“I have a small mixer I like to use for smaller gigs that does not have balanced outs. The rest of the equipment in this rig is set up for balanced in & out. How should I go about changing the signal immediately after the mixer to balanced? Will 1/4″ to XLR adapters with a passive transformer do the trick, or do I need several DI’s? Or do you have a better solution (short of buying a different mixer)?”
The first question to ask is whether or not the signal from the mixer to the next piece in the chain really needs to be balanced? If it is just going a few feet it probably doesn’t matter. I would much rather run it unbalanced than send my signal through a cheap transformer. If your other gear doesn’t have an unbalanced input you can still make or buy adapter cables (without transformers) that will allow you to connect them. The signal is still unbalanced, the cables just have the appropriate connectors for each end on them. Cheap transformers, like the ones you find built in to cables and small adapters, tend to saturate fairly easily, especially with low frequency content. And this really isn’t the job a DI (Direct Box) is intended to do. A decent one will kinda’ work in a pinch, but they are really set up (from an impedance and level point of view) to drive mic inputs, not line level inputs. You’ll have trouble getting enough level without saturating the transformer in it.
If you really need to balance this unbalanced output, which I will now assume also means you need to drive the signal a long distance, you are going to have to use a more robust solution. What hasn’t been mentioned yet, but should not be overlooked, is that your unbalanced mixer output is probably operating at a nominal level of -10 dBV or up to 0 dBu at the very most. You balanced gear is likely expecting a +4 dBu signal. So you also have a level mismatch. For MUCH more detail on this and the ramifications check out our -10/+4 paper in the Summits section of our website.
The ideal solution is to buy a device specifically designed to change your lower level unbalanced signal into the higher level balanced signal. There are several boxes on the market that do this very effectively. You also can accomplish it with transformers specifically created for this problem. They will cost less than active boxes and in many situations get the job done just fine. Your Sweetwater Sales Engineer can help you choose which is best for your situation. There are two ‘poor man’s’ solutions: If you have an old graphic EQ or Compressor laying about that has both unbalanced and balanced I/O you can use it as a line driver. Run the unbalanced output of your mixer into its unbalanced input, then use its balanced output to drive the line up to your next balanced device. You can bypass all the functions on it so it doesn’t degrade your signal much – although be careful, some devices have a ‘hardwired bypass,’ which means it will connect the input directly to the output, which leaves your signal unbalanced. The other cheap solution is to use a resistor to quasi-balance the source signal from the mixer. Details about this are in our TTOTD from 11/26/99.