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Blend Pot Wiring - it's more than meets the ear

Turnaround

Turnaround

Commercial User
May 6, 2004
11,524
24,794
Toronto Canada
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Independent Instrument Technician - Retired
#1
There are two basic ways to wire a blend pot, and a variation to one of them.

First, the conventional way that you will find on most production basses.

upload_2024-1-6_13-12-31.png

Here one pickup is connected to the centre lug of one gang of the pot, and the other pickup is connected to the centre lug of the other gang. The leftmost lug of the upper gang is connected to ground and to the right lug on the lower gang. This type of wiring uses the potentiometer as a variable voltage divider, sending more or less signal to the output and the other part of the division to ground.

The complaint most often expressed about this kind of wiring is that it doesn't take much rotation from the centre detent to throw the balance largely to one pickup. That is to say when you rotate the pot to favor the neck pickup, very little rotation is needed before the bridge pickup is almost eliminated from the audible blend.

To remedy this situation the wiring is changed from a voltage divider to a variable resistor in series with the pickup. So instead of splitting the signal between the output and ground it simply provides variable resistance between the pickup and the output stream.

upload_2024-1-6_13-14-11.png


There is no ground connection in this configuration, and thus no need to connect the black diagonal shown in the first pic. However, you should still ground the case of the pot.

The complaint about this scheme is that you cannot take one pickup out of the circuit entirely - roll the blend to the extreme neck pickup position and there will still be a bit of signal coming from the bridge pickup, and vice versa. For many it's not enough to be concerned about, while others feel the need to be able to completely eliminate one pickup from the signal.

Which brings us to the third scheme - the no-load blend. Our friend Walter has posted about this in another thread, and he will chime in with his solution shortly.

But I should mention another scheme I ran across - the single gang quasi-blend solution. It uses a regular linear pot wired like this:

upload_2024-1-6_13-25-50.png


TB member @sissy kathy commented so well on this configuration that I will just quote here:

"That single pot is using a mid line tap so there is always resistance to each pickup. The output of the pickups is never at 100%.You only ever get a continously variable split between the pickups. that equals 50% of the potential total output of the two pickups; that is 100% of either pickup at the extreme positions but the other pickup is near 0%. It'll make your amp work harder for a given volume."
 
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#2
right, the ungrounded trick "slows down" the sweep and also eliminates the extra loading loss on the signal; otherwise, a 500k volume and a 500k dual blend/balance pot is like having three 500k pots on the signal, each trimming off a little bit of volume and treble.

without that ground connection you can use a lower value blend, like 250k or even 100k, and it won't load down the treble; the lower value gives you even smoother shading between the two pickups. the problem there becomes that with the lower value blend pot the "off" pickup starts to become less "off", it might start influencing the sound more.

to my ear a 250k blend is plenty of series resistance to "dim" the pickup you want shut off; yes you can hear something when you tap on it with a screwdriver but when playing i only hear the tonal character of the "on" pickup.

to fix that tradeoff you can cut the traces of the blend pot such that when rolled all the way over the "off" pickup is disconnected entirely. that will give you the smoother shading of a lower-value blend and 100% pickup switching like a straight up 3-way toggle switch.

there's an entire thread about how to do that trace-cutting trick here (wow, i started that one ten years ago this year!)
 
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#3
as for the types of blend pot to use, i recommend the "M/N" type; they're like home stereo blend/balance pots in that at the center detent they're 100% volume for both sides, only turning one side or the other down when you turn it. one of those with the traces cut will sound exactly like a 3-way switch in the middle and at the extremes, no loss at all, while still allowing for shading in between

the other common type found in basses is "A/C", which leaves a little series resistance in even at the center detent; there's an argument that the resistance "isolates" the two pickups from each other a little and that this is a good thing, making for a smoother sweep at the cost of a little output. this type might actually sound more like the old-school method of running a vintage jazz bass where both volumes are backed off a little, again for the goal of smoother shading between the two pickups at the cost of some output

i'm not big on the single pot idea, that just loses too much signal in the middle setting
 
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#5
sissy kathy said:
Elucidate us; would the single pot idea give you a more consistent volume across the sweep of the pot?
Click to expand...
i really don't think so

a standard M/N blend pot has both pickups at 100% in the center detent and that setting is no louder than the individual pickups by themselves (maybe even slightly quieter due to the inherent loss of parallel coils)

a single pot blend would put significant series resistance across both pickups at the center setting, reducing the output
 
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#8
For those with passive pickups but active electronics, the superior option seems to be running the Invalid Link Removed.

But if running all passive, the ABC probably isn’t the best idea.

One issue with a 250K MN ungrounded blend pot is that a majority of the blending happens right near the center.

I bought several 100K MN alpha pots and managed to find one that measures ~89ohm/89ohm (the lowest resistance and one of the best matches between each of the gangs) and have been getting ready to cut the traces and re-do my Jaguar Bass’s electronics in an attempt to improve the blend curve. (I never ran the pickups solo before because of Buzz issues, but recently ordered some Hum-cancelling Tom Brantley Geddy Lee Jazz pickups and plan to install them soon). Haven’t done the surgery yet though.
 
#9
For active EMGs using a standard, non-solderless blend pot, (MN 25k ohm dual gang), is this the correct way to do it?
Screenshot_20250302_145033_Chrome.jpg


I assume that I would just connect the white wire from each pickup to the center lug and then send the output to the volume pot. Am I missing anything?
 
#10
bass-shy said:
For active EMGs using a standard, non-solderless blend pot, (MN 25k ohm dual gang), is this the correct way to do it? View attachment 7165191

I assume that I would just connect the white wire from each pickup to the center lug and then send the output to the volume pot. Am I missing anything?
Click to expand...

Never mind. I wired it up like the diagram and it works beautifully.

Hope this is helpful to someone in the future.
 
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#11
I have a question

I have an NS Design CR5 that has a 3 way selector for the two magnetic pickups.

Is it possible to wire in a blend pot to the middle position of the 3 way switch?

I was thinking that a series variable resistor (SVR) wired into the middle position of the 3-way switch would be the best of all worlds. The SVR blend knob allows a full range of blending the two pickups, then the outer two positions of the 3-way switch allow for complete on/off of each of the pickups, since a SVR blend pot doesn't allow full 100%on/100%off.

The only thing I don't know is how to go about wiring this up.
 
#12
Electriconically it is possible, though 'adding a blend isn't that straight forward. You would essentially need to rewire everything after the pickups. Right now you should have one out from the selector and each each pickup is turned on or off by the switch, internal to the switch. You don't actually need the three way switch if you have a blend pot as the extreme settings will isolate the appropriate pickup from the circuit.
 
#13
I see. Thanks.

But as @Turnaround said, a series variable resistor wired blend pot doesn't allow total 100%/0% between the two pickups - that each one is always somewhere in the mix.
That's why I thought it would be a good thing to parallel into the middle position of a 3-way switch.

I'm only a novice at electronics and wiring, so I could just be out of my element here
 
#14
Bliff Curton 2 said:
I see. Thanks.

But as @Turnaround said, a series variable resistor wired blend pot doesn't allow total 100%/0% between the two pickups - that each one is always somewhere in the mix.
That's why I thought it would be a good thing to parallel into the middle position of a 3-way switch.

I'm only a novice at electronics and wiring, so I could just be out of my element here
Click to expand...

That little bit still in the mix isn't audible at any volume. The reason there isn't 100% isolation is to prevent a POP when the pickup is actually turned off.
 
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#16
My two cureent pet projects for passive blend currently:

1) using a 50k mn blend pot, with the ‘ground’ lug wired to a 200k/470k resistor to ground instead.. i’ve always found that you only get about 20-50k worth of resistance from noon where are you actually have something of a usable sweep with a subtle gradient before it’s like 90+% whichever pickup .. so instead we maximize the feel of the knob sweep where there’s a blend.. Then you have to decide how you want to deal with the lack of hundred percent solo… most of the time I find that I just don’t need the full grounding of the unfavored pickup, but you can use switches or some other solution.. You can also apply the same thing to a vol/vol setup instead, Use a dual gang for each pick up volume, and use a variation on the no load volume pot I’ve posted in the past (I can link a pic later)

2) use a push pull single gang pot, and only have one pickup controlled by it at a time. So basically you’ll be in say ‘P’ mode, with the option to blend in the J, or ‘J mode’ with the option to blend in the P.. This gives you the full rotation of the pot to dial in the blend you like, making it easier to ‘aim.’ This doesn’t solve the “most of the rotation is useless” problem, but it does make it easier to dial in the sweet spots, qnf actually this has become my orientation for active instruments. To some people it sounds convoluted and confusing, but for the people I have talked into it, everybody seems to really love the mental framework it gives you as a player by being in one pick up “mode” or the other
 
#17
eddododo said:
My two cureent pet projects for passive blend currently:

1) using a 50k mn blend pot, with the ‘ground’ lug wired to a 200k/470k resistor to ground instead.. i’ve always found that you only get about 20-50k worth of resistance from noon where are you actually have something of a usable sweep with a subtle gradient before it’s like 90+% whichever pickup .. so instead we maximize the feel of the knob sweep where there’s a blend.. Then you have to decide how you want to deal with the lack of hundred percent solo… most of the time I find that I just don’t need the full grounding of the unfavored pickup, but you can use switches or some other solution.. You can also apply the same thing to a vol/vol setup instead, Use a dual gang for each pick up volume, and use a variation on the no load volume pot I’ve posted in the past (I can link a pic later)

2) use a push pull single gang pot, and only have one pickup controlled by it at a time. So basically you’ll be in say ‘P’ mode, with the option to blend in the J, or ‘J mode’ with the option to blend in the P.. This gives you the full rotation of the pot to dial in the blend you like, making it easier to ‘aim.’ This doesn’t solve the “most of the rotation is useless” problem, but it does make it easier to dial in the sweet spots, qnf actually this has become my orientation for active instruments. To some people it sounds convoluted and confusing, but for the people I have talked into it, everybody seems to really love the mental framework it gives you as a player by being in one pick up “mode” or the other
Click to expand...
I like these options, particularly the first. For my own basses I found that I was always using both pickups 100% or each soloed at 100%. So I replaced the blend pot with a 3-position rotary switch.
 
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#20
Rolling Thunder said:
So I came up with this wiring configuration and was wondering if anyone sees any obvious flaws. The red lines are jumper wires. View attachment 7354660
Click to expand...
So the flaw with that is exactly the same flaw that causes us to wire jazz basses how we do (with a ‘backwards’ volume pot wiring)

With this set up, you do get more or less a normal volume for the pick up you are trying to mute, but the pick up that you are trying to solo is being loaded to ground, as it is on the same note as the output of the pick up being muted) it will get darker and quieter until it is fully muted, though it will be a different taper and get quieter more slowly than the intended muted pickup
 

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