Master Vol/Blend Question

[raymondl3]

Hi.
Assuming a blend control on a passive Jazz Bass is essentially 2 stacked volume pots, when the knob is in the center position (where both pickups volume is equal) both pickups are at 50% volume are they not? Whereas with a Dual Volume setup one can set both pickups at 100% output and acheive the same thing. Is this correct? My concern is that by using the blend in 50/50 center mode there will be a darkening of the sound due to the load on the pickups, not to mention the fact that I'd be going through an additional master volume. Your thoughts appreciated.

 

[Thunderscreech]

Hi.
Assuming a blend control on a passive Jazz Bass is essentially 2 stacked volume pots, when the knob is in the center position (where both pickups volume is equal) both pickups are at 50% volume are they not? Whereas with a Dual Volume setup one can set both pickups at 100% output and acheive the same thing. Is this correct? My concern is that by using the blend in 50/50 center mode there will be a darkening of the sound due to the load on the pickups, not to mention the fact that I'd be going through an additional master volume. Your thoughts appreciated.

This is pretty much true. I had a Squire MB-5 that had passives and a blend and master volume, and It had the same problem.

2 volumes is best in a passive configuration IMO.

 

[JTE]

It's pretty much wrong. No, it's completely wrong. Here's a schematic showing a typical dual volume control, and a blend pot. Electrically they're the same thing.

A blend pot functions exactly like two volume controls with one shaft controlling both. Each element of the pot has a long section that has NO resistance. A real blend pot is wired so that from full CCW to the center detent, one PUP is wide open and the other is getting turned up. At center both are on all the way. As you go past the center towards CW, it's turning down the PUP that wasn't affected by the first half of the travel.

When you wire a blend pot you have to have the hots from the PUPs connected to the correct lug of the pot, or else it won't blend at all. And if you wire the PUPs out of phase, then you'll have a noticeable drop in volume at the center. But if you wire it correctly, it won't have those problems and it'll function like it's supposed to.

jte

 

[Thunderscreech]

It's pretty much wrong. No, it's completely wrong. Here's a schematic showing a typical dual volume control, and a blend pot. Electrically they're the same thing.

A blend pot functions exactly like two volume controls with one shaft controlling both. Each element of the pot has a long section that has NO resistance. A real blend pot is wired so that from full CCW to the center detent, one PUP is wide open and the other is getting turned up. At center both are on all the way. As you go past the center towards CW, it's turning down the PUP that wasn't affected by the first half of the travel.

When you wire a blend pot you have to have the hots from the PUPs connected to the correct lug of the pot, or else it won't blend at all. And if you wire the PUPs out of phase, then you'll have a noticeable drop in volume at the center. But if you wire it correctly, it won't have those problems and it'll function like it's supposed to.

jte

I stand corrected.

 

[raymondl3]

Thanks!

 

[raymondl3]

A real blend pot is wired so that from full CCW to the center detent, one PUP is wide open and the other is getting turned up. At center both are on all the way. As you go past the center towards CW, it's turning down the PUP that wasn't affected by the first half of the travel.


If that's the case, then the volume pots in a dual setup would have a longer taper than a blend, correct?

 

[JTE]

It MIGHT cause some audible loading, but my experience with putting blend pots into passive basses I'm pretty familiar with is that it's either not noticable, or so slight that the ease of use on stage for me is worth the change in sound.

I can't figure any use on stage for trying to find a precise 77/23 blend with two volume pots. So, the difference in lenght of travel while blending is into the realm of pointless for me. The only real objection I've heard for a blend is if you want one PUP at 75% and one at 33%- not a 75/33 blend, but that one PUP is 3/4 of the way open, and the other is 1/3 open. What I mean is that the common assertion that a blend pot only gives you half of each PUPs volume is outright wrong.

Since I tend to run all my basses (passive and active) full open on the volume, I'm using the blend as a blend of the two PUPs for tone. So, that doesn't apply to my use.

jte

 

[David Jayne]

Works fine if you like the tone. But two volumes gives more tonal options since, as stated above, you can have them equal but less that fully on, which makes a very noticeable difference. I discovered this after adding a blend, and went back to 2 vols because of it.

 

[DavePlaysBass]

The big choice if you go with a blend pot is what value. 500K blends tend to more common and may be replacing 250K volume / volume arrangements. You will not get the same low end blending with two 500K pots as you do with 250K pots. So if you like your 250K volume / volume go with a 250K blend pot. You will be adding extra resistive loading but IME it is negigible.

I have some curves somewhere in the archives on this forum showing the frequency response of the different blend pot arrangements. Basically speaking, the 500Ks tend to act more like switches and the 250Ks give your more blending.

 

[SGD Lutherie]

Assuming a blend control on a passive Jazz Bass is essentially 2 stacked volume pots, when the knob is in the center position (where both pickups volume is equal) both pickups are at 50% volume are they not?

Not always. It depends on the taper of the blend pot.

If you have something like an M/N taper, they are sort of audio taper, and reverse audio taper. At the center detent, one side of the pot's wiper is seeing more resistance t one outside lug than the other.

So if it's a 250K pot, the pickup sees 240K to ground, and about 10K to the hot. This is pretty much like having he volume all the way up.

If you wire the pan pot backwards, you will lose output in the middle.

Two volumes do give a bit more output some of the time, but not always. Some blend pots don't work as well as others. For instance the pots from Stew-mac are actually stereo volume controls, and the taper is not reversed on one side. The blends from GuitarJones and Allparts work the right way.

 

[5-string Dan]

Hello,
I hate to barge in without words of wisdom, but I'm looking for a proven hookup diagram for two passive Jpups, with Master Volume, Master Tone, Blender, and Series Switch. I'm changing over my 2 vol. 2 two tone Washburn. I have my own drawing and ideas, but I don't want to reinvent the wheel. I saw some strings from 'Lyle Caldwell' but the pictures were gone, and he doesn't answer my emails.
Any help or referral is appreciated.

 

[mjl422]

Two volumes do give a bit more output some of the time, but not always. Some blend pots don't work as well as others. For instance the pots from Stew-mac are actually stereo volume controls, and the taper is not reversed on one side. The blends from GuitarJones and Allparts work the right way.

Can you elaborate on the Stew-mac pots? I changed out my blend pot to a Stew-mac 500k blend pot and I can't get it to blend. It's acting more like a switch than a blend (I rewired it 5-6 different times already). Also, I saw where somebody mentioned that it's better to use a 250K pot instead of 500K. What are your thoughts on that?

 

[SGD Lutherie]

Can you elaborate on the Stew-mac pots? I changed out my blend pot to a Stew-mac 500k blend pot and I can't get it to blend. It's acting more like a switch than a blend (I rewired it 5-6 different times already). Also, I saw where somebody mentioned that it's better to use a 250K pot instead of 500K. What are your thoughts on that?

On a proper blend pot the two halves of the pot have the taper going in the opposite direction, since as you are increasing the level of one pickup, you are decreasing the level of the other.

The problem with the Stew-mac pot is it is really a stereo volume control, and both halves of the pot have the taper in the same direction, since it's made to increase or decrease the level of both pickups at the same time.

On a standard M/N or A/C taper blend pot, when you are at the center, there is the maximum amount of resistance between your source and ground. With the Stew-Mac pot, this is true only for one deck of the pot, and not both.

But even with good blend pots, I find you hardly get a blend, and it works more like a switch. I'm helped this a bit by soldering 150K resistors on the pots between the source and hot lugs. This flattened the taper out a bit.

Probably the higher the value of the pot, the smoother the blend, but I haven't tested it.

 

[JTE]

On a proper blend pot the two halves of the pot have the taper going in the opposite direction, since as you are increasing the level of one pickup, you are decreasing the level of the other.

Sigh...

No, it's only turning one pickup down. At center, both are wide open. As you go from center towards soloing the neck PUP, it's turning the bridge PUP down without changing the level of the neck PUP.

jte

 

[SGD Lutherie]

Sigh...

No, it's only turning one pickup down. At center, both are wide open. As you go from center towards soloing the neck PUP, it's turning the bridge PUP down without changing the level of the neck PUP.

jte

No... follow along here. Take a Stew-mac pan pot. Let's say it's the 250K.

Put the pan pot to the center detent. Now take a multi meter and read from the middle (wider) lug to one of the outside lugs, then the other.

You will see it's about 240K on one side, and 10K on the other (more or less).

On a good pan pot the other deck will be opposite. On the SM model they are both in the same direction. So that means that at center detent, one pickup would see 240K to ground, while the other sees 10K! See where the problem is?

On a good pan pot at center detent, both pickups see 240K to ground and 10K to hot (unless you wire the pan pot up backwards), so we can consider the pickups at full volume.

But they are never wide open unless you have a custom taper, and I haven't seen any of those. This is why you have a slight volume drop at the center. This is often considered a feature as the sum of the two pickups is grater than the single. but that doesn't take into consideration the effect of two coils in parallel and some phase cancellation.

 

[walterw]

i've found plenty of m/n pots that read pretty much zero at the center, or at least just a few ohms. the new allparts 250ks do.

also, my little trick of not connecting the grounds to the blend pot (so that it just adds series resistance to one pickup or the other without loading either pickup to ground) seems to slow the rate at which it "dims" the pickup in question. a 250k m/n dimming a pair of 8 to 8.5k jazz pickups actually transitions very smoothly along its whole turn, and has no drop at the center.

 

[TheMutt]

Just wanted to say that I have a Fender J with a master volume and blend that I installed. I can't tell a difference from before changing from V/V/T to V/B/T. As far as being more versatile having two volume pots instead of a blend and master volume, whatever you can do with two volume pots can be approximated with the blend pot and master volume knob.
For instance:
Neck PU 50% Bridge 75%
would be
Blend 25% towards bridge PU, and master volume down 25%