Ultimate No-load Ungrounded Blend Pot (Pics!)

[walterw]

Does this array have the same affect as cutting the ends of the traces?

not sure what you mean

that's the wiring diagram regardless of whether the traces are cut or not. in theory leaving the traces uncut causes a little bit of "leakage" from the other pickup, cutting them creates a definite "off" for the unselected pickup

 

[Ringhammer]

in theory leaving the traces uncut causes a little bit of "leakage" from the other pickup, cutting them creates a definite "off" for the unselected pickup

In the diagram, there is no wiring connected to the lugs that would have their traces cut. If nothing is connected to those lugs, isn’t the same as cutting the trace, since it’s only a fraction of an inch away from the open ended lug?

 

[Stephen Gagel]

I have been working on the issue of the blend being somewhat of an on of switch with a non-grounded blend. What I have been doing is using 100k m/n and 50k m/n pots. What I found was a 250k m/n pots have a very small blend area. I used some strat knobs with numbers on them and found that from center detent (which is 5.5) ether way (4.5 to 6.5) you were done blending and you were ether on one or the other pickup. So one number difference in ether direction is all you have to blend with. Lets say you have five numbers from center each way so 250k divided by five is 50k. So I found some 50k and 100k pots. I tried the 100k first and found that it gave me about 2.5 to 3 numbers worth of blend ether way from center and a positive solo at each end. I tried the 50k m/n and it gave me blend from one end to the other but not a good solo on ether end so I went back to the 100k m/n pot. Now the only 100k and 50k m/n pots I found or Alfa pots made for a circuit board and have prongs on them rather than solder terminals. So you just make a loop on the end of the wire, slide them on and solder. They also have a small shank diameter of .268" so I made some step down washers out of brass to adapt them to my 3/8 holes. Anyway I am using a 250k linear pot for Vol. a 100k m/n pot for Blend and a 250k audio with a DPDT switch on it for tone. The switch is for series / parallel and the entire system works wonderful.Invalid Link Removed

 

[walterw]

In the diagram, there is no wiring connected to the lugs that would have their traces cut. If nothing is connected to those lugs, isn’t the same as cutting the trace, since it’s only a fraction of an inch away from the open ended lug?

no, it's very different with the trace cut

 

[Ringhammer]

no, it's very different with the trace cut

Why?

 

[fig]

In the diagram, there is no wiring connected to the lugs that would have their traces cut. If nothing is connected to those lugs, isn’t the same as cutting the trace, since it’s only a fraction of an inch away from the open ended lug?

Maybe this drawing will help.

With one end of the pot disconnected, the pot is now a variable resistor (aka rheostat).

Left drawing, without a no-load cut, shows a slight leakage signal thru the variable resistor to ground. Slightly diminished signal goes forward.

Right drawing shows that, with a no-load cut in the proper spot, no leakage can happen. Full strength signal goes forward.

 

[Ringhammer]

In the pics earlier in this thread, he is showing a cut on the trace to a lid that has nothing connected to it, including ground, so I don’t get how cutting a trace to a lug that is in effect left open (not connected to anything) has any effect at all. Your diagram shows a cut interrupting a path to a volume control. I must be missing something somewhere…

 

[fig]

I must be missing something somewhere…

No you aren't, this was my bad. I showed you a diagram for "full-on" from a different circuit. Same concept, though. I apologize for that.

You want a "full-off", correct? Where the wiper arm is rotated to the disconnected ground terminal and no-load cut?

If so, give me a few minutes to do a diagram.

 

[Ringhammer]

No you aren't, this was my bad. I showed you a diagram for "full-on" from a different circuit. Same concept, though. I apologize for that.

You want a "full-off", correct? Where the wiper arm is rotated to the disconnected ground terminal and no-load cut?

If so, give me a few minutes to do a diagram.

What I thought was that in my ungrounded V/B/T configuration, when I dialed all the way to the neck position it would be that pickup absolutely solo, as if the bridge pickup was not there at all. Not really concerned with having it that way for the bridge because I would likely never want to solo the bridge.

Earlier in this thread there is a diagram of the ungrounded V/B/T for Jazz and I thought the unused lugs were the same ones he cut.

 

[fig]

Since a blend pot is essentially two pots, one physically reversed from the other, this drawing represents only 1/2 of a blend pot. The very same "full-off" no-load cut near the ungrounded lug applies to the second half of the blend pot.

Terminal 1 is where the ground would go. With the cut shown in the right-hand drawing, no leakage happens (no slightly hearing the 'off' pickup). Full solo function of the remaining 'on' pickup.

I hope this helps. Again, my apologies for the earlier confusion.

 

[jglunt]

I know this is a fairly old thread, so I hope someone sees this and can explain something to me. I am wondering why a linear taper pot for the volume in this configuration? Most manufacturers seem to use an audio taper for the volume pot.

 

[bigtone23]

I know this is a fairly old thread, so I hope someone sees this and can explain something to me. I am wondering why a linear taper pot for the volume in this configuration? Most manufacturers seem to use an audio taper for the volume pot.

Linear volumes are great for instruments that stay on the cleaner side of things downstream. You get a wider and finer range of adjustment, particularly on the top half of the pot's rotation. Audio taper is usually preferential for those that like distorted or crunchy tones, as the faster drop in value helps 'clean up' the tone with less rotation of the pot.
For example, I like linear volumes on my basses and audio tapers on my guitars. I play mostly cleaner tones on bass and always crunchy tones on guitar. I like when my guitar volume rolls back to about 5 or 6 and my tone cleans up. On a typical, modern audio taper pot, 5 on the knob is about 10% of the pot's value. On a linear taper pot, 5 is 50% of the pot's value. To get to that same value for a clean tone, I have to roll a linear pot back to about 1-2. That's a wide sweep and a lot of rotation for someone that rides the volume control for cleans.

The opposite is true, too. Lets say I have a clean tone and just need to drop my volume a touch. On a linear taper pot, dropping the volume to about 7 is a noticeable drop (which is also about 70% of the pot's value). The equivalent resistance on an audio taper pot is at about 8. However, on the audio taper, that drop doesn't have a forgiving wiggle room. Overshoot your desired setting (of 70% resistance) and drop to 7 on the audio taper and you are now at about 50% of the pot value and the volume really drops out. On a linear pot, dropping an extra number (to 6) is still only 60% of the value, which is not terribly lower.
This is why VVT controls on newer basses are usually linear volumes with an audio tone. It just gives the player finer adjustment of those blends. Audio taper is still the preferred tone pot-linear tones are more like a on/off switch--all the action is from 2-0. I theorize that Fender used audio taper all around just to keep the parts orders smaller. Get a batch of solid shaft 250K audio for the Teles, Ps and Js, and a batch of 250K split shaft audios for the Strats.

 

[jglunt]

Thanks Bigtone 23. So the world isn't going to end if I use a linear taper pot in my G&L SB-2 along with a blend pot? Here's another scenario. An SB-2 has just two volume controls; no tone. That's OK by me, except I like a master volume. A blend pot is one way to do this. I'm also looking at running a concentric stacked pot for individual volumes and run that signal to a master volume, but I don't know how to manage the resistance there or the tapers for that matter, so this blend pot idea might be the best. Thanks again.

 

[Ringhammer]

I would love to find a source for some solid shaft linear taper 250k and 500k CTS pots, with the short thread length for use on pick guard mounting. Anyone have that info. I usually get mine through “guitar parts factory”, but they never seem to have them.

 

[DavesnothereCA]

OK, after some prompting i finally made a diagram of the whole thing, done in my apparently now traditional goofy MS paint style
PIC of SCHEMATIC : View attachment 2779754
It also works just fine without cutting the traces.

You still get the smooth blending between pickups and you still avoid extra loading loss from the blend pot; the only drawback is that when you're cranked over to one pickup you still get a slight bit of the other, "off" pickup in the mix. (you don't really hear it though)

if you're a player who mostly shades between the two pickups rather than running either one solo, then this will work nicely without cutting the traces on the blend pot.

~
Thanks for a VERY informative thread !

I've been looking at having a blend control in one or another of my basses, and this thread has gone a long way toward me understanding the involved elements of electronics, the pros and cons of the different types of balance pots, and the various ways of wiring of them.

I now have learned what an NM taper dual pot is, compared to an AC taper dual pot, as well as some more places to buy the pots.

My first attempt will be without cutting the traces, and without the grounds, as per your drawing.

I will try more than one value of pot for the blend/balance control, starting with 250K.

- - -

One thing which is not addressed on many [if any] of the diagrams which I've seen is WHICH END of each gang of the pot is to be connected to the output, and which end to the [optional] ground.

Clearly, the response of an MN taper dual pot will not be correct if we wired this backward.

And do all makes and models of dual pots have the same direction of taper in the top wafer/gang as each other, and therefore the other direction is always in the bottom one ?

I realize that checking with a meter from wiper to one or the other end of a wafer/gang [while turning the pot shaft] will reveal the answer, but how many drawings mention any of this ?

Not knowing and wiring it incorrectly could cause confusion when trying to evaluate a particular circuit, and may mislead a person into trying a different value of pot when just a wiring change might sometimes be all that is necessary.
~

 

[fig]

For @DavesnothereCA and any others passing thru who might still be getting familiar with blend pots.

Me, and a few others, have mentioned how blend pots are "like two pots, but with one flipped", which may not be too helpful. But there's truth to it. Here's the evolution...

One thing which is not addressed on many [if any] of the diagrams which I've seen is WHICH END of each gang of the pot is to be connected to the output, and which end to the [optional] ground.

Clearly, the response of an MN taper dual pot will not be correct if we wired this backward.

I never thought about 'til you mentioned it, but here's what'd happen. Centered (detent), volumes for both pickups would be off. As you turn it one way, or the other, one pickup would start increasing in volume. HA!, I just learned something LOL.

And do all makes and models of dual pots have the same direction of taper in the top wafer/gang as each other, and therefore the other direction is always in the bottom one ?

I realize that checking with a meter from wiper to one or the other end of a wafer/gang [while turning the pot shaft] will reveal the answer, but how many drawings mention any of this ?

I think, but not %100 sure, the way I've drawn it is standard. Top deck (wafer/gang), resistive element is on the left (connected to lug 1). On the lower deck, resistive element is on the right (connected to lug 6). Many drawings may not mention it because it's standard and commonly know everywhere. I'm kinda guessing, though.

Had a few unautographed pics of me lying around, so threw one in to fill the empty spot.

Anyway, hope this helps.

 

[Stephen Gagel]

The M/N pot value to use on the blend pot is 100ohms for sure. You do not need to cut the trace just leave it ungrounded. I tried a 250ohm M/N pot to start with and that was very much like a switch. I have used this on my PJ bass and it works great. When all the way to the P pickup all you get is P pickup and the same for the J. I am using this on a 5 string jazz with Barts and again the same great outcome.

 

[DavesnothereCA]

For @DavesnothereCA and any others passing thru who might still be getting familiar with blend pots.

Me, and a few other, have mentioned how blend pots are "like two pots, but with one flipped", which may not be too helpful. But there's truth to it. Here's the evolution...
View attachment 4384120

I never thought about 'til you mentioned it, but here's what'd happen. Centered (detent), volumes for both pickups would be off. As you turn it one way, or the other, one pickup [or the other] would [turn on and] start increasing in volume. HA!, I just learned something LOL.

I think, but not %100 sure, the way I've drawn it is standard. Top deck (wafer/gang), resistive element is on the left (connected to lug 1). On the lower deck, resistive element is on the right (connected to lug 6). Many drawings may not mention it because it's standard and commonly known everywhere. I'm kinda guessing, though.

Had a few unautographed pics of me lying around, so threw one in to fill the empty spot.

Anyway, hope this helps.

~
Thanks for contributing, both now and earlier in the thread.

I learned last night to expect most of what you just explained, but the question which I raised in my last post remained at the time, and to an extent still does.

Now there might indeed be an industry standard blueprint for how these blend/balance pots are to be built [I do suspect that there is], and I'm sure that an electronics engineer would know of it.

But the vast majority of musicians are not engineers of electronics, and would not even think of what I asked, until they tried to wire up one of these pots, and lost on the 50-50 odds that it might fail in the manner which you described just above.

The only reason that I thought to ask is that my own education was electronics prior to music, and while I did not continue to be an engineer, I understood enough to notice the oversight of detail in the diagrams.

- - -

Also, while shopping for these, I have noticed that not all pots described as balance/blend have this fancy 'MN' taper arrangement.

This one, for example , Bourns 250k Blend Balance Pot , says that it has a linear taper, and while it would not pass 100% of either of the signals when set at the centre detent, it would however offer a symmetrical response, therefive it ironically would not matter in which direction a person wired it.

And there are others on the same website which claim to be of audio taper, some of which are built by the respected CTS company.

But to 'kind of' return to the original topic of this thread, if we are going to wire the blend/balance pot without grounding any of its terminals, the consequence of miswiring the direction of the gangs/wafers would not be quite the same as what you described.

But it would still be a different response than normal, confusing to a person who was not expecting it.
~

 

[Stephen Gagel]

Here is the corect pot, its an Alpha pot.alpha 100k ohm dual mn-taper | eBay Wire it just like my diagram. The diagram is looking at the back of the pickguard just like you looking at it when wiring. It will put the neck pickup clockwise and bridge pickup counter clockwise.

 

[BlueTalon]

The M/N pot value to use on the blend pot is 100ohms for sure. You do not need to cut the trace just leave it ungrounded. I tried a 250ohm M/N pot to start with and that was very much like a switch. I have used this on my PJ bass and it works great. When all the way to the P pickup all you get is P pickup and the same for the J. I am using this on a 5 string jazz with Barts and again the same great outcome.

Just to be clear, did you mean 100K ohm and 250K ohm? Or did you actually mean 100 ohm and 250 ohm?