Blend Pot Volume Drop?

[j. pierce]

I usually play this guitar with enough gain that it's not really noticable, and I generally set-and-forget it for whatever setup I'm playing with, so I can adjust the amp accordingly. But playing around with a lot of clean tones lately, I've noticed my guitar, wired with a blend pot from Stew Mac to blend between the 'bucker-sized P90 (neck) and '59 style bucker (bridge), has a noticable volume drop when dialed to the center-dentent, compared to being dialed on a single pickup.

At first thought, I thought maybe I had wired my p'ups out of phase with regards to each other, but I'm not getting that "nasally" sound I normally attribute with out-of-phase p'ups, and everything looks good just opening it up. I seem to remember having wired them out of phase when I first replaced the bridge pickup with the humbucker anyway. The metal pickup casings are all still connected to ground.

Anyway, when I have more time, I'll open this thing up and fool around with it, but I'm just wondering, does anyone else have this symptom? Is it just a consequence of the blend pot's taper that I need to learn to live with? (It's not that bad, and really, it could just be my amps settings reacting to the change in tone, I'm not certain?)

EDIT:

I just checked the resistance across the output, with the controls all the way up, and the blend pot all the way to the neck, I get about 7.5K, all the way to the bridge, about 8.5K. Sounds right for the pickups I have in there. At the center detent, I get about 50K resistance? I'm thinking this is my problem? I'll have to do some tinkering tonight.

[JoeAArthur]

Hmm, that's interesting. Based on your two values I would expect around 4K at the center. Assuming you didn't nudge your volume control down accidently when you took the center readings, about the only thing it could be is a problem with the blend pot.

I'd measure the blend pot with it set to the center detent. Measure the resistance of each section, from the center lug to each of the outside lugs.

On one lug you should be getting the reading you got for the pickups and on the other lug you should get ZERO. If the tracking of the resistance element is off at the center, you'll get something besides zero on the lug where it should be zero.

[Pr3Va1L]

Well, I think it's the balance between the 2 pickups...

I mean... a 1kohm difference between the 2 is not much as far as output goes, but the difference between the output from a neck pickup to a bridge pickup is very different...

What I mean is I get about the same volume in my SD equipped guitar with the neck 59' (at around 8 kohm) and the bridge Custom 5 (around 14 kohm)

So I think it could be that...

[j. pierce]

Well, I think it's the balance between the 2 pickups...

I mean... a 1kohm difference between the 2 is not much as far as output goes, but the difference between the output from a neck pickup to a bridge pickup is very different...

What I mean is I get about the same volume in my SD equipped guitar with the neck 59' (at around 8 kohm) and the bridge Custom 5 (around 14 kohm)

So I think it could be that...

Because of the height of the p'ups the neck is actually louder than the bridge (I usually play the neck at a clean/low-gain setting, but still want to push the amp, where as with the bridge I play with higher gain on the amp, so I like the output to be a little less so I don't push my thing into total breakup) But what confuses me is the 50/50 blend at the center detent is noticably lower in volume than *either* pickup on it's own - that's the only thing that's got me scratching my head.

I just got back to the house, I'm going to be opening this up shortly.

[j. pierce]

Yeah, opened the back up and checked it out as suggested by Joe - the "top half" reads 56K on one side and 7Kish on the other, the "bottom" half reads 8kish on one side and about 60K on the other.

I tried touching up the connections, seeing if it was a cold solder joint, and I still get the same. I just un-screwed it from the guitar, and measured the "bottom" half off of the little "eyelets" on there, and I'm still getting the same measurements. Interesting. I think I've got another one of these around, I'll have to see.

[j. pierce]

Found another blend pot, (still packaged from stew mac) and am measuring it - now I'm confused as to how this is supposed to work at all -

Measuring it unconnected - turned it to the "halfway detent", from center to one side is around 500K, (well, 480or something) to the other side is around 65 K. So what exactly is going on here? The halves are the same, as well - i.e., the 500K side is on the "left" of both the top and bottom part of the assembly)

So I'm just not sure how this works. I'm not sure how I'd get anything other than what I'm getting.

Also, looking at this diagram, my wiring after the blend pot is a little different. I take the output from the same tab of the blend as they do, but then run to the left tag of the volume pot. Right tag is grounded, and the output from the volume knob runs off the center tag to stop at the right tag on the tone, and then from there right to the output tip. Capacitor on the tone control is from the center tab to ground. Left tab is left open.

Now, those controls after the blend pot work fine, and I can't see why they'd effect anything, but I thought I'd throw that out there - but I didn't know if that would mess anything up - lord knows I've messed things up enough before.

[JoeAArthur]

Found another blend pot, (still packaged from stew mac) and am measuring it - now I'm confused as to how this is supposed to work at all -

Measuring it unconnected - turned it to the "halfway detent", from center to one side is around 500K, (well, 480or something) to the other side is around 65 K. So what exactly is going on here? The halves are the same, as well - i.e., the 500K side is on the "left" of both the top and bottom part of the assembly)

So I'm just not sure how this works. I'm not sure how I'd get anything other than what I'm getting.

With that pot you'll get even less than what you're getting with the other!! That is definitely wrong.

If you hold the pot as it's pictured in the diagram you posted, the top section should measure 500K from the center to the left and ideally zero from the center to the right. The bottom section should measure the exact opposite - ideally zero from the center to the left and 500K from the center to the right.

Your volume and tone wiring sounds fine to me.

(note to self: never buy a blend pot from Stewmac)

[j. pierce]

Hey, thanks for all the help Joe. It's good to know I'm not totally daft - I didn't think that pot made any sense.

It's very possible that I mis-ordered from Stew Mac, I think I may have my invoice still kicking around here, I'll have to check. Maybe I'll toss another one in with my next order and see what happens.

[j. pierce]

An update to this:

Unsure if I may have accidently ordered the wrong thing from Stew Mac, I ordered two new "blend" pots from Stew Mac, a 250K one and a 500K one.

The 250K one behaves as expected (now that Joe has explained what to expect!) - at the center detent, one side measures approx 250K, the other measures basically zero. The other part of the dual pot does the same thing, but with the 250K and zero sides of the pot reversed.

The 500K pot measures the same as the other ones I had ordered from them - at the center detent, it measures around 502K on one side of the pot, and about 76K on the other. The other pot on there measures 433K on one side and about 73K on the other. The "high" and "low" sides are the same on each half, of the dual pot. (Not mirror images as you would expect.)

So I'm still not sure if my original order was my fault of not, but this makes possibly 3 "blend" pots I've ordered from Stew Mac that seem to be standard dual gang 500K audio-taper pots instead. Fortunetly, I've got some pedal builds in the works that can use these, but I'm going to try and contact Stew Mac and see what I can find out about this.