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Tech Tip: Gigging with Mobile Devices: the Phantom Menace, Part 1

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Learn how to connect your iPhone, iPad, iPod touch or laptop to a PA mixer safely and noiselessly

IK Multimedia iRig Mobile Mixer

The IK Multimedia iRig Mobile Mixer makes integrating iOS gear easy for DJs, solo musicians and small ensembles. Read on for solutions to plugging into standard mixing consoles.

Performing live with prerecorded track on iPods or laptops running sequencing programs such as Ableton Live or the many mobile apps available today is getting increasingly popular. Whether you are running through your own PA or need to plug into a venue’s house system, you run the risk of damaging your expensive mobile device due to phantom power or improper cable connection from a stereo source to a mono channel. Noise can also be a problem. Here are the solutions:

Making the right connections

If you are connecting to a modern mixer such as the Mackie DL806L that offers wireless connectivity with iOS devices as well as wired connections via its Lightning connector, you’re good to go. Lucky you.

If your live gig input needs are modest, a 4-channel mixer/interface such as the the Alesis iO Mix provides a plug-and-play solution for integrating your iPad into your show. At Musician’s Friend you’ll find a broad selection of iOS audio/MIDI interfaces, many with mic preamps and mixing capabilities that can also make connecting mobile devices simple.

Learn much more about such iOS-friendly gear with our iOS Recording Gear Buying Guide.

Playing nice with conventional mixers

But what if you’ve got to connect your mobile device to a house PA or your conventional mixing console that’s not inherently iOS-friendly? Read on to find out how to connect to standard mixers safely and noiselessly.

If you have dedicated CD/tape inputs, or line-level stereo input channels, a simple Y cable from your iOS device with an 1/8” output (usually 1 x 1/8" to 2 x RCA or 1/4" depending on available input jacks) will do the trick. If your laptop has RCA audio outputs from the soundcard, male-to-male RCA or RCA to 1/4" cables are all you need. Hopefully, the tape-in section will have its own level control so that you can make it louder if necessary. As long as the mixer (powered or otherwise) is near you, there shouldn’t be a problem.

Things can get dicey, however, if one of three conditions exists: your mixer is more than ten feet away from you; you want to plug into two mic/line channels for more control over the sound, or you’re playing in a venue where you must use the house system and plug into a stage snake.

Okay, we’re a little unbalanced…

First, a little tutorial on balanced vs. unbalanced cables. An unbalanced cable consists of a single wire surrounded by a braided shield, which prevents the cable from picking up radio frequencies and noise from electromagnetic fields — but only for short lengths of cable. A balanced cable has two wires of opposite polarity surrounded by shielding. Signal is transmitted over one wire and received back on the other. No signal passes through the shield, which enables it to function more effectively (if properly grounded). The operating principle depends on induced noise such as EMI (electromagnetic interference), RFI (radio frequency interference), AC hum, or all of the above appearing equally on each wire. Each wire in a balanced line should have equal impedance relative to ground, which guarantees each wire will have equal susceptibility to noise. As signal travels into a preamp or mixer, its balanced input stage only amplifies the difference between the wires and therefore rejects noise that is common to both.

The phantom menace

Phantom power employs the same concept by sending a DC voltage equally through the two signal lines of a balanced mic cable. Since the balanced signal is only the difference between the two signals, which are equal and opposite in polarity, the power is effectively invisible to balanced equipment that doesn’t use it. Connecting a microphone with a balanced output that does not require phantom power will not damage the mic since it doesn’t "see" the phantom power, and our story ends happily. Scary version: Your mobile device does not have a balanced output. It can "see" the phantom power and worse yet, the phantom power can see it too. Connected to a channel with phantom power activated, your iOS device will find itself with +48 volts stuck up its little high-tech butt, which will make the little critter so unhappy, it’ll burn out on you just to see the look on your face.

The sound cards in laptops also do not have balanced output, and tend to be integrated into the motherboard. Trust us, taking +48 volts up the pipe will also fry your motherboard, and you know what happens when you make a bored mom unhappy—you’re grounded for life, and not in a good, balanced audio way either. Also, you’re out a few hundred or more of your favorite dollars.

Return of the DI

Now, lets get back to those three scenarios where an unbalanced cable won’t cut it. The first scenario is if you’re going to be more than 12 feet from your mixer. Beyond this length, unbalanced cables can become microphonic and otherwise noisy. Beyond 25 feet they will lose signal strength. Using a direct box (DI) will convert the unbalanced output your iOS device, MP3 player, or laptop to a balanced signal. Once balanced, long cable runs without signal loss are possible, noise is not a problem, and the world becomes a magical place of art and beauty.

Shop smart with our How to Choose the Right Direct Box.
Learn more with our tech tip What Do Direct Boxes Do?
Whirlwind IMP 2 DI BoxThe Whirlwind IMP 2 Direct Box is a low cost way to convert line or instrument level unbalanced signals to low-impedance balanced output.

Scenario number two: Converting the unbalanced output of the iPod/laptop to balanced by virtue of a transformer-isolated DI will ensure that if phantom power is inadvertently turned on, or you get accidentally plugged into the wrong channel, your iOS gear/laptop will be safe — music and merriment ensues.

The same holds true for scenario number three. A stage snake is, 99.9% of the time, XLR balanced going to the balanced mic inputs of the console. In all three cases, connecting to a transformer-isolated, passive stereo DI, such as the Radial ProD2, or two passive DIs such as the inexpensive but very effective Whirlwind IMP-2 will enable you to connect to the console safely and noiselessly. The aforementioned 1/8" to 1/4" Y-cable or stereo RCA to 1/4" cable will work in all three scenarios.

You’ll find a complete selection of cable adapters to fit your situation at Musician’s Friend.

Stereo into mono—not so hard

If you can only plug into one channel, or your mixer is set for mono output, just using a single mono cable or one side of the Y cable won’t work. You’ll lose half of your stereo mix (In Part 2 we’ll cover stereo to mono compatibility for live performance).

Radial ProAV1 DI BoxThe ProAV1 from Radial converts unbalanced stereo inputs to balanced mono outputs for easy connection to mixers.

If you want to run mono (especially for long distances, you need a DI that will sum the stereo outputs to balanced mono and provide transformer isolation to protect your equipment from the dark side of phantom power. One such device that handles all of this beautifully is the Radial ProAV1, a passive direct box with 1/4", RCA, and 1/8" stereo connectors for instruments, iOS gear with ⅛” outputs, and computers that are summed to mono via a resistive mixer. Never, we repeat, never try to combine two signals into one with a Y cable or use a single mono cable.

Here’s why. Outputs are low impedance and always must be connected to a high impedance input. If you tie the two outputs together (with a Y cable or mono cable), each output will try to drive the other, which can force them beyond the safe current limit and possibly into short circuit. At minimum, you will experience a severe loss of signal. Worst case; you can damage your mobile device or laptop. Remember, a Y cable that splits one signal into two is okay (stereo to 2 x mono). Combining two signals into one is is courting trouble!

Wrapping it up

All it takes is a little understanding and the right DI and you’re ready to gig. Read Part 2—Make Those Backing Tracks Mono.

Visit the Musician’s Friend iOS Store for all the audio gear you need to record and perform with your iPhone, iPad, or iPod touch.

Tags: iOS Direct Boxes

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