Saturday, April 23, 2016

An electronic puzzle.

I lean towards the "Keep it Simple" school of guitar electronics. Not that I have anything against instruments with all kinds of bells and whistles, mind you. It's just not something I've ever developed a powerful lust for. I guess that's why I like Telecasters. Give me a volume and a tone and I'm happy.

When Alfie Smith asked me to build him a guitar, his first concept involved having the signal go straight from the pickups through a four-way switch directly to the jack. He was interested to hear how the TV Jones Super'Tron pickups sounded unencumbered by any load from potentiometers and excess wiring. They sound great.
A Spartan control setup to be sure, but even this took some mental wrestling. The four-way switch yields:  Neck,  Neck+Bridge in series, Neck+Bridge in Parallel, and Bridge.  This is not the typical 4-way sequence, and it took several tries to accomplish. Guitar electronics forums are full of helpful diagrams, some of which work, and some of which are obviously untested speculation...

Alfie and I both knew he was going to want a volume pot.  It just makes sense for the kind of club and bar gigging he does. He was reluctant to sacrifice the direct output tone though, and suggested a three-way toggle switch to allow him to turn off the volume and go straight to the amp. He was also interested in adding a fixed tone setting, something like the "cocked wah" tone popular in some telecaster circles.

"Sure thing! I can throw a switch in."  No problem.  I should point out that I'm not a natural electronics whiz. Hand me a schematic and I can wire it up - I routinely switch pickups, replace pots and jacks, change out capacitors and go through miles of shielding tape as part of the repair side of my business. Designing guitar circuits is something else though. It's not intuitive.

There are wiring diagrams galore online but you won't find one with a toggle switch that gives a direct out option. Sometimes what seems like a simple request isn't so simple! Three-way toggles don't allow for three discrete settings. The middle position always produces a combination of the outside circuits. It took a minute or two of headscratching to realize that there was no way to wire one to allow a direct signal. It would always end up mixed with either the volume or the tone. Multi-pole Microswitches! (I hear someone holler)  But no. The same problem arises.

I came up with an idea.  What if I was to combine parts from two toggles?  I could add some pole pieces and broaden the palette of possibilites.
The standard switch is on the left and the Frankenstein is to the right. I stacked an extra leaf and insulator strip on each side. (A word of warning: the screws which go through the stack are insulated with a precisely sized plastic sleeve to keep them from contacting the leaves. I had to cut an extra piece for each screw to make up the difference and prevent them from shorting out which would be annoying in a guitar circuit. It would be extremely dangerous in a situation where the voltages are higher. )
I carefully oriented and bent the outside leaves so they only made contact when the switch was flipped to one side or the other.
This is how I work through electronics problems. Some people are gifted and see it all in their head. I need to physically diagram to visualize the possibilities. Several pages later I hit upon the right combination of couplings and contacts. It's kind of vexing that the direct out signal always falls in the central position. One would prefer it to be on the side, but it's the nature of the circuit.  The final form yields: Volume, Direct Out, Volume+Wah.

 That's a lot of spaghetti!  There's so much going on in a tight space. Heat-shrink tubing keeps the contacts from shorting.
Now there's far more choice, and yes - there is an audible difference in the direct signal. It's almost like a lead boost. (And could function that way if one set their volume and amp up accordingly.  I'm not so sure about the wah.  I used the 3.3k resistor and .01uF capacitor suggested by people in the know, but these aren't Tele bridge pickups. The effect might be a little too subtle and would probably benefit from experimenting with a higher value cap. We'll see.