[sdiy] FET to short pedal input?

[brianw]

That's a very important consideration, René. I have seen commercial products get this wrong, e.g., where an 8-channel mic preamp using an 8-to-1 analog mux for connecting one VU meter to a selected channel would latch up when the microphone signal exceeded 15V. That designer clearly chose the wrong mux chip.

That said, there are plenty of 4066 implementations that exceed the original voltage limits.

Texas Instruments CD4016BE (PDIP-14) handles +18V or ±10V
Renesas / Intersil DG413DJZ (PDIP-16) handles +44V or ±20V

You will find these parts or similar in digital-controlled mixers where high dynamic range signal levels are supported. I use Mouser to cast a broad net for SPST analog switches and then look at the Supply Voltage column to narrow the database search.

One advantage of analog switches is that they can switch on and off reliably at speeds like 1 MHz with crisp edges - plenty fast enough to selectively engage portamento on individual notes.


I also like the back-to-back N-MOSFET idea. There are boost regulators that could create 12V or more from a smaller voltage, as well as regulator designs that can use a capacitor to store intermittent voltages to provide a constant voltage. It's a lot of meticulous detail, but it could be done.

Brian Willoughby


On Nov 29, 2025, at 6:19 AM, synth at schmitzbits.de wrote:
> 4066 can only handle 0-15V, which might be ok here, depending on the KBD voltage, which likely is always positive.
> 
> Not sure if this has been mentioned: There are photo-mos optocouplers ("Photo-Relay"), that could also be the ticket. 
> If one wants to provide power passively to it's LED straight from the input jack. Could be also passively plugged into the existing jack. 
> These photo relays have two antiserial mosfets, that can act as good bidirectional switches which are floating.
> Another way could be two back to back n-mosfets, but then you'd need +/-12V (or so) at the gate to ensure they cut off. 
> 
> Cheers,
>  René
> 
> Von: Tom Wiltshire
> Gesendet: Samstag, 29. November 2025 08:52
>  
> +1 agree, absolutely this. 4066 or similar is simple and obvious. The only thing preventing it working is the power requirement.
> 
> On 28 Nov 2025, at 22:20, brianw <brianw at audiobanshee.com> wrote:
> 
> Frankly, I suspect that the goal of not providing independent power to this interface circuit is making it much more difficult. Personally, I would build a small circuit board to fit inside the ARP Odyssey and pull power from the synth. Then, all voltages would surely fall within the workable range for a 4066.