Blend Pot Value

[magillver]

Good morning! I'm thinking about replacing the 3-way switch in my Epiphone Dot with a blend pot, to smoothly blend between the 2 pups. I'm planning to use a simple linear pot, with the bridge on one of the outer lugs, the neck on the other outer lug, and the output to the jack from the center lug. I've used this method before on a slightly different application, and it worked quite well. My question is, is there a rule of thumb for what value pot I should use? The guitar is currently set up with 500k pots across the board, though I'm thinking of dropping the volume pots down to 300k, just to darken it a bit. Any thoughts?

 

[freefrog]

I'm planning to use a simple linear pot, with the bridge on one of the outer lugs, the neck on the other outer lug, and the output to the jack from the center lug.

The problem is that in center position, you'd have half of the pot resistance between each pickup and output, giving a lowered volume from both...


Not to mention that a resistive link continuously present between pickups would alter how they work even when supposedly selected alone and full up...

That's why dedicated blender controls include two stacked pots: https://www.stewmac.com/video-and-i...-and-electronics-and-wiring/blend-pot-wiring/​

[EDIT - To be clearer, stacked pots avoid the resistive track of a single pot to behave as a link between pickups, but the question of output level in center position remains: honestly, I don't remember what is the taper of blender pots like those evoked above... I'll try to refresh my memories about that.]

IMHO and IME, the best "blending" technique is to use each volume control when both pickups are selected. That's what Gibson guitars with 4 pots have been designed for.

But 'nuff said: you're not forced to take this advice in account. Do what you want and be happy.

 

[magillver]

Thanks for chiming in so quickly, Freefrog! I'm mostly experimenting on this one. I've used the traditional stacked blend pot, but the M-N pots just drop off so quickly that there's virtually no blend to be had. What about a stacked linear pot, wired with the standard blend pot wiring? I know that is still have the level dip in the center position, but would that help resolve the resistive link? I can't picture the resistive relationship between the 2 pots, if they were wired up that way...

 

[freefrog]

Well, I must have replied a bit too fast since I realize now my first answer was not as clear as wanted.

I'll do my best to reply to your 2d post but I lack of time for that right now: I'll be back ASAP, unless one of our fellow members solves your question in the meantime. ;-)

 

[Artie]

To me, the perfect blend pot would be 1M. But since those are almost impossible to find, 500k is the next best choice. The idea, as freefrog explained, is to minimize, or tailor, the load to the pup. Experimentation is your friend.

 

[beaubrummels]

I've used 500k concentric blenders. They are 500k on each side and no load in the center. There is no track when the wiper goes to the opposite side, so you aren't accumulating resistance, you are basically turning the other pickup down while leaving one full on.

 

[freefrog]

beau', thx for sharing. I understand why you talk about a "no-load" functionment if each pot of a blender adds zero resistance from 5 to 10 or from 5 to 0. Now it also means than from each half of its curve, each pot creates a continuous load of 500k to ground, which is not "no-load" in the strict meaning of the word.

Anyway and to reply to my own question about the taper of Stew Mac blenders: Phoestenix (well known for his online library of guitar wiring schematics) says on TDPRI that "The tapers shouldn't affect the center detent position - only the off-center positions. The Stew-Mac panning blend pot has both pots at max in the center position" [which is the same thing than explained by Beau' and avoids me to open the bass guitar that I've somewhere at home in order to check the resistance of its blender in center position... :-D]

But he also confirms that the mutual loading of pickups remains a potential problem by adding: "I think the issue is that the panning blend pot is always an additional load on the pickups. If you get the 500k version, each pickup always has that extra 500k resistance across it in addition to the volume & tone pots".

Hence the interest of the idea shared by Artie: a 1M pot would diminish the resistive load added by the blender.

Another idea would be to change each track of a stacked blender in an effective no-load control. Doable but not that easy: https://www.talkbass.com/threads/ultimate-no-load-ungrounded-blend-pot-pics.1096449/

My thought right now is that if one uses a double 500k blender, two 500k volume controls and two... 500k no-load tone pots, the overall resistive load will remain exactly the same than in a guitar with 4 pots + a switch. And simple 500k no-load tone pots are easier to find and/or to DIY: https://sixstringsupplies.co.uk/pages/how-to-make-no-load-tone-pot

Last but not least: an added resistive load is not meant to be systematically a problem. If the pickups used have a high resonant peak / high Q factor, the sound shouldn't suffer.

FWIW: another tedious rambling of mine.

HTH...

 

[magillver]

Thank you all for all of your input, off to the bench to start experimenting!

 

[beaubrummels]

beau', thx for sharing. I understand why you talk about a "no-load" functionment if each pot of a blender adds zero resistance from 5 to 10 or from 5 to 0. Now it also means than from each half of its curve, each pot creates a continuous load of 500k to ground, which is not "no-load" in the strict meaning of the word.

True, it's not "no-load" but it's not seeing 500k continuous. The pickup is seeing about 0.004ohm, like when a volume is all the way up. I just put a meter on a couple of my concentrics.

 

[freefrog]

True, it's not "no-load" but it's not seeing 500k continuous. The pickup is seeing about 0.004ohm, like when a volume is all the way up. I just put a meter on a couple of my concentrics.

Understood and agreed. ;-)