This is the Resonant Gate designed by Craig Lee, based on the original low pass gate Don Buchla circuit.  The complete discussion is on Muff’s message board.

There have been many variations on the low pass gate.  All share the central concept of using a Vactrol in the signal path as an amplitude controller.  Various options provide for different levels of feedback, or resonance.  Most low pass gates make us of a manual switch to select the mode of operation.  This one is different in that it features a voltage-controlled feedback, which is labelled Mode.  The mode is variable from no feedback at all to feedback large enough to make the circuit self-oscillate.  The Mode pot sets the initial level of resonance, which can be added to or subtracted from by an external Mode CV through a reversible attenuator.  The initial frequency is set by a pot I labelled ‘FR’ for frequency.  (This is labelled ‘Offset’ on the schematic diagram.)  External CV of frequency also uses a reversible attenuator.

My panel uses the ‘small knob’ MOTM grid format, which allows me to fit two identical resonant gates into a single 1U wide panel.  This choice required me to omit the second CV input that the PC board provides.

My Modification

A problem was reported about the resonance circuit.  It turned out that due to a characteristic of the Vactrol response, the resonance level could fall off over time.  (See the full discussion, linked above.)  I solved this for myself with a simple modification that set the minimum resonance to greater than zero.  This means that the plain VCA mode is no longer available, and there is still some resonance at the lowest setting of the Mode pot.  That’s OK with me.  I like some resonance in the module at all times.  Here’s the backside of the completed module:

My modification consisted of determining a parallel resistor for the resonance Vactrol.  I described the procedure for finding the value in the post listed above.  The end result is a resistor soldered across the Vactrol leads on the top of the board.  Detail:

Finally, here’s a short demo of the resonant gate. It is filtering a triangle wave. A MOTM-800 envelope generator is hitting the CV. The demo starts out with the lowest resonance with the gate all the way open. Then I bring up the CV and play around with the controls a little.

Be sure to look at the Toppobrillo page that describes the module.  Here’s a photo of my build.

Here is a DIY Mattson Mini Modular VCF in a MOTM panel.  George Mattson’s description:

4-Pole, 24dB/Octave State Variable Filter jointly designed by Synth DIY guru Jim Patchell and George Mattson.
The filter design is based off the now-obsolete SSM 2040 filter and has simultaneous Low pass, Band pass and High pass outputs.

The PC board I got from George is a prototype for the surface-mount version of the VCF that you can get from him for DIY, as shown in his online store.

I designed a Front Panel Express panel for it, based on the standard MOTM 1U filter format, similar to the MOTM-485 and MOTM-490 filters.

The DIY build was about as simple as it gets.  I made a mounting bracket from thin sheet aluminum.  All connections to the panel use MTA headers, requiring no soldering to the assembled-and-tested PC board from Mattson.  I’ve started making my own cables, using the MTA press fit tool, 59803-1. You could more easily use the premade wiring kits from Mattson.

For the potentiometers I selected 100K linear ceramic metal Bourns 91A1A-B24-A20L, which are reasonably priced high quality pots available from Mouser electronics.

This is a very clean sounding VCF.  It tracks 1V/octave pretty closely over several octaves after tweaking the onboard trim pot.  It also self-oscillates at high resonance setting and makes a clean sine wave from the low pass output, ideal for use as an auxiliary VCO.

Here’s a photo of the assembly.

The Cloud Generator, otherwise known as the e340, is shown in the photo to the left of its sibling, the e350 Morphing Terrarium. The e340 is described by Paul Schreiber:

the synthesis technology e340 contains 8 sine and sawtooth vcos with unique modulation capabilities. the term ‘cloud oscillator’ was first used by ambient musician robert rich when he was recording his ‘bestiary’ cd. he wanted to define a new type of “buzzing, swarming cloud of sine waves” and after some experimentation, was able to create such a timbre using 24 individual motm modules. now, 8 years later, the technology is available to have this new range of sounds in a 14hp wide euro module.

in its basic form, the e340 is a 2-output, wavetable vco that is generating 16 waveforms at once. modular users quickly discover that in order to get the large, fat notes multiple oscillators are needed that are slightly detuned. this can get expensive quickly, and then you have to deal with the tracking differences, additional mults for the cables and mixers for the outputs. the e340 combines all of these, eliminates the tracking errors and adds the added dimension of being able to control just how “buzzy” the cloud can go. if spread and chaos are set to ’0′, the e340 behaves like a standard analog vco, but with a very pure sinewave output (less than 0.3% thd) and a standard sawtooth wave.

simple detuning can sound really good, but the e340 adds 2 controls never seen on any modular: chaos and chaos bandwidth (bw). once you set the degree of detuning using the spread control, you can then add ‘animation’ to the detuning by dialing in chaos. the chaos randomly ‘wiggles’ every vco’s pitch, while the chaos bw controls the ‘speed of the wiggle’. this adds the “swarming of bees” effect at the extreme settings, and in the low settings the subtle pitch changes are similar to a slow-speed leslie effect.

Construction was almost identical to that of the Morphing Terrarium project.  I used some different pots I had around, a bracket I made myself, and 24 gauge wire.  I am glad I added the Spread CV attenuator pot, because that parameter is the most likely of the unusual ones to be getting CV, although both the Chaos and Chaos Bandwidth also have CV inputs.

This is my build of the J3RK Buchla 258J VCO board, as discussed on Muff’s message board:

Board thread

Build and mod thread

I put it into my famous 1U 16-position MOTM grid panel.  Here’s the Front Panel Express file.

Buchla 258J VCO FPE panel

This is a music VCO with 1V/octave tracking over several octaves and a temperature compensated exponential voltage converter.  I would say its most notable features are a voltage-controlled wave shape, and a very nice linear FM.  The schematic diagram provided by Mark Verbos matches pretty closely to the PC board.

My build and modifications

• The builder decides between mixing a square or sawtooth wave with the sine wave in the wave shaper.  The choice can be made by a selection of resistors at build time or by adding a rather complicated switch.  For simplicity I chose the sawtooth version.
• The PC board offers three outputs:  the main wave shape output, a triangle and a square wave output.  These outputs are roughly 5 volts peak-to-peak.  I added a quad op amp to the board to buffer these outputs and also the sine wave output.  The buffers have gain to bring the levels to a standard 10 volt p-p level.  (I’ll add the buffer schematic later.)
• The PC board has frequency control voltage summing for a coarse tune pot, two 1V/octave inputs, and one reversible CV input (which can easily be doubled to two inputs).  My exponential CV inputs include a 1V/octave input jack, one attenuated FM input, one reversible CV input, and also a fine tune pot for which I had to add a 4M7 resistor to the board.
• For the linear FM section I selected a 1uf polyester film capacitor with a 39K series resistor and a 50K audio taper attenuator pot.  These values work well for me, giving a good depth of FM, and control over the lower levels of modulation.  Low frequencies pass quite well, allowing for slow linear tremolo.
• I added some 100nf bypass caps to the underside of the board.
• As to the much debated choice for switching transistor (a rare 2N3638 is called out), I substituted a BC560C, which works fine.  I always print out a data sheet when installing transistors to insure correct lead placement.  The PC board marks E, B, C, for the transistor leads on the top of the board, which helps.
• I added a 100K linear pot to attenuate the wave shape CV in and left off the 150K resistor from the board.

First Impression

The initial frequency trim pot lets you set a bias point for the coarse range.  At first I set the lowest frequency to 20 Hz.  As this produced a high end of 35 KHz, I decided to set the high end to about 25 KHz and let the low end fall where it might, which turned out to be under 1 Hz!  A very nice range.

I was able to set the 1V/octave tracking for at least three octaves of accuracy and perhaps more.

Adjusting the wave shape trim pots, I had a surprise.  The VC wave shape affects both the sine and the wave outputs!  I was very glad that I brought out the sine wave (which is tapped from the drain of the J201 FET and buffered to bring up the level).  Nicely, the sine output maintains a constant amplitude as it changes shape and becomes edgy.  The wave shape output that mixes in a sawtooth increases in amplitude as it shifts from ‘sine-like’ to ‘saw-like’ in shape.  The ‘sine-like’ shape yields low harmonic content, but is not as smooth as the sine output.  (I’ll post some demo recordings.)

Pictures

Board

Behind the panel

Buffer wiring on the underside of the board

The bracket that I made from thin aluminum stock from Lowes, shown before bending.

Tony of Oakley Sound keeps updating his modules.  See here for his latest description of the famous ADSR-VCA.

Though I already had four of the earlier revision 2 ADSR/VCA, two with full voltage control, I wanted to upgrade and replace my dual rev 2 ADSR/VCA module with a couple of these rev 4.  There is little difference in the main circuit between rev 2 and rev 4.  The latter adds a looping ability and a switch to control the mode.

NORMAL – Works normally, with the envelope started by the Gate signal.

GATED – Looping will occur only when the Gate is high.

LOOP – The module’s output it will loop continuously in AD mode. The Gate input has no effect in Loop mode.

The rev 4 also provides an independent envelope output, labelled ADSR, good for controlling something simultaneously when also using the VCA feature.  The inverted output from the rev 2 panel is lost, although the rev 4 board can be built to support that as an option.

Bridechamber makes a nice panel for the new rev 4 board, and that’s what I’ve used.

Construction is straight-forward.  As with all Oakley modules, the panel is affixed to the PC board assembly by means of pot brackets.  The rev 4 boards use small Alpha pots that I ordered from Small Bear Electronics, since Mouser does not list the version with PC pins.

I always solder wires from the board to the panel jacks, it’s so simple.  Oakley sells a small PC board to mount the jacks, with a ribbon cable header, if you want to do it that way.

This is a circuit of my own, based on the XR-2206 VCO data sheet examples.  Features:

• Coarse and fine frequency controls
• Low/High range switch
• Sine/Triangle switched output
• Square wave output
• Linear, AC-coupled FM input
• Internally normalized for cross modulation

My intended use of these VCOs is as modulation sources for linear FM of other VCOs, such as the Cynthia ZerOscillator and the Fritz Teezer.  I was looking for a sine wave VCO for quite a while, but a 1U sine wave VCO in MOTM format is not commonly found.  I happened across the XR-2206 in a discussion on Muff Wiggler’s forum and found this hobby store that sells a PC board.

Electronics DIY XR-2206 PC Board

Realizing that I did not need 1V/octave tracking or other high-quality music VCO features, I bought two boards and two XR-2206 chips.  (Get the XR-2206 from Mouser for under $5.00 each).

After I got the chips I started breadboarding.  Although I used the PC boards, I didn’t follow the original circuit but built my own.  I added an FM input, set a fixed amplitude for the sine/triangle output, and selected capacitors for the low and high ranges.  The XR-2206 is powered between ground and +15V, so the output is all above ground.  The triangle is much larger than the sine wave.  So I designed a buffer circuit, using a TL072 on a Tellun MUUB-2 PC board to provide +/-5V sine and triangle waves, and a +/-5V square wave obtained with the comparator circuit that I often use.

Here is the Dual XR-2206 Front Panel Express Panel.

Here is the XR-2206 Circuit Diagram, and the Buffer Circuit Diagram.

There is a trimpot on the XR-2206 board for the sine shape, and trimpots on the MUUB board for the sine and triangle levels.  The sine/triangle switch is DPDT.  One side switches the wave selection and the other switches between trimpots on the MUUB, so that the output levels of the sine and triangle can be made the same.  The FM input is AC-coupled by necessity, because the initial frequency is set by the combined resistance of the two frequency pots from pin 7 of the XR-2207 to ground.  DC-coupling would be tricky to do, but not necessary in this application.

The sine/triangle output of each VCO is connected behind the panel to the switching lug of the other VCO’s FM input to facilitate cross-modulation without need for patch cords or multiples.

Here’s a demo recording of the module.  It starts out showing the two frequency ranges of one oscillator, using the sine wave.   (The low range is 8 Hz to 400 Hz, the high range 87 Hz to 4300 Hz.)  Then the second VCO is brought in.  The second then modulates the first, then the first the second, and then each other simultaneously.  Then both are switched to triangle and knobs are twiddled a bit.

Description:

The Trapezoid VCA is a DIY project from Jurgen Haible, renowned modular synthesizer engineer.  It emulates the EMS VCS3 and Synthi A Trapezoid Generator.  I am not familiar with the EMS module, and I wasn’t quite sure what to expect of this one.  Now I’ve built and used it, it is indeed everything I had hoped for in a combined Envelope Generator/VCA.

Download the FPD Panel

The Envelope Generator (EG) part is unique among envelope generators in that it produces a trapezoid shaped waveform with an Attack-On-Decay pattern.  When triggered, the output rises linearly to maximum at a rate determined by the Attack pot, holds for an amount of time determined by the On pot, and then decays at a rate determined by the Decay pot in combination with the Decay CV input.  At settings less that fully clockwise (max time) the Off pot determines how long the output stays at the minimum value (i.e. off) before automatically re-triggering.   I would in fact call it a Trapezoid LFO with variable rise rate, on  time, fall rate, and off time.

Be sure to check out the Dragonfly Alley page for the Trapezoid.

VC Decay

The VC Decay input has its own reversible attenuator (D CV) pot, which controls the amount of CV applied positively when right of center, and negatively when left of center.  A more positive CV increases the decay time, like turning the Decay pot clockwise.  An immediate application is to patch the minus Out envelope back to D CV, which results in an exponential decay curve more like you get with a regular EG.  This is so useful that I made it a jack-normal connection.

Trigger Modes

When Off is at max then you have three ways to trigger a cycle of Attack-On-Decay.

1. Press the handy Manual button
2. Patch a gate into GATE IN
3. Enable Auto Trigger mode

In Auto Trigger mode the EG is triggered by the audio input to the VCA reaching a threshold, which is set by a pot or a trimpot.  I chose to use a trimpot.

Envelope Outputs

The envelope is available as four different outputs from the PC board (more on this later).  I brought out the ‘S’ outputs and made a modification so that the positive output goes from zero to +5V and the negative from +5V to zero.  The ENV LED indicates the OUT + envelope level.

The VCA

Although the PC board provides many different input and output choices for the builder, I chose to use one buffered input and the buffered output.  There is no separate CV input for the VCA available; it is driven by the internal envelope.  It has trimming for zero and initial gain internally.  The GAIN pot establishes the Initial Gain level when you wish to allow some of the signal through when the EG is at zero.  Unlike the initial gain on other VCA modules I’ve used, turning up the initial gain does not lead to a higher output level when the envelope is at maximum.  That is, it does not sum with the envelope.  In fact if you turn GAIN all the way up, the envelope will have no effect!  The envelope merely increases gain up to the maximum.

Construction

I used the MOTM power connector with the on-board 12V regulators.  I made my own mounting bracket using aluminum stock from Lowes.  It worked quite well.  Also for this project for the first time I used 0.1″ MTA connectors with headers on the board.  This turned out to be really useful, since I had to remove the board to add some trimpots.  The PC board uses a clever design for pot connections, so that the builder can choose to install either a trimpot or a 3-pin connector for an off-board pot.

Modifications

I added three trimpots, which are seen in the prototyping area of the board in the photo. A 100K trimput in series with R70 adjusts the output gain of the VCA, but it turned out that it wasn’t needed.  The full-on gain using the buffered input and output is about 1.1 with the unmodified circuit and did not need to be increased.  The other two trimpots adjust the levels for the plus and minus envelope outs.  The 100K gain trimpots were inserted in series with R38 and R42 and allow attenuating the envelope levels, which from the S outputs is roughly 10V out of the box.  Using those in combination with the offset trimpots I was able to set the plus out to be zero to +5V and the minus output to be +5V to zero.

This is a DIY mixer designed to save space in a portable cabinet.  It is based on my 2U DIY Matrix Mixer.  The circuit is almost identical, except that this one has DC coupled inputs and is unity gain.  Like that one, the pots are audio taper.  As I reflected on the panel design, I realized the benefit of making the fourth input be a non-attenuated auxiliary input, a feature not present on any of my other mixers.

Internally it is two completely separate mixers, each built on a Tellun MUUB-2 board.  (You could use one MUUB-4  instead.  I happened to have two MUUB-2 boards lying around.)  The circuit is about the simplest possible.   Download the  Small Matrix Mixer Circuit.

The panel configuration maximizes utility.  It is labeled L and R (left and right), as a convention when using it as a final output mix.  Each of the left inputs is normally connected to ground with no plug inserted, and each of the right inputs is normally connected to whatever is plugged into the corresponding left input.  As an example use of the AUX inputs, imagine the two outputs from a Blacet Mixer being patched there.  Now you have a five input stereo mixer, DC coupled, with a bias pot for each channel.  Patch L OUT to AUX R IN and you have a six input mono mixer.  Or patch the output from a buffered attenuator to the AUX L IN, and you have a fourth channel, equally mixed to both outputs.

Download the Small Matrix Mixer FPE Panel.

Construction was straightforward, using a shortened Bridechamber 3-jack bracket to mount the two MUUB-2 boards. It was time to purchase more hookup wire, so I pinged George Mattson for the part number of the wire he uses.  For a 100 foot roll of Belden 24AWG UL1061 BLK it’s Mouser 566-9984-100-10.  Pricey, but excellent quality.  The pots are Mouser 652-91A1A-B24-D20, a Bourns make with very nice feel.  These have pins rather than lugs, but were easy to lay-solder to.  I bent the pins back for easy access and soldered to them after the pots were mounted.  Power to the second board is run underneath from the first board’s power connector.

Here is a Synthtech e350 Morphing Terrarium DIY project.   Paul Schreiber’s description, taken from the AnalogueHaven product page.

the synthesis technology e350 morphing terrarium is a unique wavetable vco with 2 independent waveform outputs. unlike similar designs, the e350 is a fully self-contained, 1v/oct vco. what sets the e350 apart from previous wavetable oscillators is the voltage-controlled morphing.

the module comes shipped with 3 banks of 64 ‘basic’ waveforms (192 total). each bank of 64 waves is arraigned in memory as an 8 x8 array (like a chess board). the ‘rows’ are called ‘the x direction’ and the columns are ‘the y direction’. the 2 panel controls and the 2 external control voltages (morph x and morph y) are used to “point” to where in the array we use for the data that is the xy out. the third control voltage is called ‘z morph’, and it determines the waveshape at the z out. the z control voltage ‘scans’ then wavetable bank from wave #1 (think as row 1, column 1) to wave #64 (row 8, column 8). for example: if x morph is set to 2, and y morph is set to 5, the signal at xy out is the waveform stored at row 2, column 5 (the 13th wavetable). the z out is completely independent of xy out, so if the morph z knob is at 48, then the 48th wavetable ( row 6, column 8 ) is the output.

the wavetables in the 3 banks are very carefully ordered by rows. in general, scanning in the x direction will generate a smooth progression of timbre. each row, however, is different! there are sine banks, pulse width modulations, filtered noise and even male/female vocal formants. so, then you can see that scanning in the y direction (in a column) will be extremely varied. and the beauty is that you can scan in both directions simultaneously if you want.

but we were not content with just indexing through the table 1 wave at a time. instead, the e350 implements a proprietary smoothing/anti-aliasing algorithm that allows the 2 outputs to be a continuous blending of one wave to another. the algorithm calculates 128 “in-between” waveforms, so that the 192 ‘basic’ waveforms are really expanded to over 24 *thousand* individual timbres! so as you adjust the panel controls, or add external modulation (from lfos, eg, etc) the e350′s outputs are “glitch-free” and will provide you with a near infinite range of tonal possibilities. for people that like the glitches of older wavetable vcos, there is a jumper option on the pc board to add these back in.

but, we wanted to do more, so we added a 3-position range switch for using the e350 as the world’s best lfo. at the lowest setting, the e350 will cycle once every 13 minutes and be repeatable within 20usec. the sync signal can be used to reset both outputs to zero (‘hard sync’) like any other vco. the ‘c’ bank of waveforms are specifically designed to be used in lfo settings (although they will output audio timbres as well). the lfo waveshapes are everything from ‘chirps’, sequences of individual notes to noise gates, s&h effects to exponential/log sweeps. like quadrature outputs? the e350 can have variable phase outputs under cv control.

there is nothing like the e350 in any modular format. in many patches a vcf is not needed: the timbres that are generated are already smooth and harmonically “correct”. from the precise tracking to over 24,000 waveforms possible, the e350 sets the standard in modular oscillators.

Panel Design

You can download my

Front Panel Express Morphing Terrarium Panel

Yes, I just had to fit this into a 1U panel with small knobs.  I located all the knobs at the top, the jacks at bottom, and the two switches in the middle.  I admit the downside of the closeness of the knobs, having immediately discovered that fiddling with the MX (Morph X) knob risks nudging the coarse frequency pot to its left.  But I got the 1U sinewave VCO I wanted, plus 24,000 other waveforms!  For this application I used high-quality Bourns potentiometers, Mouser part 652-91A1A-B24-B18.

Construction

The dual PC boards with SMT components fit well on a Bridechamber 3-jack bracket, cut down in length. Wiring was made harder than needed because I was out of thin wire and had to use #22 with rather thick insulation.  This resulted in a bunch of wires running under the bottom board and required that the jack wires be soldered to the top of the board, contrary to instructions.  But it all fits.  Here’s a mid-assembly photo.

And all together.