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I have a digital piano, KORG SP-250, that has unbalanced output, and a sound card Focusrite Clarett 4pre-USB that has balanced input (line level or mic). I now wonder, what will happen when I connect these two?

I don't know how the unbalanced connector work, so is the the signal sent in the shielding as well as the signal lead? Since the sound card is balanced I guess its shield is connected to ground. That makes me think that it's sufficient with either the sender or receiver to be balanced, because it's sufficient with one connecting to ground?

(Also I wonder, can both line and mic-level be balanced or is it only a mic signal that can?)

  • Just to answer the last question: line level signal can be balanced as well as mic level or anything in between. If you do a quick search on it you’ll see what “balanced” actually means. It’s really a clever way to remove interference. And it can be with an XLR cable or a 1/4” TRS cable. – Timinycricket Jun 8 at 8:51
  • but interestingly balanced 'line-level' only requires two conductors to work (signal+ and signal-). The ground connection is superfluous with line-level connections as it is only strictly required for phantom power (mic level). Additionally, a ground-connection can be the cause of ground loops between equipment, so a balanced line connection with no ground often works better than a connection with a ground. – Mark Jun 8 at 10:59
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Any unbalanced connection in a configuration such as this will unbalance the entire connection. The way to make this work is to connect the elements in the following way:

  • Ground (Piano) ----- [ Ground (XLR) (Pin 1) --- Join to --- Signal- (Pin 3) ]
  • Signal (Piano) ----- [ Signal+ (XLR) (Pin 2) ]

If you want to balance the entire connection, you will need a device called a "DI" box. (Direct Injection Box). This will balance the signal out of the piano. This will only be necessary if you are using this in an environment where there is a lot of Electrical Induction, Lighting or other RFI that might affect the signal - interference that would otherwise be rejected by a balanced connection.

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