Zenith P-202 Speech Processor

Info & Wiring:

This Speech Processor is a classic from the early 80's and is a fantastic way to boost your modulation whilst still using the standard microphone. it is the perfect companion for a radio of the era (such as a Uniden 200 or Harrier CBX). on AM and SSB this processor comes into its own, providing loud, crisp and punchy audio. As standard, this processor is NOT compatible with modern CPU controlled radio's and can possibly damage your radio.

I recently wired this unit to a President Lincoln and when plugged in it made the display go wierd. Since then I have modified the wiring on the processor (by adding a relay to seperate the radio's TX line) to make it work.

Update: Whilst using the unit for a few days I was getting reports of a buzzing. Since then I have added C1 and C2 to decouple the audio in and out.

Here are the wiring diagrams:

For this unit to work, it needs BOTH of the 9v batteries to be installed AND the red wire going to your power supply. If you do not have the batteries installed you will not get any audio at all. This unit does not have a black (negative) wire, it does not need one as it gets its ground from the microphone socket on the radio.

All of the 8 pin DIL chips used in the unit are TL061CP low power J-FET input op-amps and are very cheap to buy.

The Pots for mic gain and master gain in my unit were badly worn, so I took them out and left them in a bowl of switch cleaner for a few hours. They are still not perfect now, but are at least usable again until I get round to ordering new ones.

If you're getting a loud buzzing when tx'ing, You may need to replace the batteries. in this processor, when the batteries go flat, initially your modulation will become quieter - but if the batteries drop below a certain voltage you will get a loud buzzing.