Practical Wiring

[alder]

This is the wiring for the humbucker mode switch on my 3-pickup Strat bass. What this does is switch all three pickups simultaneously between (internal) series, parallel, or single-coil modes. Externally, all three pickups are wired together in parallel with a blade switch like a normal Strat.

Stratocaster Bass ( and Jazzmaster, and other forbidden birds )

Effectively, the switch is eight separate switches on one shaft. It takes two switches per pickup to accomplish the task, leaving two unused. The diagram shows lug-to-lug jumpers 'inside' the switch for clarity, but these jumpers are actually wired around the periphery of the switch, or 'over the top'. All the ground lugs, 5-upper, 5-lower, 14-upper, and 14-lower, are all connected together with the bottom of the switch housing. Connections are made as shown to minimize the number of solder joints on any one lug. The pickups are drawn in whatever orientation avoids drawing crossed wires, in real life you will go by the color coding. The 'outs' all go to the blade switch.

So what is the point of this? Fender gave the Stratocaster three knobs, volume, tone, and ... another tone. The first two are standard, but the third is pretty redundant, I consider it to be of little use on a guitar, and none on a bass. That leaves one extra knob then, that I can do whatever I want with. This rotary switch fits right in, and gives far more tonal variations than a typical tone-mush control.

The switch looks like this.

The hard part is finding the switch. At first I used an open-frame six-pole switch from Hong Kong that proved to be flimsy, difficult to solder, and unreliable. Then I found these closed 8-pole switches from a supplier in Taiwan. These switches have a nice solid feel, are smaller, inexpensiver, and are much easier to solder up. eBay is the place to go. Search for "rotary switch 8-pole 3-position" or "rotary switch 6-pole 3-position". The only problem with these switches is that the shaft is too tall, but that is easily fixed with a Dremel.

With the standard 5-way blade switch, this gives 15 different pickup combinations, of which 12 are humbucking. You can get anything from a thin reedy Jazz sound to a big fat Precision sound, without ever touching the 'tone' knob. With the addition of a push-pull switch on the volume or tone knob, you can add six more combinations. Someday I am going to find out what this wiring would do in a guitar ( I mean, a Piccolo Bass VI. )

Why aren't factory guitars wired like this? Because it is not easy. Look at all the pickup leads and solder joints. All of that can be screwed up or go bad later. That means rejects, re-works, and warranty issues. Compare all this mess to the simplicity of a standard Stratocaster with three single-coils and that useless extra tone pot. But you can certainly do this at home, and I've already done the hardest part for you - you have the diagram.

 

[alder]

Hi Alder,

I forgot to answer this question. Your combined bass/treble control looks fine to me. Very similar to what G&L does with two separate pots, although they use different resistance values (which I don't think will be significant, but there will be some difference).

That's some pretty intense wiring for a factory guitar.

 

[JustForSport]

alder-

Thanks for sharing this...

 

[JustForSport]

Here is the calculation.....

Nice posts- great explanations and the #'s to back it up (the calcs are over my head, tho).

And anyone -- please feel free to correct any mistakes I've made!

And that's the best yet.

I freely give of what I've learned from my experiences, but expect no one to take it (info stated) for granted/ fact.

 

[alder]

Here is the calculation showing the delta in gain between a single 500K pot and a dual M/N pot, when both are at their center positions, to be -1 dB. The amplifier input impedance is shown as Ramp.

My apologies for my penmanship -- it has never been my strong suit. But I hope I've gotten the idea across. And anyone -- please feel free to correct any mistakes I've made!

- Jeff

Thanks much for this, this is the kind of info I'd like this thread to have, not just "Fensonbacker did it this way in 1953, so it must be right."

 

[walterw]

Thanks much for this, this is the kind of info I'd like this thread to have, not just "Fensonbacker did it this way in 1953, so it must be right."

how dare you, my 1955 Fensonbacker is the best bass ever!

 

[alder]

Rubber Bands, Piezos, Buffers, and Tone Controls

My "Stratbory" ukelele bass with rubber strings uses a piezo pickup integrated with the bridge saddle. Piezos are strange things, with rather low output and very high impedance, or "Z", and it is accepted practice to use active electronics to tame their bad qualities. An active buffer circuit will match the piezo's high-Z on the input side, and reduce it to a nice amp-friendly low-Z signal on the output side.

Many if not all active circuits have the nice property of accepting a high or low impedance signal, and outputting a low one, regardless of what kind of circuit it actually is, eq, distortion, boost, whatever. I originally installed a good 2-band active EQ in the Stratbory ( that's Strat-Ashbory. ) That turned out to be overkill. Finger noise on the rubber strings is horrendous, and made worse by accentuating treble. The goal of this odd instrument is to imitate the sound of a double bass, and adding treble doesn't help with that either, so the active treble control is a complete waste.

Then I remembered I had a couple of Squier Jaguar bass-booster circuits in the junk box. Those are really lousy pieces of electronics, awful sound with way too much gain, they almost ruin what is otherwise a fine instrument. But that might be just the thing for this application, especially if you keep it turned down and just use it as a low-gain impedance buffer. So I pulled the good eq out of the uke and put it aside for some future project, and installed one of the Squier circuits.

Turns out, the factory wiring is wrong, and/or the circuit is defective, and if you wire up the power and several redundant grounds as it was done at the factory, the unit will never shut off, even when it is unplugged. One dead battery later, I took it apart, deleted all but one of the 'grounds', and wired the battery the way it should be. So now I have an impedance buffer with a bass boost built in.

For a volume control, I used a 500k pot upstream of the active buffer. A 1 meg pot might work better, but the 500k works fine. However, a standard tone control will not work with a piezo pickup, instead it simply functions as a second volume control. So instead of trying to put the tone control on the high-Z side upstream of the buffer, I tried building one on the low-Z side downstream. A standard tone control won't work there either, it has no effect at all. So back into the junk box I went, and found a b50k pot. On that I tried various values of capacitor, finally settling on a 0.5uf 'death cap' from an old amp project. ( Naturally, I didn't install the death cap in the amp, but I ordered it just in case. ) That gives a functioning tone control, not the best, but the best I could do with what I had. Note that the resistance is 1/10 of a typical control, while the capacitance is 10 times !

I ordered some 20k pots to rebuild it with, which will probably result in a much smoother response curve with a more normal-sized cap. The last part of the circuit is a bypass switch, actually a push-pull on the volume control, that disconnects the battery and shunts the piezo directly to output. The piezo actually does have a usable output on it's own, although you would never want to use it, it is weak and thin compared to the buffered output. I put the switch there mainly so I could noodle on the thing without having to find a battery, as I do not keep batteries in any of my active guitars; 9 volts all leak eventually.

So, what is the end result of replacing a good active eq circuit with a piece of crap? A better instrument, actually. You would never want to go 'up' with the tone on one of these, and now it has both bass boost and treble cut, both of which you would want to do. I installed the knob on the active gain so it is normally in the minimum position, and goes up from there. Most importantly, the new circuit buffers the high-impedance piezo pickup just as well as the old one.

The other Squier bass boost I installed in the piccolo bass, where its overbearing nature is actually an asset. In that case, I installed the knob so the gain is maximum at zero, and you cut it down, the opposite of the Stratbory. Since that guitar uses normal pickups, no problems wiring up tone controls, as long as you keep everything upstream of the active circuit. Finally, I pulled another eq from a guitar where it did very little good, and replaced it with passive bass and treble controls, leaving me two of the good eqs to play with on future projects.

What started out as a cost-saving effort turned into a very instructive study of active and passive controls, and how to combine them, not to mention piezo properties. I know I learned a few things, and I thought I'd pass it on.

Update

The 20k pots were ineffective. Using a test stand that I just built and alligator clip jumpers, I tested a range of pots and capacitors, and in the end came back to what I already had: b50k pot x 0.5uf capacitor. So that is how you build a low impedance treble control. A 100k pot also worked, but not as well. The value of a pot for any particular application is apparently much more important than the taper.

I have another bass with a single low impedance pickup on which the tone control was always ineffective. I think now that the value of the factory pot is too high - it would not surprise me, I've seen enough goofs. When I get a chance, I am going to try this tone control on it. I have lots of b50k pots from other projects, and Radio Shack carries the caps. In the meantime, I need to open up the Stratbory and make the wiring permanent.

 

[alder]

Here is a modification of the series super-switch that favors pickup combinations over singles

This modification substitutes the neck-bridge combination for the middle pickup, giving: 1-5: N-NM-NB-MB-B. I installed this in the piccolo bass. ( I violated my no-humbuckers-in-series rule, but for this application, every bit of extra oomph is welcome, and they're pretty lightweight humbuckers anyway. )

It's a pretty good trade, neck-bridge for middle. With single-coils, this is not a humbucking combination, so there is no gain or loss in that respect. Sound-wise, the new combination is somewhere between the two standard combinations. The differences are fairly subtle, but you get a much smoother transition from position to position than you would with the normal setup. Note that all of this and a bit more is achievable with my previous super-switch wiring using one extra switch. This has the advantage of being perhaps more 'natural' and easier to use.

To understand the circuit, try to imagine that the switch is not there, but the jumpers are. Now, you simply have all three pickups connected in series:

ground ==> B- B+ ==> M- M+ ==> N- N+ ==> output

Think of the ground as sort of source or 'signal', which it is not really, but it helps. The 'signal' passes through all three pickups to the output. If the 'signal' goes through the pickup, then that pickup is active, otherwise it is silent.

The super-switch is simply 4 separate switches ganged together. Each switch position connects that numbered lug to its common. So if you study the individual switches you can see, for example, that in position 1 the bridge pickup is looped onto itself, + and - connected together, while still passing ground through for the middle pickup. Or in other words, the ground 'signal' short-circuits around the pickup. Since lug 2 is jumpered to lug 1, it has the same action. Lugs 3,4, and 5 are not connected, so in these positions ground goes through the bridge pickup instead of around it.

Any pickup that is shorted like this will be silenced. Taken to the extreme, connecting the ground to the output will silence the whole chain. So the trick in deriving this wiring is to provide a suitable ground to the output of each pickup whenever you don't want it to sound. There is actually a lot more obvious way to draw out the equivalent circuitry. This drawing is modified from that to show optimized physical connections on the switch. Related pickup leads attach close together, and no lug has more than two connections for easier soldering. Any shielding can be grounded to the switch body, which can then be grounded itself.

 

[alder]

This is strange

passive bass cut control​

I rigged up one of these in a bass with P/J pickups, and it didn't work ! No effect at all. All the components checked out. After some experimenting, I settled on a version with a 1 Meg pot and a 0.00047 cap. That's three zeroes, a cap the size of a match head. This gives a noticeable effect, but no where near as strong as what I had previously done. Either all my pots and caps are leaky as hell, or something strange is going on here. I suspect it is something to do with the pickups. It works fine with guitar pickups, but failed utterly with bass pickups. The pickup impedance is not all that much different, I just can't figure it. Anyone have any ideas? Any EE's out there?

 

[walterw]

the drawing shows a polarized cap, which it shouldn't be;

also, normal guitar bass-cut pots (G&L style) only use two pot lugs; the cap goes across the two, which are also the in and out.

knob up=short across the two lugs, no bass-cut; knob down=1MΩ between the two lugs, signal has to go through the .0047μF cap instead, blocking the lows. (yes, two zeros, not three, as long as it's for normal passive stuff)

and of course this is in series with the entire guitar signal, not parallel like a regular tone pot.

 

[alder]

the drawing shows a polarized cap, which it shouldn't be;

also, normal guitar bass-cut pots (G&L style) only use two pot lugs; the cap goes across the two, which are also the in and out.

knob up=short across the two lugs, no bass-cut; knob down=1MΩ between the two lugs, signal has to go through the .0047μF cap instead, blocking the lows. (yes, two zeros, not three, as long as it's for normal passive stuff)

and of course this is in series with the entire guitar signal, not parallel like a regular tone pot.

I just drew the cap that way, although at these power levels it shouldn't matter. In any case, the same parts work perfectly in another guitar. Wiring the 3rd lug to the sweeper should have the effect of changing the taper of the pot, if anything, reducing the effect of the circuit. Again, I wired it this way and it worked perfectly before. But in this case, it does nothing, from stop to stop, not even a volume change. The cap behaves almost like a short across the pot. I'm thinking there may be a large difference in capacitance between guitar and bass pickups that disables this circuit, but my knowledge of electronics is very rusty. Actually, that doesn't seem too likely either, the whole thing is just weird.

 

[walterw]

You wanna go from "simple" to "complicated" in your troubleshooting, right? Try wiring the circuit normally, with just the two lugs used. Also, it'll usually be the last thing in line before the jack (in series of course).

Although looking at it, your version should work, maybe with a slightly different sweep.

 

[alder]

You wanna go from "simple" to "complicated" in your troubleshooting, right? Try wiring the circuit normally, with just the two lugs used. Also, it'll usually be the last thing in line before the jack (in series of course).

Although looking at it, your version should work, maybe with a slightly different sweep.

I looked at the G&L schematic, and it uses 3 lugs very similar to mine. I don't see how to do it with just two. Everything else is already as you said. This is very strange because it is a duplicate of a previous installation that works very well, yet in this case it doesn't work at all. It must be something about the pickups. The extra connection between the sweeper and the third lug probably serves to short out the pot completely on that side, for complete bypass.

 

[walterw]

I looked at the G&L schematic, and it uses 3 lugs very similar to mine. I don't see how to do it with just two.

not that i've ever seen!

they're done like this:

 

[sunbeast]

I looked at the G&L schematic, and it uses 3 lugs very similar to mine. I don't see how to do it with just two. Everything else is already as you said. This is very strange because it is a duplicate of a previous installation that works very well, yet in this case it doesn't work at all. It must be something about the pickups. The extra connection between the sweeper and the third lug probably serves to short out the pot completely on that side, for complete bypass.

The G&Ls just use two lugs (one center and one outside) for the high-pass (or "Bass-cut") circuit. Some of the G&Ls also have a second capacitor affixed from one lug to ground, but this is just a small treble-cut capacitor and not related to the bass-cut circuit. G&L use an anti-log 1Meg potentiometer for the Bass-cut, which is just the reverse of an audio pot. These pots are a bit tough to find, but you can get this taper by just using the opposite lugs of an audio pot, though this means the bass-cut will be strongest when the pot is on full. I have this circuit on a couple different basses and it works a charm using a 500K Audio pot. I like using a very small capacitor though like a .0047uf (ala Rickenbacker - I actually have such a circuit in my Rickenbacker that only affects the bridge pickup and it is great to blend with the neck pickup. Bridge on full, then roll up the neck for the desired amount of sub frequencies).

 

[alder]

The G&Ls just use two lugs (one center and one outside) for the high-pass (or "Bass-cut") circuit. Some of the G&Ls also have a second capacitor affixed from one lug to ground, but this is just a small treble-cut capacitor and not related to the bass-cut circuit. G&L use an anti-log 1Meg potentiometer for the Bass-cut, which is just the reverse of an audio pot. These pots are a bit tough to find, but you can get this taper by just using the opposite lugs of an audio pot, though this means the bass-cut will be strongest when the pot is on full. I have this circuit on a couple different basses and it works a charm using a 500K Audio pot. I like using a very small capacitor though like a .0047uf (ala Rickenbacker - I actually have such a circuit in my Rickenbacker that only affects the bridge pickup and it is great to blend with the neck pickup. Bridge on full, then roll up the neck for the desired amount of sub frequencies).

Thanks for posting that. That is the third way I've seen of wiring this up. I will give it a try. First I'm going to make a test stand, so I can try different things outside of an opened-up guitar.

I added a push-pull to my Ric to bypass the "strangler cap", as I call it. What a difference. But I wired my switch upside-down, so you pull it to get the modern sound, because it is a 4001, and supposed to sound like that. Since I used Ric's 4003 retrofit kit, I have the capacitor left over. I figure an authentic Ric cap should probably go for about $25, if anyone is interested.

 

[alder]

I made a temporary test stand from a tabletop vise, and used some alligator clip jumpers from Radio Shack to test a whole lot of configurations without having to do a lot of soldering. I took the output from the guitar and jumpered it to the test setup, then jumpered the output of that to a headphone amp. It was noisy as hell, but it worked. I did a whole range of tests:

pots:
A500
B500
A1000
B1000

caps:
0.0047 ceramic
0.0022 uf poly
0.0022 uf paper
0.0010 uf paper
0.0010 uf ceramic
0.0005 uf ceramic

I also tried several different wiring schemes. On G&L's website, I have found the control wired two different ways on basses, 2-lug, and 3-lug, always with 1M pots and 0.0022 caps. The 2-lug wiring was with an active preamp, while the 3-lug wiring was strictly passive.

The best result was audio pot + 0.0005 cap, which confirms my previous result. Pot value and taper made little difference. The G&L 2-lug wiring seemed to be smoother than mine, but slightly less effective. However, even the best result was negligible, no better than the control I had already wired into the guitar, A1000k pot x 0.0005uf cap. The type of capacitor made no difference at all - this is one of the biggest ripoffs in the business. Expensive caps in a tube amp - absolutely. Expensive caps in a guitar - rubbish. Actually, you don't need very expensive caps in an amp either, just good ones. But in a guitar it makes NO DIFFERENCE.

I think I will leave the existing wiring as it is. If I could think of something else worthwhile to do with that knob, I would.

My guess is the higher impedance of the bass pickups makes the resistance of the pot negligible - the signal just pushes its way through the pot regardless of the setting. A 1 Meg pot with no capacitor will act as a poorly-designed volume control. Adding any cap reduces the volume drop, larger caps reduce it more. It is not hard to mistake a change in volume for a change in tone, especially when that is what you are expecting. Listening as critically as I can, I do not hear a change in tone, just a volume drop, regardless of the cap. I would guess the effect is 90% volume and 10% tone, at best. A frequency analyzer would sort this all out pretty quickly.

The previous three examples where I used this control successfully all used guitar pickups: a Bass VI with stock strat single-coils, a piccolo with strat-sized humbuckers, both series-wired, and a bass with 3 strat-sized humbuckers in parallel. In all three, the bass control guts the bass right out as expected. The humbuckers actually have fairly high impedance, comparable to bass pickups, which only adds to the confusion. Possibly, it is not the impedance of the pickups, but the capacitance, that is the issue. Or it could be something else, but I am sure it is the pickups. BTW, the guitar pickups sound just fine in a bass.

The next experiment I'm going to try this on will use series lipsticks, my favorite pickups of all, and I expect it will work fine again. Unless someone can explain something I missed or did wrong, my conclusion is that this control does not work with typical bass pickups. Someone please jump in here and explain this.

 

[sunbeast]

I made a temporary test stand from a tabletop vise, and used some alligator clip jumpers from Radio Shack to test a whole lot of configurations without having to do a lot of soldering. I took the output from the guitar and jumpered it to the test setup, then jumpered the output of that to a headphone amp. It was noisy as hell, but it worked. I did a whole range of tests:

pots:
A500
B500
A1000
B1000

caps:
0.0047 ceramic
0.0022 uf poly
0.0022 uf paper
0.0010 uf paper
0.0010 uf ceramic
0.0005 uf ceramic

I also tried several different wiring schemes. On G&L's website, I have found the control wired two different ways on basses, 2-lug, and 3-lug, always with 1M pots and 0.0022 caps. The 2-lug wiring was with an active preamp, while the 3-lug wiring was strictly passive.

The best result was audio pot + 0.0005 cap, which confirms my previous result. Pot value and taper made little difference. The G&L 2-lug wiring seemed to be smoother than mine, but slightly less effective. However, even the best result was negligible, no better than the control I had already wired into the guitar, A1000k pot x 0.0005uf cap. The type of capacitor made no difference at all - this is one of the biggest ripoffs in the business. Expensive caps in a tube amp - absolutely. Expensive caps in a guitar - rubbish. Actually, you don't need very expensive caps in an amp either, just good ones. But in a guitar it makes NO DIFFERENCE.

I think I will leave the existing wiring as it is. If I could think of something else worthwhile to do with that knob, I would.

My guess is the higher impedance of the bass pickups makes the resistance of the pot negligible - the signal just pushes its way through the pot regardless of the setting. A 1 Meg pot with no capacitor will act as a poorly-designed volume control. Adding any cap reduces the volume drop, larger caps reduce it more. It is not hard to mistake a change in volume for a change in tone, especially when that is what you are expecting. Listening as critically as I can, I do not hear a change in tone, just a volume drop, regardless of the cap. I would guess the effect is 90% volume and 10% tone, at best. A frequency analyzer would sort this all out pretty quickly.

The previous three examples where I used this control successfully all used guitar pickups: a Bass VI with stock strat single-coils, a piccolo with strat-sized humbuckers, both series-wired, and a bass with 3 strat-sized humbuckers in parallel. In all three, the bass control guts the bass right out as expected. The humbuckers actually have fairly high impedance, comparable to bass pickups, which only adds to the confusion. Possibly, it is not the impedance of the pickups, but the capacitance, that is the issue. Or it could be something else, but I am sure it is the pickups. BTW, the guitar pickups sound just fine in a bass.

The next experiment I'm going to try this on will use series lipsticks, my favorite pickups of all, and I expect it will work fine again. Unless someone can explain something I missed or did wrong, my conclusion is that this control does not work with typical bass pickups. Someone please jump in here and explain this.

I can certainly hear a noticeable change in tone, and I've used variations on the passive bass-cut on more than a half-dozen basses over the last 7 or so years (when I bought my first G&L L-series bass). I've used a variation in my Rickenbacker, two P-basses, a Jazz with a Darkstar pickups, a Jazz with Thunderbird pickups, and a handful of G&L L-1000s, L-2000s, and L-2500s.

The G&L-style control with the larger valued cap is definitely more subtle than the Rickenbacker-style with the .00047uf cap, though with the large low-mid output of the G&L humbuckers it is more noticeable with them than with other pickups. The Rickenbacker capacitor is super powerful, and can make any pickup sound like a guitar pickup with the pot turned to "full capacitor" in my experience. You can even see the shift in frequency response clearly through a computer software recorder like Logic (as I did while recording bass and experimenting with different tones on my bands last album).

I wonder if the impedance of your headphone amp setup is the issue- I have a similar finding as you if I plug a passive bass into a line-level input (ie trying to play my G&L into my computer speakers, turning the bass-cut control mostly just cuts volume due to the impedance mis-match; whereas through an amp it works as expected).

 

[alder]

I can certainly hear a noticeable change in tone, and I've used variations on the passive bass-cut on more than a half-dozen basses over the last 7 or so years (when I bought my first G&L L-series bass). I've used a variation in my Rickenbacker, two P-basses, a Jazz with a Darkstar pickups, a Jazz with Thunderbird pickups, and a handful of G&L L-1000s, L-2000s, and L-2500s.

The G&L-style control with the larger valued cap is definitely more subtle than the Rickenbacker-style with the .00047uf cap, though with the large low-mid output of the G&L humbuckers it is more noticeable with them than with other pickups. The Rickenbacker capacitor is super powerful, and can make any pickup sound like a guitar pickup with the pot turned to "full capacitor" in my experience. You can even see the shift in frequency response clearly through a computer software recorder like Logic (as I did while recording bass and experimenting with different tones on my bands last album).

I wonder if the impedance of your headphone amp setup is the issue- I have a similar finding as you if I plug a passive bass into a line-level input (ie trying to play my G&L into my computer speakers, turning the bass-cut control mostly just cuts volume due to the impedance mis-match; whereas through an amp it works as expected).

Well, DUH! There is all kinds of audio software for PCs ( and Macs like mine ) including spectrum analyzers. Why didn't I think of that? Thanks for reminding me. In my defense, it was pretty late at night. Your point about the input impedance of the headphone amp is a good one, but it works fine with the three other controls, so I don't think that is the issue. My best guess is that the bass pickups ( P & J ) with the extra-heavy strings on the pico have such high output that it just muscles its way through even a 1 meg pot like it is not there.

 

[sunbeast]

Well, DUH! There is all kinds of audio software for PCs ( and Macs like mine ) including spectrum analyzers. Why didn't I think of that? Thanks for reminding me. In my defense, it was pretty late at night. Your point about the input impedance of the headphone amp is a good one, but it works fine with the three other controls, so I don't think that is the issue. My best guess is that the bass pickups ( P & J ) with the extra-heavy strings on the pico have such high output that it just muscles its way through even a 1 meg pot like it is not there.

Signal can't really "muscle through", but the way the control functions would definitely be affected noticeably by the impedance of your input.