This is my second stereo decoder/amplifier. It is similar to the decoder/amp. I built and installed in my 9 tube-3IC FM receiver. The unit can be connected to tube or solid-state FM tuners or receivers with MPX (multiplex) output to listen to FM transmissions in STEREO. The decoder uses an NTE743 IC (integrated circuit) to decode the MPX signal, and 2 LM386N-4 ICs to amplify the left and right audio signals. The unit has the following features: a stereo/mono switch, a balance control, a ganged volume control and power and stereo indicators. The audio ICs are driven at minimum power to keep audio hiss at a minimum, and the stereo separation from the decoder IC is really excellent. The unit runs on 12 volts DC and can be monitored with high-quality stereo headphones or a pair of speakers.

A ready-made 6" x 4" x 2" aluminum box houses the decoder. Controls from left: on/off, stereo/mono, balance and volume. Left and right LEDs (light emitting diodes) indicate power on and stereo transmissions respectively. Stereo phones jack is on far right.

Back of decoder. 2 RCA jacks for 12 volt DC supply and MPX signal input. MPX input level is adjusted with a trimmer pot inside the unit. I will move this trimmer to the outside eventually.

Inside the decoder. The circuit was built "Manhattan style" on a 5" x 3" copper clad board. The decoder IC and components are on the left. The MPX level and oscillator trimmer pots are on the lower and upper left respectively. The left and right channel audio ICs and components are on the right. The gang volume control can be seen top right.

Mono no more! The unit connected to my 8 tube FM receiver, with the power supply behind it. The stereo LED glowed red as the receiver was tuned to stereo transmissions. A small decoder/amp. with a lot of performance!