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