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JH. Matrix FX
The idea:
Use the concept of the EMS VCS3 (Matrix patching, a single output attenuator for each function, Joystick, Vernier Dials, monitor speakers ...) for a collection of Effect (FX) devices.
Keep enough of the VCS3's original functions in the Matrix FX to be
able to sell my Synthi
Clone some time.
| Function | Implementation | Applications |
| 3 Oscillators |
Basically providing all the waveforms of the VCS3 for
_each_ Oscillator. All oscillators can be audio range or LFO range. Different implementation, more features. Osc. 1 has a quadrature sin / cos core, and is also used as modulator for the SSB modulators. Osc. 2 can be "Shape modulated" by Osc. 3. Osc. 3 also has random S&H waveform with variable probability. |
Audio Oscillators Modulation Oscillators (LFO and Audio Range) Random Voltage Source |
| Filter | Original VCS-3 LPF plus 4-pole HPF |
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| Trapezoid Generator with VCA |
Same function as, but different implementation than , VCS3. VCA can either be controlled by Trapezoid, or by external CV. VCA has "Initial Gain" potentiometer added. |
Attack / Hold (On) / Decay envelope triggered by Gate signal
or front panel Button Self cycling mode with Attack / On / Decay / Off parameters. Voltage controlled Decay time. VCA can be used seperately from Trapezoid. |
| 2 SSB Modulators (Frequency Shifters) |
Two complete Frequency Shifters ("Single Sideband Modulators"), sharing their Modulation Oscillator - Amount of frequency shift equals frequency of Osc. 1 | Stereo Frequency Shifting Upshift->Filter function->Downshift will turn a fixed filter bank etc. into a VCF. Output signal will be in the same frequency range as input signal (again), but filter courve will be virtually shifted down. Barberpole Phasing |
| BBD Delay |
Long delay (Echo) or short delay (Flanger, Chorus, Physical
Modelling) Various Filter functions (tracking, non-tracking) 1V/Oct control for tuned comb filters and Physical Modelling |
Echo, Flanger, Chorus, Vibrator, Physical Modelling |
| Phaser | Various Phaser modes. Stereo output. |
Phasing, Vibrato, Crossover (HP/LP) |
| External FX | Send / Return Loop for external effect. Voltage controlled Wet / Dry Mix |
For Reverb, Filter Banks, etc. |
| Wave Folder |
The famous Serge Wave Multiplier, adapted to VCS3-like input
and output levels |
Dynamic creation of harmonics Mangling modulation signals |
| Envelope Follower |
Inspired by Eventide Instant Flanger Features "Bounce" function and variable Release time |
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| Inv / Amp |
Amplifier, inverting or
non-inverting high Gain or low Gain Built-in opto-electronic Limiter |
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| Front Panel design |
| Construction Drawing |
| Photo of Front Panel back side |
| Sub D connector with wires to be mounted on back of front panel |
| Trapezoid Generator / VCA board |
| Trapezoid / VCA Schematics |
| Joystick |
| Joystick Schematics |
| Wave Folder / Inv Amp board |
| Schematics of Wave Folder and Inv Amp |
| Oscillator 2 |
| Waveforms Pulse, Ramp, Triangle and Sine, with variable waveshape and waveshape modulation from Osc. 3 |
| Osc. 2 Schematics |
| Osc. 2 Photo |
| SSB Modulators (Frequency Shifters) and Oscillator 1 |
| Block diagram of signal path |
| QVCO Core schematics |
| QVCO Core board photo |
| Modulator schematics |
| NEW: Compander
Board I had built a compander system around the Philips NE572 chips, but whatever I tried in terms of operating level and time constants, that thing did sound horrible. (That's the reason I hadn't published that part in the first place.) Now I've replaced it with an OTA-based compander, similar to the one I had used in the FS-1 Frequency Shifter. Which, in turn, has been inspired by the compander inside the Roland Vocoder Plus. It has an almost infinite compression ratio (more ALC that compressor), and it's feed-forward sidechain allows 2-pole filtering after the level detector for a very smooth operation. Frequency Shifters are quite demanding for compressors, as the output signal can be so much different from the input signal, and there is none of the cancellation of distortion products many traditional companding systems rely on. Here, in the Matrix FX, the expander's control current is directly copied from the compressor's - and not derived from the expander's input signal. The only drawback of this method is that the CV is "a little too fast" compared with the signal, which is slighly delayed in the dome filter. I practise, this wasn't a problem, however. Compander circuit for SSB Modulator 1 Compander for Modulator 2, and CV distribution amplifiers for output volume modulation and wet/dry mix of several modules |
| Two dome
filters for two channel operation. The circuit is basically the same as
FS-1
Dome filter. PCB layout of Dome Filter board Component side of Dome Filter board Photo of Dome Filter Boards |
Filter
Transformation Demo (7MB .wav file)
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| To do: Build new Dome Filters that go to 32kHz,
for whole-range upshift -> filtering -> downshift operations. (As it is now, if there are ultrasonic parts of the spectrup left after upshift + filtering, they won't be processed in perfect quadrature in the down-shifter's dome filter.) |
| BBD Delay |
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| Block Diagram |
| Schematics of BBD clock circuit (inspired by Aries and Dynacord circuits; special thanks to Mike Irwin for helpful comments on Aries part.) Note the exponential -1V/Oct input, and 1/x law modulation sensitivity for the modulation matrix. |
| Schematics of BBD core circuit - TDA1022 (as in Dynacord TAM-19) for short delays; MN3005 (as in Amdek Delay Machine) for long delays; DG413 for switching. |
| Schematics of
Anti-Aliasing and Restauration Filter: Filter CV Filter Signal Path. 10-pole-VCF (5 pre BBD, 5 past BBD) allows the following modes: * 3.18kHz with
optional "Bump" in the 2 ...3 kHz Range (Amdek Delay Machine)
SE571 Compander* 15kHz (Dynacord TAM-19) * Tracking (follows the BBD clock rate) * "Open" (ca. 400kHz; hopefully emulates certain filter-less Electro Harmonix devices) VTL5C4 Limiter DG413 Switching |
| Select 5 LM13600's for identical gm (+/-3%) from Iabc =
1uA to 1mA Circuit for selecting LM13600's (Do not use LM13700 or NE5517!) |
| Sketches
for making a "Pseudo-PCB layout" on Veroboard (BBD clock, and
tracking filter) - in case you ever wondered how to get from schematics to veroboard. |
| Phaser Board |
| Some thoughts about phaser control law |
| Modes No phaser model on this planet sounds like any other. The underlying principle is always the same: all pass filtering, mixing of the filtered and dry signal to create notches, and some amount of feedback to create peaks. But that's about it, what all phasers have in common. The all pass filters (APFs) themselves can be implemented with different circuits. The number of stages differs. And there are countless ways to apply feedback and to create a second output for stereo effects. I have chosen opamp-based all pass fiters with Vactrols to control the pole (and zero) frequencies. There are 2 chains of 6 APFs which can be used in series or parallel. A preset switch with 6 positions controls an array of 24 electronic switches for different configurations. Some of these configurations or topologies are inspired by classic phaser circuits, such as Moog, Schulte or Mutron. The APF technology used is different in these, though. Mode 1 Actually not a phaser. In Mode 1, the LPF and HPF outputs of a state variable filter are routet to output 1 and 2, respectively. Think of this as a 12dB/Oct crossover with VC separation frequency and variable resonance. Mode 2 Modelled after the Moog 12 Stage phaser, with only 4 stages in use. (4 stages phasing, and 4 stages feedback.) Feedback polarity is positive, resulting a very fat sound. Feedback is AC coupled to avoid amplification of offset voltages. Output 2 is the "Auxiliary" output of the Moog, created by subtraction of Output 1 signal and the dry signal. Compared to the original, which used OTA-based APFs, there is a bit of CV slewing. Mode 3 Also modelled after the Moog 12 Stage phaser, but using all 12 stages in series. (12 stages phasing, and 12 stages feedback.) See Mode 2 for details. Mode 4 Modelled after the Schulte Compact A Phasing. 8 stages of APF. Feedback taken from stage 2. Negative feedback for pronounced resonant sound. This unique compination creates 4 noches, but only one resonant peak on the main output (Output 1). Output 2, just as in the original, is the signal after the feedback summing , before any all pass filtering, creating only a peak and no notches. Slewing is less than on the original, as the Compact a uses incandescent lamps instead of LEDs. Mode 5 Modelled after the Mutron Bi-Phase. 2 x 6 Stages of APF with opposite polarity modulation for wide stereo effect. Positive feedback for fat sound. Slewing should be similar to the original (LED->LDR technology). Mode 6 "Thin Stereo". Just like Mode 5, but with negative feedback, and mixing of inverted APF signal with dry signal. There's a table in the schematics PDF file that shows in detail what's going on in the various modes. |
| Phaser
Board Schematics Please note that these are my raw design notes, from which I've developed and built the phaser board. This is no clean drawing. For instance, some circuit parts are shown twice, in different context, on different pages. Oh, and I used a NOS SSM2024 quad VCA chip for 2-channel wet-dry mix. I've used this chip only because I ran out of space on my circuit board. I recommend using a pair of CA3280s, or similar linear controlled current-output VCA chips, instead. Ground-reference the control current inputs with four pnp transistors with their bases grounded, in that case. (Collector goes to 3280 Iabc inputs, emitters act like SSM2024 inputs.) |
