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Ultimate No-load Ungrounded Blend Pot (Pics!)

#221
Thanks for such a detailed response DavesnothereCA.
I replaced the 250k mn blend with a 100k today and can't say how much if any difference there is.
One thing that I did notice is that the neck pickup and centre blend settings appeared to be louder than the bridge pickup solo'd. Once again, I can't say for certain that this wasn't already the case with the 250k blend pot, however I did balance the pickup volumes previously with the 250k. Lowering the neck pickup a bit seems to have evened them out.
It could be my imagination but there might be a bit more gradual movement when adjusting the blend.
 
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#227
Just did this mod to a brand new 100k MN pot, and it is super smooth.

I opened both sides of the pot, in order to cut the traces as carefully as I could, and measured to see if I got an open circuit. It was one of the easiest mods ever.

Thank you for all the info, Walterw!!
 
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#229
For anyone interested, this is a circuit derived from one by Bill Lawrence of Bill Lawrence Pickups. He has some creative passive circuit ideas.

A different and, in my opinion, improved blend circuit for two parallel pickups (PU). This circuit offers some advantages over using a double-deck M/N blend pot.

It uses a regular pot and a dpdt switch. Or use a dpdt push/pull pot.

Just to recap, a regular blend pot leaves one PU full on, the other PU is adjustable. But, the adjustable PU is restricted to only half rotation of the blend pot.

The major advantage of Lawrences's circuit is the adjustable PU isn't restricted to half-rotation of a regular blend pot, but now uses the full rotational range of a normal pot. The switch selects which PU will be always-on and which PU will be adjusted by the pot.

Advantages:
-'Usable' range will be stretched out across full length of pot rotation instead of within half a rotation. (lowering pot value can improve usable range, same as M/N).
-Pot ground can be removed for 'ungrounded blend' operation (same as blend pot ground removal).
-Pot resistive trace can be cut for 'no-load' operation (same as blend pot no-load cut). This also allows solo PU operation (same as blend pot).
-Regular pot uses less space in control cavity. Might be available in more values than blend pot selections. Likely less expensive than blend pot.

Disadvantage (maybe for some folk):
-If using a separate switch, it needs to be installed in existing, or new, hole in bass. If using a switched push/pull pot, this disadvantage doesn't apply.

Excuse the word 'Pan' in the following drawings. Substitute 'Blend'. Or whatever you wanna call it LOL.

Blend Select using toggle switch, Master Tone and Master Volume. Circuit shown neck full on, bridge adjustable. Toggle to reverse operation:
Full Pot Range Blend with Toggle.jpg


Blend Select using Push/Pull pot, Master Tone and Master Vol. Push for Neck full on, Pull for Bridge full on. Circuit shown Pushed:
Full Pot Range Blend with PushPull.jpg


Anyway, was doing some reorganizing in my comp and thought I'd throw this out. Use your preferred method. If I ever use a blend, this is the method I'd use instead of a regular blend pot.
 
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#232
I discovered this weekend that all my VBT configured basses that were originally done with grounded blend ala a Seymour Duncan schematic I’ve used for years are better than the ungrounded blend I have been using recently. When I dial out the bridge pickup (or neck), there is zero output from the pickup that is dialed out. With the ungrounded blend, when I do a tap test (tap a small screwdriver to the poles), there is still a little output from the pickup that is dialed out…
 
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#233
Ringhammer said:
I discovered this weekend that all my VBT configured basses that were originally done with grounded blend ala a Seymour Duncan schematic I’ve used for years are better than the ungrounded blend I have been using recently. When I dial out the bridge pickup (or neck), there is zero output from the pickup that is dialed out. With the ungrounded blend, when I do a tap test (tap a small screwdriver to the poles), there is still a little output from the pickup that is dialed out…
Click to expand...
That's why many folk with ungrounded blends do the extra step of adding a cut in the pot's fixed resistance trace (I think you can buy them this way now, too). Totally disconnects the adjustable pickup from the circuit when dialing the ungrounded blend pot to Off, so no more residual sound. Which also allows full solo of the other pickup.

Fortunately those same mods work with the Blend (mislabeled Pan Volume) pot in post 229.
 
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#234
Ringhammer said:
Hey, I’ve seen this in another thread…..
Click to expand...
Discovered I credited the wrong person for the circuit in post 229. It wasn't derived from a Bill Lawrence circuit. It was derived from your request in the thread you referred to. My bad.

Credit for the final idea and diagram goes to @jesterbass .

Two pickup blend wiring, fade from both full to neck only?
Idea post 14
Diagram (repurposed one of mine) post 15

Sorry 'bout the mis-credit. I'm old, man. Gimme a break... :)

In my weak defense, I had schematicized two diagrams from Bill Lawrence about a month before. He does stuff I've never seen for passive circuits. Both of these concern two pickups in series. Posts 24 and 29, if anyone's interested:
Capacitor on a Blend Pot......What does it do?
 
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#235
fig said:
In my weak defense, I had schematicized two diagrams from Bill Lawrence about a month before.
Click to expand...
I have no idea if that’s a real word or not but I’m stealing it. In my years of tinkering with old tube equipment I’ve documented a jillion circuits and parts of circuits. I only learned today that I was actually schematicizing them! I feel so much smarter now!

And yeah…. Bill Lawrence was a clever guy.
 
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#236
Lo-E said:
I have no idea if that’s a real word or not but I’m stealing it. In my years of tinkering with old tube equipment I’ve documented a jillion circuits and parts of circuits. I only learned today that I was actually schematicizing them! I feel so much smarter now!

And yeah…. Bill Lawrence was a clever guy.
Click to expand...
I ran into that word online, thought it was funny, have been using it whenever possible LOL. It's not in the Merriam-Webster dictionary (just looked LOL).

Yeah, in over 20 years in the avionics world, I never heard that word. But it makes so much sense LOL.
 
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#237
Ringhammer said:
I discovered this weekend that all my VBT configured basses that were originally done with grounded blend ala a Seymour Duncan schematic I’ve used for years are better than the ungrounded blend I have been using recently. When I dial out the bridge pickup (or neck), there is zero output from the pickup that is dialed out. With the ungrounded blend, when I do a tap test (tap a small screwdriver to the poles), there is still a little output from the pickup that is dialed out…
Click to expand...
“Better” is subjective of course. The purpose of the ungrounded blend is to decrease the loading effect (ie a typical blend at any position is decreasing the amplitude of the resonant peak of the pickups due to its added paths to ground) of the blend control when used as a voltage divider (normal blend pots are just dual voltage dividers splitting a pickup’s output between hot and ground). Without a ground the blend is instead just turned into a dual resistor network that simply adds resistance between one pickup and ground. Cutting the traces as @fig mentions above gives most of the effects of a typical blend but without the loading effect (best of both worlds, subjectively!).
 
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#238
Can anyone tell me where I might find a 100k MN taper blend pot with a shaft bigger than 6mm in the US? I found one at Black Dog Music in the UK, but with shipping being what it is these days, it would probably cost a fortune to have one or two sent to the US, plus who knows what year it will be when I get it. As an alternative, if any of you have installed a blend pot with a 6mm shaft, can you suggest a good way to shim it into place? I'm thinking my current 250k blend pot has an 8mm shaft.
 
#239
I recently purchased a couple MN100k blend pot. I bought two in case I messed up one pot trying to cut the trace, which is exactly what happened. So I installed the other one in my G&L Tribute MJ-4 ungrounded but without making the trace cut. The MJ-4 comes from the factory with an MN250k grounded blend pot, which gives about 1/8" of usable blend area. The 100k ungrounded has expanded the usable blend area of the bass, but not really as much as I was expecting considering the way folks talked about it on this thread. Still, it's a definite improvement, as the factory installed MN250k acted much more like a switch than a pot. I have one question, so I'm hoping somebody reads this and can help me. What would the difference be between an ungrounded MN100k blend pot and a grounded version of the same? In other words, what does ungrounding the pot actually achieve in a working bass?
 
#240
A grounded blend will insert a new resistor in parallel to ground. This will allow for a full cut of one of the pickups. However, it will also load the pickup that’s on.

By removing the ground connection, you are adding a reostate, which never fully takes the other pickup out of the circuit, but perfoms in a smoother way. The trace cut at the end makes sure that, at either end, there is absolutely no loading and the solo pickup sounds as it should.

I settled on the MN100k ungrounded connection and it works wonderfully. Smooth blending, full cut at either end without loading.
 
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