From bruce@ashbysolutions.com Wed May 19 10:07:46 2004
Subject:Balanced outputs

Hello All,

There's been an awful lot of extremely animated discussion about the use of balanced outputs in "professional" gear lately. Here's my $0.02:

1. Balanced = Professional? Maybe, but a lot of pro-level gear we all use doesn't have balanced outputs. My Korg BX-3 doesn't have them, and the CX-3 I had before that didn't, either; nor do the Voce V3 and V5, or the Nord Electro. My Access Virus doesn't have balanced outputs, nor did the Yamaha AN1x it replaced. My Alesis QSRs don't have them. The Speakeasy Classic preamp doesn't have balanced outputs unless you order a 122-style interface; and it doesn't have balanced inputs, anyway. Nevertheless, all of this equipment is used by sound professionals around the world.

2. In theory, balanced outputs are always better; however, practice is another matter. Most of the internal signals in an electronic instrument are single-ended (unbalanced), and must be converted to balanced prior to leaving the instrument; usually, this means creating a second mirror-image of the signal for balanced output. In a perfect world, this conversion doubles the output and reduces susceptibility to noise -- AND NOTHING ELSE. In the real word, though, one cannot create a mirror image of a signal without introducing phase and level changes, and one cannot add more components to a circuit without increasing the possibility of adding unwanted noise, too. If the manufacturer spends enough time and money, these changes can be made negligible; however, balanced circuits cost more than unbalanced ones, and given the pressure to keep costs down, there's no guarantee that the manufacturer will use the best components in the output circuits. For the exact same money, I would
prefer that the manufacturer spent it on a simpler, high-grade single-ended audio path, rather than a more complex balanced path.

3. Balanced operation becomes more important as cable lengths get longer and setups become complex. If your setup is using nothing but 3-6 foot (1-2 meter) cables and less than 3-4 sound sources, the benefits of balanced operation may be too small to bother with. Balanced cables are harder to find on a Saturday night in a small town, and they cost more.

4. As already mentioned, balanced vs. unbalanced is not the only reason why one audio setup has noise while the other doesn't. Ground loops are the biggest cause of audible noise, and eliminating them normally takes transformer isolation and separating the grounds -- i.e., a direct box, or its equivalent in on-board electronics. Also, digital noise coupled in from the instrument's other electronics can be as big a problem as any noise coupled through cables back to the PA. (Early generations of PC audio are wonderful examples of this!) Since the balanced circuits are located after this noise enters the system, balanced outputs won't help eliminate the digital hash.

5. More than balanced outputs are necessary for use in situations with long cable paths. LOW-IMPEDANCE balanced outputs are needed to minimize the high-frequency losses. Some balanced outputs are low impedance (600 ohms or less), but a lot of what's out there is more like mid-impedance; a typical 5K transformer-less unbalanced setup will look like 10K in balanced mode. This situation will help reduce noise pickup, but it won't allow the setup to connect to a mixing board 100-200 feet away without some loss in treble response.

6. I use a compromise solution very similar to the approach suggested earlier for PA use: All of my instruments and modules go into a Behringer RX1602 (8 mono or stereo sources) line mixer, using unbalanced cabling. The two outputs (L+R) then go to a pair of Whirwind EDB-1 direct boxes. These ~$25 (US street) boxes aren't as bullet-proof as the IMP-2, but Whirlwind claims that they use the same isolation transformer. Since I mount them inside my rack -- their screw hole pattern lines up with the mounting strip in the back of the rack -- they're good enough, and they have ground-lift and 0dB/20dB/40dB adjustments. From there, the signals connect to a stereo power amp for my stage amplification. Normally, I give the board a pair of ground-lifted unpadded XLR connections from the EDB-1's, which usually brings a smile to the mix engineer's face! :^)

Regards,

-BW
--
Bruce Wahler
Ashby Solutions™ http://music.ashbysolutions.com
978.386.7389 voice/fax
bruce@ashbysolutions.com