Trapezoid quadrature through zero VCO (Euro version) with waveshapers

Posted on February 11, 2021 by Harald

**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 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 main PCB**

**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: Screenshot trapezoid 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 triangle 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 trapezoid through zero out**

Quad waveshaper for trapezoid quadrature thru zero VCO

Posted on October 5, 2019 by Harald

**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**

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.

**Triangle screenshot from quad waveshaper for quadrature thru zero VCO**

**Sine 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**

**Quad waveshaper for auadrature thru zero VCO back view**

Trapezoid quadrature VCO

Posted on August 26, 2019 by Harald

I always wanted a VCO with through zero capacity. Why not combining this with a unusual wave form and quadrature outputs? Usable as LFO as well? 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. The addressing hardware for the DG409 is changed. A LFO option is added. Another reference voltage device is used. And quadrature square outputs are implemented. The additional wave forms triangle, sine, ramp up, ramp down and pulse are covered in an extra module

Specs and features

Trapezoid quadrature output
Square quadrature output
Through zero modulation
V/Oct, FM log and trough zero CV input
Temperature compensated
Voltage controlled pulse width
LFO Range switch
Coarse and fine frequency setting
Runs on +/-15V and +/-12V
Power consumption around 65mA each rail

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

J. Donald Tillman did an excellent job describing the core of his Trapezoid VCO. Please refer to the original article as linked above. The exponentiator I use is a well known and classical design. You can find many description of it out there. The rest is straight forward. The LFO option is implemented with the DG202. Here are just four capacitors added switchable in parallel to the audio frequency capacitors. The connectors shown are for adding the waveform module to generate triangle, sine, ramp up, ramp down and pulse.

Trapezoid VCO quadrature output — **Trapezoid VCO quadrature trapezoid output**

**Trapezoid VCO quadrature square output**

**Trapezoid VCO through zero modulation**

NGF VCO Core one (Elektor Formant based) Part one

Posted on September 23, 2014 by Harald

To start with this Blog i want to write about a new PCB project which roots go back to the seventies. At this time a German electronics magazine published an diy analog synthesizer. The Elektor Formant. They sold PCB’s and some third party vendors sold kits as well.

So i bought and build my first few modules of an analog synthesizer. The VCO was build around the Fairchild uA726 temperature controlled differential pair, the same one used in the Mini Moog second oscillator board. Over the years a added some features to the VCO that i found useful. For instance: octave switch, sync in and out, fixed square out, FM lin, voltage reference, output mixer and some more. Getting rid of the 5V PSU was a big step. I made the changes recommended in the second Formant book as well. This leads to some wiring …

and an additional stripboard.

So i decided to consolidate what i have done and put all those changes on one PCB. This was possible because i have all the used obsolete parts at hand. If you want to follow this path first make shure that you can get hold on those parts (uA726, 74LS13). They are still available at a price but you have to search for them.

I only did the core VCO here. The wave shaper will be tackled later in a separate project. There are two categories of changes i did. Additions i found usefull to have and changes to increase stability. Usefull additions: Octave switch, FM lin, Sync in, Sync (pulse) out. Increased stability: Stabilized control voltages, getting rid off the 5V power suplly. Details and schematic can be found on my website.

The PCB just arrived. Now time to stuff it.

VocLog

Analog Synthesizer DIY

Tag Archives: VCO

Trapezoid quadrature through zero VCO (Euro version) with waveshapers

Specs and features

Quad waveshaper for trapezoid quadrature thru zero VCO

Specs and features

Trapezoid quadrature VCO

Specs and features

NGF VCO Core one (Elektor Formant based) Part one