I order audio taper, and they keep sending me linear taper. Or is it me?

[jscomposer]

This is the second 500k blend pot I've gotten. The first was Bournes from allparts, the second was Alpha from stewmac. In both, there's essentially zero change in the tone until you hit the center detent. So it's more like a switch. Both pots say MN500K.

I should add that the pickups are Q-Tuner BS, neck and bridge. Is this a peculiarity of Q-tuners, that they don't blend smoothly?

Or am I actually using audio taper blend pots, when what I really need is a linear taper blend pot?

For reference, the blend pot that came with my bass says B250KX2 (no brand name anywhere), as part of an active Bartolini harness, and it did blend smoothly between 2 Duncan pickups. Figured I'd swap it for a 500K pot for a little more highs.

[line6man]

B denotes a linear taper, unless you are in Europe, where for some bizarre reason, they use B for audio.

[jscomposer]

Yeah, it just occurred to me, "B250KX2" probably means "linear taper, 250K, times 2 (for either side of the detent)!"

So can someone please explain to me why a blend pot should be linear, while a volume or tone pot should be audio? Isn't blending just fancy volume control of two pickups?

Still confused.

[jscomposer]

Ah, wait a sec. I just read that audio taper can be approximated on a linear taper pot by adding a resistor.

So, what kind of resistors do I add, and where? (I'm guessing I'd need 2, one for each side of the blend?)

[sidd_laroy]

wow! the answer is obvious! it's your pickups! look at the name! "Q-Turner BS" ....duuhh! the answer was in the name of the pickups the whole time!

i actually have no idea why you're not getting the results you want, and i have never heard of the pickups you have, but i'm sure they're fantastic. sorry if i offended you in anyway.

[jscomposer]

Tell me about it. Every time I type out Q-Tuner BS, I find myself wishing they'd have come up with a better name.

So uh, anyways...

I think I'm having this problem because the blend pots are linear taper. (I confirmed this with a multimeter.) But I can add resistors to approximate a log taper. I just need to know exactly what kinda resistors, and how to hook 'em up.

[gumtownbassman]

a linear pot's resistance changes in equal proportions from one end to the other.
A Log pot's resistance changes at a rate of x10 or in a logrythmic curve, so one end of it's travel there is a huge change in resistance, and the other end of the travel see's little change. This is because human hearing follows the log scale, and is not linear.
If you look at a graph where one side is resistance (ohms) and the other axis is knob travel, a linear pot will give a straight diagonal line, and a log pot will sart off very flat then suddenly climb at a steep angle.
Same thing said for watts, where 1000 watts is twice as loud as 100 watts, even though it burns 10 times as much power to add 6dB.
Every 6dB increase in level is twice the level.

sorry about the theory lesson, i though it might be useful to put it all into perspective.

the pickup mix has to be a linear pot, or else you end up with all one pickup until almost the end of the knob travel, and won't be centre balanced.
And if you have a linear one for a volume, it will be everything on at number 2, and little change after that.

[jscomposer]

Originally Posted by gumtownbassman

the pickup mix has to be a linear pot, or else you end up with all one pickup until almost the end of the knob travel, and won't be centre balanced.

But that's what I'm getting now. From fully clockwise to just short of center detent, there's virtually no change in tone. Then all of a sudden you hit center detent and BAM, significant change in tone. Continue turning counterclockwise, and just a hair past the center detent you get another significant change in tone, and then virtually no change in tone the rest of the way counterclockwise.

Here's what I got with a multimeter on the 500K blend pot (by Alpha): at the center detent, on the top row of lugs it reads 530K and 0K on lugs 1 and 3, respectively. On the bottom row it reads 70K and 540K on lugs 1 and 3. (So it seems reversed on the second row.) Turned fully clockwise it reads 530K and 0K on lug 1 and 3 on both rows. Turned fully counterclockwise it reads 0K and 530K on lug 1 and 3 on both rows.

That tells me that a blend pot is basically a dual volume pot:

Fully clockwise: bridge pickup 100%, neck pickup 0%.
Center: both pickups 100%
Fully counterclockwise: bridge pickup 0%, neck pickup 100%.

So for example, from fully clockwise to center, the neck pickup should increase in volume from 0% to 100% in a log taper. But I confirmed with the multimeter that the taper is linear. So basically, the neck pickup is off and stays off until you hit the center, where it suddenly shoots to 100%.

[walterw]

yep, that's how they tend to sound.

try this:
get a 250k m/n pot, install it as per normal, but leave all the ground connections off, including the jumper from one ground tab to the other.

(ground the pickups themselves elsewhere, obviously).

this pot will now have zero effect on tone when in the middle (just like a switch), and will only add series resistance to one pickup or the other when turned, "dimming" its volume without loading it to ground.

i've had good luck with this trick, as it no longer loads the pickups with the extra ground path, and seems to pan a little more smoothly.

[walterw]

Originally Posted by gumtownbassman

...if you have a linear one for a volume, it will be everything on at number 2, and little change after that.

nope.

try it.




(it is true for guitar through distorted amps, but not for bass through a clean rig. linear volumes work perfectly even from "0" to "10" on basses.)

[dmusic148]

Originally Posted by jscomposer

For reference, the blend pot that came with my bass says B250KX2 (no brand name anywhere), as part of an active Bartolini harness, and it did blend smoothly between 2 Duncan pickups. Figured I'd swap it for a 500K pot for a little more highs.

I suppose going to a 500k may be goofing up the Bart circuit. I suggest trying the 250k.

[FunkMetalBass]

If you're using a 500k blend and a 250k volume, you aren't fixing anything. The blend is actually wired before the volume in the circuit, so you'd need to bump the volume to 500k as well, otherwise the 250k volume is just cutting off any of the signal that the 500k let through.

[jscomposer]

I ditched the Bartolini harness for all-passive controls. I got a volume, tone, and blend, all 500K. I also threw in a 4-way rotary for choosing series/parallel combos. Everything works fine. I'm just not getting a smooth taper on the blend.

Originally Posted by walterw

yep, that's how they tend to sound.

try this:
get a 250k m/n pot, install it as per normal, but leave all the ground connections off, including the jumper from one ground tab to the other.

(ground the pickups themselves elsewhere, obviously).

this pot will now have zero effect on tone when in the middle (just like a switch), and will only add series resistance to one pickup or the other when turned, "dimming" its volume without loading it to ground.

i've had good luck with this trick, as it no longer loads the pickups with the extra ground path, and seems to pan a little more smoothly.

Interesting. I'mma try adding resistors first. If that don't work, I'll try your suggestion. And if THAT don't work, I got an audio taper blend on the way from guitarpartsdepot. I had the guy on the phone confirm that it's audio--it says "A500K/C500K" on the pot casing.