This is a switched tone control for a humbucker pickup, using a 1x12 rotary switch. There’s nothing revolutionary here, but it puts together several types of tone shaping, into a single control:
A Bright humbucker tone from a ‘no-load’ tone control
Sweeping the resonant peak by adding capacitors across a humbucker
The reduction of high treble from 10 to about 1.5 on a standard tone pot
Coil cut by bypassing one coil
Coil bypass with capacitors, to give a single coil sound with more low end
The device uses a standard switch with 12 settings, as follows at positions 1 to 12:
1 A tone control, at minimum, using a 0.022uF cap 2-5 as 1, but with tone capacitance x1/2 at each step, to change resonance and roll off in ½ octave increments 6 Unloaded, max humbucker brightness and also the last increment in the series 1-6 7 Coil cut 8-9 Coil bypass with capactor, in two steps 10-12 a standard tone control, at settings approximately 9, 6 and 1 ½
The component values are worked out as series chains, to make best use of the switch lugs. The main chain of caps for sweeping the resonant peak, starts with position 6, no cap, which is assumed to be the self capacitance of the cord and pickup, about 0.7nf total. From 6 to 1, the net capacitance of the chain doubles at each step until it arrives at a normal tone control value of 22nF = C1.
I think there’s a good range of useful sounds in this, considerably wider than any normal single tone control. Although there’s quite a few parts, they are all small and cheap and it can all be made away from the guitar, then connected with just three wires, ground to the central pole, pickup hot and pickup centre tap.
JohnH That's quite an interesting idea. You've probably figured out the series capacitor values but I thought I'd type those out anyway.
From terminal 5 through the pickup Hot side of C1 the capacitance is .686 nf From terminal 4 2.2 nf From terminal 3 5.0 nf From terminal 2 10 nf From terminal 1 22 nf
Capacitance From terminal 7 to 8 82 nf From terminal 7 to 9 33.3 nf *************************************** Resistance Terminal 10 through 1 379 K Terminal 11 through 1 109 K Terminal 12 through 1 27 K (Edited to correct errors) *****************************************
newey - thanks for comments. I dont have a target guitar for this just now, ideally a pair of them could replace the tone pots on a 2Hb guitar such as an LP, except that most rotary switches could not go through the thick top of the body. Something with a control plate to mount to would work well, maybe a fat-strat or similar, or maybe an SG with a thin top.
Wolf - thanks for posting the numbers. If you add to the first series of capacitances, about 0.7nF to each one (that which is inherent in the guitar and cord approximately), you'll see that the net result is a capacitance that doubles near enough at each step, so the resonant frequency goes down by sq root 2 = 1/2 octave. I think the resistance summation you have is not quite right, the intention is 27k at 12, 82k+27k at 11 and 270k+82k+27k at 10. (EDIT - OK thats better!)
I think I would order them differently though, so that it acts a little more logically. Seems like we'd expect the brightest position (the SC position, which is "no load") at the most clockwise rotation, and progress down from there. I think I'd go through the two "broadbucker" positions, then to the full HB "no load", then down through the resistors, and then up through the capacitor series.
This way it almost acts the way we'd expect a Tone control to act.
Ash - yes, its quite a puzzle to think of the best order arrangement for these tones. Where a standard tone control has basicly one range from bright to dull, this one has three transitions going on, being the sweep of resonant peak from 1 to 6, the muting with resistors 12 to 10, and the single coil sounds 9 to 7. I put the full untamed humbucker 6, next to the full coil cut 7, since iI thought these might be the most useful. From there, the other transitions flow from one to another without large steps, with the most muted sounds being at 180 degrees, at 1.
Of course, on the guitar, the knob can be pointed wherever wanted depending how it is installed, it doesnt have to point at these numbers.
Further on this, thought it would be interesting to see all the range of frequency response settings on one chart. I managed to get 5Spice to analyse most of these settings, so here is a range, made by overlaying three graphs:
I’ll spare the details, but these frequency response plots are based on my usual type of Spice modelling of a PAF humbucker and a 10'cord to an amp, and represent settings 1, 4, 6, and 7 to 12 of the 12Tone. The missing ones 2, 3 and 5 add some extra values to the series of peaks at the top of the chart.
So I reckon there has to be some fun to be had with all those tones!