• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Jazz Bass Blend Pot Wiring - HELP!

stingray69

stingray69

Talkbass Legit
Aug 11, 2004
5,498
7,470
St Louis Area
#1
I want to add a blend pot to my '08 American Standard Jazz bass this evening. I'm pretty handy with an iron & solder, replacing pots, etc., just never added a blend pot before. My problem is I've found a couple of inconsistencies with some schematics I found on TB regarding how to wire this up. Other than the jackplate in the Rothstein image being bass-ackwards, the blend pot seems to be missing a cross-connection from the upper set of lugs to the lower set of lugs as shown in image 2. Which of these 2 schematics is accurate? I'm leaning towards image 2, but I'd appreciate any assistance to point me in the right direction.

Rothstein Image:
JazzBasswithBlendPotMod.gif


Image 2:
jazz_bass_blendwiringdiagramfromTal.jpg
 
#6
One caveat. Make sure you have the correct type of blend or pan pot. I understand that some will produce only 50% volume at the center detent. Not sure what type or value of these though.

I once had a "blend, volume, tone" on my Jazz and it worked fine. Didn't suffer any perceptible volume loss at center at all. As a matter of fact, I'm thinking of going back with this configuration, as it's so convienient to have a single master volume control.
 
#7
lbwdog said:
One caveat. Make sure you have the correct type of blend or pan pot. I understand that some will produce only 50% volume at the center detent. Not sure what type or value of these though.

I once had a "blend, volume, tone" on my Jazz and it worked fine. Didn't suffer any perceptible volume loss at center at all. As a matter of fact, I'm thinking of going back with this configuration, as it's so convienient to have a single master volume control.
Click to expand...

I agree - I know it's all just personal taste, but I one of those people who just prefer to be able to shut down things in a hurry from a single volume knob. I'll also be sure to record a quick little something both before & after for A/B purposes to make sure I'm not losing any volume or anything else in the process. The blend knob I went with was this one after pouring through many TB threads: http://www.allparts.com/store/electronics-500k-pots-ep-0386-000,Product.asp
 
#9
stingray69 said:
I noticed that too, as I was sitting here wondering how much grief it was going to be trying to solder those tiny jumpers. I'll give the Rothstein schematic the first crack at it. Thank You very much for your help! :cool:
Click to expand...

I soldered numerous little jumper wires onto a 6-pole, 4-position rotary switch for my 'VI by:

- snipping thin, solid wire into appropriate lengths,

- then using needle-nose pliers to crimp the ends of the wires through the holes in the switch's lugs,

- and then soldering the connections.​

Please note: if the wire you are using to make jumpers is coated with plastic insulation, then remove the insulation before performing the above steps.

Soldering short lengths of plastic-coated wire will cause the plastic to melt and make a mess.
 
#10
Electrically they're both the same, and BTW, neither one is a schematic. They're both wiring diagrams, the equivalent of tab...

Anyway, there are two common problems wiring blend pots, at least based on the almost weekly thread about them. First, make sure you wire the pickups in phase with each other. Otherwise you'll hear a distinct loss of volume and low end in the center position. Second, check your pot with a VOM to determine which side of the pot is the resistance side.

The way a blend pot works is that there's only resistance in one gang from the center to fully CCW. From center to CW, there's no change. The other gang is a mirror immage of that. So, if it's hooked up correctly, as you sweep from fully CW to center you're turing UP one PUP without affecting the other. At center both PUPs are on full. As you continue to sweep from center you're turning down the other PUP without affecting the first one.

Here's a schematic that shows how you need the pot to be wired.

3284625829_ba5bc22451.jpg


jte
 
#11
So I followed the Rothstein diagram but I get no sound!

My soldering is a bit messy but still I'm surprised there is no sound, as I doubled-checked the wiring. I wasn't sure which pickup wire was hot or ground so i tried both but still nothing. The only thing I can think that might be a problem is the "0.47UF" thing. Mine is kind of small and green. (see photo) Do I need to change this component to complete this modification? Also I only bought the balance pot (with the two tiers of wire holders), do I need to change the rest of them?

I've got 2007 CIJ Jazz bass with Seymour Duncan Antiquities and it worked fine before.

Any ideas?
 

Attachments

  • pup photo.jpg
    pup photo.jpg
    45.5 KB · Views: 1,083
#13
One important thing about bland pots, you have to wire them the right way. This varies from brand to brand.

What I mean is that you can't just take the pot and follow one of the diagrams. You will note that on some the lug that goes to ground is on the other side.

You need to get a meter and then put the pot at the center detent. Now check the center lug to one of the outside lugs, and then the other. You should see a very low resistance to one side, and the other should be almost the full value of the pot.

The low resistance side goes to the output, and the high side goes to ground. The top and bottom decks will be opposite. This is very important, because if you wire up the low resistance side to ground, it will dull your tone and reduce the signal level.

Currently my favorite blend pots are made by Bourns.

This is what you should see on an Ohm meter with a blend pot. These were the measurements for a 500K Bourns pot.
blend_pot.jpg
 
  • Like
Reactions: Sundiegojc
#14
Thanks for the responses. I ended up confusing upper and lower lugs but the strangest thing happened when I switched the wires: the tone and volume knobs worked fine, but the blend pot from 1-5 was full blend of both picups then from 6-10 was completely silent!!! Really strange.

This is what you should see on an Ohm meter with a blend pot. These were the measurements for a 500K Bourns pot.
blend_pot.jpg
Click to expand...

Your image is a little different than the Rothstein: from the higher resistance end of the lugs you have wires coming from both sides. The Rothstein only has one coming from the lower lug. Am I right in assuming that there is a wire going diagonally from the lower right lug to the upper left lug?

In the end I took off all the wires and cleaned up the extra solder. I'll try again when I have some more time.

Kind of frustrating after spending hours working on it to get nothing. but I'm a newbie at this sort of thing so I guess it's a learning experience.
 
#16
might as well toss in a mention of the "ungrounded blend" or "unloaded blend" trick here;

on SGD dave's picture of the bourns pot, see that connection from upper left to lower right, and the "ground" symbol coming off of it? leave it off.

this will eliminate the extra loading from the two pots in the blend control, leaving only series resistance on one pickup or the other when you turn it off of center. in the middle, it will have no loss at all, just like a selector switch.

it'll also blend a little more gradually, giving you more control of the "sweet spot" between the two pickups.

(i like 250k M/N pan pots for this, as they blend more smoothly, and with no grounds still don't load the signal any more than 500ks do.)
 
  • Like
Reactions: davidchampoux
#17
walterw said:
might as well toss in a mention of the "ungrounded blend" or "unloaded blend" trick here;

on SGD dave's picture of the bourns pot, see that connection from upper left to lower right, and the "ground" symbol coming off of it? leave it off.
Click to expand...


Okay. I've got the 250K bourns blend pot. The resistance levels check out good on the meter. I will leave the upper left to the lower right off. Do I still leave the lower right with the "ground" symbol connected to ground?

...or do I leave the blend pot totally ungrounded?

Thanks, Tom
 
#18
As Walter says, leave ground off. Also, check to ensure the hot from blend goes on the outside lug of vol and middle lug of vol goes to tone/output. The first time I did a blend, I had it backward and had strange results.

I had to remove my blends due to faulty pots, they must have become damaged when I pressed the knobs on: the bridge gang became intermittent after a short while, jiggling the knob would get it full on again but you know how good that is.... Waiting for my Bourns blends to arrive, I hope they don't suffer the same fate.
 
#19
Thanks...no ground to the blend pot...got it. I wasn't sure if it was just the upper left to the lower right or the entire connection to the back of the volume pot or tone pot...
depending which diagram is used.
 
#20
Does it matter that the Rothstein and Basslines diagrams handle the input to the tone pot differently?

On the Rothstein, the input to tone pot is the INPUT to the master volume, whereas on the Basslines, the input to the tone pot is the OUTPUT of the master volume.

Naturally if you run the volume pot wide open they should act the same, but wouldn't this difference show up if you run the volume turned down halfway or more? Seems to me that using the input to the volume pot, like Rothstein means the tone control's influence would be a lot greater when you turn down the volume...just guessing.
 

Latest posts

Top Bottom
Back