Blend pot : how and why?

[terb]

I wanted to create a post dedicated to the blend pots.

What is a blend pot ?

A blend pot is used to mix two audio sources into one. On a bass with two pickups (which are two signals = two audio sources), there are often one volume pot per pickup (think Jazz Bass) or a 3-way switch (very “guitar-style”, think MIM Mustang Bass for example). A blend pot is a third solution that allows to mix the pickups with more progressivity than with a basic switch, while keeping a master volume pot.

The blend pot curves : MN pots

A blend pot looks like a “double pot” and a common confusion would be to think it’s like a stereo volume pot. There is a major difference : a blend pot has a very special curve called a MN taper, which looks like this :

This diagram shows that, when the pot is centered, both signals are at 100% and not less (like 50% on a linear stereo pot), exactly like the center position of a 3-way switch. When you turn the pot, one signal decreases while the other one is still at 100%. There is often a detent in the center to let you know that both signals are fully open.

How a blend pot is wired into the electronics of a bass

A blend pot physically looks like two pots stacked together, so there is two distinct tracks. We need to wire them together to make the output be a mix between the two input signals. It is wired like this :

“Source A” and “Source B” are obviously the signal coming from the two pickups. the Output goes to the master volume, exactly like the output of a 3-way switch. so, a blend pot is almost a straighforward replacement to a 3-way switch as it takes the same inputs, same ouput, and does not require any other component.

Here is how the wired pot looks on my Ibanez AGBV200A :

Overall a blend pot can be a cheap and easy way to add intermediate tones on a bass, compared to a 3-way switch. If you have a round-hole 3-way switch (like on a MIM Mustang Bass) it’s a non-destructive mod and it’s totally reversible. Also it can easily look pretty clean and neat :

[John_E]

this is great. can you find an as simple explanation of how the two vol/vol pots work across a similar graph etc? You have a great way of explaining this.

[terb]

it works exactly the same, except than each curve (M and N) are separated : one distinct volume pot for each pickup. but electronically, it’s the same, which means that each pickup level is controlled by a variable resistor, and both are wired together to a common output.

[Wombat-metal]

So what does an active blend pot throw into the mix? My EMG EQ came with an active blend/insertion pot but I’m not exactly sure what makes it different.

Great post

[terb]

it’s the same on a functional perspective, but a blend pot is often way more progressive and linear in an active circuitry. that’s because the active electronics allows to manage the relative impedance of the different elements (pickups, pots, other resistive components) so they interact way less together.

[Mac]

Great post @terb .
Thank you for taking the time to do this

[ebxx]

My Ibanez bass wiring looks a bit more complicated than your Ibanez bass does. I counted 6 different tiny circuit boards crammed in the small electronics cavity.

https://drive.google.com/file/d/1BD-7QFgaIa_ApyJ0-KY1j-bHpaJnr3TG/view?usp=sharing

[terb]

that’s certainly an active bass

[howard]

A bit blurry but it just looks like a few PCB-mounted pots to me. Plus the preamp of course

[terb]

Playing with by modded Ibanez, I have another idea derived from the blend pot.

The thing is that, on a 2-pickups bass, I never use the bridge pickup alone. it’s even more true with those Ibanez pickups (that I also have on my other Ibanez bass : the Jetking JTKB200 - I’m pretty sure those are the same pickups). On both of those two basses I can use the neck pickup alone, or the neck pickup at 100% blended with the bridge pickup at a variable level. but I actually never lower the neck pickup, it’s always fully open.

So my idea is to replace the blend knob with a volume knob only for the bridge pickup. The neck pickup would always be blended at 100%, so it would be a volume pot that would act like the “bridge pickup part” of the current MN blend pot. So the controls would be :

• Master volume (stock)
• Master tone (stock)
• bridge pickup mix (instead of the 3-way switch which I replaced by the blend pot)

this would be a very easy mod : just one pot to replace by a different one. (I’m talking only about the archtop Ibanez here, not the Jet King which is wired Vol/Vol/Tone like a Jazz Bass, which is fine for me in a studio context)

'might try this next week, I’ll let you know.

[sshoihet]

@terb

What is a blend pot ?

and here i thought it was like when you smoke Granddaddy Purple and Sour Diesel together

[howard]

@terb

The thing is that, on a 2-pickups bass, I never use the bridge pickup alone. it’s even more true with those Ibanez pickups

Yeah same here. It’s too thin, and especially on a bright bass like an Ibanez it’s going to lose a lot of body by going fully to the bridge. I’m more likely to go full neck.

[terb]

yeah and the blend with the bridge pickup is really relative to the mix I’m working on at a given time. more than searching for a very different tone, it helps manage with the dynamic and the spectrum width. I’m not searching a lot of various tones ouf of a bass, I’m more choosing a bass for its character and then using the pickups to hopefully find a right place into a mix.

[Wombat-metal]

@howard

Yeah same here. It’s too thin, and especially on a bright bass like an Ibanez it’s going to lose a lot of body by going fully to the bridge. I’m more likely to go full neck.

I think it depends on the pickup. On my Surveyor 400 with the Jay Wray in MM mode, the bridge pickup by itself sounds funky. I could play it like that, Play that Funky Music White Boy vibes.

When I get to 70s funk, this is the beast for it.

[terb]

yeah it depends, and obviously a MM-style bridge pickup works alone. I was not saying that like an universal rule

[John_E]

@Wombat-metal

I think it depends on the pickup. On my Surveyor 400 with the Jay Wray in MM mode, the bridge pickup by itself sounds funky. I could play it like that, Play that Funky Music White Boy vibes.

Agree. The Lakland “dual J” in the bridge position gives it a lot of great tones. Maybe that’s the fix.

[howard]

Hmm. This is tempting. The 3-way switch on my Cort is junky junk.

[howard]

@terb I am guessing you would want a 500k or 1M MN pot for this to avoid tone suck? How did this work out for you?

I just took a look and there’s room to do it in my Cort. It’s already got a decent looking 500k linear volume pot; the tone pot is a push/pull I’d probably leave in place too, looks and works fine. The only junky thing is the 3-way, and it looks like there’s room around it.

The Cort wiring job actually isn’t half bad, definitely nicer than my Warwicks were. 3-way toggle is at the top.

[howard]

Another option would be to convert to dual volume/master tone I guess too.

Edit: meh, just ordered a 500k MN. It’s 0 ohms at the center which is what I want anyway usually, so should be no tonal issues there at least

This seems like a really nice mod.

[terb]

it’s a bit different on a guitar and on a bass : adding resistors, which means reducing the resistance that effectively loads the pickups, tends to make them sound darker. maybe a counterintuitive point : the more powerful the pickup is (more wiring, more DC resistance) the more it is sensitive to the resistive load. (that’s because when you get more voltage output from more wiring, you also get less current output)

what’s different on a bass and on a guitar is that, if it sounds a bit darker, it’s rarely a problem on a bass but it can be on a guitar.

I think that a 500k MN should be fine, but if it sounds too dark for your tastes you could consider changing the volume pot for a 1M one.

on my Ibanez I think I will replace the blend pot for a volume pot dedicated to the bridge pickup, and leave the neck pickup always at full volume. I don’t see any interest in lowering the neck pickup so it’s somewhat more logical to have it always at full volume. So I would have : master volume, bridge pickup volume, master tone. Obviously this kind of wiring is totally irrelevant on a guitar.