Hum-> Single pan pot

[flateric]

Returning to an unfinished project after about a year on the shelf, I have a problem working out the wiring for this:
I have two 4-conductor humbuckers, one master vol, one master tone, a standard 3-way selector switch, all standard stuff, then also a double-stacked pan pot (with centre detent) to pan from full humbucker to full coil tap.
Can anyone help with a circuit for this please? I'd like the pan pot to do the coil tap thing on whichever pup is selected (or both)with the 3-way toggle.

[sumgai]

eric,

With only a "standard" pickup selector switch (as in Gibson LP style?), I don't think you're gonna be able to reach your goal. Check this out, it's pretty close to what you're trying to do:

guitarnuts2.proboards45.com/index.cgi?board=wiring&action=display&thread=1146359636&page=1#1146401181

See where there are about a gazillion wires to the pot(s)? Even a 'standard' Strat-style switch (2 poles) won't have enough "connectivity power" to do the job, you would need to use a 4 pole version (the SuperSwitch, or one of the new MegaSwitches). Alternatively, a rotary switch would also have enough options to make everything happen, but IMO, those don't often fall under the moniker of 'standard'.

Of course, now that I've said that it probably can't be done, one of our resident wizards will prove me wrong! (That's a management technique for getting others to do your work for you, hehehe. )

HTH



sumgai

[flateric]

Well, that's not exactly what I'm after. Vintage started doing this ctrl config last year, now other manufacturers are putting out models, like Washburn and Framus. The blend pot does not act as a volume at all, just as a gradual sweep between full HB and full coil tap. As coil tap is simply grounding half the HB to earth, introducing a resistance to that should allow a sweep between HB and coil tap, allowing any amount of graduation between the two. I'm sure its not that complex a circuit, only too complex for my rudimentary knowledge of electronics.

[JohnH]

I would think it could be done with a normal dual-gang pot, I cant see that a centre detent indicates a useful position, since it would be all Sc at one end and full Hb at the other. I think the way to do it would be to wire the two hbs normally with the 3-way, followed by normal volume and tone. Then put the two halves of the sc/Hb pot, one each to shunt each Hb centre tap to ground via a variable resistance, using just the centre and one outer lug of each pot half of the dual gang.

Ive been playing with similar arrangements using the tone control, and I find that the range of values over which the shunting resistance changes the sound from Sc, to audibly full Hb is quite low, about 20k to 50k. So my guess is that what you want is a dual gang 100k log pot, wired so that the Sc setting is the fully anticlockwise position, to give a good sensitivity to the transition from Sc to Hb. As you turn it, it changes both pups at once.

If you are smart, you will be able to get a North coil of one pup and a South coil of the other for your Sc's, hence keeping a hum-canceling combo.

Did that make any sense?

John

[flateric]

Much sense, John. The neat twist in the N-S pole switch proves again you are God on this forum. Also agree the centre detent thing is meaninless in this setup, only the dual-gang stacked pots tend to be supplied with one built in.
If I cannot recreate a suitable schematic from your words of wisdom, are you available for further consutation?

[JohnH]

Thanks and of course. what are your pups? If they were say, Seymour Duncan, the way to get that N/S mix of the Sc combo is that one pup is wired as normal:
Black hot, Red/white centre tap, green ground
And the other has the coils swapped in position, but still pointing in the same direction:
Red hot, green/black centre tap, white ground

Heres a few more things to consider as you figure out your wiring:

Are then open coil or covered? If covered this may lead you to having one of the Scs under the cover, in which case, youd need to think about which pup to have which coil as an Sc. Also, at the bridge, do you want the Sc to be the one nearer the neck or nearer the bridge?

cheers

John

[flateric]

The pups are GFS Zebras [therefore uncovered....] but wire colours are as per SD standards.
Purely aesthetic but I like the zebras to be Black/Cream --- Cream/Black from neck to bridge, so the black adjustable poles (which will be the s/c section) are furthest apart from eachother for the widest tone differences.

[ChrisK]

Blend Pot Coil Split, Done Was.....



Also, Red Rhodes (Peavey) Tone_Coil Split Pot (circa 1990)

[flateric]

Thx - I remember coming across these some time ago on the board and trying to figure how to turn them into a simple schematic i could solder together. I failed, sadly. I came close to getting my brain into gear then it stopped working and I had to lie down.

[ChrisK]

Well, when you're tired of resting and if you find that you still need assistance, let me know.

[flateric]

Heh, ok, I'll work on a schematic to post up then you can show me where I went wrong...

[JohnH]

Cool circuits from Chris as always, but different to the simpler one that I was describing based on your first post. So theres several choices - go schematic!

cheers

John

[flateric]

OK lets see if this is along the right lines. Not sure about the wire colouring being correct or the earthing of the central blend pot contacts, but the idea is both humbuckers gradually short to earth as the blend pot is turned, thus tapping the coils.

[JohnH]

Good start but not quite.
I suggest
at the neck: Black hot, Red/white centre tap, green ground

at the bridge Red hot, green/black centre tap, white ground

Thats if you want to have a hum-cancelling Sc combo. Youd get the adjustable bridge coil and the slug neck coil. Or, do them both like the bridge if you want both adjustable coils (but not hum cancelling - unless you are willing to open the pup to flip a magnet - another story)

I agree with the lugs on the blend pot you are using (ie left side on the diagram). Connect the centre-tap wire pairs to the left lugs of the blender and the center lugs to ground (or the other way round, it doesnt matter)

cheers

John

[flateric]

Nice one, thx John. :-)

[flateric]

OK, the wiring has been done, it works fine across the pickup selections and it really makes a nice difference dialling in the full humbucker position, like a volume control with added 'meat'. But the problem is such a big difference in vol levels between tapped and full HB, it would really be helpful to have a situation where the volume did not drop off quite so much when the pan pot was turned to coil tap position.

[ChrisK]

but the idea is both humbuckers gradually short to earth as the blend pot is turned, thus tapping the coils.

Uh, no.

The basic function of a blend pot is two-fold:

For a true blend pot, where both sections are full on in the center detent position ("5" to you Strat-o-holics), both sections are full on in the center detent position and only one goes to ground either side of the center detent.

For a true pan pot, where both sections are -3dB on in the center detent position (equal power as delivered out of a stereo mixer), both sections are -3dB on in the center detent position and only one goes to ground either side of the center detent.


So, a blend/pan pot will not equally tap (a misnomer here) two pickups by coil shunting/shorting.


I can see the following being achieved with a true blend pot in the middle LP toggle switch position (both pickups on):

1. Full CCW. One pickup is in series humbucker config and the other is coil shunted/shorted.
2. Center. Both pickups are in coil shunted/shorted config.
3. Full CW. The other pickup is in series humbucker config and the one is coil shunted/shorted.

or

1. Full CCW. One pickup is in series humbucker config and the other is coil shunted/shorted.
2. Center. Both pickups are in series humbucker config.
3. Full CW. The other pickup is in series humbucker config and the one is coil shunted/shorted.


Other permutations exist, but not what you've asked for unless you're willing to tie the inter-coil center-taps together.

I would think it could be done with a normal dual-gang pot,

This type of pot will do this. It is a dual element/single shaft pot. I don't know where you get one specifically within the guitar parts channels. You might have to go electronics surplus.

Or, use a concentric shaft dual pot where you can blend each pickup individually.

Yow! Just use the concentric shaft dual pot for the Red Rhodes patent (expired is) wiring to effect both tone and coil shunting on an individual pickup basis (in the blend pot position), and retain a master volume and tone control. If you want to stay with just two controls, lose the master tone.


Red Rhodes

[JohnH]

Eric – The Sc is inherently less output than the Hb, but there’s a couple of things you could try to reduce the difference:
1. Adjust the adjustable pole heights so that the poles of the coil which is selected as Sc is nearer the strings than the other
2. On the Sc/.Hb pot, instead of having the lugs connected to ground to fully shunt one coil, ground them via capacitors of something like 0.1 to 0.18uF in series with the pot. This will get rid of the upper harmonics of the shunted coil as before, which will provide most of the Sc character from the non-shunted coil , while keeping some of the low-end meat of the full Hb sound from both coils. The smaller the cap, the more low end is kept, but too small and you lose the Sc character, so need to experiment.

One version of the Red Rhodes scheme (see Chris’ post) also has this effect, and I used this on my LP, with the extra cap adding some weight to my Sc bridge sound.

BTW - congrats for getting it going. What value of pot do you have in there at the moment and how do find the transition from Sc to Hb as you turn the pot - is it all the change at one end of th eturn or is it spread out over the arc of he pot turn?

Cheers

John

[flateric]

Thx guys. Its a 500k dual pot (the master vol and tone are also 500k as is the norm for dual HB guitars). The transition is reasonably good actually - I would say most of the change in sound character happens between 4 o'clock and 10 o'clock where 1 is full tap and 12 is full HB. 6 gives quite a nice attack and a bit of a stratty quack, but thicker than a strat single coil.

[JohnH]

Eric – thanks for the feedback. I’m not quite clear on the knob positions – (it depends how you place your clock! plus pots cant usually go all the way from 1 oclock to 12 oclock)

So just to be clear, since Id like to get this info for future reference: Your Sc/Hb pot, is it a standard 500k dual gang pot? log or lin? Or is it one of those detented blend pots that has all the resistance over one half, like 500k 0k 0k? And if you say that 0 is fully anti-clockwise and 10 is fully clockwise and 5 is half-way, is 0 the full Sc?, and at what setting as you turn it up from 0 does it start to sound like a full humbucker, with no further audible change with more turn towards 10?

With thanks

John

[flateric]

Sorry I'm not being much help, I bought the pot from one of the online guitar spares outlets.
Probably this blend pot from Axes R Us:
It has a centre detent but the resistance definitely does not stop at the centre point. I don't know if its log or linear taper.
The way I've wired it, 0 position (fully anti-clockwise) gives full HB and 10 gives fully S/C.
Going anti-clockwise starting from 10, the HB sound starts coming in at about 7, 5 is halfway, then full HB keeps building through 4, 3 and 2 to 1. Does that help any more?

[ChrisK]

So, is this a blend pot (where the resistance change is the opposite for each element), or a dual element pot (where both elements are identical)?

[flateric]

They sell it as a blend pot, but I guess it makes no odds if you reverse one set of wires

[JohnH]

I had a look on axes r us, see about 2/3 down this page:

www.axesrus.com/axeknobs.htm

and its described as :

"An A500k/C500k pot for controlling the mix of signals from two pickups or sources. Pan from one source to another;"

so Chris, is a C500, a reverse audio taper? It would mean that if wired as I was describing youd expect to get get one pup changing from Sc to Hb in a different position or more rapidly than the other, although it still would work.

John

[ChrisK]

is a C500, a reverse audio taper

It sure sounds like it.

it would mean that if wired as I was describing you'd expect to get get one pup changing from Sc to Hb in a different position or more rapidly than the other, although it still would work.

Yes, but in a convoluted way. At the end of CCW travel, both coils would be shunted, but in the middle, it depends on your definition of "still would work".

As I've been saying, in the center detent position, a 500K blend (as in PAN) pot has an approximate resistance of 80K from the wiper to the CW terminal and about 420K to the CCW terminal on one element, and an approximate resistance of 80K from the wiper to the CCW terminal and about 420K to the CW terminal on the other element.

A true 500 K BLEND pot will have an approximate resistance of 0K from the wiper to the CW terminal and about 500K to the CCW terminal on one element, and an approximate resistance of 0K from the wiper to the CCW terminal and about 500K to the CW terminal on the other element.

Anyway, either way, the effect is opposite (hence the ability to blend/pan between two signals).