pot, 250k VS 500k issue

[CaneyBoniface]

This is a very old thread with one of the participants banned and probably some others have come and gone.

I'd make this a new post.

well, i just found this thread. hehehe

 

[Zoobiedood]

On our STC-2A and -3A preamps, we use a 100k blend pot.

 

[walterw]

On our STC-2A and -3A preamps, we use a 100k blend pot.

ooh!

i've been looking for a 100k M/N blend pot! that's really a thing?

This is a very old thread with one of the participants banned...

still a fun little read, and it bums me out about said banned member; he was a good tech/electronics resource here on TB, it just apparently turned out you couldn't do business with him.

 

[RobbieK]

I doubt it's an mn pot Walter. but I'm happy for a Seymour Duncan guy to jump in. with buffered pickups, a regular dual gang linear pot should work fine as a blend. finding one with a centre click might be tricky though.

 

[Zoobiedood]

Going over the wiring diagrams, that's what it says. I have no reason to believe it has changed, but if it has, I am sure someone will let me know...haha!

 

[PawleeP]

I will describe two scenerios that are identical. One with a blend pot and the other with two volumes.

Scenerio 1:

Two 250K volumes like the typical three pot jazz bass harness. The pickups connect to the middle lug or wiper of each of the pots (like this [Invalid or Expired Link Removed]).

With both volumes wide open (ignore the tone for simplification), the pickup hot leads are both connected together and two the output jack with a 125K parallel load on the combined pickups.

Now let's go for the Jaco tone. Bridge is still wide open and the neck is rolled to lets say 50% (I know the Jaco tone is actually a little less). The neck pickup hot lead sees 125K to ground and 125K to the output jack per its volume pot. The bridge is still straight to the output jack and has a 250K load to ground per its volume pot plus the loading from the other pickup and its associated volume pot.

Scenerio 2:

We have a 250K blend pot. This is actually two 250K pots that share one shaft. When the shaft is in the center position both wipers are at one extreme of the pot. When the shaft is twisted off center one direction, one pot wiper stays at its extreme position while the other pot wiper sweeps thru its range. The pickups are connected to the wipers. And the side of the pot outputs that is zero ohms in the center position is connected to the output jack.

Lets hook up the pickups to the two wipers. In the center position as already stated both wipers are at one end of the pot. This is exactly the same as two volume / volumes wide open.

Now lets rotate the shaft the direction that moves the wiper of the neck pickup. At some point in the travel the neck wiper will be 125K from ground and 125K from the output jack.


So how are these two scenerios different? At full on they are the same. Leaving one pickup full on and turning down the other pickup, they are both the same. These are the two scenerios that matter to most players.

As stated previously, you cannot turn them both down at the same time with a blend pot. But that is not how the majority of players operate a volume / volume bass.

wow, nice.. so if you run vvt on a jazz or pj.. with two 500k pots, the pickups are not as bright when using both pickups (a say using 2 1meg pots), because the pickup behave as if there is only a 250k total?
i usually try to switch most of mine to linear volume controls. thanx p