When it's three minutes before the worship team takes the stage, or five minutes to ‘air' and you've got a nasty buzz, hum, or other noise that you just can't solve, you're in luck – if you've got a handful of transformer isolators in your tool kit. Transformer isolators are a quick and simple way to eliminate most audio noise problems, so that you can keep the Ark sailing smoothly.
How They Work
Transformer isolators break the Galvanic connection between one circuit branch and another, yet still pass audio. No other component or device does that. They can also balance an unbalanced line, or unbalance a balanced line. Certain types are designed as splitters, such as when one microphone needs to feed several different consoles or preamps. A precision transformer will provide excellent Common Mode Rejection, which is the measure of how much hum and buzz is cancelled while the desirable signal content passes through.
By keeping a handful of transformer isolators equipped with the appropriate I/O connectors in your work box, you can become the hero of the day. This is true for audio systems, which most people already know about, but less well known are the use of transformer isolators for solving problems in video distribution systems. Ground loops in video cause hum bars that scroll through the screen, making the images less than desirable, or sometimes downright unusable.
What is Galvanic Isolation?
As stated above, transformers provide ‘Galvanic isolation,' a term that's worth becoming familiar with. Unlike active electronic circuits that buffer signals and can provide impedance matching, only a transformer can provide true Galvanic isolation.
In simple terms Galvanic isolation means that the electrical potential between one circuit in relation to another circuit – or possibly several other circuits in some cases - is fully isolated electrically. Useful signals pass through, but uneven ground references, the cause of noisy, untamed ground loops, do not.
Under the Hood
The input of a transformer is called the primary side and receives the input signal voltage. The transformer converts the signal to electromagnetic energy by passing the voltage through coils of wire wound around the all-important core –which is usually constructed with a high content of iron - but other materials are also employed for specific applications.
Next, the output, or secondary, comprises another set of coils wrapped around the same core, or a portion of the core. The energy is then transferred electromagnetically through the core without any direct electrical potential between the primary and secondary. The primary creates a magnetic field that the secondary responds to, generating a functionally equivalent, but fully isolated output.
The primary creates a magnetic field that the secondary responds to, generating a functionally equivalent, but fully isolated output.
To Everything - Turn, Turn, Turn
The number of turns of wire in the primary, in relation to the number of turns of wire in the secondary, determines the nature of the voltage transfer. A 1:1 ratio, which is common, provides isolation but no voltage gain or loss. An uneven ratio, such as 1:4 or 3:1 (as just two examples), transforms the voltage by either increasing it or decreasing it. That said, there's no free lunch. You cannot generate power, which is the product of voltage times current (P = V x I) from a passive device. But you can increase the voltage from the very low output of a ribbon microphone (for example), to an appropriate level for the microphone to properly interface with a mixing console or other preamp.
Conversely, you can reduce the voltage when a given circuit topology requires it. And at the same time the transformer provides the highly desirable benefit of galvanic isolation that we've discussed above.
The Good the Bad and the Ugly
There's much more to a transformer than just Galvanic isolation - named after Luigi Galvani, by the way. A precision transformer also can increase CMRR, which stands for Common Mode Rejection Ratio. Common Mode Rejection refers to the ability of a circuit to cancel the hum, buzz and noise that is so often induced into interconnecting cables and audio devices from EMI (Electromagnet Interference) and RFI (Radio Frequency Interference). A precision isolation transformer can turn a nightmare scenario into a quiet, usable finished recording or live sound mix in which you could hear a pin drop in the quiet passages without fear of hum and noise wrecking havoc.
Theatrical sound designers and broadcast engineers have been using – and prefer - transformers in their systems for many decades. The rock and roll industry hasn't been as keen because a low level hum or buzz was usually masked by crowd noise. But now that most travelling bands want to record every performance, a low noise floor has become important to live music, be it clubs and pubs, stadia and arenas or churches.
Often surprisingly to some folks, the same rules hold true for video. The all-too-familiar hum bars that you've seen on video screens, especially those located some distance from the main sanctuary (think digital signage), may seem an elusive problem to solve --- especially for an audio practitioner. Enter the transformer isolator, once again. A quick insertion of a transformer in the feed line will almost always isolate the uneven ground references and restore a crystal clear picture, instead of generating a plethora of complaints each Sunday.
Conversely, a poor quality transformer with uneven windings will do nothing to help CMRR problems, it will add distortion, mess with the frequency and phase response, and generally bring havoc to the system. It's important to use premium quality products when the entire signal chain is passing through the isolator.
Simple but Subtle
So why don't we know more about transformers already? Well many of us older sound practitioners do, but the younger among us have been focusing more on digital console features than on basic signal integrity. Who can blame them? Digital consoles are formidable, challenging, and a lot more interesting than passive coils of wire wound around metal cores. Or so it would seem.
But the best console in the world, coupled to the best amplifiers and loudspeakers, cannot perform properly without a fully functional signal path. Fully functional = clean, clear audio, free form the smallest detectable hum, buzz, or low level RF interference. That's the criteria for achieving sonic perfection and one way to mitigate interface issues is to use precision transformers. Hum and buzz are not just annoying background sounds that can deal-break a recording or intimate performance. They can also modulate music and voice, adding harmonics that are not part of the original program material. Not a good thing.
Where to Get Them? What do they look like?
There are several leading brands in the world, but only a few have achieved status as technology leaders. Lundahl Industries in Sweden manufacturers a wonderful range of transformers for inclusion in manufactured products, along with two or three styles of hand-held ‘emergency' fix-it XLR “isolation barrels” which are nearly imperceptible in any alteration of the sound quality. However, they are rather difficult to obtain in North America, and because of their high performance characteristics, they are quite expensive.
A popular solution for quick fixes is the Sescom IL-9. This product has been around for decades. The latest model has recently grown larger as the transformer core has apparently been increased in size to improve LF (low-frequency) performance. As a rule of thumb, low frequencies require a large core to avoid core ‘saturation,' which basically equates to increased distortion as the operating level increases. High frequencies do not require as large of a core at a given operating levels as low frequency content.
Jensen Transformers, Inc. is arguably the world leader in precision designs. The late Dean Jensen, who founded the company, was nothing if not fanatically searching endlessly for the finest materials, the most accurate manufacturing techniques, and the most useful designs for his large customer base.
Over the years, prominent companies such as Wally Heider Recording, McCune Sound Service, Masque, Sound Associates, and Pro Mix in New York, John Hardy, Meyer Sound, and many, many others relied on Jensen Transformers for their preamps, mic splitters, console outputs, and many other aspects of the signal chain, when they deployed their equipment on live shows and broadcast events.
Mic splitters, line drivers, and numerous other audio applications played a big part in those days and still do, in many circles. And while it's true that digital signal distribution though AVB, Dante, and other systems have, to some degree reduced the need for Galvanic isolation at the head end of the signal chain, many, if not most, sources are still analog and require proper impedance matching and CMRR noise reduction that often exceeds the ability of the integrated circuit solutions that are built into the front end and line drivers of many modern pieces of equipment.
If you look carefully, many leading-edge preamplifiers, direct boxes, summing amplifiers, and even large format consoles themselves, derive benefits from the use of transformers.
