Is my wiring diagram correct?

[StuartV]

Okay, so I completed this project last night. It was late and people were sleeping, so I didn't really get to try it out. I did plug it in and pluck a few soft notes and play with the controls to see if it was all working correctly.

I now have a couple of questions:

- It seems that the Tone knob works backwards from what I would expect. I.e. when I turn it fully clockwise, I get treble rolloff (and definitely not as much as I would expect). Fully CCW, I get the full, bright tone. Based on my last wiring diagram, above, is that right? What do I need to do to make it work the opposite way (like a regular Fender Tone knob)? Looking at another wiring diagram, for a P bass, it looks like maybe I should move the wire that is connected to the Input lug on the Tone pot over to the Ground lug instead.

- It seems like when I start turning down any of the 3 volume knobs, it rolls the volume off really quickly. Like, the last 1/2 of the rotation is useless because it's already completely off by 50%. The bass had 2 250K pots to start with. Now it has 4 500K pots. I had understood that that should result in the bass sounding and working just like it used to - if I leave the Master and Tone open and just use the 2 individual Volumes. If I want all the Volumes to work more progressively - or maybe I should say less aggressively - do I need to change to all 250K pots? If I do that, how will it affect the bass' sound when I have the Master and Tone wide open and just make adjustments to the individual pickup Volumes?

- Will fixing the Tone pot change how the Volumes are working?

 

[lakefx]

For the tone knob, if you reverse which lug is connected to the input wire and which lug is connected to ground it will reverse which direction the pot turns, but shouldn't change anything else about its behavior.

What you describe with the last half of the pot being very small change is typical of audio taper pots. Some people prefer them and others prefer linear taper for volume controls.

As for the bass working just like it used to, when you changed to 500k pots, you made the bass a bit different. Instead of thinking of the pots as decreasing the signal, think of them as sending it somewhere else (in this case to ground where you can't hear it). The lower the resistance of the pot, the more signal gets sent to the ground when it is completely open. The character of the signal also changes as you send more or less of it to ground because different frequencies behave a bit differently at different points in the process. When you increased the resistance of the pots, you changed their behavior because to get the same amount of signal through to the output jack, you need to have to pots rolled part way off now. This is somewhat simplified because things like pickup impedance and the interaction of the pots changes everything a bit too.

For the tone knob, when you changed to a 500k pot, you made the bass brighter and now need to roll off some of the tone to get close to what wide open was before, but because you are now engaging the capacitor to roll off the highs, it will only effect certain frequencies, further changing the character of the bass. I doubt you can get the bass to sound exactly how it did before while adding a tone pot and master volume, but going to a larger capacitor (maybe .1uf?) may get part of what you want. Going back to 250k pots for the pickup volumes may get you closer. I'm not enough of an expert to tell you what the best way to get there is, but it's pretty easy to play around with these things.

If you find that rolling the volume off about 25% on each pickup gets the tone you want, go back to 250k pots. If the tone pot doesn't roll off enough highs, swap the cap for a larger value. If you find that the tone pot is useless for the last half, try wiring up the SB-1 style circuit. This is the joy of modding something; you learn a lot by almost never making it work right the first time!

 

[StuartV]

As for the bass working just like it used to, when you changed to 500k pots, you made the bass a bit different.

I asked about this pot arrangement a long time ago (before I ordered the parts, which have just been sitting around for a while). The explanation I got was that, since I was starting with only 2 pots at 250K, going to 4 pots at 500K would result in the same overall impedance, since it's all wired in parallel, so the bass should sound the same - at least, with everything open.

Not true?

 

[lakefx]

More or less true. The total impedance when everything is all the way up should be about the same, but as soon as you start turning knobs at all, that goes out the window. It also means that the range of adjustment of each pot as it relates to the overall sound is going to be different.

 

[StuartV]

I guess, really, I just need to move the wire on the Tone pot, to get that how I want it, and then play with it some.

Thanks for the help!

 

[StuartV]

The Final Word:

I moved the wire from the input lug to the ground lug on my Tone pot and all is now well. And, I'm very happy to say that this mod seems to have given me exactly what I wanted. The Tone control works just like I wanted. I can roll it all the way off, solo the neck pickup, and get exactly the thumpy P sound that you get from any regular P with the Tone off. Perfect for some kinds of R&B or maybe reggae. And the Master Volume works.

All I have left to do is a sample recording, to compare it to the recording I made just before I took it apart.

Anyway, thanks again to everyone who helped me with the wiring diagram I have updated it for posterity, to match what I actually did. That is posted below.

But, one final note is, the diagram has the pots in each stack backwards. When I drew it, I mistakenly assumed the bottom pot would correspond to the bottom knob in the stack. So, if you wire it just the way I diagrammed it, the Master Volume will be the bottom (ring) knob in the stack. Tone will be the top (center) knob. And the pickups will be backwards.

When I have time, I might get around to flipping everything around, to reflect what I actually did, which is Master Volume and Neck Pickup as the 2 top knobs and Tone and Bridge Pickup as the 2 bottom (ring) knobs.

In the meantime, here is the (otherwise) correct diagram.

or http://s227.photobucket.com/user/stuartv/media/MVVT12-1.png.html to get to a bigger version.

 

[WeThePeople]

The Final Word:

I moved the wire from the input lug to the ground lug on my Tone pot and all is now well. And, I'm very happy to say that this mod seems to have given me exactly what I wanted. The Tone control works just like I wanted. I can roll it all the way off, solo the neck pickup, and get exactly the thumpy P sound that you get from any regular P with the Tone off. Perfect for some kinds of R&B or maybe reggae. And the Master Volume works.

All I have left to do is a sample recording, to compare it to the recording I made just before I took it apart.

Anyway, thanks again to everyone who helped me with the wiring diagram I have updated it for posterity, to match what I actually did. That is posted below.

But, one final note is, the diagram has the pots in each stack backwards. When I drew it, I mistakenly assumed the bottom pot would correspond to the bottom knob in the stack. So, if you wire it just the way I diagrammed it, the Master Volume will be the bottom (ring) knob in the stack. Tone will be the top (center) knob. And the pickups will be backwards.

When I have time, I might get around to flipping everything around, to reflect what I actually did, which is Master Volume and Neck Pickup as the 2 top knobs and Tone and Bridge Pickup as the 2 bottom (ring) knobs.

In the meantime, here is the (otherwise) correct diagram.

or http://s227.photobucket.com/user/stuartv/media/MVVT12-1.png.html to get to a bigger version.

Glad this worked out for you Stuart. Quick question. I have a similar project that I'm interested in. Thinking of adding a master vol pot on top of a tone pot. Current set up is v/v/t. If all pots are currently at 500k each would the new 2 stacked pots have to be at 1meg each to result in the same impedance?

 

[line6man]

Glad this worked out for you Stuart. Quick question. I have a similar project that I'm interested in. Thinking of adding a master vol pot on top of a tone pot. Current set up is v/v/t. If all pots are currently at 500k each would the new 2 stacked pots have to be at 1meg each to result in the same impedance?

Two 500k volume pots makes 250k. Adding a third makes 166.67k. Three 1M pots is 333.33k.

 

[RobbieK]

If you are worried about the dulling effect that all those pots are having, then I'd suggest trying the circuit with the earth removed from the stacked volumes. You won't be able to truly solo each pickup, but IME, that doesn't really matter. With one pickup's vol all the way down it is only just audible.

 

[WeThePeople]

If you are worried about the dulling effect that all those pots are having, then I'd suggest trying the circuit with the earth removed from the stacked volumes. You won't be able to truly solo each pickup, but IME, that doesn't really matter. With one pickup's vol all the way down it is only just audible.

Robbie are you saying instead of doing 1 meg stacked (for the master volume and tone), a 500k/500k stacked with the earth removed would be sufficient? There won't be a lost in volume?

 

[RobbieK]

You want to remove the earth from the stacked volume, not the master vol/tone stack. It will also help you to blend the pickups slightly more gradually. TBH, if it were me I would use a blend pot instead of your stacked vols. The circuit is essentially identical (you can also leave the blend pot unearthed). Depending on the pot, you may also be able to cut the track of the tone pot gang to make it no-load, further reducing the load on pickups but you'd have to stick with the tone control as the top knob of the stack.

I'm not really a passive jazz bass player, but I can't really understand why guys go to so much trouble to get the tiniest bit of extra brightness from their passive bass. But if you really want to go all out, then with a standard VVT, you can remove the earth wire from the two vols and use a no-load tone pot for maximum brightness from the (now completely un-loaded) pickups. The only drawback is that you can't turn the bass all the way down to zero. With both vols down, you'll still have maybe 10% of the sound. In practise this is no biggy, especially if your amp has a mute switch, or you can wire a push-pull as a kill switch or as a switch that grounds the volume pots to return to normal operation.

Having said all this, if you are a player who rides the volume knob(s) a lot, then all of this is academic. The tiny bit of extra brightness only kicks in with all knobs at 10.

 

[line6man]

Robbie are you saying instead of doing 1 meg stacked (for the master volume and tone), a 500k/500k stacked with the earth removed would be sufficient? There won't be a lost in volume?

Pot values don't really cause a loss of volume. It's more of an equalizer effect, where the resonant frequency drops down a little bit.

In general, people spend way too much time worrying about pot values, when it's such a subtle difference that it's not worth bothering with.

 

[StuartV]

Glad this worked out for you Stuart. Quick question. I have a similar project that I'm interested in. Thinking of adding a master vol pot on top of a tone pot. Current set up is v/v/t. If all pots are currently at 500k each would the new 2 stacked pots have to be at 1meg each to result in the same impedance?

I think you've mostly gotten as good an answer as you're going to get. The only thing I'll add (and I'm NO expert - line6man is, though - listen to him!) is that the problem with changing a VVT setup to have a Master volume is simply that nobody makes the right pots to let you do that and keep your overall impedance the same. With my wiring diagram above, I was able to keep the impedance the same because I was going from 2 pots in the original circuit to 4 in the final. 2 pots at 250K to 4 pots at 500K gives the same final impedance (I believe). But, when you're going from 3 pots to 4 pots, you would need 4 pots that are 667K (I think) - and nobody makes those (that I know of).