Varitone with capacitor only

[PBE6]

My very first project was a capacitor-only "varitone" for my bass. The basic theory I used can be found here:

http://buildyourguitar.com/resources/lemme/

http://www.billlawrence.com/Pages/All_About_Tone.htm/CableandSound.htm

I wired up a bunch of capacitors from ground to a rotary switch in order to move the frequency peak of my pickups a bit lower and remove some of the brightness. It actually worked out OK for a few sounds (despite the hack-job I did wiring it up), giving me a bit more bite on a midrange setting and a neat reggae-type sound on a bass setting, but one side effect was a fairly significant volume cut on bassier settings.

I was thinking of resurrecting this one, possibly in a passive form but most likely with an active gain control added to makeup some volume. I have a few questions though:

1. Is there a big difference between adding capacitance from the pickup to ground (i.e. inside the bass and across the volume pot from lug 3 to lug 1) vs. adding it from output to ground (i.e. outside the bass and essentially across the volume pot from lug 2 to lug 1)? The articles above seem to suggest there isn't (in fact it's the basis of Bill Lawrence's cable-faking analysis), but if the volume is down won't there be a series resistance in the second case? Will that have much of an effect?

2. Will adding an opamp boost after the capacitor to ground impact the frequency response much? I assume it won't since most amps have high input impedance already, but it's good to double check the basics sometimes.

[pinkjimiphoton]

i'd breadboard it. in my experience so far, filters can vary greatly in how they interact with recovery stages... putting the tone stack before or after a preamp can make a huge diff even tho it's for all intents the same component.

i annoyed poor EW i think a while back when i discovered the hs shatterbox seemed to change completely when the "swell" control was moved from the output of the first half of the ciricuit to the input of the second...

huge difference in tone, all because of where it came in reference to the footswitch.

that said, i think it sounds a little "cleaner" to put a bit of a boost/buffer before a filter than after... less noise. ymmv.

[Mark Hammer]

I made a little box with a JFET booster feeding Andertons EPFM passive tone control - essentially a varitone-like LCR circuit with variable cut.  I installed a toggle that would bypass the cap/s in the circuit so that it was an inductor with variable resistance to ground (lo-cut), or bypass the inductor (variable hi-cut), or bypass the whole caps+inductor (passive full bandwidth attenuator).  Handy little circuit.

[pinkjimiphoton]

that sounds wicked useful, mark.

i have to admit i know zip about inductors. can you please reccomend any good resource for a moroon like me to learn about them?
cuz like, i see various sizes of inductors at places, but never seem to find them as big as what i'd read about... like bill lawrence's passive mid control.

could you combine the low and high pass filters on that at the same time? cuz man that could be wicked useful too i'd imagine....

my late brother woden wanted a "wah" kind of pedal, where when ya stepped on the toe, you could get a sweepable treble boost, and when ya stepped on the heel a bass boost so you could swell into either at will, with the natural midrange fuzzed out of recognition. i liked the idea but seemed kinda wah wah ish...  maybe one day i can build something and see if his vision was sound, or mescalito pooping on his head.

[Mark Hammer]

All the necessary info can be found here: http://www.diystompboxes.com/smfforum/index.php?topic=100781.msg888238;topicseen

Putting it all together, imagine you had a simple JFET gain stage or perhaps an AMZ MosFET booster, just ahead of the 47k input resistor.  I suggest this because you will experience passive loss from the tone circuit, and it's nice to both a) not face impedance issues, and b) not lose too much signal.

The booster stage WILL have a DC-blocking cap on its output.  You can vary the value of that cap to alter the low-end rolloff.  The mid-cut can ow be added to that, via the varitone-like circuit.  Or, you could simply bypass the inductor, and alter both the low end and top end.  Or, if you felt like it, you could bypass all the caps in the diagram here, use the inductor and pot, alone, to trim bottom end, and supplement that with the cap on the booster output to chop the bottom even more.

very handy little tool.

[PBE6]

Finally got around to building my external varitone, and I'm really happy with the result. I checked out the difference between pre- and post-pickup placement using CircuitLab, and there's little to none even when the volume is rolled off. No need to drill any holes in my bass - bonus!

It's amazing what a difference a little capacitor makes. The pickups on my bass are 3.8 H, and the capacitors go from 1 nF to 68 nF in 11 increasing steps (and one open step to remove it from the circuit). The resonant frequency goes from about 5.7 kHz when open to 2.5 kHz at 1 nF and 300 Hz at 68 nF. The low capacitance settings are subtle and the high settings are not, but there is a wide variety of cool sounds in the mid settings. Would love to try this on guitar too.