Ultimate No-load Ungrounded Blend Pot (Pics!)

[claudel]

Like you, I ruined the first MN100k blend pot trying to cut the trace, so I just installed the second one without the cut. However, my bass was a G&L MJ-4. The original wiring went from the pickups to the blend pot, then from the blend pot into the circuitboard of the preamp. The preamp didn't like the 100k. It felt like it castrated the bass. All the growl of that bass disappeared. It went from being Superman to being Clark Kent. I went back to the original grounded MN250k. It reacts more like a switch than a pot, but the growl of that bass is back. Sometimes, you have to reach a compromise. While I believe this method works, it doesn't always work with a bass that is active. I'm glad you got yours working.

Sorry it didn't work for you. I like it way better than VVT on this one.

It's completely passive so that circuit seems to work fine.

I tried B250K/A250K and B500K/A500K volume/tone before settling on B500K/A250K.

500K tone made it seem too shrill.

I still need to figure out where the "mwah" is hiding on this one.

It's there unplugged.

Action is reasonably low. Neck is true and the neck/body combo is plenty resonant.

I'm gonna put a bit more padding under the pickups and see if setting those closer to the strings brings it out a bit more

I'm playing it through a Babyface Pro directly into phones with no amp sims or EQ so that's probably an accurate rendition of what's coming out of the jack.

Once I figure that out all it will need is a final setup tweak, final cleanup, a fresh set of strings and it'll be done.

 

[jglunt]

Sorry it didn't work for you. I like it way better than VVT on this one.

It's completely passive so that circuit seems to work fine.

I tried B250K/A250K and B500K/A500K volume/tone before settling on B500K/A250K.

500K tone made it seem too shrill.

I still need to figure out where the "mwah" is hiding on this one.

It's there unplugged.

Action is reasonably low. Neck is true and the neck/body combo is plenty resonant.

I'm gonna put a bit more padding under the pickups and see if setting those closer to the strings brings it out a bit more

I'm playing it through a Babyface Pro directly into phones with no amp sims or EQ so that's probably an accurate rendition of what's coming out of the jack.

Once I figure that out all it will need is a final setup tweak, final cleanup, a fresh set of strings and it'll be done.

I'm sure that my lack of success was due whatever the preamp does with the signal. I'm told on Basses by Leo that it was actually designed by Paul Gagon with an Alpha B250k blend, but he changed the pot to an MN250k later. I could've tried ungrounding the stock MN250k, but I was seeking a wider blend area. The bass comes V-B and 3-band active EQ, with the B an MN250k. It reacts more like a switch, but the bass sounds great with it just at center, so that's the way I mostly play it.

 

[poochiecheeks]

I just finished doing this mod on my PJ bass as per the diagram posted on the first page of this thread, have to say it works perfectly and enhances both the utility and coolness of this bass significantly. It's unfortunate that the actual blending arc of the pot is incredibly small, but it's worth it to find the sound I want- usually slightly towards the bridge with the tone slightly off- and be able to turn the volume off and on without changing it.
I used an Allparts/Bourns 250k MN and a B500k volume. Haven't read through all 16 pages of this thread but a 250k blend sounds like a good compromise between brightness and the usuable blend sweep. Made sure to leave the blend ungrounded, you can tell with the PG on since touching the blend knob introduces noise to the signal just like touching an exposed pickup pole piece. Took a few hours but I went overboard with trying to be neat and thorough. Definitely worth the time if you ask me

 

[sunbeast]

I just finished doing this mod on my PJ bass as per the diagram posted on the first page of this thread, have to say it works perfectly and enhances both the utility and coolness of this bass significantly. It's unfortunate that the actual blending arc of the pot is incredibly small, but it's worth it to find the sound I want- usually slightly towards the bridge with the tone slightly off- and be able to turn the volume off and on without changing it.
I used an Allparts/Bourns 250k MN and a B500k volume. Haven't read through all 16 pages of this thread but a 250k blend sounds like a good compromise between brightness and the usuable blend sweep. Made sure to leave the blend ungrounded, you can tell with the PG on since touching the blend knob introduces noise to the signal just like touching an exposed pickup pole piece. Took a few hours but I went overboard with trying to be neat and thorough. Definitely worth the time if you ask me
View attachment 5341407
View attachment 5341408

You can (and should!) still ground the casing of the blend pot in this case, just don’t send any of the pot lugs to ground/pot-casing as you do on a typical blend pot. From the looks of it your pot is wired correctly, so no issue grounding it at all to add some shielding (and prevent that buzzing when touching it)

 

[poochiecheeks]

You can (and should!) still ground the casing of the blend pot in this case, just don’t send any of the pot lugs to ground/pot-casing as you do on a typical blend pot. From the looks of it your pot is wired correctly, so no issue grounding it at all to add some shielding (and prevent that buzzing when touching it)

Ahh ok, got it. thank you

 

[fig]

It's unfortunate that the actual blending arc of the pot is incredibly small, but it's worth it to find the sound I want

Passin' thru, taking a quick break.

I made a drawing awhile back from an idea TB member jesterbass came up with.

With a switch and a regular pot (not a 2 layer blend pot), you can use the full rotation of the pot. Full rotating range means the smaller arc of audible blending you hear is stretched out farther for finer control of the pickup blending.

The switch selects which pickup you want full-on all the time, and makes the other pickup controllable for blending. That's the same operation as a regular blend pot except not in 1/2 the rotation anymore. Toggling the switch will reverse which is full-on and which is controllable.

Also like a regular 2 layer blend pot, you can unground it and no-load it if desired.

Example circuit:

Anyway, just throwing this out. I don't like the half pot rotation thing either LOL. Cool to hear you have the bass sounding as you like.

 

[JKos]

Note the note at the bottom, “Blend volume pot can be ungrounded or no-load cut…” I’d go for ungrounded, cut trace maybe 10k. Good blend control and then 100% only the selected pickup with no additional loading.

 

[Yahboy]

I just finished doing this mod on my PJ bass as per the diagram posted on the first page of this thread, have to say it works perfectly and enhances both the utility and coolness of this bass significantly. It's unfortunate that the actual blending arc of the pot is incredibly small, but it's worth it to find the sound I want- usually slightly towards the bridge with the tone slightly off- and be able to turn the volume off and on without changing it.
I used an Allparts/Bourns 250k MN and a B500k volume. Haven't read through all 16 pages of this thread but a 250k blend sounds like a good compromise between brightness and the usuable blend sweep. Made sure to leave the blend ungrounded, you can tell with the PG on since touching the blend knob introduces noise to the signal just like touching an exposed pickup pole piece. Took a few hours but I went overboard with trying to be neat and thorough. Definitely worth the time if you ask me
View attachment 5341407
View attachment 5341408

500K volume pot just open up entire PJ tone than 250K pot.

A500K / MN250K + unground blend pot , consistent volume from solo P <> Blend <> solo J.

 

[garfoid]

Like you, I ruined the first MN100k blend pot trying to cut the trace, so I just installed the second one without the cut. However, my bass was a G&L MJ-4. The original wiring went from the pickups to the blend pot, then from the blend pot into the circuitboard of the preamp. The preamp didn't like the 100k. It felt like it castrated the bass. All the growl of that bass disappeared. It went from being Superman to being Clark Kent. I went back to the original grounded MN250k. It reacts more like a switch than a pot, but the growl of that bass is back. Sometimes, you have to reach a compromise. While I believe this method works, it doesn't always work with a bass that is active. I'm glad you got yours working.

I'm under the impresson that the original MN250k Blend pot you had on your bass, by being connected to the Preamp's input, was actually part of the issue and also the solution. Without fully knowing how the preamps input is designed, and always needing an input resistance load (often used with a resistor to ground or to a Voltage Reference), my guess is that the MN250k pot was creating that load. If you use the MN100k (or even the MN250k) but ungrounded your are messing with the preamps input Bias.
Here is what I think the solution could be if you still want to use a MN100k/50k Ungrounded and Unloaded. Just add a 250k resistor straight from the preamps input (or from the MN potentiometer output) to Ground.
If what I think it's happening, is in fact happening, then that would be the solution. You would retain the right impedance that preamp wants to see at the input (to properly bias the preamps input) note: I have no idea why the preamp was designed this way- it's very odd, but I don't know the reasons behind this design.
Hope you will have the chance to look at this. I would be curious to see if it would work and you would end up with a Blend that is less of a 3 way switch and more of a Blend.

 

[jglunt]

I'm under the impresson that the original MN250k Blend pot you had on your bass, by being connected to the Preamp's input, was actually part of the issue and also the solution. Without fully knowing how the preamps input is designed, and always needing an input resistance load (often used with a resistor to ground or to a Voltage Reference), my guess is that the MN250k pot was creating that load. If you use the MN100k (or even the MN250k) but ungrounded your are messing with the preamps input Bias.
Here is what I think the solution could be if you still want to use a MN100k/50k Ungrounded and Unloaded. Just add a 250k resistor straight from the preamps input (or from the MN potentiometer output) to Ground.
If what I think it's happening, is in fact happening, then that would be the solution. You would retain the right impedance that preamp wants to see at the input (to properly bias the preamps input) note: I have no idea why the preamp was designed this way- it's very odd, but I don't know the reasons behind this design.
Hope you will have the chance to look at this. I would be curious to see if it would work and you would end up with a Blend that is less of a 3 way switch and more of a Blend.

Thanks!! I believe you are correct that the preamp needs a 250k blend pot to work properly, whereas in a passive bass that wouldn't be as much an issue. That preamp was designed by Paul Gagon specifically for G&L, and was used in two of their basses. I have not been able to find a schematic for it, but everything you say makes sense.

I know it's just my OCD kicking in. It sounds great with the blend at center detente, but if I have a blend control, I want it to blend. If it acts like a switch, I'd rather they'd just put a switch there. When I get a chance, I'll try your solution and see if that helps. Thank you!

 

[garfoid]

I think that could work. Electrically, the fixed 250k resistor to ground would replace the function that, I suspect, the grounded MN250k Blend is having. If you do this, then, you will be free to use an Ungrounded and Unloaded Blend pot and use a value that will allow for more subtle Blending. I suggest you go with 100k, 50k or even 20k.
I have tried 100k, it's considerably better than a 500k, but still not as good as what I was expecting (I am used to active Blends which are unbeatable if well designed). So, as MN50k are hard to find, I will try with MN20k also.

 

[garfoid]

Just a heads up on this subject. I have now tried an MN20k unloaded and ungrounded pot.
Compared to the MN100k, it went too far off the desired linearity. It's hard to explain but, using this unloaded and ungrounded system, it's hard to find a balance where there is a more noticeable difference across the whole potentiometer rotation.
Until MN50k blend pots are available and I can test these, MN100k seems to be the best option for me.
If using ungrounded only, I prefer the MN500k since it offers less load on each pickup extremes but, it also works mostly as a 3 way switch with absolutely no difference in the in-betweens of the 3 positions. The advantage of this is that from one side, to the middle, to the other side, the pickups outputs are more constant and balanced.

 

[garfoid]

With the ungrounded and unloaded MN Blend pots, there is a little clicking noise on both ends of the positions. Has anyone else experienced this and/or come with some thoughts on how to avoid this? Or is it just a byproduct of the unloading?

 

[tidbits]

Just stumbled upon this thread while thinking of ways to update the wiring on my bass. I particularly liked @fig's example of a switchable single pot blend (here). I think this particularly suits my need for my PJ as this is basically how I always run it - the neck pickup full on with the bridge blended in to add highs/texture. I'm thinking I'll just re-use my existing hardware to start. It's currently wired VVT - linear volumes and audio tone, all 250k pots, .047 orange drop cap.

Anyone have any experience running this particular circuit? 250k pot values alright?

 

[SharpCat]

Just stumbled upon this thread while thinking of ways to update the wiring on my bass. I particularly liked @fig's example of a switchable single pot blend (here). I think this particularly suits my need for my PJ as this is basically how I always run it - the neck pickup full on with the bridge blended in to add highs/texture. I'm thinking I'll just re-use my existing hardware to start. It's currently wired VVT - linear volumes and audio tone, all 250k pots, .047 orange drop cap.

Anyone have any experience running this particular circuit? 250k pot values alright?

View attachment 7168776

I tried it. In use, I didn’t think it was better than VVT, so I say don’t bother. Basically it acts like VVT with a push pull to swap the volumes. I think VVT takes less thought—you don’t have to check which way the push pull is set before adjusting a pickup. YMMV of course.

250k works fine.

 

[tidbits]

I tried it. In use, I didn’t think it was better than VVT, so I say don’t bother. Basically it acts like VVT with a push pull to swap the volumes. I think VVT takes less thought—you don’t have to check which way the push pull is set before adjusting a pickup. YMMV of course.

250k works fine.

Thanks for the feedback. I was thinking this, like a regular VBT let me have a master mute - I’ve been rolling down my neck pickup, and forgetting to do my bridge, or having to fiddle and reset the blend when coming back.

I guess I could just as easily change one control to a push/pull master mute.

 

[mrperkolator]

Thanks for the feedback. I was thinking this, like a regular VBT let me have a master mute - I’ve been rolling down my neck pickup, and forgetting to do my bridge, or having to fiddle and reset the blend when coming back.

I guess I could just as easily change one control to a push/pull master mute.

You could modify that schematic so the blend mutes when pulled up

 

[SharpCat]

You could modify that schematic so the blend mutes when pulled up

I guess a push pull mute could be added to just about anything. I never thought about it, could be useful.

 

[tidbits]

So my bass has 3 push pulls on it, and I really only use 1. Thinking this is how I would redo it...

Master Vol - push/pull series parallel on P split coil (I actually run it parallel most of the time)
Blend - push/pull to switch between bridge blending into full neck & neck blending into full bridge (I often blend in about 30% bridge to add a little extra bite, occasionally 80%)
Tone - push/pull function is undecided... it was series/parallel between pickups, but I don't like that tone. I'm thinking about using it to audition other cap values, but still be able to bail to old faithful 0.047 cap? Clone the Nordstrand Tone Drop?

You could modify that schematic so the blend mutes when pulled up

Currently my bridge vol removes it from the circuit, and I've found it to have no noticeable effect. Maybe it would be noticeable in a VBT? Unsure.

 

[Brian Patterson]

I'm looking to wire the two passive pickups on my custom bass build separately with V/T controls with a blend between them. Then output eacj pickup to two mono jacks to 1) send discreet signals from each pickup to two amp inputs and/or two audio interface channels, or 2) join them with an adapter for a mono signal where needed. Any reasons this won't work?

Is there any diagramming for that scenario?