Two Transistor Surround Sound Decoder / Vocal Remover Preamplifier

A very simple two transistor surround sound decoder or vocal remover preamplifier based on two combined common collector and common emitter Class A audio amplifiers. This method of surround sound decoding simply isolates the out-of-phase audio in a stereo mix.

Watch the video on how to build: https://youtu.be/4wfMt4YOYYA

Features & Usage

Features

• Low power consumption: ~10mA @5v.
• No frequency band limitations on output.
• Can be used with virtually any linear input audio amplifier at any power output.
• Very high linear quality, being based on the Class A audio amplifier.
• Small and low cost design; makes it easy to integrate into any application.

Usage

Refer to the schematic diagram to follow these steps.

1. Connect a linear audio source to resistors R5 and R6. The audio source must be a stereo mix.
2. Connect the input of your audio amplifier to the output of the preamplifier on the collector pins of transistors Q1 and Q2.
3. Change the resistance of R5 or R6 to change the gain of the preamplifier; if the output volume is too loud or too quiet.

Troubleshooting

• Mid-high range frequency constant click/popping sound: This is caused by wireless interference. The circuit is not protected from EMF interference. Please remove any wireless devices (such as a cellphone) at least 10 feet away from the circuit or turn them on airplane mode while in use.
• Some vocals/mono audio sound is still leaking into the out-of-phase audio: Assuming that the audio you are playing doesn't natively have any vocals in the out-of-phase audio, it is important that you use ±1% tolerance resistors or less to limit this from happening. Regardless, vocals can still leak through as a result of the resistor and other componant tolerance.

Licensing & Attribution

• This repo is licensed under the BSD 3-Cause license. Any images are licensed under CC BY-SA 3.0. Refer to LICENSE for more info.