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Old 4th July 2007, 04:18 PM   #1
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Unhappy HELP with new jazz bass blend pot

Hi, I just adquired a new Di Marzio set of PUP's for my Fender jazz bass, I also replaced the blend pot, but instead of blending the signals of the PUP's it works more like a volume control, in the center position there is no signal, and if you start to turn it either side for example clockwise the neck pickup's signal starts to be heard and viceversa.

What is causing this are the pickups out of phase?
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Old 4th July 2007, 04:43 PM   #2
Minion is offline Minion  Canada
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Location: Cowican Bay , vancouver island
Are you sure you replaced the Pot with the Right Value and Taper as Before and you conected it correctly......

I assume that this Pot would be a Linear pot and not a Log Pot and to create the Blend function each pickup would be connected to each side of the Pot with the output coming out of the wiper of the Pot, so with the Pot at 12:00 you would get an even blend of each Pickup, and when you turn it in either direction it would make one pickup louder and the other quieter....

Is this how you have it wired up???


Cheers


PS: it shouldn"t be out of Phaze if you have the hot wires of each pickup going to the Blend pot and both have a Common Ground...
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Old 4th July 2007, 06:19 PM   #3
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Quote:
Originally posted by Minion
Are you sure you replaced the Pot with the Right Value and Taper as Before and you conected it correctly......
Yes I replaced it with the recommended pot for this pickups its a 500k audio taper pot, I connected it like in the attached pic (from stewmac.com).

Quote:
Originally posted by Minion

PS: it shouldn"t be out of Phaze if you have the hot wires of each pickup going to the Blend pot and both have a Common Ground...
Yes they share the same ground.
Attached Images
File Type: jpg stewmacblendpot.jpg (6.3 KB, 135 views)
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Old 4th July 2007, 07:50 PM   #4
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I think that is has something to do with internal pot construction because when I measure resistance to ground from the center position it measures 0, this is true for both sections in the pot.
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Old 4th July 2007, 09:43 PM   #5
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Yes, it is definitely that... Ive removed the pot and measured resistance between the center lug and each other, at center detent position.

From center lug to left lug my tester measures 500k and from center lug to right lug it measures 0. My old pot measures 125k on each side.


What kind of pot is this? in which application one may want a pot having cero resistance at its center position?
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Old 5th July 2007, 12:15 AM   #6
Minion is offline Minion  Canada
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I have personally never seen a Blend Pot like that...a 250K Linear Pot would measure 125k on each side at the 12: 0 Clock position.....

Most Blend Pots I have used were Linear Taper pots with each side going to each Pickup and the output being the wiper, so when the Pot is at 12: oClock each side sees equal resistance so each Pickup passes the same signal through the Pot but when you turn the pot the resistance increases on one side but decreases on the other side which which increases the Volume of one pickup and decreases the volume of the other pickup......

Try a Linear Pot and connect the hot wires from each Pickup to each side and the Wiper to output and the blend function should work.....

The pot in your drawing looks like a Dual Ganged Linear Pot that is wired in series so each gang of the Pot controlls the signal for each Pickup and they are mixed together by being wired in series and I believe the one side is wired in reverse or is a Reverse taper.... It seems that doing what I explained above does the same thing but with a less expensive pot and less wireing.....


Cheers
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Old 6th July 2007, 04:00 AM   #7
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Stewmac makes mention that it is an audio taper pot, not a linear pot and that image is the recommended wiring for that pot,

I bought it from Allparts and the description they give is the same blend/balance audio taper pot.... I will have to buy another one to see what is wrong the pot or me.
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Old 7th July 2007, 04:39 PM   #8
Artie is offline Artie  United States
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You have the output and ground connections on the pot reversed. Switch them and it should work as normal.

In other words, when in the center, you have both sides shorted to ground, rather than shorted to hot.

Artie
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Old 7th July 2007, 04:47 PM   #9
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Can you explain me how this pot works?

Ive talked with the guy that sells them and he told me that the pot is ok.
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Old 7th July 2007, 05:49 PM   #10
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Thanks guys I analized how it works, it is different from other balance pots, the reason fo having 0 resistance from center to one lug at the center position is that both signals are at 100%.
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