mystery varitone circuit

[barret77]

Hello all

I bought this passive varitone pedal from someone at the HC forums, sometime ago (he might eve stick around here);

I never used it too much; it sounds kind of weird, I never figured out out to extract good tone variations from it - it kill to much of the sound (it always sounded better with it turned off)

So, I decided to transform it into a variable-capacitance java boost, with variable input and output cap values.

I opened the box expecting to find a bunch of capacitors an nothing more, but instead I found a circuit that my limited knowledge cannot fully understand. And worse: two gooped components.

Does anyone has ever seen a schematic for this? Any ideas on how to mod this baby?

It works like this: one selector (select the capacitor value) and one pot (don't know what it does, never worked well) three switches (one turns on/off, other two extend capacitor value).

There seems to be a transformer and something else gooped. No idea how this works.

[puretube]

tnx for the pic!
the "search" button (the 2nd one on top of this page...) had a.o.,
the following to offer:
http://diystompboxes.com/sboxforum/viewtopic.php?t=33101
http://diystompboxes.com/sboxforum/viewtopic.php?t=29282
http://diystompboxes.com/sboxforum/viewtopic.php?t=28422
http://diystompboxes.com/sboxforum/viewtopic.php?t=23621
http://diystompboxes.com/sboxforum/viewtopic.php?t=23493
http://diystompboxes.com/sboxforum/viewtopic.php?t=4241
http://diystompboxes.com/sboxforum/viewtopic.php?t=7993
...

[toneman]

looks like it's a capacitor(in your hand) & inductor(other yellow blob),filter.
the switch switches caps, inductor legs in/out for different frequency responses.
A passive filter....
check out these links (i googled)....
http://www.blueshawk.info/varitone.htm
&
http://www.exotic-scales.com/varitone_circuits.htm

stayfiltered
tone

[Mark Hammer]

It is more than likely either the Gibson Vari-Tone circuit or the Anderton passive tone control circuit from EPFM.  Both of these use a capacitor and inductor (and that's the transformery-looking thing in the corner) to produce a midrange notch  whose location/width can be varied, and in the case of the Anderton/EPFM one the depth varied as well.

The rotary switch selects between different cap values to produce notches at different locations.  Since the inductor value remains constant as you rotate the cap switch, the unit will not behave exactly as, say, a sweepable midrange boost/cut would.  Often, it is possible to be able to select taps from the inductor so that a whole other range of notch frequencies can be selected with the rotary switch.

One of the things I ended up doing with mine was to make it more of a Swiss Army Knife type box by including a switch to shunt the caps, and another to shunt the inductor.  The first turned it into a variable bass-cut box, and the second turned it into a variable treble-cut box.  That may well be part of what is going on with the switch bank, though obviously it's hard to tell from just the photo.

Sound close enough?

Incidentally, since it is a passive circuit, obviously it requires no power.  On the other hand,it tends to eat up signal level since it works by selectively bleeding signal.  I stuck a Stratoblaster circuit in a box just ahead of mine to allow me to compensate for volume loss by means of a simple clean FET booster.

[puretube]

T-man: tnx f.t. "exotic" link - never seen it b4...
staylinked!

[aron]

BTW: Remember that 1.5H inductor discussion? I got a few of those 1.5H inductors so, if anyone needs some, let me know.

[barret77]

thanks for the info. I'll study it to try to figure out the best way to mod my varitone.

And I had searched the forum before posting, but I mistankenly thought that the threads were not mentioning the inductor (that I've called "transformer" earlier)... sorry for that[/i]

[lovekraft0]

FWIW, I'd be willing to bet large sums that those yellow goop-covered "inductors" started life as either those Hi-Q/Mouser subminiature audio transformers, or something very similar, perhaps from Radio Shack. Torres uses a 42TL024 as the inductor in his "Super Varitone" kit.