This DIY random voltage generator is based on the #3 Standard WoggleBug Circuit schematics given by Grant Richter on his website, together with the block diagrams of the Wogglebug on the Wiard website. It is one half of a WoggleBug, with some added features. The original WoggleBug was inspired by the Buchla Model 265 Sources Of Uncertainty module. It’s housed in a Front Panel Express file. The entire schematic covers several pages, which you can view here:
General Description
The Wogglebug has six principal outputs. Three are audio and three are control voltages. All of these outputs vary randomly, and they are interrelated in interesting ways. Let’s examine the Block Diagram.
The top section shows the Smooth section, comprised of the VC LFO clock, a 4046 linear VCO, and a Sample & Hold. Notice a few important points. One: The output of the VCO, an audio frequency sawtooth wave, is fed back to the S&H input. Two: The output of the S&H is fed through a VC lowpass filter to the VC input of the VCO. Three: The clock rate and the lowpass filter are controlled in tandem (by two Vactols), so that as the rate of sampling increases, the rate of change of the SMOOTH output also increases. This is how voltage-controlled rate of change of the smooth output is achieved via the RATE CV input. The SMOOTH output is a slowly varying random voltage that internally controls the frequency of the VCO, whose sawtooth wave becomes the Smooth TONE output. The Smooth RANGE pot adjusts the overall range of the smooth VCO. The SMOOTH output is uniquely suited to natural sounding applications, such as wind and surf when used to control a filter.
Now look at the lower right portion of the Block Diagram, which shows the Woggle section. Here is another 4046 VCO. This one is controlled by a lowpass filtered control voltage emitting from a phase detector that compares the outputs of this VCO and the Smooth VCO. If the frequencies of the two VCO’s are close enough, the feedback CV produced by the phase detector tends to move the Woggle VCO toward the frequency of the Smooth VCO, but overshoot results in a tremolo effect, which sounds “woggly.” Like the SMOOTH output, the WOGGLED output is a control voltage, which similarly controls the Woggle VCO. Disturbance is a voltage applied that changes the range of the VCO, through the Woggle RANGE pot. Normally, disturbance is conveniently provided by the STEPPED S&H, which periodically jogs the range, adjustable by the DISTURB Pot. The Woggle Pot manually adjusts the lowpass filter cutoff, impacting the settling time of the phase lock. The Woggle TONE is simply the output of the VCO. As a bonus, the square waves of the two VCO’s are combined by XOR logic to produce the RING MOD output.
At the lower left of the Block Diagram, we see the STEPPED Sample and Hold with its sample input, clock input and sampled output integrated to the rest of the module via normalized jacks. By patching into the Step Clock and Step In inputs, this becomes useable as a stand-alone S&H. It also features a correlation pot, STEP LIMIT, that mixes the output and the input for the next sample.
All outputs of the Wogglebug but the CLOCK and the RING MOD are normally in the zero to +10 volt range. However, the STEPPED S&H will sample negative voltages and pass them through to its output, if you patch something that goes negative to the Step Input.
Smooth Function
Voltage Controlled Clock
The clock LFO is integrated with the smooth function generator. Its output is useful to coordinate external events with what’s going on in the Wogglebug, such as triggering an Envelope Generator.
Outputs
- A +/-5V clock pulse output – CLK OUT
- A smoothly varying 0-10V random control voltage – SMOOTH
- A randomly varying 0-10V sawtooth audio output – S TONE
Pots
- Correlated clock rate with smooth CV change – RATE
- Range of smooth tone frequency (1-6 octaves) – S RANGE
Inputs
- RATE CV
Stepped Function (S&H)
An independent sample and hold module whose input is normally connected to the woggle tone and whose output is normally connected to the disturb B input.
Outputs
- S&H output – STEPPED
Pots
- Correlation between S&H input and output – STEP LIMIT
Inputs
- Input to the S&H, normalled from woggle tone – STEP IN
- External clock for the S&H, normalled from internal clock – CLK IN
Woggle Function
The Woggle VCO is controlled by the phase difference between the woggle tone and the smooth tone.
Outputs
- A woggly varying 0-10V control voltaged – WOGGLED
- A woggly varying 0-10V sawtooth audio output – W TONE
- The +/-5V XOR of the two tone outputs – RING MOD
Pots
- Lock-in time of the phase detector – WOGGLE
- Range of smooth tone frequency (1-6 octaves) – W RANGE
- Mix between range “disturbance” inputs – DISTURB
Inputs
Disturbance of range inputs – DISTURB A and B
Feedback Patterns
The Wogglebug uses this internal feedback by default:
- The Smooth TONE feeds back to the Sample & Hold that controls its frequency.
- The phase detector controls the frequency of the Woggle VCO, which is one of its inputs.
- The Woggle TONE feeds back to the Sample & Hold that controls the disturbance.
You can patch up other feedback patterns, such as:
- Patch Smooth TONE to STEP IN, overriding Woggle TONE.
- Patch SMOOTH to STEP IN, overriding Woggle TONE.
- Patch WOGGLED to STEP IN, overriding Woggle TONE.
- Patch SMOOTH to DISTURB A.
- Patch WOGGLED to DISTURB A.
- Patch SMOOTH to DISTURB B, overriding STEPPED.
- Patch WOGGLED to DISTURB B, overriding STEPPED.
- Patch SMOOTH to DISTURB A and WOGGLED to DISTURB B.
For crazy random clocking, use an external attenuator:
- SMOOTH through attenuator to RATE CLOCK.
- STEPPED through attenuator to RATE CLOCK
- WOGGLED through attenuator to RATE CLOCK
Sound Samples
Three Wogglebug outputs are used in succession to modulate the frequency of the triangle wave of the MOTM-300 VCO. The sound isn’t especially interesting. The point is to demonstrate the way the Wogglebug voltages change. It starts out with the SMOOTH CV, then switches to the STEPPED, and finished up with the WOGGLED. The Wogglebug controls are not changed during this demo.
Same idea as above, but here the voltages are used in succession to control the cutoff frequency of a MOTM-440 Low Pass Filter with pink noise as the input.
Now listen to each of the three audio outputs in succession: Smooth Tone, Woggle Tone, and Ring Mod. These are straight out of the Wogglebug with no filtering. The controls are set the same as before and there is no knob twiddling. If you’ve heard the Wogglebug before, you will recognize the Ring Mod output as the replicator of “Ancient Krell Music.”
Here the MOTM-440 filters the Woggle Tone audio, and the WOGGLED CV is used to modulate the filter frequency for a type of tracking. This time I fiddled around a bit with three knobs on the Wogglebug: Smooth Range, Woggle Range, and Woggle Time. A wide range of woggle effects is obtainable by different settings of these knobs, only a few of which are evident in these demos. The disturbance on each trigger of the Stepped S&H (into the Disturb B input) is quite evident.
Similar to the above, but this time the filtered signal is the Wogglebug Ring Mod output and the filter frequency is modulated by the SMOOTH CV instead. Knob twiddling added.
Conceptual differences from Grant Richter’s design
- The smooth tone output is a sawtooth instead of a square wave, making it suitable for S&H input.
- I hooked the internal smooth S&H input to the smooth tone instead of the woggle tone. This keeps the smooth function independent. But it really doesn’t make much difference, because both of these are audio rate sawtooths.
- The stepped S&H input is externally available, normalled to the woggle tone. This makes the stepped S&H useable as a stand-alone module.
- The woggle range pot “input end” is fed from a buffered mix of two disturb inputs, A and B. The stepped output is normally connected to the B disturb input. This works like the WoggleBug, but the disturb pot allows a blend of the stepped and the A inputs. The stepped disturbance can be eliminated by turning the disturb pot fully counter-clockwise to the A input or by patching something else to the B input.
- I have just two LEDs that indicate when each S&H is being triggered.
Construction
As you see from these photos, the MOTM protoboard is stuffed full. I used IC sockets for all chips.
