This design comes from a long term project/idea to make a noise gate for Eurorack. I've attempted several designs for a noise gate over the last year but haven't been happy with the result (yet). In the latest attempt I used an analog switch and a comparator and had some success. I decided that those two parts of the noise gate would be fine as individual modules so that's where this came from.
It's really a very simple module, there's a buffered input and ouput and a gate input to turn the switch on or off. When it's on the audio or whatever input signal is passed through to the output.
The schematic calls out the DG418LDJ (normally open) analog switch. The DG417 should work as well for a normally closed version.
The gate circuit is using a few generic NPN transistors to turn whatever the gate input is into a sharp 5V logic signal for the analog switch. There's a simulation here.
Of course the design started on the bread board.
Then I designed and ordered a few PCBs and a nice front panel for it.
- So far the only issue is that any input over 7.8V is clipped. This is probably something to do with the internal rail limits in the DG418LDJ. To fix that v2 could attenuate the input and then use more gain on the output to bring it back to a known level. That might introduce noise but making a circuit to allow that option is pretty easy. I likely won't bother with this anytime soon.
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