Jazz Bass control circuits (passive) - what works for you?

[JapanAxe]

2 hours ago, jd56hawk said:

VVT with a turbo switch.

 

What does the Turbo switch do? I’m kind of afraid to ask…

[neepheid]

Which Jazz circuit works best for me?  Probably the one with no output jack...

 

Merry Christmas!

[HeadlessBassist]

1 hour ago, JapanAxe said:

What does the Turbo switch do? I’m kind of afraid to ask…

 

It forces a rush of compressed air into the tone wood molecules and makes them vibrate more quickly. As a result the bass resonates faster, making the sound sweeter, generates a more purposeful tone, and thusly the player becomes faster, with improved technique and accuracy, and becomes more God-like.  🤣

 

You did ask. 

 

Happy Christmas one and all!

Edited December 25, 2025 by HeadlessBassist

[Geek99]

2 hours ago, HeadlessBassist said:

 

It forces a rush of compressed air into the tone wood molecules and makes them vibrate more quickly. As a result the bass resonates faster, making the sound sweeter, generates a more purposeful tone, and thusly the player becomes faster, with improved technique and accuracy, and becomes more God-like.  🤣

 

You did ask. 

 

Happy Christmas one and all!

What if it’s vintage tonewood? 🍿
I’m also assuming that a longer g string screw on the bridge saddle makes it sound different also 

Edited December 25, 2025 by Geek99

[HeadlessBassist]

38 minutes ago, Geek99 said:

What if it’s vintage tonewood? 🍿
I’m also assuming that a longer g string screw on the bridge saddle makes it sound different also 

For best results, dredge your vintage tonewood from the bottom of a lake, same as they do for those highly expensive drum kits.

 

As for that screw in the G string saddle, I’m selling them for £40,000 each. Right, who wants some Magic Beans then..?

[JapanAxe]

41 minutes ago, Geek99 said:

What if it’s vintage tonewood? 🍿
I’m also assuming that a longer g string screw on the bridge saddle makes it sound different also 

Well spotted! The bass came without the correct 6-32 intonation screw (actually a bolt). The original would be  1 7/16in (39mm) long. I sourced some 2in bolts and cut one a bit longer, as I suspected the original had been lost because it didn’t adequately engage with the bridge saddle.

 

This topic is crying out for a PhD thesis!

[ezbass]

My J type has Delano pickups, which are actually split coils in a single coil casing. These are wired to a VBT config. I can achieve 5 tonal settings from this, not including the tone control (.100uf) roll off: if 6 o’clock is typical 50:50 blend, 5 and 7 o’clock give either a more neck or bridge flavour of the mid position, whereas anything beyond those points is either all neck or bridge.

[JapanAxe]

2 hours ago, ezbass said:

My J type has Delano pickups, which are actually split coils in a single coil casing. These are wired to a VBT config. I can achieve 5 tonal settings from this, not including the tone control (.100uf) roll off: if 6 o’clock is typical 50:50 blend, 5 and 7 o’clock give either a more neck or bridge flavour of the mid position, whereas anything beyond those points is either all neck or bridge.

That’s the thing, once you back off a stacked volume control or a VVT volume more than one notch out of 10, I don’t hear any further change. 
 

EDIT: Hoping for more variation on a blend…

Edited December 25, 2025 by JapanAxe

[JapanAxe]

I mentioned earlier today I had 'another idea' - I've implemented it, and it works!

 

When thinking about what didn't work for me about the stacked-knob setup, the main issue was the tone pot taper, where there was little effect until the bottom quarter turn of the pot. I removed the extra 56nF caps and added a 510k resistor between the wiper and the 'hot' lug of each tone pot, thereby converting the existing 500k tone pots to 250k with a somewhat different taper. The tone pots behave much better!

 

Curent plan is to to stick with this, but also acquire a 3-control plate and build it as Vol/Switch/Tone or Vol/Blend/Tone.

 

Watch this space...

 

[jd56hawk]

8 hours ago, JapanAxe said:

What does the Turbo switch do? I’m kind of afraid to ask…

The tone switch is Series/Parallel switch. 

[itu]

Yoy could even add another J pickup to the bridge position. Talk about supercharge. 

[Sté]

VVT. And those stock from my Sire U5 are really efficient. 

[tauzero]

Edited: see later post for correction to this and much clearer diagram. The non-hot end of the blend tracks should be connected to ground.

 

As regards V/B/T, I thought I should post a version of the wiring diagram that I worked from:

 

 

This may be clearer:

 

 

In this, the opposite ends of both tracks are cross-connected, rather than leaving one end floating as in the diagram in the OP.

 

 

Edited December 26, 2025 by tauzero
Wrong diagram.

[JapanAxe]

12 hours ago, tauzero said:

As regards V/B/T, I thought I should post a version of the wiring diagram that I worked from:

 

 

This may be clearer:

 

 

In this, the opposite ends of both tracks are cross-connected, rather than leaving one end floating as in the diagram in the OP.

 

Thanks, I came across these when I was looking into options.

 

I drew out the circuit in the OP and added in the second cross-connection as per the lower diagram, then compared the two. The OP circuit simply puts a resistance (let's call it R) in the path of one of the pickups at a time, to attenuate its signal. The effect of adding the cross-connection is to add a second resistive path in parallel:

1. At zero attenuation there is no difference.
2. At maximum attenuation the resistance in series with the pickup is now ½R instead of R.
3. At the halfway point, it becomes ⅜R instead of ½R, so the taper of the blend has changed.
4. Also with this circuit you wouldn't get the effect of completely disconnecting a pickup if you cut the resistive tracks near the end.

It would be a quick and easy thing to try though.

 

In the upper diagram, the second cross-connection is tied to ground, which is a different approach altogether and has the effect of loading the pickups, which the OP circuit doesn't.

[tauzero]

I was trying to find the original diagram that I worked from and didn't, and I didn't download it either which is annoying. However, I did find another reference page which shows clearly what I did, as I do have text notes to tell me what connections to make. I should have checked those wiring diagrams properly against what I used.

 

https://www.stewmac.com/video-and-ideas/online-resources/learn-about-guitar-pickups-and-electronics-and-wiring/blend-pot-wiring/

 

 

My notes definitely say to connect the crossovered non-hot ends to ground. If you compare that to a V/V/T setup, the pickups are loaded exactly the same - at one end of travel the pickup hot goes to ground, from the halfway point to the opposite end the pickup hot is straight to volume hot, and in between fully off and the centre point there is a varying amount of resistance.

 

https://www.stewmac.com/video-and-ideas/online-resources/learn-about-guitar-pickups-and-electronics-and-wiring/learn-about-wiring-stewmac-pickups/stewmac-bass-pickup-wiring-diagrams/ - second diagram

 

[JapanAxe]

5 hours ago, tauzero said:

I was trying to find the original diagram that I worked from and didn't, and I didn't download it either which is annoying. However, I did find another reference page which shows clearly what I did, as I do have text notes to tell me what connections to make. I should have checked those wiring diagrams properly against what I used.

 

https://www.stewmac.com/video-and-ideas/online-resources/learn-about-guitar-pickups-and-electronics-and-wiring/blend-pot-wiring/

 

 

My notes definitely say to connect the crossovered non-hot ends to ground. If you compare that to a V/V/T setup, the pickups are loaded exactly the same - at one end of travel the pickup hot goes to ground, from the halfway point to the opposite end the pickup hot is straight to volume hot, and in between fully off and the centre point there is a varying amount of resistance.

 

https://www.stewmac.com/video-and-ideas/online-resources/learn-about-guitar-pickups-and-electronics-and-wiring/learn-about-wiring-stewmac-pickups/stewmac-bass-pickup-wiring-diagrams/ - second diagram

 

 

Yes I'm trying to avoid that.

 

Here's the P-bass circuit. The pickup is connected to lugs 1 and 3 of the 250k pot so always sees that impedance (in parallel with whatever it's plugged into).

Here's the VVT Jazz bass schematic. Each pickup is connected to lugs 2 and 3 of its corresponding volume pot, so it sees everything from 250k (volume up full) to zero (volume at minimum). At (say) 20% it is seeing just 50k resistamce to ground. The OP circuit avoids this by adding resistance in series with the volume pot, forming a potential divider that can be used to reduce the output of either pickup.

As I said in the OP, there are plenty of people who are happy with this, and it sounds like you get on with your blend setup. That's all good, I'm just looking for something that works for me

Edited December 26, 2025 by JapanAxe

[TRBboy]

I've used the VBT circuit pictured at the start on 3 basses now, and it's my go-to! Seems to work well. I haven't bothered cutting the traces, and find it to be just fine.

 

Just reflecting on the fact that I pretty much only ever use it centered, so next build may not have a pickup selector of any sort 😅

Edited December 30, 2025 by TRBboy

[JapanAxe]

4 hours ago, TRBboy said:

I've used the VBT circuit pictured at the start on 3 basses now, and it's my go-to! Seems to work well. I haven't bothered cutting the traces, and find it to be just fine.

 

Just reflecting on the fact that I pretty much only ever use it centered, so next build may not have a pickup selector of any sort 😅

Both pickups on full is definitely my favourite Jazz bass sound.

[jonno1981]

Vol, Vol, Tone, with tone pot wired to pull up to switch between series/parallel. It’s monster! 

[JapanAxe]

The VVT control plate arrived yesterday but, despite being used, it is considerably shinier than the relic’d stack-knob plate. I intend to attack it (gently) with some fine wire wool before treating it with acetic acid fumes from white vinegar. I also could do with some raw sheep’s wool from a fence as the lanolin is apparently good for dulling bright metal.