You may use this speaker balance calibrating circuit when using a stereo amplifier, there are many possible mechanical problems that may influence the amplifier’s output performance. The usual culprit is the mechanical potentiometers which are not rarely unsync in their stereo resistance pads. This results to unbalanced volume levels on the audio channels. Most good stereo units have a balance control to compensate for this imbalance.
In using this balance indicator circuit, its left and right input channels are connected to the corresponding speaker outputs of the amplifier. Identical signals are then fed to the amplifier’s stereo inputs. When a signal of exactly the same amplitude is coming out from both speaker outputs, the meter M of the speaker balance circuit will stay at its zero setting. The meter M is a type with a zero setting at the middle of the scale. This enables one to see at first glance when one channel is louder than the other channel
Calibrating the speaker balance indicator circuit
Inject a signal in one channel and set the amplifier’s volume to maximum.
While doing this, turn the potentiometer P1 until the meter swings to end of the scale in the direction of the channel.