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Tuesday, October 13, 2009

Universal High Quality Preamp

This is a circuit for universal pre-amplifier. This circuit has high quality for amplifying a signal. This circuit should be simple to use it as a low impedance mic amp or as a high input impedance preamp for mic or, with a suitable RIAA equalization, for phone pickup or similar. It can even be used as a balanced input mic preamp. This is the figure of the circuit.

R1 will define the impedance if the high impedance input - say 100K. R4 charges the output capacitor only. R3 defines the operating current in Tr4, say 1K for 500µA or so. The feedback paths have been separated: DC feed back is via the two the 100K resistors, which are decoupled so they don't affect the AC feed back. The AC feed back if via the network Zf, which can be RIAA for phone or whatever as required.

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