| Created: 2017/12/21 | Last update: 2017/12/21
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Information and comment about the TX-429D used by some Korg peddles.

Dateline: 2017/12/21

TX-429D devices as used in the KORG phasers etc.

Korg were trying to make a voltage controlled resistor, i Jfets have a problem due to the internal diode between gate and D,S, and mosfets have problem with a diode between D and S, if you can tie off the substrate somewhere then MOSFETs might be useful.

I don't think the device is similar to the typical dual gate RF MOSFET. In the circuit applications the drain and source can reverse polarity i and MOSFETS can't do that because of the body diode connected to the substrate. Also the TX-429D device is a P-channel device. It looks like it operates similar to a "transfer gate" in 4000 series CMOS or the switches in a CD4016.

For the TX-429D

You could probably replace it with a pair of P channel MOSFETS with

This is a reasonably common way to make an AC switch.

Compare with a CD4007

TX-429D CD4007
1 1
2 14
3 2
4 3
5 3

You could also make it more symmetric by using other devices in the package.

Source: BobT

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