microphone pre-amplifier - with symmetrical signal transfer

microphone preamplifier elektor february 1985 Microphone extension cables are typical sources of noise. Signal losses caused by such cables are normally compensated by an input preamplifier, but this also amplifies the noise generated in the cable, as well as any random noise picked up by the cable. For those cases where the extension cable exceeds, say, one or two metres, it seems sensible to amplify the microphone signal before and after the cable. The advantages of this suggested configuration are a much improved signal-to-noise ratio and more effective hum suppression. microphone preamplifier with symmetrical signal transfer The proposed circuit consists of two parts, of which one is inserted between the microphone and cable and the second terminates the cable at the other end. A block schematic of the set-up is shown in figure 1. The signal from the microphone is therefore amplified by 20 dB before any cable-induced noise or hum is superim- posed onto it. The two amplifiers a...