VC LFO and Dual ADSR

If you wonder why both the attack and release LEDs are lit it is because of long shutter time on the camera...

Designs used

2 x MFOS ADSR Envelopes MFOS Project Page
Front Panel express file A100EnvLFOFinal.fpd


To get the pushbuttons, switches and sliders nicely aligned and attached to the front panel I solder them to a piece of stripboard. All these components follow some 7mm height standard, so they will all protrude equally from the board. Each slider has two M2 threads which I use to attach the aluminium front plate with. The switches used are from NKK's GW-family. I use both pushbutton style and lever type. The lever ones are available with built-in LEDs NKK-GW illum.

Alpha sliders and NKK switches soldered to the panel stripboard. Empty FPE Panel above it.

Since all sliders have LEDs I needed to invent some logic to control them. For the envelopes the logic is obvious, light up each stage as the envelope cycles through them. The envelope output level slider LED will indicate output voltage. For the LFO I chose SIN output for the fine freq slider and SQR output for the PW slider.
Detecting ADSR stage for lighting the correct LED is a bit cumbersome in the MFOS design. I had to use three voltage comparators (3/4 LM339) and three analog switches (3/4 CD4066) per envelope. For the LFO LEDs I use a simple V/I converter built around an op-amp tapping into the signal I want the LED to indicate.

Logic for the envelope and LFO LEDs built on a piece of IC euroboard

Wiring on the back side of the front panel. If I ever do a dual ENV + LFO again I would probably make a custom PCB for the panel parts...

Oscilloscope showing one of the envelopes in action. Triggered by the LFO.

All four PCBs mounted on the front panel. (One LFO, two ENVs and my custom LED driver card)

Phew, finished at last. This one probably took at least 40 hours to build. With a going rate of 100 EUR / hour for an engineer in Sweden it adds up to:

PCBs: 35 EUR
Components: 45 EUR
Front Panel: 50 EUR
Labor: 4.000 EUR
Total: 4.130 EUR

If you're interrested I might give you a small discount, say 4.000 EUR flat and it is yours!

Next: Dual AR