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All circuits are for personal use only

Also, take care with circuits shown, I don't guarantee anything, they should work, but, as always,
try not to fry components and yourself...

© Marjan Systems/Marjan Urekar 1999.-2001.  All rights reserved.


This is modified Electro Harmonix Bass Balls Envelope Filter Pedal, with some design inputs from EH Dr.Q and Jack Orman's Dr. Quack. Basically BB has two bandpass filters, tuned to emulate human vocals, with center frequency controlled by envelope derived from input signal. All the controls were Sense (amount of envelope), and select fuzz/clean signals as filters input. Dr.Q is basically the same, with single filter stage, without input buffer (lame!) and with Normal/Bass response selection.

I liked it's funny sound, and while it's guitar pedal, it sounds very interesting on vocals and synth bass.
If you take a look at it's schematics, you'll find it easy to add many modifications with ease. While you can use all my mods, you can also discard some of them and fit it to your needs, and tweak some part values to your taste. It may seem too complex, but it has very good potential for such a simple cct.

How it works:

Switching On is standard, inserting jack in Input for battery or DC In jack for ext supply. Bit of filtering and diode
protection, I've skipped standard 7809 as I have nice & clean external PSU. True bypass, based on Jack's ideas, with effect-on indicator. Input is buffer/amplifier, with gain adjust trimmer (x1-x50). I need this, as I use various external signals from processing, maybe your guitar won't need it (stock BB doesn't have it), but my practice
is to amplify guitar signal to line level (S/N ratio is then better). Set it to your taste. Input 22u caps make cheap bipolar cap - just in case of signals with bias (this may be too much for guitar use).

Next stage is amplifier/rectifier. Set trimmer to get largest envelope out from your signal. It feeds diode rectifier to extract envelope which controls filter. Envelope follower has Sense pot to select how "sensitive" envelope follower will be to input signal, it also has switch with three "response" ranges set by different caps, variable attack (lag to input signal) and decay (time needed to "recover" from last signal), simple buffer with 2 pots controlling amount of envelope feeding each filter. You can choose to control them separately, or to control both of them with single pot (SYNC2->1). Also, there's manual control of center freq, simple pot, routable to first or both filters. Default is DC but inserting FILTER CV jack makes it controlable by any ext voltage source (CV, pedal, LFO...). Those strange diodes in there protect cct from inserting too large/negative voltage.

There's nice feature borrowed from Dr. Quack with LED lifting ref. voltage at 2-3V for TL072 follower, which also can be nice external POWER ON indicator. LED in series with ATTACK control is envelope level indicator.

U3A is V/2 reference needed for correct opamp supplies. Filter stages are pretty the same, standard cookbook
bandpass filters (as in wah-wah), with different ranges. Each has 3 way range switch, to cover broad spectrum
of frequencies. Tweak those caps to get octave response for your specific guitar. By inserting signal in different
points, you acheive different responses (NORMAL/BASS MODE). First stage has lower frq range so I made it that
it can filter the same signal as the second one (PARallel mode, as in BB), or to use signal from second stage's
output for some strange effects (SERial mode, hipass like). Transistors are used as VC resistors here to tune
the filter. Not perfect, but simple and cost effective for such cct. 100p caps prevent self-oscillatons in opamps,
those sole 100n caps should be close to each IC (or soldered beneath) across the rails. Envelope follower section
is also used as fuzz generator, with two modes - standard BB one, no clipping (1) and mode (2) with Ge diodes
used to clip signal in standard Rat fashion. You can select it as SOURCE for filters, or to use clean signal.

Outputs from both filters, clean boosted, and fuzz section are mixed via level pots and large 10u caps (you
may use lower values here like 100n or smaller for guitars), into standard inverting summer, with main volume
pot at the output. Mixing all the sources makes rich sound.

Place to tweak also is fuzz section, experiment with nuber and type of diodes, and cap too (use smaller value or no cap at all).

There are also RESONANCE pots, those are not tested yet, you may experiment with values or bypass it with
piece wire. I also had idea to add envelope inverter, to sweep filters in opposite ways, but I'm too uninspired to do so. You can "steal" opamp from V/2 reference (it will still work without it) and make simple inverter.

Some switch arrangements may seem strange - that's because of on-off-on toggles I used (they don't
have pin for middle position).

Some switches have A and B suffix. Those are the poles of the same switch.

Making Attack pot larger than 1K is not very usefull. Decay pot may exibit some problems. Original BB used
330K resistor. Try JFET (like BF245) in place of Q2 (new opamp stage would be even better).

Change R27 and R12 for different Fuzz levels. D1 and D2 should be LEDs from the same batch, with matched
voltage drops (around 2-3V, like regular Red LEDs).

Opamps can be any standard duals (TL0X2, LFXXX...). Some might need those 100p caps, some don't (or
some smaller value like 22p).

R50 could be subbed with Ge diode to protect cct from wrong polarity but you'll get smaller supply voltage
(or some regulator caould be used, like 7809).

If you find all this above too simplistic, well, I'm too lazy to go into details :)

Front panel:


Filter1 Cutoff
Filter2 Cutoff
Filter1 Resonance
Filter2 Resonance
Manual/External Filter Control
Envelope Follower Sense
Envelope Follower Attack
Envelope Follower Decay
Clean Signal Level
Fuzz Level
Filter1 Level
Filter2 Level
Main Volume


Effect On/Off  (Bypass)
Fuzz Mode 1/2
Envelope Follower Range Lo/Mid/Hi
Filter Sync 2->1 On/Off
Filter2 Man/Ext On/Off
Filters Source Clean/Fuzz
Filters Serial/Parallel
Filter1 Mode Normal/Bass
Filter1 Range Lo/Mid/Hi
Filter2 Mode Normal/Bass
Filter2 Range Lo/Mid/Hi


Booster Gain Adjust
Envelope Follower Gain Adjust


Input (Power On/Off)
External 9V DC In  (Battery On/Off)
Filter External CV (DC On/Bypass)

LED Indicators

Power On
Effect On
Envelope Level

Schematics (in PDF format)

Schematic1            Main guts
Schematic2            Jacks, PSU, Bypass

More Mods

If you have any comment regarding the cct, found errors, have some interesting mods or need help

constructing it, mail me

 Marjan Systems and ForceMajeure
by Marjan Urekar