Tuned Capacitor Tap

[Brian Austin]

Hi Guys, I have been reading a great book that some of you may have heard of called "How to make your own electric guitar & Bass" by Dennis Waring & David Raymond. On page 82 of my copy there is a little article on how make a tuned capacitor tap to try and get a better single coil sound out of a coil tapped Humbucker.

This is done by increasing the bass by way of substituting the earth wire of the mini switch with a capacitor and a resistor in parallel, however they really don't tell you what value capacitor to use. Has anybody tried this mod and if so, could they please tell me what value capacitor they used and whether of not it improved the single coil sound of their guitar? Any help would be much appreciated. Thanks, Brian.

[lvs]

I'd say 10-12-15-18 nanoFarads are values worth trying. This cheap and simple mod was in a guitar of mine for a while, but now not anymore. I tested a large range of cap values on both pickups and it didn't work for me with the bridge HB but it sounded okay with the neck HB (and with the HB coil closest to the neck connected to earth, IOW the cap in parallel with that coil).

[psw]

I have been excited to try a variation that is eluded to kind of in that book. I like the idea, but I found an idea that uses a normal tone control to add this feature at the extreme end of the tone knobs travel (between 8 and 10).

Basically, how it works is to add to split the HB by turning all the treble out of the other coil instead of lifting it or shorting it completely. There are benefits to noise canceling (both coils are still in circuit, so it is still somewhat humbucking) and helps the often weak sound of a split HB (you still get the bass tones of the full HB and a little more power). Still won't sound like a fender, but it could sound really good.

I found that hidden in the DBG Studio site that there is something called a "special tone"...basically it works as a normal tone to about 8 on the dial...the rest cuts one coil by applying the pots resistance and the cap. Unfortunately I have not had a chance to actually do it. draw anything or determine values. For this kind of thing though, I would expect small values as Ivs has suggested...

I'd say 10-12-15-18 nanoFarads are values worth trying.

I have the book, it's odd that a value isn't given...however, they have a resistor in there to "tune" the circuit to what suits. You might even consider replacing this fixed resistor with a small trim capacitor in the guitar of about 2K and turning that would "tune" the circuit to taste with each pickup.

I like the idea of a variable tone control split version. Apparently Peavey tried it on something moons ago and I am sure there are variations with experimentation. This keeps the tone control and adds to it the ability to "boost" treble by way of a coil split at the extreme end...8 would be full HB. There is the benefit of it not adding switches and using existing tone pots.

As I say, haven't tried it yet, but there is a project in the works that I hope to make this a feature.

pete

[Workingman]

I have coil taps on three guitars and one bass. My experiance is that it takes a fairly hot pickup to sound good with a coil cut. You are after all going to have half the resistance you started with. A PAF type pickup with around 8 ohms is going to give you 4 in coil cut mode which is less than a typical tele pickup. A 12 ohm pickup will give you 6 which is in the range of some strat type pickups. less resitance usualy gives you more treble. I would think the best capasitor to use would vary with the pickup. The hotter the pickup the less treble you would have to roll of to ground for a good sound no?

[lvs]

From a quick & dirty SPICE sim I understood basically the following about the cap's working. Anyway, I feel this concurs with the experiences I had with it.

- It causes a dip in the hi mid frequency range. As a result lows and highs sound of course more prominent. Since the dip can be fairly deep, it makes sense to tame that a little (or make it adjustable) with a (variable) resistor. Btw I accidentally found this mod when during a rewire I made a wrong tone pot connection.

- Right before that dip, there's a small resonance peak.

- Right after the dip, there's another, larger resonance peak with a frequency higher (1200ish Hz) than the resonant frequency of the whole pickup by itself, giving a little more single coil character.

- The result appears to be sensitive to signal phases too. Think locations of the coils under the strings, also not excluding a combination of two SC pickups. Btw, Armstrong incorporated it into his 3-toggle Super Strat circuit using 10 nF caps that not only work as lowpass tone control - which in a Strat I find much more usable than traditionally larger values - but also work like the cap we're discussing here, when pickups are switched in series.

[psw]

I have coil taps on three guitars and one bass. My experiance is that it takes a fairly hot pickup to sound good with a coil cut. You are after all going to have half the resistance you started with. A PAF type pickup with around 8 ohms is going to give you 4 in coil cut mode which is less than a typical tele pickup. A 12 ohm pickup will give you 6 which is in the range of some strat type pickups. less resitance usualy gives you more treble. I would think the best capasitor to use would vary with the pickup. The hotter the pickup the less treble you would have to roll of to ground for a good sound no?

Ummmm...no you are misunderstanding the principle here...

We are not just talking splitting the pickup (by the way, your values for pickups should be Kohms).

The idea is to use a cap (and resistor) to short one of the coils to ground...this means you get the bass of both coils and the full output of the other (you might consider this variation for your own splits if they are not satisfying to you.

"sounding good" is subjective and also depends on the musical application. Some pickups sound better than others, and very nice tones can be had by splitting one or both pickups but in combination for instance.

The biggest mistake is that some people think that splitting a pickup, you might bet a "fender" single coil sound...this is wrong for numbers or reasons. And, you are right it depends on the pickup and the position how it might sound...but by no means can they necessarily be dismissed as "bad"....so what value to make the partial split (which is what this is and the meaning of a tuned split) depends on the effect liked, the pickups and the guitar it is used in. My suggestion of a tuning trimmer inside, or the idea of adding it into the tone control allows for this tuning to taste..."good sound", yes?

pete

Ps...Ivs, still on the money there! I have used as low as 10nF in tone controls for "special effects" in the tone control department...with the right combination and experimentation, these unusal values can give a nice wah like response in some guitars!

[Workingman]

Thanks for clarifying the concept, and noting my KOhm mistake.

I was not trying to tell people how to get a Fender tone rather using the KOhm range of well known pickups for reference. I also agree that good or bad sounding is very personal personal.

[Brian Austin]

Hello Everone, thanks for all your replies and advice. I will have a go at the cap values suggested and post the results soon afterwards. Thanks, Brian.