Yet another sample and hold

This is a Kosmo format version of René Schmitz’s YASH sample and hold.

Sample and hold is something used in a lot of contexts other than / more commercially important than synthesis, so there’s such a thing as sample and hold ICs that are readily available. This uses the LF398 chip. All Schmitz’s circuit does is to provide a clock oscillator (an external clock can be used too) and some parts to clean up the clock pulses, flash an LED, and narrow the pulses to the very small width appropriate for a S&H.

I didn’t do much to the original circuit. I added an output jack for the clock, an attenuator for the input signal, and a switch that allows shorting the capacitor in the clock processing. That changes the circuit from a sample and hold, which grabs the voltage on the rising edge of the clock gate and holds that, to a track and hold, whose output tracks the input as long as the gate is on and holds the final value once the gate turns off. (Really it does the same thing in sample and hold mode, it’s just that the gate is internally shortened to 3 µs.) There are a few other little tweaks but no other significant changes.

You might notice an unusual feature on the circuit board, a rectangle of copper around two of the LF398 pads and one of the capacitor pads. This is a guard ring, as recommended in the LF398 datasheet.

What else to say? It’s straightforward. I built it, plugged it in, it worked. I love it when that happens.

Schematics, KiCad design files, Gerbers, and documentation in the GitHub repo:

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