Stratocaster Midrange Shaper

"Praise God from whom all blessings flow, Praise Him all creatures here below,
Praise Him above ye Heavenly host, Praise Father, Son, and Holy Ghost. Amen."

(Click on images for a full view)

There is quite of bit of information (and confusion) regarding a midrange shaping circuit
for Stratocasters floating around the 'net. I have done a lot of wiring modifications to Strats
over the years and have settled on three mods that I use on all Strats that I wind up owning.
The first is to make the middle tone control universal to all three pickups, the second
is to install a switch (a push/pull type on one of the existing tone pots) to engage
the neck pickup in and out at will in order to combine it with the bridge pickup,
and the third is a passive midrange shaper which I will describe below.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

The image below shows the cuircuit I began experimenting with in incorporating a midrange
shaping circuit to my guitars. I found some problems with it, however, and experimented
extensively to find a circuit that works well and achieves some very interesting and useful tones.

The circuit shown below is the one I settled on. This type of tone shaping circuit is a modified Varitone
type circuit as found in some Gibsons, and to a lesser extent, some Gretsches.
Changes from the above original circuit include doing away with the 220K and 1 Meg resistors in
parallel with the caps as I found they did next to nothing at all with the tone.
Also, rather than having one leg of one cap grounded, I found that
having both caps' tail legs soldered to the one leg of the inductor gace a smoother sweep
and much better overall tone. And finally, in this particular circuit you have to use varying values of caps
to achieve tonal results that suit you persoanlly. I settled on a 0.082 microfarad on one side
and a 0.01 microfarad on the other, however you can feel free to experiment to your hearts' content.
I've used caps varying from 0.0033 microfarads up though to 0.10 microfarads and again, I
settled on the values given here. I would personally recommend a range of between 0.03 to
0.08 on one side and from 0.01 to 0.05 on the other. Again, it's a matter of personal taste.

Now, as to the parts needed, I will try to eliminate as much of the confusion as I can.
The capacitors needed are pretty straightforward, you can use anything from cheap ceramic disc caps
to older Sprague black beauties or pretty much anything in between that will fit in the guitars' cavity.
Also, as to fitting, I do not solder the parts directly to the pots as shown, but make a little package of the
inductor and caps soldered together as required, tape it all up with wire leads coming out from the package,
tuck the package in between the selector switch and the pickups under the pickguard,
and run the wire leads to the pot as needed. Just a personal preference is all. Anyway, back to the caps,
different caps of identical value but of different construction will affect the quality or timbre of the tone,
the same as using Sprague black beauties or Philips mustard caps sounds much better than ceramics.
Again, it's just a matter of personal taste.

As for the pot, you need a 500K linear taper pot. I use a push/pull 500K linear taper pot
and use the switching option to engage the neck pickup as I mentioned earlier.
Again, a matter of personal preference. Just ensure the pot body is grounded to the rest of the guitar.
Also, I wire mine to my tone pot (which is as mentioned above a universal tone control)
rather than to the switch as shown. Once again, personal taste.

Now, as to the inductor. Believe it or not, you can use pretty much any inductor at all, again
keeping in mind physically fitting it into the guitar. However, in this type of circuit the tones achieved
are dependant on both the inductor and cap values, so as the type/value of the inductor varies,
so must the capacitor values. The inductor I use is cheap, easy to get, and works with the cap values
mentioned and shown in the circuit. I use a Xicon signal transformer that has a center tapped
primary and center tapped secondary. The actual transformer can be acquired from Mouser,
and you can either order it directly from them or get your local electronics supply store to order
it from Mouser for you. Locally here, in Nova Scotia, you can go to Jentronics in Burnside, give them
the part number you need, they'll order it, and have it for you within a few days.
The Mouser part number is 42TL021-RC and it only costs a few dollars.

The transormer has three leads on each side, with the primary side marked with a "P" stamped on it in ink.
Cut off all three secondary leads and cut off the center primary lead. The two remaining leads
are the leads needed for the the circuit. Simple as that. In the future, I am going to experiment with
some low cost toroidal inductors of varying values, and will post the results when I do.

Another way of using this type of circuit is to use a multipole switch and use varying values of caps
in series with a common inductor to make a Varitone for your guitar. The possibilites are pretty much
limitless. It's just a matter of experimenting to find tones that work for you.

If anyone has any comments on this modification or has any other ideas or experience with
this type of modification, please let me know. I'm particularily curious as to what type of inductors as
well as what values of inductors you may have had luck with. Please feel free to e-mail me letting
me know your results, if any, and as I mentioned, when I do more experimenting
I'll post the results here, too.

Thanks, and good luck!

Please feel free to e-mail me at any time.