Trapezoid quadrature through zero VCO (Euro version) with waveshapers

Trapezoid quadrature through zero VCO with waveshapers: Front
Trapezoid quadrature through zero VCO with waveshapers: Front

This is my third take on the Trapezoid VCO core designed by Don Tillman. My first implementation for a 15V banana system with separate waveshaper can be found here. My second implementation for a 15V banana system with integrated waveshaper can be found here.This time I moved on to the 12V Eurorack format. The core is still based on the original design from Don (used with permission). I found the original article and schematic about the Trapezoid VCO on Don Tillman’s site (Link to original article from 19 July 2003). The article consists off three parts with the core implementation in part 2. I kept the basic idea and changed nearly everything else. I use an other exponentiator scheme and temperature stabilization. Another reference voltage device is used. A octave switch is added. And quadrature square outputs are implemented. As well as the additional waveforms triangle, sine, ramp up, ramp down and pulse.

Specs and features

  • Trapezoid quadrature output
  • Square quadrature output
  • Triangle quadrature output
  • Sine quadrature output
  • Pulse output, 0deg, 90deg
  • Ramp up output 0deg, 90deg
  • Ramp down output 0deg, 90deg
  • Octave switch
  • Through zero modulation
  • PWM input
  • V/Oct, FM log and trough zero CV input
  • Temperature compensated
  • Fine frequency setting
  • Runs on +/-15V and +/-12V
  • Power consumption around 110mA each rail

The documentation and the Gerber files for download (link) can be found in my website (link).

Trapezoid quadrature through zero VCO with waveshapers: Schematic control PCB
Trapezoid quadrature through zero VCO with waveshapers: Schematic control PCB
Trapezoid quadrature through zero VCO with waveshapers: Schematic main PCB
Trapezoid quadrature through zero VCO with waveshapers: Schematic main PCB
Trapezoid quadrature through zero VCO with waveshapers: Schematic main PCB
Trapezoid quadrature through zero VCO with waveshapers: Schematic main PCB

J. Donald Tillman did an excellent job describing the core of his Trapezoid VCO. Please refer to the original article as linked above. Don Tillman gave me the advice to use only two capacitors in the core. The exponentiator I use is a well known and a classical design. You can find many description of it out there. The rest is straight forward.

Trapezoid quadrature through zero VCO with waveshapers: Populated control PCB
Trapezoid quadrature through zero VCO with waveshapers: Populated control PCB
Trapezoid quadrature through zero VCO with waveshapers: Populated main PCB
Trapezoid quadrature through zero VCO with waveshapers: Populated main PCB
Trapezoid quadrature through zero VCO with waveshapers: Back view
Trapezoid quadrature through zero VCO with waveshapers: Back view
Trapezoid quadrature through zero VCO with waveshapers: Side view
Trapezoid quadrature through zero VCO with waveshapers: Side view
Trapezoid quadrature through zero VCO with waveshapers: Screenshot trapezoid wave out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot trapezoid wave out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot square wave out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot square wave out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot sine wave out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot sine wave out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot triangle wave out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot triangle wave out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot pulse wave out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot pulse wave out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot triangle through zero out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot triangle through zero out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot trapezoid through zero out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot trapezoid through zero out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot trapezoid through zero out
Trapezoid quadrature through zero VCO with waveshapers: Screenshot trapezoid through zero out

Trapezoid quadrature VCO through zero (flat version) with waveshapers

Trapezoid quadrature VCO through zero (flat version) with waveshapers
Trapezoid quadrature VCO through zero (flat version) with waveshapers: Front view

This is my second take on the Trapezoid VCO designed by Don Tillman. My first implementation can be found here. This time I mounted the PCB’s parallel to the front to save space and integrated the wave shapers. The core is still based on the original design from Don (used with permission). I found the original article and schematic about the Trapezoid VCO on Don Tillman’s site (Link to original article from 19 July 2003). The article consists off three parts with the core implementation in part 2. I kept the basic idea and changed nearly everything else. I use an other exponentiator scheme and temperature stabilization. Another reference voltage device is used. And quadrature square outputs are implemented. As well as the additional waveforms triangle, sine, ramp up, ramp down and pulse.

Specs and features

  • Trapezoid quadrature output
  • Square quadrature output
  • Triangle quadrature output
  • Sine quadrature output
  • Pulse output, 0deg, 90deg
  • Ramp up output 0deg, 90deg
  • Ramp down output 0deg, 90deg
  • Through zero modulation
  • PWM input
  • V/Oct, FM log and trough zero CV input
  • Temperature compensated
  • Coarse and fine frequency setting
  • Runs on +/-15V and +/-12V
  • Power consumption around 135mA each rail

The documentation and the Gerber files for download can be found in my website.

Trapezoid quadrature VCO through zero (flat version) with waveshapers: Back view
Trapezoid quadrature VCO through zero (flat version) with waveshapers: Back view

Quad waveshaper for trapezoid quadrature thru zero VCO

Quad waveshaper for trapezoid quadrature VCO
Quad waveshaper for trapezoid quadrature VCO

This is the waveshaper for my Trapezoid quadrature through zero VCO. It gives the quadrature outputs for triangle, sine and the outputs for saw (ramp up, ramp down) and pulse. To use it you need my Trapezoid quadrature VCO. The waveshaper has no external input for waves, it is internally connected with the Trapezoid quadrature VCO

Specs and features

  • Four triangle quadrature outputs
  • Four sine quadrature outputs
  • Two saw (ramp up) outputs 90° apart
  • Two saw (ramp down) outputs 90° apart
  • Two pulse outputs 90° apart
  • Voltage controlled pulse width
  • Runs on +/-15V and +/-12V
  • Power consumption around 50mA each rail

The documentation and the Gerber files for download can be found in my website .

Schematic 01 quad waveshaper for quadrature thru zero VCO
Schematic 01 quad waveshaper for quadrature thru zero VCO
PCB quad waveshaper for quadrature thru zero VCO
Schematic 02 quad waveshaper for quadrature thru zero VCO

The triangle waves are created by algebraically averaging two trapezoid waves 90° apart. This is done here with IC3A for 270° and 0°. IC3C adds and averages 90° and 0°. You can use other combinations as well. IC3B and IC3D gives the inverse triangle waves. The sines are derived from the triangle with well known “old style” circuitry. The ramp outputs are build from two triangles 180° apart, level shifted and switched between them with the square wave. IC5A takes the 90° triangle, shift it up to 0..10V and lowers the amplitude to 0..5V. IC5B takes the 270° triangle shift it down to 0..-10V and lowers the amplitude to 0..-5V. IC6 (DG409) switches between this two triangles with means of the 270° square. Switching in the right moment put the needed parts of the triangle back together to the saw. The pulse outputs are done with the usual technique moving the switching point of a comparator around with the ramp wave.

PCB quad waveshaper for quadrature thru zero VCO
Triangle screenshot from quad waveshaper for quadrature thru zero VCO
Triangle screenshot from quad waveshaper for quadrature thru zero VCO
Sine screenshot from quad waveshaper for auadrature thru zero VCO
Sine screenshot from quad waveshaper for auadrature thru zero VCO
Saw screenshot from quad waveshaper for auadrature thru zero VCO
Saw screenshot from quad waveshaper for auadrature thru zero VCO
Pulse screenshot from quad waveshaper for auadrature thru zero VCO
Pulse screenshot from quad waveshaper for auadrature thru zero VCO
Quad waveshaper for auadrature thru zero VCO back view
Quad waveshaper for auadrature thru zero VCO back view

NGF Project: Dual Sample and Hold

Dual Sample and Hold: front view

Dual Sample and Hold: front view

Storing analog signals is a often used function in analog synthesizers. This sample and hold implementation follows closely the original Elektor Formant version of Book 2 “Formant Erweiterungen” p84ff. It is build for my Next Generation Formant project. Because I use the LM13700 here as replacement for the CA3080 I have build a dual sample and hold version. The PCB size is reduced from 100x160mm for a single version to 50x70mm for the dual version.

Specs and features
• Dual sample and hold
• 10Vpp input and output
• Runs on +/-15V and +/-12V
• Power consumption below 25mA each rail

The documentation for download can be found in my website.

Dual Sample and Hold: schematic

Dual Sample and Hold: schematic

This implementation follows closely the original Elektor Formant implementation. Refer to the original documentation if needed. You can find it on the net. My changes are the input buffers, using the LM13700 instead of the CA3080 and the adaption to my 10Vpp signal level.

Dual Sample and Hold: populated PCB

Dual Sample and Hold: populated PCB

Dual Sample and Hold: back view

Dual Sample and Hold: back view

NGF-Project: Elektor Wave Processor

NGF Project: Elektor Wave Processor

NGF Project: Elektor Wave Processor

A small but very versatile module. It is derived from the original Elektor Formant book “Formant Erweiterungen” p87 ff. Some resistor values are changed to handle the 10Vpp signal level of my system. You can shape the input signal in many ways. You can clip the signal. You can fold the signal. You can emphasize the third harmonic. You can unsymmetrical emphasize the clipped and unclipped signal. You can reverse the input signal. The clipping level is voltage controlled.

Specs and features

• Clipping the signal
• Folding the signal
• Emphasize the third harmonic
• Unsymmetrical emphasize the clipped and unclipped signal
• Clipping level voltage controlled
• 10Vpp input and output
• Runs on +/-15V and +/-12V

The documentation for download can be found in my website.

NGF Project: Elektor Wave Processor, schematic

NGF Project: Elektor Wave Processor, schematic

This implementation follows closely the original Elektor Formant implementation. Refer to the original documentation if needed. You can find it on the net. My changes are the adaption to my 10Vpp system signal level.

NGF Project: Elektor Wave Processor, populated PCB

NGF Project: Elektor Wave Processor, populated PCB

NGF Project: Elektor Wave Processor, rear view

NGF Project: Elektor Wave Processor, rear view

Divide and add

Divide and add front

Divide and add front

An interesting module to add more color to your sounds. The input signal triggers the 4024 binary counter whenever the signal crosses zero. Therefore you can use nearly any input signal not only squares. The outputs of the 4024 is are added together in two ways. One weighted the other with equal values. The weighted output gives you a more triangle shaped output. You can add lots of harmonics in widely adjustable different combinations.

Specs and features
• Divides nearly any signal
• Weighted and unweighted added output signal
• Add widely adjustable harmonics to you signal
• Runs on +/-15V and +/-12V

The documentation for download can be found in my website.

Divide and add: schematic

Divide and add: schematic

On every zero crossing the input signal triggers the binary counter 4024. The outputs of the counter are adjustable added together weighted and unweighted and the two signals are brought out.

Divide and add: populated PCB

Divide and add: populated PCB

Divide and add: back view

Divide and add: back view

NGF Project: Dual Ringmodulator

NGF Project: Dual Ringmodulator front view

NGF Project: Dual Ringmodulator front view

I was a bit hesitant doing this module because it uses the now obsolete LM1496 balanced modulator-demodulator. But you can still source them and I have some in my stock. So I decided to make a PCB and module for my Next Generation Formant project. I started with the original Elektor Formant schematic published in “Formant Erweiterungen” p35ff. I left out the microphone and envelope follower part because I already have such modules. I have added input buffers and raised the signal level to my 10Vpp used throughout my system. I was able to put two ringmodulator on a 50x100mm PCB.

Specs and features
• Dual ringmodulator
• 10Vpp input and output
• Runs on +/-15V and +/-12V

The documentation for download can be found in my website.

NGF Project: Dual Ringmodulator schematic

NGF Project: Dual Ringmodulator schematic

This implementation follows closely the original Elektor Formant implementation. Refer to the original documentation if needed. You can find it on the net. My changes are the input buffers and the adaption to my 10Vpp signal level.

NGF Project: Dual Ringmodulator populated PCB

NGF Project: Dual Ringmodulator populated PCB

NGF Project: Dual Ringmodulator back view

NGF Project: Dual Ringmodulator back view

Modulation Sequencer

Modulation Sequencer populated PCB

Modulation Sequencer populated PCB

This is a small easy to use and easy to build sequencer. The sequence is adjustable from 2 to 8 steps. The output range is switchable from 0..1V to 0..5V. So you can cover 1 or 5 octaves. The sequencer is clocked from an external source. The clock range goes from very slow (LFO) to way above the audio range. When used in the audio range you can realize quite interesting envelope patterns. With the reset input you can start and reset the sequence. This is useful for creating a gated repeating pattern. Many more applications are possible.

Specs and features
2..8 steps
Switchable output 0..1V, 0..5V
Clock input
Reset input
Positive and negative output
Runs on +/-15V and +/-12V (with minor changes)
Power consumption below 10mA each rail

The documentation for download can be found in my website.

Modulation Sequencer schematic

Modulation Sequencer schematic

The sequencer is build around the decimal counter 4017. The clock and reset input needs at least 1/2 off the positive supply voltage to trigger. Therefore the inputs are amplified (IC5C, IC5D, IC1) so you can run the sequencer with lower input voltages. The input circuitry also protects against negative input voltages which are not allowed for the 4017. With the rotary switch you can select the length of the sequence. The rotary switch selects the output which is feed to the reset input of the 4017. The outputs are buffered with the transistors Q1 ..Q8. The emitters are connected to potentiometers which adjust the output voltage. The transistors are driving the LED for the step display as well. The output is buffered with the operational amplifier IC5B. IC5A provides the negative output.

Modulation Sequencer back view

Modulation Sequencer back view

Modulation Sequencer front

Modulation Sequencer front

NGF Project: Waveshaper

This is my waveshaper version for the NGF Project. It is basically the same schematic as for my waveshaper version 0.9.5 with an added output circuitry and wiring option to be used with a rotary switch or some SPST switches as in the original. I kept all the waveforms of the original Elektor Formant, but changed the circuitry significantly. The only thing i added is a symmetrical square out, that i found useful for sync. For converting the saw wave to triangle a precision full wave rectifier is used, followed by a level shifter. The originally used matched Germanium diodes are hard to obtain these days. Here you only have to match two resistors. The switching glitch is not audible and can be suppressed with means of a capacitor of some 100pF if wanted. Don’t choose the capacitance to high, it rounds the edge of the triangle. For triangle to sine conversion i used a well known circuit that works better then the two diodes approach from the original Elektor Formant. This circuitry can be found at various places in Electronotes and others. The circuitry is very sensible to the used resistor values and input voltage. The resistor values are done for a BF245B. BF245A or C will not work. If you use another input voltage you probably have to change type of FET and resistor values. For wave shaping from saw to spaced saw I kept the original circuitry from the Elektor Formant. I only have to change some resistor values due to the different signal level. New added is the saw to square waveshaper because I found it useful to have a symmetrical square output. The saw to pulse shaping is quite different to the original but quite standard.

The documentation for download can be found on my website.

NGF Project: Waveshaper stuffed PCB

NGF Project: Waveshaper stuffed PCB

NGF Project: Waveshaper schematic

NGF Project: Waveshaper schematic

NGF Project: Waveshaper output saw, square and spaced saw

NGF Project: Waveshaper output saw, square and spaced saw

NGF Project: Waveshaper output saw, triangle and sine

NGF Project: Waveshaper output saw, triangle and sine

NGF Project: NGF VCO Core two

NGF VCO core two faceplate

NGF VCO core two faceplate

I have build my first original Elektor Formant VCO’s in the 70’s. They worked quite well and do so until today. Over the years i did implement some changes and extensions. I have developed a PCB Version with my changes and extensions published as VCO Core one. But only for those few lucky ones with some spare uA726. Here is the second VCO for my Next Generation Formant project. As in the NGF VCO core one I tried to keep the basic architecture of the original Elektor Formant. With the goal using only today available parts. This means finding a heated transistor pair for the expo converter and a Schmitt Trigger with hysteresis for the switching. Because there are no heated transistor pairs obtainable in the market today I was on my own. There are some solutions for a heated expo pair out there. Most of them build around no longer available parts or quite expensive. A still easy to get and cheap part is the LM3046. The SMD version is still in production today (2017 March) and the DIL version is easy to source as well. Though not longer in production. The PCB for the NGF VCO core two holds both versions. You can stuff it with the SMD- or DIL version. The 4093 is used as Schmitt Trigger for switching. Using the 4093 makes some level shifting necessary for proper switching. The switching capacitor is reduced to 470pF which give an even more better volt per octave characteristic then the original over the audio range. A LFO option is implemented as well. In conjunction with the waveshaper you have now the same waveforms available as voltage controlled LFO.The uA726 is replaced with LM3046 and the 7413 with 4093. All internal control voltages are stabilized. I removed the need for the +5V current supply, added an octave switch, FM lin and sync in. A new feature is the LFO switch. The signal level is raised to 10Vpp to get a better SNR throughout the system.

The documentation is available for download on my website.

VCO Core two: stuffed PCB

VCO Core two: stuffed PCB

VCO core two saw out

VCO core two saw out

All changes I have made to my original Elektor Formant VCO are implemented: No extra 5V source is needed, all control voltages are stabilized, Octave switch, FM lin, 10Vpp output. New LFO option.

NGF VCO core two schematic

NGF VCO core two schematic

To keep the characteristic of the original Elektor Formant I kept the heated exponential converter, here build around the LM3046. The PCB is developed to hold the DIL and the SOIC version as well. The Schmitt Trigger used is the 4093. Due to different switching levels in the original some transistors are added for level shifting. The octave switch is build with the OPA2277 and the voltage reference REF102. Switch SW1 turns the LFO option on and off. The level for the Sync input is adjusted with P1. Fine tune of the pitch is done with P2. If you need a wider range for the tuning you can change it with changing the potentiometer or the resistors values here. The basic pitch is set with TR4. Output voltage is set with TR3 and the DC offset with TR1.

NGF VCO core two schematic heater

NGF VCO core two schematic heater

This circuitry is part of my NGF VCO Core 2. It make use of two transistors to heat the LM3046. It works with the SMD and DIL Version as well. The given resistor values keep the current values and the power dissipation below the maximum ratings. T3 is used to measure the actual temperature. The voltage drop over T3 is direct proportional to the chip temperature. It is compared to the voltage at pin 2 of the LM3046 which is derived from TR6. The temperature is easily adjusted with TR6. Between heating off and maximum temperature. The testing bridge is driven with a stabilized 10V voltage source. T4 and T5 are used as heaters. R41 and R43 limit the maximum current. The different values are selected with purpose to keep pin 13 of the LM3046 (the substrate) the lowest negative point at the chip.