This is a (no longer) new, reissue EH Small Stone that I hacked into in a number of ways.
Now, let’s see if I can remember. . .

There’s a 4PDT switch that switches all four filter caps in one fell swoop (drilled into the “S” in the word “small”). The down position is stock, 0.0068uF on all four stages. The up position is UniVibe values (0.15u, 0.22u, 470p, 4n7, or something like that). I tried some different values, and went with what sounded good to me. If you want more info on this mod, you can do a search on Google or check out this web site: DIY Analog Guitar and Bass Music Effects.


The bright switch switches the input cap to the phase stages (C3 in the issue J layout), between the stock 10uF and a 0.1uf. It kind of takes the edge off of the Small Stone’s inherent “darkness.”

Electric Guitar

Stock Univibe
Stock Univibe Stereo
Univibe Vibrato
Phase Filter Stereo
Vibrato Phase Filter

I installed a SPDT, center off, toggle switch on the outgoing end of each of the four filter caps. The stock setting is with all four switches in the up position, all four stages configured as all pass filters. Switching any of them to the down position diverts the filter cap to ground, converting that stage to a low pass filter. This is the PhaseFilter mod that Mark Hammer came up with, except that I did it on all four stages instead of just the last two. It’s pretty cool when you have all different cap values (‘Vibe values) in each stage. For more info, see The center position on each of these four toggle switches simply breaks the connection at the outgiong end of each filter cap. This effectively turns off the particular filter stage. And, guess what? A single stage Small stone actually sounds kind of cool. It’s neat to be able to isolate each filter stage when the caps are switched to UniVibe values, too.

Electric Bass

Univibe Stereo
Phase Filter
Phase Filter Stereo

Then, there’s the mono/stereo switch. This actually does a couple of things. Primarily, it’s a vibrato switch, breaking the part of the circuit that blends in the clean, unmodualted signal, leaving only the modultaed signal at the main output. The other thing that this switch does is sent the clean, unmodulated signal to the second output jack that I added, providing pseudo-stereo outputs. See the photos, and check out the sound clips that I recorded in stereo. (Man, that square hole in the middle of the PCB is whacked, ain’t it?)

Finally, I replaced the goofy 1/8″ power supply jack with a standard 2.1mm barrel-type jack.