I've decided to continue the thread of cable wiring into today. Tuesday we learned how to wire XLR - XLR cables and how to reverse polarity on them. Yesterday we did the same for TRS - XLR cables. But all of those are balanced. What if one has to connect an unbalanced device to a balanced device?
There are many possible scenarios. More than we could possibly cover here, but there are a few very common situations. Today we will explain how to wire a cable between an unbalanced output and a balanced input.
Conceptually you have to be aware that the balanced line has three wires in it: a shield, a positive (hot) wire, and a negative (cold) wire. Of course, unbalanced devices have only two wires: a hot and a shield. So how does one properly get from a two-wire system to a three-wire system? On the case of an unbalanced output feeding a balanced input the most common way of doing it is as follows:
| XLR Male connector (input) | Unbalanced output (usually a phone or phono plug) |
| Pin 1 - Shield................... | Sleeve - Shield/Cold (negative) |
| Pin 2 - Hot (positive).......... | Tip - Hot (positive) |
| Pin 3 - Cold (negative)........ | Sleeve - Shield/Cold (negative) |
So the (negative) pin 3 wire gets tied to the sleeve and shield wire at the unbalanced end. However just because this is the most common method doesn't mean it is always the right method. Consult the manuals for your equipment. Occasionally you may find that a piece works better by floating that pin 3 wire at the other end. Typically we've found this just acts as an antennae, picking up all sorts of unwanted stuff, but there are times when this method can work better.
Keeping with the polarity reversing theme of this week's TTOTD. If your balanced device happens to be pin 3 hot, then you would wire the connectors as follows:
| XLR Male connector (input) | Unbalanced output (usually, a phone or phono plug) |
| Pin 1 - Shield................... | Sleeve - Shield/Cold (negative) |
| Pin 2 - Cold (negative)........ | Sleeve - Shield/Cold (negative) |
| Pin 3 - Hot (positive).......... | Tip - Hot (positive) |
Just like in the other examples this week reversing the polarity is as simple as reversing the pin 2 and 3 wires at one end of the cable.
All of this wiring does not take into account any level differences between the equipment. In many cases unbalanced equipment operates at the lower -10dBV levels while most balanced equipment operates at +4dBu levels. The difference can be significant so wiring up adapter cables in these circumstances probably still isn't going to produce desired results. One is better off to use an active level matching amplifier. There are several models and price ranges to choose from. Contact your Sweetwater Sales Engineer for more details.
So you'd think that the same wiring rules would apply to male XLR (outputs) connecting to unbalanced gear, but unfortunately things get a bit more complex there. We'll tackle some of those configurations tomorrow.
