In this article, Pat Brown will show you a little trick to convert Ipod unbalanced stereo output to a balanced Ipod output.t.
Last issue I reviewed some portable media players to determine their usefulness as program sources for sound system testing. The Ipod family did especially well. The 1Vrms (0dBV) output level is more than adequate for driving microphone inputs and line level inputs with a gain stage. But, this level may be insufficient for one of the most attractive uses of these devices – as a program source for driving powered loudspeakers for room testing. The required drive voltage for full output for the two units that I own are +4dBV and +6dBV respectively. This means leaving 4-6dB of sound pressure level on the table due to the inability of the Ipod to drive them to clip.
Here’s a little trick for getting the extra level. The Ipod has an unbalanced stereo output, but with a special interconnect cable and waveform it can be converted to a balanced output. No modifications to the Ipod are necessary. The benefit is 2-times the output voltage, which is 6dB greater than the level that is available from a single channel.
1. Be sure to switch phantom power “off” before using this cable, as no DC isolation is provided.
2. Since the two channels are reverse polarity, typical stereo program material will playback with the vocals canceled.
3. Keep a DI with proper summing network in the bag for summing the L/R outputs into a single input channel (note: The L/R inputs of some DI’s are wired as Y-cables!).
The very low output impedance of the Ipod should allow it to drive about any audio input.
Since the Ipod is electrically insulated from the loudspeaker there should be no ground loop issues. Of course, this will work with any unbalanced source, not just Ipods. It beats adding a gain block with power supply or battery to get the extra 6dB. pb