Category Archives: Project

Track (Sample) and Hold

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Track (Sample) and Hold: Front view
Track (Sample) and Hold: Front view

One more module for my Shakuhachi to Synths project. Not exclusively of course. This is a Track and Hold. Which is quite useful for other patches as well. In the Shakuhachi patch it is used to suppress an incomplete pitch to voltage conversion from the Pitch to voltage converter when the player stops blowing. The module tracks the incoming (control) voltage as long as the gate input is high. When the gate goes low the output voltage is kept. The module is DC coupled to track slowly moving voltages. For this one I have used some obsolete parts, which I had laying around. So, if you want to build it, make sure that you can get those parts. You can use it as Sample and Hold as well. Instead of a gate apply a trigger at the gate input.

Specs and features

  • Track or Sample and Hold
  • DC coupled
  • Gate input with LED
  • Signal input
  • Signal output
  • Threshold
  • Runs on +/-12V and +/-15V
  • Power consumption below 20mA each rail

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

Track (Sample) and Hold: Schematic
Track (Sample) and Hold: Schematic
Track (Sample) and Hold: Populated PCB
Track (Sample) and Hold: Populated PCB
Track (Sample) and Hold: Back view
Track (Sample) and Hold: Back view
Track (Sample) and Hold: Side view
Track (Sample) and Hold: Side view

Gate Delay

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Gate Delay: Front view

This module starts as a need for my Shakuhachi 2 Synth project. I was in need for a short Gate Delay of about 10ms (which is easy to realize). But then I thought about a more flexible solution with adjustable delay time and optional trimming the gate at the end. To be used elsewhere in the synth as well. So I came up with this solution. The hardware is still simple and the functionality lies in the software. So far I have only realized the function which I need for my Shakuhachi to Synth project. But you can easily improve about this with changing the software.

Specs and features

  • Gate delay with variable timing
  • Coarse and fine time adjustment
  • Gate in and out with LED signaling
  • End of gate trim
  • Runs on +/-12V and +/-15V
  • Power consumption below 30mA positive rail. 5mA negative rail.

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

Gate delay: Schematic control board
Gate delay: Schematic control board
Gate delay: Schematic main board
Gate delay: Schematic main board
Gate delay: Populated control PCB
Gate delay: Populated control PCB
Gate delay: Populated main PCB
Gate delay: Populated main PCB
Gate delay: Back view
Gate delay: Back view
Gate delay: Side view

Sequencer Nostalgia

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This was my first build when I came back to SDIY. A three row/16 step sequencer. Completely build on stripboard. Still working after all this years. Only hand sketched schematics. Nothing to publish. Pictures only.

Sequencer three rows/16 steps: front
Sequencer three rows/16 steps: front
Sequencer: Clock close up
Sequencer: Clock close up front
Sequencer: Clock close up back
Sequencer: Clock close up back
Sequencer: Inside
Sequencer: Inside
Sequencer: Inside
Sequencer: Inside

Pitch to voltage converter

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Pitch to voltage converter: Front view
Pitch to voltage converter: Front view

This is the software driven replacement for my all hardware pitch to voltage converter from my Shakuhachi to Synth project. The software driven approach has the advantage of easily adaption for different frequency ranges. In my case it is the range of the Shakuhachi. To change the range just adapt the software. It is completely temperature independent. The needed input is a pulse train derived from your original signal. You can use my Signal to Trigger converter to provide the pulse train. An offset voltage is added to the V/Oct output to fit the needs of your VCO (Synthesizer).

Specs and features

  • Software driven pitch to voltage converter
  • 12bit resolution
  • V/Oct output
  • Offset CV Fine and coarse adjustment
  • Runs on +/-15V and +/-12V
  • Power consumption around 45mA positive rail, 15mA negative rail

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

Pitch to voltage converter: Microprocessor board
Pitch to voltage converter: Microprocessor board
Pitch to voltage converter: Control board
Pitch to voltage converter: Control board

The incoming pulse train is feed to the microprocessor. IC1 (301-F) prevents the microprocessor from negative inputs. Zener D2 prevents from overvoltage. The trigger starts an internal timer of the microprocessor in input capture interrupt mode. The ticks are counted and the count is then looked up in a table. The lookup table provides the values for the V/Oct conversion. The read value is the send to the DAC MCP4921 which is follwed by a low pass (IC1A, 301-B)). IC2A (301-F) adds the offset voltage and IC2B (301-F) corrects the phase.

Pitch to Voltage converter: Populated PCB's
Pitch to Voltage converter: Populated PCB’s
Pitch to Voltage converter: Side view
Pitch to Voltage converter: Side view

Compressor with optional pedal steering

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Compressor: Font view
Compressor: Font view

This is the revised version of my Limiter/Compressor. First built for my Shakuhachi to Synth project to handle the great dynamic range of the Shakuhachi. Here I left out the limiter and added a make up amplifier. The structure used is derived from “Small Signal Audio Design”, second edition by Douglas Self p682ff. The audio signal did not flow through a VCA as in many other implementations. Instead the compression is done by subtracting the audio signal at the output summing node according to the control voltage derived from the audio signal. The compression rate and the make up gain is adjusted by hand or/and optionally with foot pedals. The foot pedals are an additional option particularly made for wind players. It works without this option in your setup as well.

Specs and features

  • Compression rate and gain adjustable by hand or/and foot pedals
  • Audio path not affected when no compression is used
  • Runs on +/-12V and +/-15V (with minor resistor value changes for best performance)
  • Power consumption below 20mA each rail

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

Compressor: Schematic
Compressor: Schematic

When the ratio is set to zero and the gain to one the input signal passes through the circuitry unaffected (IC2C, IC2A IC6OTA1, IC6OTA2, IC2D). When the compression rate is turned up a DC voltage is derived from the input signal wit a precision full wave rectifier and some filtering (IC1A, IC1B, IC1C, IC1D). This voltage is used to open the VCA in the side chain (IC3OTA1, IC3OTA2, IC2B). The signal from the side chain is then subtracted from the main signal (R13, IC2A). The now compressed signal is then potentially amplified (IC6OTA1, IC6OTA2)

Compressor: Populated PCB
Compressor: Populated PCB
Compressor: Back view
Compressor: Back view
Compressor: Front with pedal connector
Compressor: Front with pedal connector

Foot switch connector

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Foot swithc connector: Front view
Foot swithc connector: Front view

As a Shakuhachi player I need my hands on the flute. So I use me feet to manipulate parameters and switches on the synthesizer. This module was originally build for my Shakuhachi to Synth project to provide the possibility to connect foot switches with the synthesizer and keep the patch intact when they are removed. The signal is not routed through the foot switch. Instead CMOS switches are used, turned on and off with the foot switch. So the signal stays within the synthesizer and the connection to the foot switch carries only DC. Removing the foot switch does not interrupt the signal flow in the synthesizer.

Specs and features

  • Four independent switches
  • Signal flow stays intact when foot switch removed
  • Runs on +/-15V and +/-12V
  • Power consumption below 10mA each rail

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

Foot switch connector;: Schematic
Foot switch connector;: Schematic

The switch in the DG202 is hold in on position with a 100k resistor against the positive rail. With a foot switch attached you can pull down the hold voltage when you close the foot switch.

Foot switch connector: side view
Foot switch connector: side view
Foot switch connector: Back view
Foot switch connector: Back view

Signal to Trigger Converter

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Signal to Trigger Converter: Front view
Signal to Trigger Converter: Front view

This module was originally build for my Shakuhachi to Synth project to provide the start/stop pulse for the Pitch to voltage converter. But it turned out to be much more useful. When you have the basics for your synthesizer like VCO, VCF, VCA, ADSR, LFO,… and some controllers and you want more, then using your keyboard to steer the synthesizer it is time for some modules to produce trigger signals out of different sources. Here is one of them. A signal to trigger converter. You can feed in a changing signal and every time the signal went through zero a trigger is generated dependent on the direction from where the zero point is crossed. You can add a threshold manually or CV controlled to move the zero point up or down as well. You can feed the signal in through input one ore two. When both inputs are used the signals are added together. When the signal crosses zero from positive to negative a trigger of about 0.1msec is generated at output -Trig. When the signal crosses zero from negative to positive a trigger of about 0.1msec is generated at output +Trig. Output +/-Trig provides both triggers. This output can be used to generate interesting rhythmic patterns when the threshold is set by a slowly moving CV or some DC offset is applied to the signal.

Specs and features

  • Two added inputs
  • Threshold manually and with CV
  • Output for +Trig, -Trig and +/-Trig: 0.1msec
  • Runs on +/-15V and +/-12V with minor resistor changes
  • Power consumption below 25mA each rail

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

Signal to Trigger Converter: Schematic control board
Signal to Trigger Converter: Schematic control board
Signal to Trigger Converter: Schematic main board
Signal to Trigger Converter: Schematic main board
Summed signal to trigger
Summed signal to trigger

The incoming signals are summed up. Every time when the summed signal changes polarity (moving through zero) a trigger is generated. Moving from plus to minus generates a trigger at the negative trigger output, moving from minus to plus generates a trigger at the positive trigger output. Trigger length is about 0.1msec.

Screenshot sine to trigger
Screenshot sine to trigger

The uppermost line (Yellow) shows the input signal. The second line (Blue) shows the trigger when the input signal moves to the positive site. The third line (Purple) shows the trigger when the input signal moves to the negative site. On the fourth line (Green) you can see both triggers added. This picture is taken without any threshold.

Signal to Trigger converter: Back view
Signal to Trigger converter: Back view
Signal to Trigger converter: Side view
Signal to Trigger converter: Side view

Output Module

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Output Module: Front view

Output Module: Front view

This is my replacement of the original Elektor Formant COM module. I discarded the original circuitry because of the TL085 used with his unusual pinout and the availability of dedicated audio operational amplifiers. I used a more effective filter implementation for tone control. The tone control is derived from “Small Signal Audio Design” by Douglas Self Chapter 15. A optional level indicator makes it easier to find the right volume level for best SNR. The maximum output volume is adjustable to protect your PA. You can connect the output directly to active monitors.

Specs and features
• Bass, middle, treble tone control
• Adjustable maximum output volume
• Optional volume indicator
• Direct connection to active monitors
• Runs on +/-15V and +/-12V (with minor resistor changes)

The documentation for download can be found in my website.

Output Module: Schematic front PCB

Output Module: Schematic front PCB

Output Module: Schematic back PCB

Output Module: Schematic back PCB

A description can be found in “Small Signal Audio Design” by Douglas Self Chapter 15

Output Module: Stuffed PCB back view

Output Module: Stuffed PCB back view

Output Module: Stuffed PCB side view

Output Module: Stuffed PCB side view

Output Module: Side view

Output Module: Side view

NGF Project: Dual Sample and Hold

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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