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Jazz Blend Pot -Center Detent Volume Drop

Ampig

Ampig

Feb 9, 2000
1,261
351
Manteo, North Carolina
#1
My new PJ bass project has an excessive volume drop on the blend pot center detent. I've seen this topic discussed here may times and one quick fix suggestion that I see over and over is reversing polarity on the pickups.

What does that mean exactly? Reversing the ground and hot on just one of the pickups?
 
#2
When you say volume drop, does the tone get quieter or do you also lose a lot of low end?

If you are loosing low end, and you would know it, I mean like all the low end, then the pickups are out of phase, and that's when you want to change the polarity.

But you do lose some volume with some blend pots at the center detent.

One important thing to look for is that you wired the blend pot the right way. It matters which lug is ground, because when measured from the wiper (center lug) you will see a lot of resistance to one outside lug, and very little at the other. For a 250K blend, you might see 240K from the center to one of the outside lugs, and 10K to the other side. You want the lug with the most resistance to go to ground. The other side is hot. The other deck of the pot will be reversed.

If you wire the pot up the wrong way you get a drop off in the middle.

Here's the correct way to wire them up:

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Also, some blend pots just don't work well. I like the M/N taper pots sold at Allparts and GuitarJonesUSA.

If it's a polarity issue, just swap the hot and ground wired on one of the pickups.
 
#9
I spent about 3 days soldering the heck out of the electronic department of my bass before I found the solution to the "volume drop in middle position with blend pot". The sound was silent and muddy. After a lot of attempts and discussions, I simply tried rewiring the lug connections "randomly" to see what happens and found out that the diagram I was using was wrong and mirrored in both axes: top was down and left was right.

Wrong (for my bass and wiring):
Link Removed

Correct (for my bass and wiring):
Invalid Link Removed

If you have the pot installed in the control plate and have the control plate with knobs showing down so you can solder, here's what you have to be careful about.

HOT are the centre lugs (bridge down/closer to control plate)
OUT is left upper and right lower lug
GROUND is right upper and left lower lug
as shown on the "correct" diagram in link above.

I hope this saves somebody at least a bit of time and desparation ;)

Karol
 
#10
That all depends on which direction the taper is set up. That might not work for some brands of pots.

If you have access to a meter, measure from the center wiper lug on one deck of the pot, to either outside lug. The lug with the higher resistance goes to ground.

The other deck will be in reverse.

So for your brand of pot, it worked in that direction.

Some work this way:

3764_1.gif


This is the pot Stew-Mac carries. You can see it's backwards from the diagram that works for your pot. The pot Allparts carries is wired the same way.
 
#11
My pot is from a german manufacturer called Göldo, they are part of the Duesenberg Guitars company. If you want to buy a pot here in Germany, you most likely run into their products. They also make switches and all kinds of electronic for guitars.

So obviously the wiring of balance pots is different depending on vendor.
 

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