Driving a balanced +4 dBu signal into an unbalanced +4 dBu device

“I have a mixer with unbalanced tape returns and a multitrack with balanced +4 outputs. The mixer will support -10 or +4 levels. The problem is when I set it at +4 it seems that the +4 level from the tape machine is too low. But when I set it for -10 the level from the tape machine is too high. Does this have something to do with it being unbalanced?” Yes, it does. When a device has a balanced output of +4 dBu (or any other level) it achieves that level through a difference between the voltage on the positive leg and the opposite polarity equal voltage on the negative leg. In XLR terms, we’re talking about pins 2 and 3 here. If you reference the voltage between either pin 2 or 3 to ground (or the shield [pin 1]), the “difference” between that voltage and the 0-volt ground reference is only half what it is between the other pin of the balanced signal. So when you connect only one pin and ground to the unbalanced input of your console you are sending it half the voltage it is expecting and no doubt your meters show the signal level is down 6 dB from where it should be (half the voltage is -6 dB). When you switch your mixer to -10 dBV the level from either side of the balanced +4 dBu signal out of the tape machine is still too high, as you have reported.Solutions? Usually most devices that are switchable between -10 dBV and +4 dBu are also switchable between balanced and unbalanced operation. If this is the case, you simply need to figure out how to get your mixer to accept the fully balanced signal. Over the years, however, a number of mixers have been made that accept +4 levels, but are unbalanced. Why anyone would do this is beyond your inSync editor’s comprehension given the standard audio wiring conventions we use today, but since I own just such a mixer myself I can verify the dilemma.Many modern balanced outputs have a circuit that compensates for driving an unbalanced input. This may be called a “Ground Compensated” output. In those cases you can short the unused side of the balanced signal to ground and the device will raise the level on the remaining side accordingly so it will have the full +4 dBu of voltage between that pin and the shield.If you have a way to switch your tape machine to -10 dBV operation you may save yourself lots of headaches assuming this would also unbalance the output (since most -10 dBV gear is unbalanced). If your cable length between the two isn’t more than 20 feet you can easily get away with an unbalanced -10 dBV signal between them (unless your studio is in an environment with a lot of EMI).If none of the above solutions are workable for you then you are faced with one of the following remedies.§Choose a way to convert the signal from balanced +4 dBu down to unbalanced -10 dBV and inject it at the mixer that way. There are many commercially available devices that will do this at different price points and quality levels.§Modify your mixer so it can accept the signal level your machine is giving it. While this sounds daunting it may not be as difficult as you think. If your mixer is switchable between -10 dBV and +4 dBu then there must be a way to make it work at what is effectively -2 dBu, or a about a 0.615 volt nominal level.For some more background and information on working with dBV and dBu, particularly the -10 dBV and +4 dBu confusion, please check out our article posted in the Summits section of the inSync web page.

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