Category Archives: CV Sources

Looping ADSR – Electric Druid

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Looping ADSR front view

Looping ADSR front view

This Module is build around the LOOPENV 1B Pic chip from Electric Druid.I have bought the pic chip and added some protection and level shifting circuitry around it. For details of that chip please refer to the original documentation from Electric Druid.

The documentation for download can be found in my website.

Looping ADSR: schematic

Looping ADSR: schematic

Nothing special here. Just some standard input protection for the pic chip and a filter for the PWM signal to generate the output voltage.

Looping ADSR: populated PCB

Looping ADSR: populated PCB

Looping ADSR: back view

Looping ADSR: back view

Scaled Voltage Reference 1V and 83,3mV steps

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Scaled Voltage Reference

Scaled Voltage Reference

This module provides high precision CV outputs in 1V (octaves) and 83,3mV (halves) steps. The 1V output goes from 0 to 8V. The 83,3mV steps goes from -5 to plus 5 steps (halves). This module is thought for all who are missing octave switches in some modules. Especially in VCO. With this module you can switch octaves and halves as well.
Specs and features
High precision output 0-8V in 1V steps (octaves)
High precision output in 83,3mV steps, +/- 5 steps (Halves)
Runs on +/-15V and +/-12V

The documentation for download can be found in my website.

Scaled Voltage Reference schematic

Scaled Voltage Reference schematic

The precision voltage is derived from the REF102. The negative voltage is provided with the INA105. It is crucial to match the resistors in the voltage dividers as good as you can. The outputs of the voltage dividers are buffered to avoid loading of the dividers. The resistors around the OpAmps must be matched as well. The one volt and the 83,3mV steps are added together with IC4A. The three outputs are individual buffered.

Scaled Voltage Reference populated PCB

Scaled Voltage Reference populated PCB

Scaled Voltage Reference back

Scaled Voltage Reference back

Logic Module

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Logic Module front

Logic Module front

I needed a module to combine gate and/or trigger events for steering sequencers, ADSR and other gear. So I build one. This one here has and, or, ex-or and neg logic gates. The states of the inputs and output are signaled with LED. The inputs takes audio as input as well. This makes for some interesting patches. The minimum input level can be set to your needs.

The documentation for download can be found in my website.

Logic Module schematic p. 01

Logic Module schematic p. 02

Logic Module schematic p. 02

Logic Module populated PCB

Logic Module populated PCB

Logic Module back view

Logic Module back view

Modulation Sequencer

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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 LFO: flat Version

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NGF LFO flat version side view

NGF LFO flat version side view

This is the LFO module for my Next Generation Formant project. It provides triangle, ramp up, ramp down and square wave output (-5V to +5V). This design follows closely the original from the Elektor Formant.
Most noticeable change is moving to a “flat” design. The depth of the module is significantly reduced and most important no more potentiometer wiring is needed!

The documentation for download can be found in my website.

LFO flat Version Schematic back PCB

LFO falt Version Schematic back PCB

LFO flat Version Schematic front PCB

LFO flat Version Schematic front PCB

The oscillator consists of an integrator IC1A and an OpAmp Schmitt-Trigger IC1B. The triangle wave of the oscillator arises through the feedback of the trigger output to the input of the integrator. At the integrator output IC1A arises a triangle with the amplitude of the hysteresis of the Schmitt-Trigger. The input voltage of the integrator sets the rise and fall time of the voltage output. The square wave output is buffered with IC1C. The circuitry around IC1D provides the saw output. IC3C inverts the saw.

LFO flat Version populated front PCB

LFO flat Version populated front PCB

LFO flat Version populated back PCB

LFO flat Version populated back PCB

LFO flat Version faceplate

LFO flat Version faceplate

NGF ADSR: flat Version

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NGF ADSR flat side view

NGF ADSR flat side view

This is a derivation off the ADSR for my NGF-E project. Because this one is a stand alone module I have removed all additional features from the Next Generation Formant project. Nonetheless it is still based on original Elektor Formant ADSR schematic. I made some error corrections and added my changes to the design. All parts are updated to today (2017/10) available parts. I have made a few changes to fix some shortcomings of the original. A triple range switch was added for finer adjustment of the ADSR CV-output signal. The attack rise time is shorter now as in the original. The gate input is buffered. The fixes a fault in the original when working with analog sequencers. A manual single shot is added. This comes in handy while testing patches and in live performance. The output voltage is slightly raised to reach really 5V. Due to the design of the original Elektor Formant ADSR the output of the original ADSR keeps a residual voltage of about 0,5V. I have put an (adjustable) compensation in my design to correct this and keep the original behavior if needed as well. The driver circuitry for the output indicator LED is changed for better linearity.
Most noticeable change is moving to a “flat” design. The depth of the module is reduced and most important no more potentiometer wiring is needed!

The documentation for download can be found in my website.

NGF ADSR flat back PCB populated

NGF ADSR flat schematic back PCB

NGF ADSR flat front PCB populated

NGF ADSR flat schematic front PCB

This is a close clone of the Elektor Formant ADSR. Here i only describe the changes i have made. The description of the other parts of the circuitry can be found in the original Elektor Formant documentation. The gate signal input resistance is raised from 33kOhm to 1megOhm with the input buffer IC1A. This protects against double triggering with the falling edge of the gate signal when using sequencers. R30 is used to fix the input to a defined potential when no signal is attached to the input. R34 and R35 in combination with a push button give you the single shot feature. C1 was lowered to 6n8 from 10nF. In combination with C2 and the raised charging voltage through IC1B/R9 this makes for faster attack time. The load capacitor of 10u was replaced with three selectable capacitors of 2,2uF 3,3uF and 6,8uF. This make for a finer adjustment of the response times of the ADSR. The voltage divider R19/R21 was adjusted to ensure that the output level of 5V is reached when the offset option with R32/R33 is used. If this feature is not used R25 should be lowered to 5k1. Construction conditioned the output at IC1D only reaches a minimal voltage of about 0,5V. To compensate for this i added IC2A. With R32/R33 you can trim the output down to zero volts. If the ADSR is not used the output voltage is now at -0,5V. If you don’t want to use this feature just leave R33 out and you will have the original behavior of the original Elektor Formant ADSR. The current consumption was lowered with using the TL064 and a low current led.

NGF ADSR flat front PCB populated

NGF ADSR flat front PCB populated

NGF ADSR flat back PCB populated

NGF ADSR flat back PCB populated

NGF ADSR flat module side view

NGF ADSR flat module side view

NGF ADSR module front view

NGF ADSR module front view

NGF-E Project: ADSR

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NGF-E Project: ADSR stuffed PCB

NGF-E Project: ADSR stuffed PCB

This is my take on the ADSR. Because this one is for my Next Generation Formant project i started with the original Elektor Formant ADSR schematic and added my changes to the design. All parts are updated to today (2017/09) available parts. The connections are the same as in the original to keep the possibility for internal wiring. If you don’t need those features just leave them out. This PCB provides all functions as in the original Elektor Formant ADSR. I have made a few changes to fix some shortcomings of the original. A triple range switch was added for finer adjustment of the ADSR CV-output signal. The attack rise time is shorter now as in the original. The gate input is buffered. The fixes a fault in the original when working with analog sequencers. The output voltage is slightly raised to reach really 5V. Due to the design of the original Elektor Formant ADSR the output of the original ADSR keeps a residual voltage of about 0,5V. I have put an adjustable compensation in my design to correct this and keep the original behavior if needed as well.

The documentation for download can be found in my website.

NGF-E Project: ADSR schematic

NGF-E Project: ADSR schematic

This is a close clone of the Elektor Formant ADSR. Here i only describe the changes i have made. The description of the other parts of the circuitry can be found in the original Elektor Formant documentation. The gate signal input resistance is raised from 33kOhm to 1megOhm with the input buffer IC1A. This protects against double triggering with the falling edge of the gate signal when using sequencers. R12 is used to fix the input to a defined potential when no signal is attached to the input. R33 and R36 in combination with a push button give you the single shot feature. C1 was lowered to 6n8 from 10nF. In combination with C2 and the raised charging voltage through IC1B/R9 this makes for faster attack time. The load capacitor of 10u was replaced with three selectable capacitors of 2,2uF 4,7uF and 10uF. This make for a finer adjustment of the response times of the ADSR. The voltage divider R24/R25 was adjusted to ensure that the output level of 5V is reached when the offset option with TR2 is used. If this feature is not used R25 should be lowered to 5k1. Construction conditioned the output at IC1D only reaches a minimal voltage of about 0,5V. To compensate for this i added IC2C. With TR2 you can trim the output down to zero volts. If the ADSR is not used the output voltage is now at -0,5V. If you don’t want to use this feature just turn TR2 to ground and you will have the original behavior of the original Elektor Formant ADSR. The current consumption was lowered with using the TL064 and a low current led.
Calibration procedure and more information on my website.

NGF-E Project: ADSR faceplate

NGF-E Project: ADSR faceplate

NGF-E Project: ADSR back

NGF-E Project: ADSR back

NGF-E Project: LFO

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NGF-E Project: LFO PCB

NGF-E Project: LFO PCB

Here is the LFO module for my NGF-E project. It provides triangle, ramp up, ramp down and square wave output (-5V to +5V) This design follows closely the original from the Elektor Formant.

The documenatation for download can be found in my website.

NGF-E Project: LFO schematic

NGF-E Project: LFO schematic

The oscillator consists of an integrator IC1A and an OpAmp Schmitt-Trigger IC1B. The triangle wave of the oscillator arises through the feedback of the trigger output to the input of the integrator. At the integrator output IC1A arises a triangle with the amplitude of the hysteresis of the Schmitt-Trigger. The input voltage of the integrator sets the rise and fall time of the voltage output. The square wave output is buffered with IC1C. The circuitry around IC1D provides the saw output. IC3C inverts the saw.

NGF-E Project: LFO faceplate

NGF-E Project: LFO faceplate

NGF-E Project: White and coloured noise, random voltage

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NGF-E Project: White and coloured noise, random voltage PCB

NGF-E Project: White and coloured noise, random voltage PCB

This is the noise module for my Next Generation Formant project. It is a combination of two original Elektor Formant modules. The Noise module from Elektor Formant book one and the Coloured Noise (CNC) module from book two. It provides a white noise output, a fixed coloured noise output, a variable coloured noise output “red” “blue” and a random voltage output. The noise is derived from the reverse biased BE diode of an NPN transistor.

The documentation for download can be found in my website.

NGF-E Project: White and coloured noise, random voltage schematic

NGF-E Project: White and coloured noise, random voltage schematic

Noise source is the reverse biased BE diode of NPN transistor Q1. The following operational amplifier IC1A and IC1B amplifies the noise to 10Vpp. IC1C is the buffer for the white noise output. The high pass filter C5/R23 and R13/R19 in the feedback loop of IC1D provides a bass boost for the fixed coloured noise output. IC2B is configured as a 12dB low pass. So you get a low frequency random voltage. The changing speed is set with P1A/P1B which sets the corner frequency of the low pass filter. IC2A / LED1 makes the fluctuation visible. Tr1 adjust the brightness of LED1. In the feedback loop of IC3B is an adjustable filter combination which gives you a wide range of adjustable coloured noise with P1 and P2. The output is buffered with IC3A.

NGF-E Project: White and coloured noise, random voltage faceplate

NGF-E Project: White and coloured noise, random voltage faceplate

NGF-E Project: White and coloured noise, random voltage

NGF-E Project: White and coloured noise, random voltage

NGF Project: Envelope Follower

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This envelope follower was first build for my Shakuhachi 2 Synth project. But it is useful for any other input signal which you want to derive a control voltage from. It provides a gate and a trigger signal as well. The envelope follower is used to detect the amplitude variations of the incoming signal and produces a control voltage that resembles the variations in the input signal.

The gate and trigger signal is derived from the input signal as well. You can vary the threshold to determine at what minimum signal level the gate goes high and the trigger fires. Gate level is +5V. Trigger level is +5V/1msec.

NGF Project: Envelope follower

NGF Project: Envelope follower

The incoming signal is rectified with a precision full wave rectifier. Then feed to a low pass filter for smoothing. The given filter values here are optimized for use with the Shakuhachi, but can easily changed to your needs. The filter values affect the ripple and the timing of the output control voltage.

The gate and the trigger signal is derived from the filter output with means of a comparator. You can adjust the sense level with the threshold potentiometer. The gate is indicated with a LED. The trigger pulse is derived from the gate with an differentiator.

Envelope follower: Scope picture with square cv

Envelope follower: Scope picture with square cv

The picture above shows the control voltage of the envelope follower following a signal of 200Hz sine wave from a VCA (purple line) with a square control voltage (blue line).

Envelope follower: Scope picture with ADSR cv

Envelope follower: Scope picture with ADSR cv

The picture above shows the control voltage of the envelope follower following a signal of 200Hz sine wave from a VCA with a control voltage set by an ADSR.

Envelope follower: stuffed PCB

Envelope follower: stuffed PCB

Envelope follower: Module

Envelope follower: Module

Envelope follower: Front

Envelope follower: Front