Unique tone circuits?

G&L has some interesting circuits and wiring schemes, such as bass cut and OMG (“bass boost”$..

Varitone is also interesting, tho I prefer just capacitors (ie, cap selector switch, like Tonestyler). Shapes the resonant frequency.

Then there’s Q-filter (Wilde/Bill Lawrence), which is an inductor fine tuned with caps and resistors. This I’m not 100% clear what it does, but it’s been described either as a mid-cut or a way to “sweeten” the tone.

Some Rickenbackers have a cap on the bridge pickup, which makes it blend differently with the neck pickup (cap cuts bass, which then leads to different frequencies getting cancelled when blending pickups).

 

The Rickenbacker treble pickup cap, when both pickups selected, yields a very usable tone with plenty of depth and plenty of mids. It’s a very interesting but very simple trick to do; I was pleasantly surprised the first time I used it. I think I might do it again, on another bass.

I recently tried out Bill Lawrence’s P-J Wiring Diagram. Bill was a genius, of course, and had lots of neat tricks up his sleeve. That circuit puts both pickups permanently in series, and the “blend” pot is really a tone pot for the bridge (J) pickup. Sweeping through that “blend” pot, there isn’t a bad tone to be had. In my bass, however, there wasn’t a lot of difference from one end of that sweep to the other, so I’m going to try something else I think.

The G&L OMG thing is pretty cool too.

 

I'm eternally interested in passive tone circuits. Although, in my tinkering, I've also discovered that just because it's possible doesn't mean it's useful!

I think capacitor switches can be an interesting alternative to the traditional tone pot. But because some cap values can create an unpleasant resonant peak and because of the variable nature of LCR circuits (what sounds good with one pickup doesn't necessarily sound good with another), I think they can benefit from the addition of a switchable resistor (6.8K or 8.2K) between the the capacitors and ground to smooth out the peaks as needed--a 'smooth switch,' if you will.

Some Hofner and G&L basses hardwire a resistor in series with the tone cap to eliminate the resonant peak. In effect, this means the tone control can never be turned to 0. (Just wire the resistor between the capacitor and ground.)

In addition to the normal treble cut capacitor values (between .022uF and .1uF), very small value capacitors, in the .001 to .005uF range, can be really interesting. These can be used to load a pickup to alter its resonant frequency, sometimes with pretty dramatic effect. If there's a particular value that changes the tone for the better, it can either be hardwired (across the output jack is easy, or between the volume pot input (hot) lug and ground) or put on a switch, which then gives the bass two difference voicings.

By the way, the easiest way to test capacitors (assuming they're being used in parallel to the circuit) is to unscrew the barrel from the instrument cord (the end that's plugged into the bass), attach test leads to hot and ground on the 1/4" plug, and then put various capacitors between them (leaving volume and tone dimed on the bass).

Another interesting use of very small value capacitors is as a bass cut. For instance, G&L has a passive treble bass setup on some of its instruments. Diagrams and schematics are here.

And a simple bass cut capacitor (.005uF to .01uF) wired in series with the bridge pickup of a two-pickup bass (a la Rickenbacker) will reduce comb-filtering and improve blending. But it does thin out the soloed bridge pickup tone, so making it switchable is nice.

As mentioned above, another interesting G&L circuit that can be used with dual-coil humbuckers (like a MM pickup) is the OMG mode, which puts a .1uF capacitor in parallel with one of the coils; this shunts the highs from that coil to ground while leaving the other coil unaffected--the ear perceives it as a bass boost.

These and other passive tone possibilities that have been used on production basses can be discovered by combing through this opus of bass wiring diagrams.

And I've never tried the Wilde Q-filter, but it seems interesting. From another thread, here's the best description of it I've seen: