Jazz bass wiring help - master volume + blend, with a push-pull tone pot for series/parallel

[harrumphicus]

I use to be able to do this wiring business in my head, but I feel like there's a lot going on here that I just don't know enough about and it's breaking my brain a little bit. Hopefully you guys can help.

Like the title says, I want to replace the two individual volume pots with a master volume (which will reuse one of the existing pots) and an audio taper stacked blend. I think I could use this pot for that, but I'm not sure if the shaft will retrofit the stock knobs. I'm also not sure if part two of my wiring setup will affect how I wire the master+blend.

Second, I want to replace the tone pot with this push-pull, but again I don't know what all the different shaft types are for or how to retrofit them with existing hardware. I'm also having trouble mixing the two diagrams together. I'm guessing I'd have to wire the pickups to the DPDT switch and then to the blend, then to the master volume and then back to the tone pot and out? Is there any way someone could put together a diagram for me? I can't seem to find one with both mods on it.

 

[line6man]

There are several ways to wire the scheme, but arguably the best way would be to choose an ungrounded M/N taper blend, so that you can bypass the blend in series mode. You won't be able to completely solo either pickup, but the unused pickup should be so quiet that the soloed pickup will dominate. You should find that blending is very smooth, and there won't be as much loading on the pickups.

The wiring is done like this, although you will want to put the push/pull switch on the tone pot, rather than the volume pot, as shown.

 

[harrumphicus]

So the blend itself isn't grounded, it just grounds at the master volume? What is an M/N pot?

 

[line6man]

So the blend itself isn't grounded, it just grounds at the master volume? What is an M/N pot?

The pot's chassis still gets grounded as usual. You just don't have any connections to ground on the six terminals. Typically a blend pot puts a resistance parallel to the signal path, as well as in series with it. This scheme relies on only series resistance.

M/N is the taper of the pot. The taper is crucial, because the scheme will not work without the proper kind of pot. A/C taper blends are just two volume pots running in opposite directions, so there is always an attenuation of both inputs, whenever you are away from the clockwise and counterclockwise extremes of the rotation. M/N tapers work by running both inputs directly to the output, when you are the center detent, and only attenuating one of the inputs, when you move away from it. At any given point in the rotation, at least one of the inputs goes straight to the output.

The way that this scheme works is by shunting the two inputs of the blend pot together, when you are in series mode. Since both inputs carry the same signal, that signal always has a direct path to the output, regardless of what the pot is set to. You could bypass any "standard" blend pot by rerouting the series signal straight to the volume pot, if you wanted to, but it would take additional poles of switching, preventing you from using a push/pull pot.

 

[Cadfael]

So the blend itself isn't grounded, it just grounds at the master volume? What is an M/N pot?

On "normal JB the pots don't need to be grounded - and Leo did't do ...
The pots are grounded via the chromed control palte. If you ahve a "custom JB" without control plate, the/all housing(s) should be grounded ...

 

[BStringJerry]

@line6man:
Any chance of posting that wiring diagram again you had up in your post #2? Thanks!

 

[line6man]

@line6man:
Any chance of posting that wiring diagram again you had up in your post #2? Thanks!

@BStringJerry
I had ended up backing up my Flickr pics and then removing a bunch of them, so some of my diagrams got pulled. I'll have a look for the diagram and then get it back up.

 

[BStringJerry]

I don't suppose you can highjack a 7-1/2 month old thread, and since my question is pretty much alone the same line, I will post it here. I am wanting to wire my Jazz bass for a Master Volume - Blend - Tone - Tone with a series/parallel switch. I am going for a mini toggle switch rather than a push pull because I can't find a push pull pot that lets me use the original Fender knob. I have what I believe to be the correct wiring diagram, but I would like someone much more tech savvy and knowledgable than myself to correct me where I missed the boat.

500k Linear Volume Pot
500k Dual MN Taper Blend Pot
500k Audio Tone Pots
.1 Cap on Neck Tone Pot
.022 Cap on Bridge Tone Pot
Jack will be relocated to a side jack.

I read somewhere that by putting a .1uF Cap on the Neck PU Tone Pot and a .022uF Cap on the Bridge PU Tone Pot you could increase the tonal range of your J-Bass. Of course that was meant for parallel, not sure what that will do in series. Would someone chime in on this and tell me if I'm wrong with either the wiring and/or the Caps.

 

[line6man]

Here is the original diagram that I had posted.

As for the dual tone control diagram, there are a couple of problems.

With an M/N taper blend, there will not be any position in the rotation where one of the two tone controls is not a master tone. This is because the M/N taper always passes one signal path straight to the output, without series resistance. To get isolation, you would either want to choose an A/C taper blend, or add resistors in series with each tone control to isolate the signal paths. An A/C taper blend is two ordinary volume pots running inverse parallel, so as you adjust the pickup blend, both pickups see series resistances that isolate their tone controls. While this is useful for isolating the tone controls, it is not ideal, as you don't get full volume from either pickup unless it is soloed. Likewise, if you add resistors to an M/N taper blend, you won't be getting full output from the pickups. This sort of compromise is one of the reasons that multiple tone controls are not popular. The other main reason is that it offers little practical value. Whatever treble you cut from one pickup will just be added back by the other pickup. A better option is having one tone control for both pickups, and choosing between different capacitors to get additional control and tonal variation. In any case, the second problem with your diagram is that it does not account for the volume drop that will occur if you put the pickups in series while the blend pot is set anywhere other than the soloed neck pickup position. Since there will only be one signal feeding the blend pot, the blend pot simply becomes a second volume pot feeding into the master volume pot. This is not practical, so you will want additional poles of switching to bypass the blend pot in series mode.

 

[BStringJerry]

Thanks for that info... I thought that my idea seemed too easy. I think I'll stick with your original diagram above. Again, Thanks.

 

[bassman_al]

Line6man is the best wiring guru on TB, IMO. I've used his diagram many times and it works great. I'm going to try it for the first time with an Aguilar OBP pre-amp this week. I'll report back.

 

[heavyfunkmachin]

Thanks for that info... I thought that my idea seemed too easy. I think I'll stick with your original diagram above. Again, Thanks.

hi @line6man (and anyone else who can help…

I just tried this wiring to find out the blend is acting more like a “switch”
Center is blended, but the second I move to either side, it’s either 100% neck or 100% bridge (or so it sounds), not much blend…

min using a MN250k pot for blend… any ideas on what could be the issue?

 

[dwizum]

Sorry if this is an insulting question, but have you played many basses with MN taper blend controls? They can tend to have a very on/off nature since one pickup or the other is always at 100% (by design) and then you're tapering whichever pickup isn't 100% within a very short throw on a very steep curve. If it is literally an on/off switch then something may be wrong, but if you're getting a LITTLE blending that just sounds kinda sudden, that's the nature of the beast. People not used to how they work often seem to think something is wrong.

You can try an AC taper blend, which gives a smoother transition but no possible way of having both pickups at 100% at the same time.

Or you can switch to two volumes, or some other non-blend-pot solution. Personally, I prefer two volumes over a blend, since it gives you the same electrical circuit but with independent control, and the control is spread over the whole rotation of the pot instead of being crammed into half the rotation.

 

[heavyfunkmachin]

Sorry if this is an insulting question, but have you played many basses with MN taper blend controls? They can tend to have a very on/off nature since one pickup or the other is always at 100% (by design) and then you're tapering whichever pickup isn't 100% within a very short throw on a very steep curve. If it is literally an on/off switch then something may be wrong, but if you're getting a LITTLE blending that just sounds kinda sudden, that's the nature of the beast. People not used to how they work often seem to think something is wrong.

You can try an AC taper blend, which gives a smoother transition but no possible way of having both pickups at 100% at the same time.

Or you can switch to two volumes, or some other non-blend-pot solution. Personally, I prefer two volumes over a blend, since it gives you the same electrical circuit but with independent control, and the control is spread over the whole rotation of the pot instead of being crammed into half the rotation.

Not insulting at all… the “blend” area is only a few milimeters, close to the center detent, then 50/50, then anothe couple milimeters of blend and most of the swipe left or right sounds like a single pickup without any other blend

I guess I was trying to change the feel of the blend so the “blended” area was bigger, and only sounded as a single pickup in the far extremes of the swipe

(For future reference, @line6man diagram shows the push/pull pot upside down, parallel is pulled and series is pushed)

 

[dwizum]

This is somewhat of a personal judgement call, but you're describing exactly how I'd expect an MN blend pot to work. Right in the middle you get both pickups on full, then there's a very small area in either direction where you can get some in between tones that favor one pickup or the other. But then it sounds like the knob stops having any effect at all and it's all one pickup or the other for what feels like a good portion of the travel after that.

 

[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.

 

[mrperkolator]

the schematics I'm looking at above seem to disconnect the top half of the blend when in series. What is the point then? Or am I missing something?

 

[mrperkolator]

I read somewhere that by putting a .1uF Cap on the Neck PU Tone Pot and a .022uF Cap on the Bridge PU Tone Pot you could increase the tonal range of your J-Bass. Of course that was meant for parallel, not sure what that will do in series. Would someone chime in on this and tell me if I'm wrong with either the wiring and/or the Caps.

Best I can tell, when in series your bridge tone and top half of blend will be disconnected, so you'll just be using the neck tone.

In parallel, the capacitors sum, so your total tone rolloff will be ~.150 uf. The blend knob may help separate it a little and make this quite an interesting setup in parallel. I'm just not sure on the series. Waiting on smarter heads to show up.

 

[Crater]

the schematics I'm looking at above seem to disconnect the top half of the blend when in series. What is the point then? Or am I missing something?

Putting the pickups in series essentially turns them into a single large pickup, so the blend will act as a second volume control. There's no way around it using a standard DPDT switch., even with a VVT setup only one volume works in series.

There was a long and very involved thread in this forum about whether it would even be possible to have a scheme with series/parallel switching AND still have individual volume and tone for each pickup. Long story short, it is possible but requires a FOUR pole, double throw toggle switch to switch between series and parallel.

 

[difesa98]

Here is the original diagram that I had posted.
View attachment 2793317

As for the dual tone control diagram, there are a couple of problems.

With an M/N taper blend, there will not be any position in the rotation where one of the two tone controls is not a master tone. This is because the M/N taper always passes one signal path straight to the output, without series resistance. To get isolation, you would either want to choose an A/C taper blend, or add resistors in series with each tone control to isolate the signal paths. An A/C taper blend is two ordinary volume pots running inverse parallel, so as you adjust the pickup blend, both pickups see series resistances that isolate their tone controls. While this is useful for isolating the tone controls, it is not ideal, as you don't get full volume from either pickup unless it is soloed. Likewise, if you add resistors to an M/N taper blend, you won't be getting full output from the pickups. This sort of compromise is one of the reasons that multiple tone controls are not popular. The other main reason is that it offers little practical value. Whatever treble you cut from one pickup will just be added back by the other pickup. A better option is having one tone control for both pickups, and choosing between different capacitors to get additional control and tonal variation. In any case, the second problem with your diagram is that it does not account for the volume drop that will occur if you put the pickups in series while the blend pot is set anywhere other than the soloed neck pickup position. Since there will only be one signal feeding the blend pot, the blend pot simply becomes a second volume pot feeding into the master volume pot. This is not practical, so you will want additional poles of switching to bypass the blend pot in series mode.

2. A 3PDT switch can be used to bypass the blend pot in the series mode, so that you don't need to worry about where it is set when you switch from parallel to series. This eliminates the possibility of using push/pull pots, and slightly complicates the wiring, however.

Sorry for bothering you, this is the last thread (i think) where we talk about series/parallel switch. Can you post the wiring diagram that uses a 3pdt switch in order to exclude completely the blend on series mode? Then the blend can be grounded? Thank a lot!