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The original ‘brick’ had the same transformer…. and there’s a story behind that! That transformer was originally designed as a ‘line matching’ transformer for line level audio. To most designers it is physically wastefully big to use as a mic transformer, but in a professional studio one often gets large audio signals that could send a smaller transformer into distortion. This ‘line’ transformer has winding tappings on it so that it can be configured to get the right impedances. It has a high permiability core using 90% mu-metal, and it is wound using a ‘bi-filar’ technique that makes for high efficiency, good frequency response and excellent common mode rejection….. in short, it’s a good mic transformer.
But at the same time, the circuitry around the transformer has to be right too. The original ‘brick’ had a circuit that I developed for radio broadcast mixers; it uses integrated circuits, but spreads the gain requirements so that the maximum gain provided by any amplifier is less than 25dB, this eliminates transient distortions within the amplifiers; (an effect ignored by other manufacturers) making a warm and full sounding pre-amp.