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Old 28th February 2013, 10:25 AM   #1
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Default Providing both balanced and unbalanced inputs

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.)
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Old 28th February 2013, 02:15 PM   #2
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an input transformer on rca. secondary connects to 2&3 on xlr.

another way: isolate the rca from the chassis. rca tip to 2 rca sleeve to 3.
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Old 28th February 2013, 03:25 PM   #3
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Originally Posted by DavesNotHere View Post
an input transformer on rca. secondary connects to 2&3 on xlr.

another way: isolate the rca from the chassis. rca tip to 2 rca sleeve to 3.
This is the way I have done it. The rca gets its ground reference at the source end. This way you can just connect the rca to the xlr without issue.

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