coil tap blend pot

[flateric]

apologies if this has already come up, I guess it's bound to have done, but I searched in vain for a while.
I am interested in trying out the old Peavy coil tap blend pot, as is now being used in Trev Wilkinson's re vamped and improved Vintage guitars, advanced series.
This seems such an excellent tonal addition to a coil-tap humbucker set up but I can't figure out how it should be wired.
I'm looking for a master pot to control whatever pickup(s) are selected, i think the Vintage people call it a 'Roll control'. This enables any degree of coil tap from full on (single coil) to full off (pure humbucker).

[ChrisK]

Well, you can find wiring for the "Red Rhodes (Peavey) Tone_Coil Split Pot" here:

guitarnuts2.proboards45.com/index.cgi?board=schem&action=display&thread=1145315219

I sussed out the connections some time back.

Note that the patent on this circuit has expired.

[flateric]

thx chris, would the pot restsance be standard 500k for this? What about the capacitor?
Note: The Vintage 'roll control' is additional to the standard tone pot, not instead-of.
In this case, does the circuit remain valid? I want to keep my master vol and master tone intact.

[ChrisK]

would the pot resistance be standard 500k for this?

Yep.

What about the capacitor?

I'd use a 0.022 uF with humbuckers.

Note: The Vintage 'roll control' is additional to the standard tone pot, not instead-of.
In this case, does the circuit remain valid? I want to keep my master vol and master tone intact.

Don't know. I guess. Your choice.

You can fool around with capacitor values and location variations as shown in my link.

[flateric]

I've been really struggling to figure out a workable wiring diagram for what I am after.

I am thinking PRS McCarty-type wiring but with the push-pull pot replaced by a blend pot,

-Neck and bridge humbuckers (SD 4-conductor types)
-Master volume
-Master tone
-coil tap blend pot
-three way LP-type toggle switch

If I take it that the red and the white wires are the coil-tap wires on each pup, I connect the red neck and the red bridge wires to blend pot lug 1, I then attach the whites from both pups to the middle lug, and just earth the third lug, will that work?

I will then have the black wires from each pup going to the up and down lugs respectively on the 3-way toggle swith.
That just leaves the green and bare wires from each pup to earth.

Will that work?

[flateric]

Here's a sketch I came up with, please don't laugh I'm very rusty on electronics!

The bridge wires are reversed to give hum cancelling when selected together on coil-tap mode - well that's the aim anyway.
Will this work?

[UnklMickey]

i like that you have "stacked" the coils of the HBs so that you get hum canceling when both are split.

but, this still doesn't look like such a good plan to me.

there are a couple of problems.

first, when you adjust the pot so the coils aren't split, the series links of both HBs are still connected together.

this will sound a little different than having them separate, when you select both pickups.

this will sound a LOT different than having them separate, when you select just one pickup.

second, Chris knows more about blend pots than i do, but i don't think what you've drawn is quite right. it looks like when you try to adjust for a full split, you will have the full resistance of the pot in series with the pickup(s).

we should wait for Chris or John to weigh in on that part.


unk

[ChrisK]

This enables any degree of coil tap from full on (single coil) to full off (pure humbucker).

It goes from a full series humbucker connection to a single coil coil shorted configuration (blasphemy aside).

i like that you have "stacked" the coils of the HBs so that you get hum canceling when both are split.

Indeed, a good extrapolation!

but, this still doesn't look like such a good plan to me.

While it looks GeScrewy, it ain't all that GeFooey.

there are a couple of problems.

Yes and no.

first, when you adjust the pot so the coils aren't split, the series links of both HBs are still connected together.

Yep.

this will sound a little different than having them separate, when you select both pickups.

Maybe a little.

this will sound a LOT different than having them separate, when you select just one pickup.

Since you have the bottom coil of each pickup coil stack permanently wired in parallel, you won't get the sound of each pickup alone. Try it, you might like it, you can always revert to dual tone/tap pots (either separate or a dual-shaft concentric OR a dual element one(s)).

second, Chris knows more about blend pots than i do, but i don't think what you've drawn is quite right. it looks like when you try to adjust for a full split, you will have the full resistance of the pot in series with the pickup(s).

Indeed, when the coils are shorted, the output will be almost insignificant. You have wired it completely GeScrewy as compared to the Red Rhodes scheme, but what you show has its merits also! It is now a coil tap (short) pot alone since the tone cap "has gone to be with Jesus".

If you connect the blend wiper and the blend CW terminal together, you will have a variable split of both pickups simultaneously (actually a coil short, shudder) as you may have intended.


If you really just want variable coil tapping, take a (re)look at this for a true series to single coil to parallel blend with no coil shorting;
guitarnuts2.proboards45.com/index.cgi?board=schem&action=display&thread=1145315219

we should wait for Chris or John to weigh in on that part

I'll just wait out.....

[flateric]

Thanks guys, so to get this to work the way I was intending I need a proper mixer-type blend pot, which has 2 separate resistance sweeps working together, to keep the pups separate, right?

[UnklMickey]

i'm not certain that's gonna be the answer.

the blend pot might be 2 pots in tandem, but if one has a forward taper, and the other has a reverse, one of the coils will begin to 'split' way, way, WAY, before the other.

if it's linear, or if both tapers are in the same direction, then that won't be an issue.


unk

[flateric]

How about something like this?

We have master vol, master tone, pickup blender instead of a 3-way switch, plus a dual 500k linear pot for coil splitting. Have I got the wires wrong on the coil split pot? Didn't have space to add the duplicate set of lugs below.

[flateric]

[bump] Can any electrica gurus see any flaws in this scheme above?^

[ChrisK]

flateric,

First, the blender pot appears to be a single 500K linear. Blending with this scheme is questionable since at mid-point each pickup is connected thru a 250K resistor (one half of the blend pot). Anemic volume is.

One should use a proper dual element blend pot such as the StewMac one that has both elements full-on at the center detent position.


Second, you could represent the concentric pot (either dual element/common shaft or dual element/separate shaft [more common]) as side by side pots with the dual notation betwixt. It's difficult to determine the "ownership" of each wire/pot. (And I'm too lazy to guess.) Based on what I think that I see, I can't even determine your intent at this circuit point, but it appears to be more of inter-pickup coil blending at best. I would expect that the coil shorting node would involve the series coil tap connection wire pair from each pickup to each wiper and not the end lugs. Absolute detail is an absolute must here.


Third, I don't see any connection to common for either pickup.

[flateric]

Thanks Chris, I think I'm going to have to rethink this scheme, get some proper blend pots. Appreciate the feedback.

[UnklMickey]

chrisk said:

...such as the StewMac one that has both elements full-on at the center detent position....

i've always wondered if that were the case.

did you get this information from StewMac, or did you actually measure one, in-hand?


cheers,

unk

[ChrisK]

did you get this information from StewMac

Sort of. They won't tell me that the resistance is 0 Ohms to one end terminal and full value to the other for each element in the center detent position. They will only say that both elements are "full on" in this position. (Ya know, like that warm, woody sound.)

or did you actually measure one, in-hand?

No, I won't spend for the cost and shipping just to verify what is their lack of meaningful specificity. When I actually need something from them, I'll add a few on to the order.

However, I have seen it posted about that this is true. Hopefully it isn't from folks repeating what I've posted.....


The Fender bass guitar blend ones that I use are linear only (I have both dual 250K and dual 500K).