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Providing both balanced and unbalanced inputs


2011-12-12 1:12 pm
My fully-balanced power amp design has both a balanced input (via an XLR socket) and an unbalanced input (via phono/RCA). At present, I have a resistor network that eliminates the need for any input selection switching, but the problem is that it is wasteful of signal level and reduces the effective gain of the amplifier. I could throw away the resistors and simply have a switch that shorts the "cold" pin of the XLR socket to ground when the unbalanced input is being used, but this arrangement isn't foolproof.

I am interested to hear people's views on the best circuit configuration for connecting the two sockets to the input stage. (By the way, I am aiming for a balanced input sensitity of 2V and an unbalanced sensitivity of 1V.)