Correct caps and pots value in '60s Guild Starfire

[slidincharlie (Carlo P)]

I have a '66 Guild Starfire V guitar.
I am in the process of setting it up to have it work right, but I've noted that the wiring is most probably non-stock.
My only guide is the Starfire VI wiring diagram foun on the Guild website.

What makes me make me scratch my head in this Starfire VI diagram:
i) the volume pots are 500k while the tone pots are 200k;
ii) there is a .047 tone cap on the neck pickup, and a .02 tone cap on the bridge pickup.

Is this normal for such model?
My '66 Starfire V has four (apparently stock) pots that read between 500k and 800k, while the tone caps are non-stock.
What are the stock values in a '66 Starfire V?

Carlo

[Mark Hammer]

The use of a .047uf cap on the neck and a .02uf unit on the bridge makes perfect sense. In fact I'm pleased to see such a forward-thinking arrangement. Larger-value caps allow you to get a more mute tone. If you wanted a mute tone, why the hell would you attempt to get it on the bridge pickup? In my perfect world, tone caps should always be smaller in value for the bridge pickup than for the neck pickup, and that's irrespective of pickup type or brand/model.

The wiring diagram is a bit of a head-scratcher. Although the tone pots are wired up "normal" in that they provide a variable path for treble bleed from the "input" of the volume pot, normally individual volume pots are wired up as voltage dividers with the input being a side lug, and the output being the wiper. As the wiper moves from the input towards the ground end, you lose more signal.

The master volume here IS wired up that way, which is how I figured out what the individual pots were doing.

Consider that the master volume provides an output proportional to the ratio of the resistance between its wiper and ground versus the sum total of all resistances leading from the pickup to the input. If both pickups were hardwired directly to the master volume and you stuck a 100k fixed resistor between the neck pickup and master volume input lug, it would be tantamount to having a 500k pot for bridge pickup at the same time as having a 600k pot for the neck, with the neck pickup always being turned down just a bit more than the bridge at any position of the master volume pot.

When the individual pots are wired up to the master pot in this way, as you adjust the individual pot level, you are essentially adding series resistance to the input of the master volume pot for that pickup. So, if the neck pickup were turned way down, and the bridge and master up full, it might be equivalent to having a 900k master volume pot for the neck and a 500k master volume for the bridge, with the neck pot turned down more than halfway.

The weird tone pot values (200k) are probably because of this unusual wiring. If it were my guitar, I would probably do the following:
1) I would use a single 500k tone pot for the two pickups, wired up as a tone-balance control. Instead of each pot going to ground, a single linear pot would provide a path to ground for both pickups. One tone cap would be soldered to one outside lug of that tonal balance control, and the other tone cap would be soldered to the other outside lug. The wiper of that pot would then go to ground. Rotate the pot one way and the neck pickup sounds darker than the bridge. Rotate it the other way, and the bridge sounds darker than the neck. Set it to the middle and you have both tones "off".

2) I would replace the other tone pot with a 500k pot and connect it like a second master tone control on the master volume pot. In other words, the input lug of the master volume would go to a cap then the wiper of the tone pot, and the outside lug would go to ground.

Since the treble cut effect of both pots is additive, you should probably reduce the values of the tone caps for the tonal balance control. Neck value of .027 to .033uf and bridge value of .01uf to .015uf is probably about right. The master tone control could then have a .047uf cap on it.

This scheme allows you to go from a mute neck to super crisp bridge (master tone full up, balance rotated fully towards neck position), or "rounded" bridge to clean clear neck, and ease up on the edge of both simultaneously via the master control.

A second approach involves using smaller value caps on the balance control and tying the wiper of the tone balance control to the input of the master volume pot, rather than ground. This would provide variable volume compensation, or "bypassing" the individual volume pots as one sees on a Telecaster. Here, the tone cap and extra resistance from the portion of the tonal balance pot between the outside lug and wiper provides a parallel path for high frequencies, such that as you turn the individual volume down, the high frequencies encounter less attenuation. This lets you get thinner sounds than you currently can.

Consider this example. A 500k linear tonal balance pot is tied to the input of the neck volume pickup via a 1000pf cap, and the input of the bridge volume pickup via a 1500pf cap. When the tonal balance pot is rotated fully towards the neck position, you have a 1000pf cap completely bypassing the neck volume pot such that the neck volume affects bass and mids much more than it affects treble (i.e., a thin, almost out-of-pase sound). The bridge pickup has a 1500pf cap in series with 500k of resistance, so it provides no advantage for treble in the bridge pickup. As you rotate the tonal balance pot to the middle, both pickups have a tiny bit of advantage for the treble, but this can be easily offset by the master tone control.

This is a VERY flexible arrangement, capable of many many different tonal colours. The first one is probably better for rock and jazz, because it can provide many variations of "mellow", and the second one is probably better for funk, R&B, country and clean-soundiong forms of rock (e.g., surf music) because it can provide many variations of thin and bright OR full sounding.

Is my explanation clear?

[slidincharlie (Carlo P)]

Mark,
thanks a lot for your explanation.
I am not sure that I want to go that way though, although it is a very interesting approach.
As you certainly know, tying the pickup hot leads to the center lug of each volume pot lets me to have independent volume controls: this should allow me to blend both pickups to taste when are both engaged (hence the master volume).
I like this approach. Unfortunately it does not works well in this guitar, because as soon as I roll either volume just a tiny bit (both pups engaged) it acts as a switch that cuts the other pickup. So there is no chance to blend them pickups at all...
I normally wire my two-hb guitars with one master volume and two separate tone controls (one volume pot stays disconnected): thus I can adjust the overall volume very easily although I cannot blend the pups.

Please give a look at my other post here (Odd behaviour...): I'd love to read your comment on that one also.