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From the Q&A

With TJ Byers

Don’t Bogart That Signal


I have the audio line out of my computer connected to both computer speakers and a stereo receiver. As a result, the volume of the stereo receiver is lowered severely, and if the computer’s output volume is raised to compensate, distortion occurs. Do you have a low-distortion stereo preamp circuit to increase the sound level before it reaches the receiver?

John S.


What you have is a conflict between the impedance of the speakers and the stereo receiver. In other words, the speakers are sucking the life out of the audio signal, leaving little for the receiver input. The way to solve the problem is to put a signal buffer between the sound card and the speakers and receiver, like the circuit shown here.

The op-amps are high output devices configured as a voltage follower. This prevents the speakers from loading down the output of the sound card.