Help figuring out an unusual series/parallel scheme

[Stealth]

Hey, everyone,

a friend's jazz bass clone ended up at my place with the intent of adding a series/parallel push-pull to it. A long time ago I stumbled upon a schematic that promised the ability to dial in a bit of each pickup, something that usually doesn't work in series mode. (click to expand)


I sold(i)ered on, wired it all up and what happened is, the blend function just plain doesn't work. Well, among other things. The parts list is two 250k pots Here's the sound-clip.
Soundclip of the rewired bass.

The settings in the clip are normalized to series volume:

• Series, volumes full, tone full
• Series, volumes full, tone zero
• Series, neck zero, bridge full, tone full
• Series, neck full, bridge zero, tone full
• Parallel, volumes full, tone full
• Parallel, volumes full, tone zero
• Series, neck zero, bridge full, tone full
• Parallel, neck full, bridge zero, tone full

So here are the things bugging me:

1. The series output is incredibly hot - I know that's because of the series wiring, summing the signals instead of averaging, but is the difference really supposed to be that big?
2. The neck volume seems to act like a master volume, so blending obviously doesn't work. Also, it gets loud really quick, basically from 1-2 and it's already at its loudest.
3. The tone control seems to do zilch in parallel mode (which is odd since it worked perfectly on stock wiring and it works perfectly in series, a .047 )

Is that schematic fundamentally broken, can it be fixed, is there any schematic that actually lets you blend pickups in series as well as parallel or should I just GTFO and wire it up the proper S/P way?

[cbarrow7625]

Are you sure those schemes are drawn correctly? It doesn't make sense to me that you only have output from the bottom pickups 3rd lug in 1 of the 3 drawings. Also, I can't make out what the wiring of the switch is supposed to be; the way it is drawn it looks like it would do nothing. Also, are you using linear or audio taper pots?

Can you just draw the two pickups, two pots and wiring to the switch exactly as it is wired inside the bass? I understand that the 2nd two schematics are the way you think it's wired, but without a single full scheme it's hard to determine for sure.

[Stealth]

I should have clarified. In the image above, the left is the actual wiring scheme. The right is the behavior depending on the switch position (up is parallel, down is series with a regular DPDT on-on push-pull). The hot goes to a regular tone pot and out a regular mono jack.

[cbarrow7625]

I figured that is what it is supposed to be, but if that is the case then there are some wires missing that are not shown. Are there really only two wires going to 2 pins on the DPDT switch? The two wires / switch shown would not produce the results shown to the right.

[cbarrow7625]

Oh, I see now. You used numbers to represent the other switch / wire positions. OK, I'll see what I can figure out from that.

[cbarrow7625]

I just listened to the tone clips now that I get how you drew the schematic. Here's my thoughts:

1.) Can't help with the tone control because you didn't show where or how it was wired.
2.) If the volume is really as different as it sounds in the clip, something is wrong.
3.) The schematic as drawn should work fine. The fact that it doesn't work fine (plus the volume differences) probably means that it is not wired up correctly. Check it, check it, and then check it again.

If the blend doesn't work and one volume works as the "master", then you have wired one of the pickup leads to the wrong pot lugs And/or your switch moves the connection to the wrong lugs. And/or/or you have the Middle and end lug of one of the pots wired together somehow (again check the switch wiring too).

Are you sure which switch position is Series & which is parallel? The internals of some switches switch to the terminals under the toggle bat, others switch to the side opposite the toggle bat. The reason I ask is that it is much more likely that the working (louder) version is the parallel wiring and that you somehow have a pot in series with the second pickup (instead of the 2 pickup in series) in the series wiring. That would explain the drastic volume differences.

[Stealth]

Tone control: hot from the above schematic to central lug, hot from central lug to output, cap from outer lug to pot chassis.

I'll check the wiring again, but I did my best to avoid shorts of any kind. Since I used a the innards of a guitar cable that had faulty connectors for wiring, I used bits of the sleeve to cover the solder points and avoid shorts.

Also, I'm sure which position is which, I tested continuity with a VOM in both switch positions.

[Stealth]

To answer the pot taper suggestion, I'm not sure what the vol pots are, I forgot to check them. The tone pot used to be an A250K, now it's an A500K P/P. As far as I can tell, the increased resistance of the tone pot should only increase the resonant peak of the pickup somewhat.

Could part of the problem stem from the fact the volumes might be audio taper? I know a common suggestion for basses is linears for volume, logs for tone.

What additionally confused my dad (who knows just enough of electronics to notice when something's amiss, and who checked the wiring and soldering with me) is the fact that in series mode, the pin marked 3 (top left) on the switch is open, while the mid left and pin 1 (bottom left) get shorted.

[cbarrow7625]

Could part of the problem stem from the fact the volumes might be audio taper? I know a common suggestion for basses is linears for volume, logs for tone.

That would just change the rate at which the volume rises as you turn the knob. Linear rises more quickly that audio taper. Since yours rises too quickly, you might want to try audio taper (if they are not already).

What additionally confused my dad (who knows just enough of electronics to notice when something's amiss, and who checked the wiring and soldering with me) is the fact that in series mode, the pin marked 3 (top left) on the switch is open, while the mid left and pin 1 (bottom left) get shorted.

That is the way it needs to be though. It is designed so that you are not adding the potentiometer resistance in series with the pickup in series mode. If you added series resistance from the pots, the volume would go down more than expected. In series mode, the two pots basically just short around the pickups. Actually, you could leave the upper leg of the upper pot disconnected from the middle lug (pin 1) and it wouldn't make any difference. If you did that,the upper & lower pot (in series) would be wired exactly the same. Draw it out like that, it might help you visualize it better.

It worked before, you changed the wiring and now it does not. Troubleshooting 101: go after the thing that changed. Try to modify one thing at a time until you see improved results. There is no magic wand to make it work. Many thousands (millions?) of guitars are wired using the parallel blend wiring used in this schematic. It should blend for you too.

The best thing for you to do is probably to eliminate the switch for now & get just the parallel blend working. When you get that figured out, then hard wire the series wiring (without the switch). Once you have both of those working you will know how they are supposed to react; then you can add the switch back in. Who knows? Maybe you just have a bad switch. Overheating switches while soldering kills them, you know.

[Stealth]

Right-o. The reason I doubted the schematic initially was because no pickup maker I know of, that also provides schematics on their site, has ever included this particular wiring - maybe because it's this complex and requires a lot of effort to get done right. I literally stumbled upon it on the net and thought it'd work - and it doesn't. Since you've seen this wiring already, that only proves I messed somewhere up.

Thanks for the troubleshooting help. I'll report back after the weekend with the results - hopefully the wiring isn't completely FUBAR:

[Stealth]

cbarrow7625, thanks again for steering me in the right direction. We took the bass apart again and found a short on the neck pickup volume. Since the wiring was getting pretty tangled up everything was desoldered and resoldered and it works perfectly now. I can definitely head the difference between S and P positions.

[cbarrow7625]

Nice! Glad it works. I would love to hear additional sound clips of the working version.

[Stealth]

Will be recorded in about six hours, stay tuned!

[Stealth]

Phew. That's what happens when I make guesstimates.

Anyway, here's the soundclip link.
The samples are:
Kiwi Requiem - The Decision, fingerstyle
- neck, bridge, parallel, series
Kajagoogoo - Too Shy, slapping
- parallel, series, moderate compression
Cream - Sunshine of Your Love, fingerstyle
- parallel at full tone, half tone, zero tone, then series at full tone, half tone, zero tone
Siouxsie and the Banshees - Israel, pickstyle
- parallel, series

I hadn't the time to record, but blending works as well and the tonal palette is now extended by far.
Shame I have to return the bass to the friend, I've really grown to like it post-mods (and I haven't had a Jazz of my own).

[cbarrow7625]

Sweet. That's what it should sound like! Nice job.