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Q. Are balanced connections essential?

By Hugh Robjohns

I recently bought an old Trident VFM mixing desk, but I was disappointed to discover that it only offers unbalanced line inputs. Almost all my gear has balanced line outputs, and I have previously always used balanced connections all-round.

Should I splash out on new unbalanced leads, connect all the various earths and run an unbalanced system, or should I cut my losses, sell on the mixer and save up for one that can handle balanced inputs? Part of me wants to keep the old VFM: it may be bulky, but it works and has a usable four-band EQ. I also read that unbalanced connections have better bass. Is this true?

Daniel Miller

Technical Editor Hugh Robjohns replies: I remember the Trident VFM console because I bought a 16:8:2 version for the college PA back in my student days, 25 years ago! Looking back, it was a fairly uninspiring desk with a pretty basic design and budget components, and nothing like the classic Trident consoles of the preceding decades in terms of sonics or build quality. I remember the unbalanced line ins, but back then it didn't bother us, because none of the very small amount of outboard we had was balanced anyway! As to whether to swap the desk for something else, I wouldn't just because of the unbalanced line inputs, but there are certainly better-sounding desks out there.

If you stick with the VFM desk, I wouldn't worry too much about the inputs being unbalanced, provided that your studio connections are all fairly short, and all the equipment is powered in a star distribution system from a single wall socket.

There is no need to purchase new cables, and you can still use your standard balanced cables; the cold side of the balanced signal will simply be ignored by the Trident's unbalanced input stage. Obviously, you'll lose the balanced interface advantage of better interference rejection, but with short cables this is unlikely to be a significant problem anyway.

There are a few issues to be aware of, though. Firstly, although most balanced outputs don't mind being connected to unbalanced inputs, some fully active designs do object. I doubt this will be a problem for you, but I'd advise checking the manuals for your equipment, and when you connect it up, check that all is working as expected.

Also, if any of your balanced sources have fully active outputs then, depending on the design of the output circuitry, you may also experience a 6dB reduction in signal level due to only half the signal being received at the mixer. This is unlikely to be a practical problem, though, as it can be easily corrected by adjusting the equipment gains appropriately.

Perhaps a more important concern is that of ground loops. In a proper balanced interface, the signal references itself rather than to ground, whereas an unbalanced interface has to use the ground as the reference. The potential problem here is that, if the ground is a slightly different voltage in different equipment (usually because of poor mains grounding practices), then the reference voltages vary and you'll hear hums. However, if the mains earthing is arranged sensibly, you'll probably not have any problems anyway. If you do, isolating the screen connection on the problematic equipment's audio cables at the mixer end will solve the problem.

As for the suggestion of 'better bass' in unbalanced interfaces, there is no intrinsic reason why this should be the case. However, a poorly designed balanced interface can certainly sound noticeably inferior to a well designed unbalanced interface in various ways, particularly in terms of general sonic transparency. This is because most equipment uses unbalanced circuitry internally, and so the balanced interfaces to and from the outside world add additional conversion circuitry, which often degrades the signal path to some degree.

The renowned American mastering engineer Bob Katz even argues the case for unbalanced interfaces in mastering rooms, in his excellent book, Mastering Audio

Published March 2007