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: 440CPS

NGF-E Project: 440CPS front view

NGF-E Project: 440CPS front view

Not much to say. A 440CPS module. Quite useful for tuning in a bigger system. OK, one more sentence. It is the replacement for the 440CPS module from the Elektor Formant in my Next Generation Formant project Project.

Specs and features
• On/Off Switch to keep the 440Hz out of the system when not needed
• Runs on +/-15V and +/-12V
• Power consumption below 25mA +rail / 5mA -rail

The documentation for download can be found in my website.

NGF-E Project: 440CPS schematic

NGF-E Project: 440CPS schematic

Everything is done in software. Output is a 440Hz Square wave. That’s it.

NGF-E Project: 440CPS populated PCB

NGF-E Project: 440CPS populated PCB

NGF-E Project: 440CPS back view

NGF-E Project: 440CPS back view

Limiter / Compresssor

Limiter / Compressor front view

Limiter / Compressor front view

To handle the great dynamic range of the Shakuhachi I needed a compressor for my Shakuhachi 2 Synth project. Because a limiter is not that different I added this feature as well. This comes in handy with my Vocoder project also. The structure used here is derived from “Small Signal Audio Design” by Douglas Self p682ff. The audio signal did not flow through a VCA as in many other implementations. Instead the compression or limitation is done by subtracting the audio signal at the output summing node according to the control voltage derived from the audio signal.

Specs and features
• Switch compress or limit
• Switch Compression/Limit rate 50% or 90%
• Compression/Limit rate adjustable 0–max
• Runs on +/-15V and +/-12V (with minor resistor changes)
• Power consumption below 15mA each rail

The documentation for download can be found in my website.

Limiter / Compressor schematic 01

Limiter / Compressor schematic 01

The audio signal flows unaffected through IC1A/B. When the compressor – limiter kicks in the inverted signal is added (=subtracted) at the summing node of IC1A. The signal level to subtract is regulated through a Sims VCA. The CV generation for the VCA is pretty standard. Linear for the compressor and exponential for the limiter.

Limiter / Compressor schematic 02

Limiter / Compressor schematic 02

Precision full wave rectifier with filter to generate the control voltage for the VCA from the audio signal.

Limiter / Compressor populated PCB

Limiter / Compressor populated PCB

Limiter / Compressor back view

Limiter / Compressor back view

Clock Divider with prime numbers

Clock Divider with prime numbers

Clock Divider with prime numbers

This clock divider divides the incoming clock signal down to the prime numbers /11, /13, /17, …. /31. The output is a 5V positive pulse. The length of the incoming pulse is kept. The trigger is on the rising edge of the incoming signal. The reset input can be used for syncing with other clocks. All outputs are buffered and brought out parallel with LED signaling the pulse.
Specs and features
• Regular input clock/square wave +5V
• Input signal divided by prime numbers
• Output +5V pulse with the length of the input signal (pulse)
• Runs with +15V/-15V or +12V/-12V (with minor changes)

The documentation for download can be found in my website.

Clock Divider with prime numbers, schematic

Clock Divider with prime numbers, schematic

Most work is done by the microprocessor. The micro takes care of the input and output timing. All outputs are independently buffered. The clock is made visible with LED.

Clock Divider with prime numbers, populated PCB

Clock Divider with prime numbers, populated PCB

Clock Divider with prime numbers, rear view

Clock Divider with prime numbers, rear 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

VCA LN

VCA LN: populated PCB

VCA LN: populated PCB

A well known way to reduce noise in VCA is using the VCA’s in parallel. Here is my approach. A LM13700 used in parallel reduces the noise floor around 3dB.
Specs and features
• VCA with reduced noise floor
• Runs on +/-15V and +/-12V (with some resistors changed)

The documentation for download can be found in my website.

VCA LN: Schematic 01

VCA LN: Schematic 01

Nothing special here. Just two plain forward designed VCA with LM13700. With the signals added together.

VCA LN: Schematic 02

VCA LN: Schematic 02

Standard circuitry for Iabc and level control.

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

Sequential Switch

Sequential Switch: Front view

Sequential Switch: Front view

This Module is build around the counter 4017. It provides you with with 8 bidirectional toggle switches. The active switch is signaled with a LED. All switches are brought out to the front panel, so you can patch this module with maximum flexibility. Audio signals are switched as well as control voltages. This module is clocked external and can be clocked with high frequencies. Way above the audio range if needed. You can select the stepped sequence length between 2..8 steps with a rotary switch. The reset input is brought out as well.
Specs and features
• Sequential switch with 2..8 steps
• Bidirectional toggle switches
• Audio and control voltages switchable
• External clock way above audio range
• Runs on +/-15V and +/-12V

The documentation for download can be found in my website.

Sequential Switch: Schematic

Sequential Switch: Schematic

The 4017 is clocked through the clock input with IC5C and IC5D. RS1 selects the sequence length. The DG419 toggle switches are successive toggled with the every active step of the 4017. The LED signals the active step.

Sequential Switch: Populated PCB

Sequential Switch: Populated PCB

Sequential Switch: Back view

Sequential Switch: Back view

Looping ADSR – Electric Druid

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

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