Blend pot + master volume + master tone

[moshuajusic]

This is for a 5-string with 2 Rio Grande Muy Grande J pickups. I want to use a blend pot, 1 master volume and 1 master tone. If I use a 250k blend pot, will i notice any difference between 250k and 500k volume and tone pots? I'm having trouble figuring out how the pots interact--are they parallel to each other or in series, and how will they effect the tone? (I want to retain as much high end as possible, but I've found that 500k blend pots act more like 3-way switches. 250k blend pots have a smoother transition.)

Here's a basic diagram:

[Invalid or Expired Link Removed]

 

[walterw]

tons of threads on this (search "blend pot").

i say keep the 500k volume (use linear taper or it too will act like an on-off switch) and the 250k blend. make sure the blend is an "M/N" type, or you'll get a bunch of loss from it.

here's the secret, though. don't wire any of the grounds on the blend pot! just the two pickup hots in, and the one hot out to the volume pot.

you'll avoid the extra loading, and the pot will pan even smoother.

add a 500k audio taper tone and your "loud jazz" is all set.

 

[moshuajusic]

Yeah, you told me about that method of wiring the blend pot. The question here was whether 500k or 250k vol/tone after would be any different.

Now about your trick, what did you mean in the other thread when you said, "this pot will now have zero effect on tone when in the middle (just like a switch)?" I didn't realize a blend pot wired traditionally results in a change in tone in the middle, except what you'd normally expect by having both pickups fully on (lower volume and scooped mid in parallel, stronger output in series).

 

[walterw]

oh dear, now i'm repeating myself?

what i meant is that the unloaded blend pot in the middle will have no series resistance at all (or almost none), and no parallel path to ground to bleed off signal. therefore, it will electronically be just like a switch set to the middle, which is to say, just like wiring the two pickup hots right to the volume pot.

it's only when you turn it one way or the other that it does anything at all, adding series resistance to "dim" one pickup or the other.

a grounded blend pot OTOH will always be loading down the signal with two extra paths to ground, either 2x500kΩ (250kΩ total) or 2x250kΩ (125kΩ total). this is true whether it's in the middle or not.

 

[SGD Lutherie]

I find 500K blends work better, loaded or unloaded. When they are grounded you have less loading, and both ways you have move travel for blending.

 

[SnakeKappele]

Using 500K pots will increase the volume at the pickup's resonant frequency over 250K pots, giving you more highs.

Link Removed

 

[SGD Lutherie]

Using 500K pots will increase the volume at the pickup's resonant frequency over 250K pots, giving you more highs.

You are forgetting something: parallel resistance. We are adding a master volume. You have two 500K decks on the blend; that's 250K. Then you have your master volume. Assuming that's 250K, what are you left with? 125K. Walter posted this before.

Now let's assume you use a 250K blend. That's 125K right off the bat. Add in a 250K volume and you have 83.33K. That will sound darker than usual.

With a Standard Jazz bass you have 125K (two 250K volumes in parallel). So use a 500K blend.

 

[SnakeKappele]

You are forgetting something: parallel resistance. We are adding a master volume. You have two 500K decks on the blend; that's 250K. Then you have your master volume. Assuming that's 250K, what are you left with? 125K. Walter posted this before.

Now let's assume you use a 250K blend. That's 125K right off the bat. Add in a 250K volume and you have 83.33K. That will sound darker than usual.

With a Standard Jazz bass you have 125K (two 250K volumes in parallel). So use a 500K blend.

Isn't that what I said? Use 500K pots.

 

[SGD Lutherie]

Isn't that what I said? Use 500K pots.

Oh, OK, I misunderstood... you said:

Using 500K pots will increase the volume at the pickup's resonant frequency over 250K pots, giving you more highs.

So I took it as saying that would be brighter than normal.

I like brighter myself so....

 

[moshuajusic]

You are forgetting something: parallel resistance. We are adding a master volume. You have two 500K decks on the blend; that's 250K. Then you have your master volume. Assuming that's 250K, what are you left with? 125K. Walter posted this before.

Now let's assume you use a 250K blend. That's 125K right off the bat. Add in a 250K volume and you have 83.33K. That will sound darker than usual.

With a Standard Jazz bass you have 125K (two 250K volumes in parallel). So use a 500K blend.

But don't you also have a tone pot?

Also, which blend pot are you using exactly? Brand and taper. I tried a 500k MN taper blend pot (Alpha, I think) and it sounded like a 3-way switch.

I wonder if this whole discussion is futile? I looked at the bass wiring diagrams on Seymour Duncan's website, as well as Bartolini and Delano, and not a single 500k pot to be found, not even with humbuckers like on Music Man basses.

 

[SGD Lutherie]

But don't you also have a tone pot?

Also, which blend pot are you using exactly? Brand and taper. I tried a 500k MN taper blend pot (Alpha, I think) and it sounded like a 3-way switch.

I wonder if this whole discussion is futile? I looked at the bass wiring diagrams on Seymour Duncan's website, as well as Bartolini and Delano, and not a single 500k pot to be found, not even with humbuckers like on Music Man basses.

The tone pot figures in a bit, but I was showing the effect of the added volume pot.

Try the Bourns M/N blend pots. They are way better than the Alpha pots. You can get them from Invalid Link Removed and Invalid Link Removed

I like them so much I'm going to have them on my website too.

Also, removing the ground from the blend pot makes them blend better, as per Walter's advice.

 

[walterw]

allparts now has the bourns blends as well.

nicely made, and just about zero resistance in the middle.

i'm not so sure about the taper thing, though; ungrounded, we're just talking about adding series resistance to one pickup or the other. it stands to reason that a 250k blend will at a given degree of turn present less resistance than a 500k at the same point, and so the 250k will "dim" the pickup a little less, therefore shading a little more gradually than the 500k will.

the trade-off (isn't there always a trade-off?) is that it doesn't turn the pickup quite as "off" as the 500k would. you still hear a little something if you tap on the "off" pickup with a screwdriver. (i don't hear it when playing, though, so i don't think it's a big issue.)

if i ever come across a 100k or 50k M/N, i'm going to try that, maybe modded to true "no-load" by cutting the carbon traces at the ends. it might get really smooth blending, combined with truly cutting off the pickup when turned all the way.

 

[SGD Lutherie]

Or get like a 250K or 500K linear taper center detent, connect a pickup to each outside terminal, and the output from the wiper.

 

[moshuajusic]

Or get like a 250K or 500K linear taper center detent, connect a pickup to each outside terminal, and the output from the wiper.

???

Even if that did work (for reasons I don't know), wouldn't the center be 50%, meaning even more of a volume drop in the middle?

 

[SGD Lutherie]

???

Even if that did work (for reasons I don't know), wouldn't the center be 50%, meaning even more of a volume drop in the middle?

That's how active blends that use a single ganged pot are wired up. Yeah, passive it might have a little drop, but you also are summing two signals.

 

[SnakeKappele]

For heaven's sake, just buy some pots and try them!

I used 500K audio pots for volume and tone and a 250K linear blend (for a very scientific reason: they didn't have a 500K).

It sounds great.

I also used a .047uF paper-in-oil capacitor - but let's not open that can of worms.

In the end the only thing that matters is how it sounds, so hook it up and listen to it.

http://www.bestbassgear.com/pots.htm

 

[walterw]

Or get like a 250K or 500K linear taper center detent, connect a pickup to each outside terminal, and the output from the wiper.

???

Even if that did work (for reasons I don't know), wouldn't the center be 50%, meaning even more of a volume drop in the middle?

That's how active blends that use a single ganged pot are wired up. Yeah, passive it might have a little drop, but you also are summing two signals.

yeah, you lost me on that one, too.

you'd have each pickup turned quite a bit down in the middle, and since they're just in parallel, they don't "sum" with the dB boost that entails. (after all, there's no boost even with a 3-way switch, which has no attenuation at all.)

 

[SGD Lutherie]

Yea I was thinking of active mixers, but it wouldn't work passively. But that's how panning controls work. Probably how the single ganged blend pot on the Audere works too.

(or you use a 500K and put the ground to the wiper)

 

[moshuajusic]

So I'm ready to wire it up. I'll be using a series/parallel switch, and I want the blend control to choose bridge fully clockwise, and neck fully counterclockwise. So is this right?