Blend pot tapers

[dj5]

I expect a lot of you already know this, but if you don't-
I always thought the volume drop when the blend pot was centered was due to pick-up loading, but I recently found that some blend pots only go up to 75% vvolume on each side in the centre position. I checked mine, and sure enough it was of this type.
I changed it for the other type, and now I get almost equal voumes whether the blend is centred or at either extreme.
The older 75% type are (usually) labelled C A, or C 500K A 500K etc, and the 100% types are labelled MN.
Well worth it, and it does affect the tone quite substantially in the cenre position.

 

[DLM]

The older 75% type are (usually) labelled C A, or C 500K A 500K etc, and the 100% types are labelled MN.
Well worth it, and it does affect the tone quite substantially in the cenre position.

My tech just told me yesterday I have an AC blend pot and he would suggest going to an MN pot for the very reasons you state above...no dip in volume when both pickups are equally blended. However, you mentioned it affects "tone quite substantially." Is that true or is it just a volume difference? If it does affect tone, in what way?

 

[BassLife77]

I have an MN type blend pot and it works great. the key is don't connect any of the lugs to ground. when you connect to ground its like a tone suck vacuum

 

[walterw]

I have an MN type blend pot and it works great. the key is don't connect any of the lugs to ground. when you connect to ground its like a tone suck vacuum

hey, that's my trick!

by leaving off the grounds, the blend pot does nothing at all in the middle (both pickups are full on with no extra load to ground).

when you turn it, you just add series resistance to one pickup, "dimming" it without affecting the other one.

i've posted this idea a few times waiting for someone to share previous experience, or to pick up on it and try it.

do you find that the sweep is improved a little, as the sound doesn't jump to all one pickup or the other quite as quickly?

 

[SGD Lutherie]

A/C is audio, reverse audio taper. M/N is a much better taper for blend pots. At the center detent you have almost the full 500K on one side and almost zero on the other. Make sure you wire it up the right way! The higher resistance side goes to ground, or even better, leave the ground disconnect as Walter suggests. The Bourns blend pots have a nice taper.

 

[walterw]

i've found the 250k m/n works great for the "unloaded blend pot"; no ground still equals no tone loss, and the sweep is a bit more gradual between pickups.

+1 to the bourns that allparts currently offers. nicely made, and read pretty much zero ohms in the middle.

 

[johnk_10]

on one of my jazz basses, with duncan sjb-1's, i tried the bourns and the other 'MN' one from allparts (and both 250K and 500K versions of both brands) and tried all of them grounded and ungrounded. leaving the ground off does dim the pickup, but it is still slightly on (if you tap the magnets with a screw driver you can still hear it), and if you tap on it when it in the center detent and then roll it to full on you can hear the pickup get louder, so i ditched the blend idea on that bass and went with a rotary three way switch, which i think sounds ALOT better. the taper on them was okay, but really most effective blending near the center.

on my other EMG JV equipped jazz bass, i have a TBC and a blend control. most likely, because they're active, the blend range is perfect throught the sweep of the balance pot, and the pickups don't seem to load down at all in the middle since they go from the blend to the TBC and then the master volume to the output jack.

 

[ZolkoW]

on my other EMG JV equipped jazz bass, i have a TBC and a blend control. most likely, because they're active, the blend range is perfect throught the sweep of the balance pot, and the pickups don't seem to load down at all in the middle since they go from the blend to the TBC and then the master volume to the output jack.

+1
I didn't find a passive way to make a good balance pot, yet.
maybe I didn't try everything, but active seems to be the only perfect method :-/

 

[johnk_10]

i just found and ordered some actual Fender 250K blend pots which are supposed to be the best ones for passive instruments. from what i've heard, in the center detent position, they are 'true on' with no resistance. all of my current 250K's measure at least 30-35ohms in the center position and affect the tone of the pickups. i'll post the results after i try them.

 

[blastjv]

Johnk,

What 3-way rotary did you use? I'm thinking that's the way I might like to go.

Thanks,

-John

 

[johnk_10]

here's a pic of it. it's a 4 pole, 3 position, but you only use two of the poles:

Fry's has 'em: [Invalid or Expired Link Removed]

 

[DLM]

So then, why would anyone want to use AC pots if the MNs are so much "better?"

Are there situations where an AC pot would be preferred?

 

[walterw]

on one of my jazz basses, with duncan sjb-1's, i tried the bourns and the other 'MN' one from allparts (and both 250K and 500K versions of both brands) and tried all of them grounded and ungrounded. leaving the ground off does dim the pickup, but it is still slightly on (if you tap the magnets with a screw driver you can still hear it), and if you tap on it when it in the center detent and then roll it to full on you can hear the pickup get louder, so i ditched the blend idea on that bass and went with a rotary three way switch, which i think sounds ALOT better. the taper on them was okay, but really most effective blending near the center.

very cool that you've actually tried all the variations.

yes, you will hear a little bleed-through when you tap on the "off" pickup with the unloaded blend pot. i don't hear it when playing, though.

also, with the switch you will still hear the pickup get louder when tapping on it as you switch away from the middle setting. that's not loss from the pot (if it's a good one with only a few dozen ohms resistance in the middle), but just the difference from the other pickup loading down the first one when they're in parallel.

i wired up a jazz for a guy years ago who wanted the rotary; i spec'ed a 5-way rotary, wired with series resistors to give:

1 neck
2 both favoring the neck
3 both full-on
4 both favoring the bridge
5 bridge

but he only wanted the "blended" variations, so i used a three-way rotary with just the middle settings.

it worked pretty well, except i noticed that different inputs would load the pickups differently, so the "shaded" settings weren't always the same from amp to amp.

i since figured out that the unloaded blend accomplished the exact same thing electronically but allowed for adjusting the "shading".

 

[johnk_10]

also, with the switch you will still hear the pickup get louder when tapping on it as you switch away from the middle setting. that's not loss from the pot (if it's a good one with only a few dozen ohms resistance in the middle), but just the difference from the other pickup loading down the first one when they're in parallel.

when i use a screwdriver to tap on the magnets with the switch set to both on, or just the neck or just the bridge pickup, i do not hear any change in volume in any position of the three way switch.

i'm looking forward to trying the genuine fender 'pan' pots though. if they can blend in the same manner as my active EMG's, i'll be thrilled, but right now i'm a little skeptical if they're going to be any better than the Bourns or MN's.
.....and if that's the case, i'll just stick with using a 3-way switch.

 

[johnk_10]

okay, i received two of the genuine Fender 250K 'pan' pots (blend controls) on saturday. first, what's really cool about them is that they have solid 1/4" shafts and use 3/8" holes (and nuts). i tested both of them with my fluke meter. the part # 0056162000, measured only 2.1 ohms in the center position for each pot. so each pickup is about as close to full volume in the center detent position, which is way better than the previous stacked 250K Bourns or Alps MN pots that i've tried that measured about 70 ohms. i installed it in the bass. the blend control's taper is pretty good too, but most of the blending going on near the detent.

the other Fender 'pan' pot, part # 0049441000 measures 70 ohms on one of the pots and 2.1 ohms on the other in the center detent position. i haven't tried that one yet.

while i'm actually happy with the result of the Fender 'blend ' control, on this particular jazz bass, the simplicity of the 3-way switch just seems to suit me more for live gigs, so i'm sticking with it in this one.

 

[SGD Lutherie]

okay, i received two of the genuine Fender 250K 'pan' pots (blend controls) on saturday. first, what's really cool about them is that they have solid 1/4" shafts and use 3/8" holes (and nuts). i tested both of them with my fluke meter. the part # 0056162000, measured only 2.1 ohms in the center position for each pot. so each pickup is about as close to full volume in the center detent position, which is way better than the previous stacked 250K Bourns or Alps MN pots that i've tried that measured about 70 ohms. i installed it in the bass. the blend control's taper is pretty good too, but most of the blending going on near the detent.

The 500K Bourns blends I use read 2.9 Ohms in the center, they also have a 1/4" shaft and use a 3/8" hole. I like them much better than the MN taper pots I have used.

Since Fender doesn't make pots, it's a good chance those are Bourns. They used to use Alps.

A 500K blend would have helped from having everything crowded near the detent.

 

[johnk_10]

actually the fenders are alpha pots.

my Bourns must be different pots than your's. they have smaller shafts and don't use a 3/8" nut. they also didn't meaure 2.9 ohms at center (the 250K ones measured about 32 ohms and the 500K ones measure around 70 ohms). my 500K pot's taper was actually focused more at the center than my 250K ones. all of my tests were done with seymour dunan sjb-1 pickups.

 

[BassLife77]

hey, that's my trick!

by leaving off the grounds, the blend pot does nothing at all in the middle (both pickups are full on with no extra load to ground).

when you turn it, you just add series resistance to one pickup, "dimming" it without affecting the other one.

i've posted this idea a few times waiting for someone to share previous experience, or to pick up on it and try it.

do you find that the sweep is improved a little, as the sound doesn't jump to all one pickup or the other quite as quickly?

I mainly use 5 positions - far left, mid left, center, mid right, far right. to my ears I don't hear any leakage in the far positions. since there is no ground connection the signal is very bright but the EQ takes care of that. I'm reading 12 Ohms between the center lugs. I bought the MN blend pot here http://www.gpdusa.com/500K_Pots-500K_Blend_Control_LinearTaper_1.html since it's a cheap pot the specs of each pot might be different so YMMV.

 

[walterw]

my 500K pot's taper was actually focused more at the center than my 250K ones. all of my tests were done with seymour dunan sjb-1 pickups.

my impression as well, especially when "unloaded". it only makes sense, as the lower resistance pot would create, wait for it, lower resistance at a given setting, meaning that it would dim the pickup a little less.

the trade-off then becomes the residual signal of the "off" pickup is increased due to the lower series resistance blocking it. i don't hear it when playing with a 250k blend, but i wonder how a say, 100kΩ m/n pot ran "unloaded" would do? i'd expect smoother shading, but maybe not a totally single pickup sound when thrown all the way over to one side. (i've never found a 100kΩ m/n pot to try it.)

hmm, how about customizing a "no-load" blend pot? a popular trick on guitars is to modify a tone pot by cutting the end of the carbon trace with an x-acto saw, so that when turned up to "10", it disconnects entirely.

a blend pot could be modded this way, so that when turned all the way over, the max resistance side actually opens entirely. that way, a much lower resistance version could be wired "unloaded" for smooth panning and no loss, but still give 100% single pickup operation (like a switch) when turned all the way.

 

[blastjv]

Yeah, I'm really thinking a rotary switch is the way to go for me. While in theory I prefer the idea of being able to dial in subtle shades of each pickup, in practice I really only ever USE both pickups full on about 95% of the time and the bridge pickup solo'd the other 5%.

-John