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Re: Opinions on Octave Fuzz circuits

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6/26/2000 3:47 PM
Ed Rembold	Re: Opinions on Octave Fuzz circuits Dutch, before you pass on the FTM, sub in some 2N5088, or 2N5089's for all the transistors. the higher gains will really wake your pedal up. Ed R.

6/26/2000 6:23 PM

Also important to note that one of the key elements in producing the octave sound is the matching of emitter and collector resistors on the transistor immediately prior to the emitter/collector diode outputs. Don't go nuts about it, but I'm told that such a configuration (which you can see in other octave pedals) works as a full-wave rectifier when the two resistors are of equal value, so you may just want to be sure that you don't have two 5% resistors at the opposite ends of their tolerances in there.

Also a good idea to make sure the diodes have a small enough voltage drop, and are reasonably matched. As I'm fond of pointing out, diodes have variations within the same part number, so you may want to check for actual drop, since this will contribute to output level, as well as octave/fundamental level-matching. If you measure your diodes with a DMM each one reads around .5v, that would be good. Much better than finding out that one reads .49 and the other reads .72.

6/26/2000 8:48 PM

Mark, Ed--
Thanks for the tips. I'll have to try bread-boarding it again, once I've finished the device below. Maybe I'll see about adding the octave bit to this box, to have an "all-in-one" unit....

I already yanked everything out of the breadboard and built a close approximation of a Vox Suppa Tone Bender, which I think is pretty nice as a straight fuzz.

Then, once I decided that I liked the basic tone of the beastie, I started adding stuff to it. So now it has an extra stage on the front end. Also, the stage just before the diode-feedback clip stage now has a direct coupled emitter follower attached to it and a nice switchable "twin-T" wah circuit (the one in RG Keen's "Tech of the Wah Wah" page) built around it for a bit of midrange focus to the obnoxious gain this thing produces.

I think it sounds pretty cool. The wah circuit I borrowed for the wah stage has variable "Q" (a 1K pot as its emitter resistor), so you can control the peakiness of the mid boost as well as where it occurs. I had some problems with oscillation until I put in a fixed resistor to set the max "Q" for the filter. Now at the highest "Q" setting, you can hear the filter ring a little, but it doesn't oscillate.... Fun! :^)

It adds a nice, focused midrangey sustain/feedback quality at lower "Q" settings (Santana in a box, sort-of), and can sound rather obnoxiously nasal at higher "Q" settings. It would also make a nice fuzz-wah pedal if I "remoted" the freq. pot.

A SPST switch can bypass the filter section for full-bandwidth gain if you want, although the "Q" knob still affects the gain/distortion of the signal and having no negative feedback around the stage kicks the gain up a bit. I suppose a more complicated bypass switching arrangement for the filter section could accomplish a more "normal" bypass action.

I've got a schematic of it to post, so I guess I should contact Aron....

C ya,
Dutch

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