Onboard wiring harness help...aka grounding issue?

BunchyMutt

BunchyMutt

Supporting Member
Jul 3, 2014
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#1
After building a fearful 12/6/1 I got the soldering bug and I'd like to try my hand at wiring up a passive onboard preamp. The signal chain will be:

signal chain.png

(Blend only works when the pickup selector is in the middle position, or both pickups)

Control layout:
controls.png


I'm needing some confirmation on parts though. Do the components I've linked look good?
  1. Single/Parallel/Series switches (3 Way Switch - On On Mini Switch - Best Bass Gear)
  2. Tone/Tone stack I'm trying to go with Bourns pots as much as possible. Do they make a 500/500 tone stack?
    1. Audio taper
    2. 500K/500K
    3. .022 (bridge) / .047 (neck) (http://www.stewmac.com/Pickups_and_...n=2017-07-gp&gclid=CIz3pZCFgNUCFYSEaQodTwsGMw)
  3. Pickup selector switch (3 Way Switch - On On Mini Switch - Best Bass Gear)
  4. Blend (Passive, m/n)
    1. Bourns Bourns Blend Pot 500k/500k MN Split-shaft
  5. Volume
    1. Linear
    2. 500K
    3. http://www.bourns.com/docs/product-datasheets/95.pdf
  6. Wire (Guitar and Pickup Wire | Allparts.com) What wire do you recommend for onboard passive electronics?
  7. Output jack (Switchcraft Number 11 1-4 inch Input Jack | Allparts.com)
I know this is an involved question so many thanks ahead for your help.
 
#2
This is a schematic, not a "pictorial diagram" but since no one else has posted one, this is what you get. :D I didn't show the single coil switching because parallel mode sounds extremely close to 'pure' single coil mode but it's still hum-cancelling. L1 is the neck pickup, L3 is the bridge pickup, S1 is the series-parallel for the neck pickup, S5 is the series-parallel for the bridge pickup, the rest of the components are labeled with their function.

The blend pot is only active when the pickup switch is in the center "both" position. I show a dotted line on the center of the blend pot because I'm unsure if that's supposed to be grounded or not. (someone more experienced than me will know.)

Not sure if the pickup switch you selected will work with this diagram...

There's no such thing as a "passive preamp" by definition. Just call it a wiring harness. As far as wire choice, I recommend stranded wire because it's more flexible and doesn't break as easily when flexed. I think 20 guage or 22 guage is fine.


Gent-P-harness.png
 
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#3
Crater said:
This is a schematic, not a "pictorial diagram" but since no one else has posted one, this is what you get. :D I didn't show the single coil switching because parallel mode sounds extremely close to 'pure' single coil mode but it's still hum-cancelling. L1 is the neck pickup, L3 is the bridge pickup, S1 is the series-parallel for the neck pickup, S5 is the series-parallel for the bridge pickup, the rest of the components are labeled with their function.

The blend pot is only active when the pickup switch is in the center "both" position. I show a dotted line on the center of the blend pot because I'm unsure if that's supposed to be grounded or not. (someone more experienced than me will know.)

Not sure if the pickup switch you selected will work with this diagram...

There's no such thing as a "passive preamp" by definition. Just call it a wiring harness. As far as wire choice, I recommend stranded wire because it's more flexible and doesn't break as easily when flexed. I think 20 guage or 22 guage is fine.


View attachment 1175566
Click to expand...

Thanks for that! Thread title edited :)
 
#4
UPDATE: Ok, all components are in.

For the 3-way pickup selector switch/blend pot setup, I'm not sure how to translate the schematic above to knowing where wires go on lugs from this:
on on on switch A.JPG


to this (Bourns m/n blend pot):
mn blend.JPG


and then to this Bourns volume pot (before going out to the jack)
volume.JPG


Thanks for any help.

@line6man?
 
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#6
line6man said:
That's not the right switch. What you want is a DP3T switch. They physically take the form of a 4PDT On/On/On switch, and have twelve terminals.
Click to expand...
Well shoot. Wasn't sure if it was the right switch, but would never have guessed one with 12 lugs. Thanks for clarifying that. Two questions then I guess,

1) It's the right switch if it was just a 3-way switch and no blend, correct?

2) Does this diagram show the correct wiring?
4DPDT.jpeg
 
#7
Maybe I missed something…but you don't usually have a pickup blend and a pickup selector switch in the same passive harness. It's usually one or the other. And if you're using a blend there's usually just a master volume rather than individual volume controls. Otherwise there's redundancies in your wiring scheme.

So…

a) master volume plus pickup blend and no selector switch

- or -

b) Individual volume pots for each pickup plus a pickup selector switch. (Note: some designs that do it this way may also decide to include a master volume pot.)
 
#8
40Hz said:
but you don't usually have a pickup blend and a pickup selector switch in the same passive harness. It's usually one or the other. And if you're using a blend there's usually just a master volume rather than individual volume controls.
Click to expand...
You did miss something, read (or re-read) the first post. This is the setup he asked for, and I drew a schematic accordingly. The blend pot is only active when the pickup switch is in the "middle" (both pickups selected) position. When either pickup is selected individually, it bypasses the blend control and has full volume. There are individual tone controls for each pickup and a master volume.
 
#9
40Hz said:
Maybe I missed something…but you don't usually have a pickup blend and a pickup selector switch in the same passive harness. It's usually one or the other. And if you're using a blend there's usually just a master volume rather than individual volume controls. Otherwise there's redundancies in your wiring scheme.

So…

a) master volume plus pickup blend and no selector switch

- or -

b) Individual volume pots for each pickup plus a pickup selector switch. (Note: some designs that do it this way may also decide to include a master volume pot.)
Click to expand...

The scheme I was going for was indeed a three way switch and a blend (when the switch is set to both pickups). By redundancies do you mean conceptual or control redundancies, or signal loading redundancies? I know one or the other is typical. I also know that passive blends at fully neck or fully bridge positions still aren't completely isolated from the other pickup, hence the switch.
 
#10
GentProvocateur said:
By redundancies do you mean conceptual or control redundancies, or signal loading redundancies? I know one or the other is typical. I also know that passive blends at fully neck or fully bridge positions still aren't completely isolated from the other pickup, hence the switch.
Click to expand...

Control redundancies mainly and possibly tonal. But if you want both control configurations that's fine too.
 
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#11
Crater said:
You did miss something, read (or re-read) the first post.
Click to expand...

I did read the first post. And thank you for checking. I was just politely disagreeing with the design spec.

This is the setup he asked for, and I drew a schematic accordingly. The blend pot is only active when the pickup switch is in the "middle" (both pickups selected) position. When either pickup is selected individually, it bypasses the blend control and has full volume. There are individual tone controls for each pickup and a master volume.
Click to expand...

Yes. I see that too. And as I said in a later post, there are redundancies doing it that way that needlessly complicate the circuit.

Having all those additional components in there may also adversely affect the tone he's shooting for since the additional resistance added by those will have an effect on the overall tuning of the circuit.
 
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#12
line6man said:
Since you have an M/N taper blend pot, there is an alternate scheme that you can use, which will work with the DPDT switch that you have. The tradeoff is going to be having an ungrounded blend, but arguably, that's a good thing, especially given that you don't need to be able to solo the pickups with the blend pot, since the switch will do it for you.

Were you set on having a standard blend wiring scheme, or is the ungrounded M/N blend a consideration?
Click to expand...
I don't know enough to know what the ungrounded scheme would be, but I don't want to wait to order new parts so I'm open to anything that uses the parts that I do have :)
 
#15
I don't think you need two tone controls, but simply a master tone. Two tones in a passive circuit can't be isolated from each other, and you will be wrestling with them in conjunction with the blend control. Using different value caps for each pickup is a nice idea but also redundant.
 
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#16
Axstar said:
I don't think you need two tone controls, but simply a master tone. Two tones in a passive circuit can't be isolated from each other, and you will be wrestling with them in conjunction with the blend control. Using different value caps for each pickup is a nice idea but also redundant.
Click to expand...

Thanks. Since it looks like I'm going for just a switch instead of a blend (at least for now), it should be less of an issue.

As for tone controls, different strokes I guess. Dual tone control jazzes are highly sought in some circles. And then there are Rickenbackers. The main reason why I'm trying that route however is that the two pickups are from different manufacturers and I do want them to have different effects.
 
#17
The problem with having multiple tone controls is that they are not independent. Each tone control effects BOTH pickups, unless you have the volume pots turned down. To get isolation, you need to put resistance between the pickups, but that resistance kills output, so there really is no winning. Gibson style schemes where you have separate volumes and tones for each pickup plus a pickup selector can be useful for "presetting" the controls to different settings for when you solo the pickups, but when the switch is in the middle, you will still have same problem with the tone controls interacting.

Perhaps a worthwhile use of having multiple tone controls is choosing two different capacitances, so that you can have different frequency cutoff points, but even then, it's easier to just have one tone control with a switch to select capacitances. At the end of the day, there is a reason why most basses have only one tone control. Multiple tone controls are impractical.
 
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#18
line6man said:
The problem with having multiple tone controls is that they are not independent. Each tone control effects BOTH pickups, unless you have the volume pots turned down. To get isolation, you need to put resistance between the pickups, but that resistance kills output, so there really is no winning. Gibson style schemes where you have separate volumes and tones for each pickup plus a pickup selector can be useful for "presetting" the controls to different settings for when you solo the pickups, but when the switch is in the middle, you will still have same problem with the tone controls interacting.

Perhaps a worthwhile use of having multiple tone controls is choosing two different capacitances, so that you can have different frequency cutoff points, but even then, it's easier to just have one tone control with a switch to select capacitances. At the end of the day, there is a reason why most basses have only one tone control. Multiple tone controls are impractical.
Click to expand...
Thanks for the insight
 
#19
GentProvocateur said:
Dual tone control jazzes are highly sought in some circles. And then there are Rickenbackers.
Click to expand...

Stack knob Jazz basses are highly sought out, but I think it is a stretch to say that it is because they have two tone controls. Again, the two tone controls are redundant on a stack-knob Jazz, because with both pickups dialed in either can act as a master tone control, and turning down both sums the values of the two caps (which are in parallel, thus double the capacitance) and therefore darkens the tones. Those Jazz basses don't allow you to, say, hear the neck pickup with the tone rolled off but the bridge pickup with the tone rolled up, simultaneously. This is a myth propagated by those that simply don't understand the role of the two resistors in series with the output of each volume pot in the stack circuit. It is repeatedly stated online that the resistors somehow isolate the tone controls, whereas they were there (and deleted from subsequent reissues) simply to isolate the volume pots from each other. The resistors also cut down on the output of the bass, so to some they sound sweeter because of this. A matter of personal preference, and you could ape the tone by simply wiring a fixed resistor in series with the output of your Jazz bass.

As for Rickenbackers, the wiring scheme in these is cunningly devised so that, in stereo, each pickup has a complete set of circuitry that is isolated from the other. Each pickup has a volume and tone, with each side of the pickup selector never 'seeing' the other. Very cunning, and when run in stereo the two tone controls do not interact, though apparently there is some bleed between the two channels somehow. Rickenbacker could have wired up the strictly mono 4003S basses with with a tone control and the second tone control acting as a bass cut control for the bridge pickup, removing the need for the vintage/modern switch on the bridge tone control.
 
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#20
With a single tone control you don't have to settle for only a single capacitor. You can put a simple SPDT switch in with a different capacitor on either side so you can toggle between something like an .033 and an .047 or a .1

You could implement it either as a push-pull on the tone pot or install it as a separate switch. Or use a rotary switch for more choices like the Tonestyler does.

You can also get some interesting tone variations through different pickup switching schemes. Coil splitting and series/parallel switching can provide some additional tonal variations beyond what your tonestack can give you.

That's the beauty of passive wiring. So many interesting variations to explore. :thumbsup:
 
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