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Star Grounds, Loop Areas, & Electrical Safety In Project Studios, Edit Suites, & Other Compact Audio Installations Part IV by Neil A. Muncy

Wednesday, December 19th, 2007

Surge Suppressors are widely advertised as the answer to noise and interference problems in all kinds of systems. Consider a few points. First, as mentioned in previous issues, conventional Metal Oxide Varistors (MOV) surge suppressors incorporated into power bars are in widespread use. Unfortunately, unless they are built to a robust standard, which many of the older ones weren’t, they may constitute a serious fire hazard, because when MOVs fail, they often get hot enough to melt the plastic housing of a typical power bar long before the fuse or circuit breaker operates. (Murphy at work!) Newer ones must meet a considerable more demanding UL/CSA specification, and are supposedly safer.

Let’s suppose the computer(s) in your installation are fed by a power bar with a built-in MOV. When a surge comes along, the “bad stuff” is diverted into the equipment ground conductor and supposedly finds its way back to the service entrance. If the equipment ground path is more than a few feet in length, the natural inductance of the equipment ground conductor will be enough to significantly limit the flow of high-frequency noise current, which is what transients and surges are made of in the first place. Instead of getting rid of surge energy, what happens is that for the duration of the event the entire computer systems’ ground reference voltage goes up towards the level of the surge itself, which can be hundreds of volts – if not more.

If the computer is sitting there all by itself and is not connected to any other equipment, this problem may be more academic than real. But if the computer is connected to something else, and the rest of the studio equipment is either not on a MOV surge suppressor fed by the same power circuit, which feeds the computer, or worse yet, is fed by a different power circuit altogether, during a surge there can be sufficiently high voltages between the computer’s “protected” ground reference and an “unprotected” studio equipment ground reference to cause major noise and even permanent damage.

If you are absolutely convinced that you need MOV surge suppression, the best way to minimize this problem is to first configure your studio power as described above, and then use the same kind of MOV suppressor on each power circuit feeding the room. Connect all of them to the central hub of your power distribution system, and then run all branch circuits from there. A much better solution is a new Series Mode surge suppressor technology, which does not contaminate equipment grounds. A bit more expensive than good MOVs, but much safer and much more effective in the long run. You can find out about it at www.surgex.com.

Getting rid of noise in audio systems is nothing more than applied Good Engineering Practice (GEP), the formula for which is: BP + GOCHS = GEP (Basic Physics + Good Old Common Horse Sense). The proponents of alternative esoteric grounding schemes would do well to keep in mind that Mother Nature wrote the original script for the show – and she don’t do re-writes!

Neil Muncy has been around since the days when recorded sound was analog mono and vacuum tubes ruled the audio landscape. He has been a consultant in the audio field for many years, and can be contacted by e-mail at: nmuncy@allstream.net.

Chris’ Plug-in Script by Chris Crerar

Friday, October 19th, 2007

In today’s digital audio recording environment there are a wide variety of plug-ins to choose from, ranging from homemade EQs to $1,000+ bundles. All can be useful if used in the proper applications.

The most consistently useful plug-ins for me seems to be in the WAVES bundle; including “renaissance strip.” The EQs and compressors are predictable and always do what you require without adding too much colouration to the sound.

Another great plug-in I use a lot is Isotope Trash. By far the most in-depth distortion plug-in I have ever heard. It takes a little more fiddling with the controls to get the sound you want, but will yield great results in the end. It works fine on bass as well.

For reverb, I still prefer the classical outboard digital reverbs like the Lexicon 480 and 960, but Rverb and TLspace are also superior sounding plug-ins. I also have found Dverb is useful from time to time … but don’t tell anyone I said that.

So basically, if you’re able to afford it, go with WAVES. If not, the Digidesign plug-ins can do you just fine. For cool FX and nice distortions check out the Isotope series.

Chris Crerar is an Engineer at Metalworks Studios. Visit www.metalworksstudios.com.

Star Grounds, Loop Areas, & Electrical Safety In Project Studios, Edit Suits, & Other Compact Audio Installations Part III by Neil A. Muncy

Friday, October 19th, 2007

Still have noise left? If you have reworked your power as described in previous issues, you have done everything you need to do to make your power and grounding system safe and legal.

The Pin-1 problem is a term coined to describe the almost universal practice employed by most audio equipment manufacturers, in which the old-fashioned (pre-1970) method of connecting cable shield terminals (Pin-1s) on I/O connectors directly to the chassis at the point of entry has given way to connecting Pin-1s to some convenient nearby ground circuit trace on the motherboard. The consequence of this practice is that the moment you connect a cable, you have just attached an antenna to the most sensitive inner workings of your equipment! See the AES publication cited below [1] for how to do a Pin-1 test, and suggestions on how to deal with the consequences.

Once you uncover Pin-1 problems, send the manufacturer a letter/e-mail outlining your observations. Surveys conducted by the author suggest that only about 10 per cent of all the equipment presently in use in the audio industry is demonstrably free of Pin-1 problems. If the manufacturer in question doesn’t respond, or implies that you’ve gone bonkers, tell them that you are going to sell off the offending equipment and buy an equivalent unit from another manufacturer who has seen the light. That should get their attention. If not, you now know whom you’re dealing with.

If you still have RF Interference (RFI) problems, start looking for equipment with less than major Pin-1 problems. Just because a piece of equipment doesn’t exhibit a significant Pin-1 problem at powerline frequencies doesn’t guarantee that it will not be susceptible to RFI. A piece of ground wire a couple of inches long inside a piece of equipment, which is employed to internally chassis ground Pin-1(s) can be a very effective re-radiator from well below 100 MHz to the upper limit of the RF spectrum. An RF signal generator can be utilized for this type of Pin-1 test.

The scenario described above will make your system virtually immune to farfield magnetically coupled interference. Wall warts, line lumps, and power transformers in your gear are all sources of strong extreme nearfield magnetic field energy, which will also cause hum problems if you aren’t careful. Locate wall warts, line lumps, and anything else that has big power supply as far away from your low level equipment as practical. Make use of the Inverse Square Law, which dictates that as you increase the distance between a source of interference and the “victim” equipment and cables, the strength of the interference decreases as the square of the distance. In other words, in this case an inch is (almost) as good as a mile.

Pick up the December issue of PS for Muncy’s conclusion and his invaluable tips on MOV surge suppressors.

References:
[1] The June 1995 issue of the AES Journal, Shields & Grounds reprinted as a Special Publication by the Audio Engineering Society. On the web at: www.aes.org.

Neil Muncy has been around since the days when recorded sound was analog mono and vacuum tubes ruled the audio landscape. He has been a consultant in the audio field for many years, and can be contacted by e-mail at: nmuncy@allstream.net.

Everything Is An Amplifier Part III by Bryan Martin

Friday, October 19th, 2007

Every amplifier has a sound. Mankind is still searching for the audio grail of a “straight wire with gain.” What a great amplifier does is transfer the maximum amount of the information from its input to its output with as little damage as possible. This translates into full bandwidth, wide dynamics, and undamaged transients: the essentials of great sounding reproduction.

In the brave new world of the 21st century, technology has brought incredibly powerful tools to the everyday. Recording studios live in a laptop, and declining are the great temples of sound recording and the monks who populate them. We take music for granted. We take technology for granted. We want it all in a bundle. And very few people have the privilege of experiencing music in an ideal listening environment. Ear-buds, iTunes, and laptop speakers are a pale copy of a breathtaking audio system. As the audio chain gets dumbed down, there is all the more reason to give recorded sound the best possible vehicle on its way to immortality. Because after it is committed to a stream of digits, the road it takes back to sound will be challenging.

Equalization, compression, and the like are often reached for in an attempt to correct a sound source that is lacking. I have always been baffled by manufacturers who package a mic preamp, EQ, and compressor all in on package. If the mic preamp was good in the first place, then why the need for the compressor and EQ to fix the sound coming out of it? Note: Manufacturers spout specs and tech-speak, which may well sound impressive, but to the educated reader is often contradictory or plain rubbish.

Audio specs are like accounting: you can make them look like whatever you want. But specs don’t translate into good sound. There are plenty of horrible-sounding units out there with amazing specs. To cheaply achieve good bandwidth, hideous mechanisms are employed in the signal path. Using a large amount of negative feedback will drive the bandwidth into the nether regions of the sub and supersonics, and also completely kill the sound quality. People listen with their eyes these days, not their ears. How often do we find ourselves staring at the waveform while it plays back out of a workstation. It has become a reflex almost totally associated with the listening experience. The box looks great; it has to sound great. But that is not always the case.

Bryan Martin owns Sonosphere Mastering. Over his 20+-year career he has worked with David Byrne, Rufus Wainwright, Max Roach, Run DMC, and White Zombie. He can be contacted via e-mail at bryan@sonosphere.ca or on the web at www.sonosphere.ca.

Star Grounds, Loop Areas, & Electrical Safety In Project Studios, Edit Suites, & Other Compact Audio Installations Part II by Neil A. Muncy

Sunday, August 19th, 2007

A Star grounding scheme, in which all equipment in an installation is bonded to a central ground hub, can be useful for minimizing low frequency common mode voltages between various pieces of equipment if it’s properly implemented. If not properly implemented, star grounding can result in performance, which in some cases is actually worse than that resulting from a completely haphazard approach.

Any secondary grounding system installed in parallel with already existing equipment U-Ground conductors in an installation has the instant effect of causing far more potential ground loops between equipment than would otherwise exist. Sometimes it makes a difference, sometimes it doesn’t. The $64 question is whether it reliably, and without exception, makes noise go away permanently and completely. Not likely.

A popular Star Grounding practice involves using separate ground wires to bond all equipment in the ensemble to a central hub, and then connecting this hub to a dedicated earth-grounding terminal, which is not bonded to the main building ground system. This practice is very dangerous and is completely illegal in the context of North American Electrical Codes.

One connection between an ensemble of equipment and building ground is all that is needed to make the system safe in terms of both the letter and intent of applicable electrical codes. Most installations usually involve more than one AC power circuit, whether actually required due to the size of the total load or not.

What is not considered in such a scenario is how long and by what path(s) the power circuits and their respective equipment ground conductors take before they get back together at the breaker panel. Just because two outlets are within a few feet of each other does not necessarily mean that they are on the same circuit.

In smallish installations in which all equipment is in one area/room and the longest audio cables are perhaps less than 100′ in length, and assuming that the breaker panel is somewhere else in the building, a very effective approach is to arrange to have all of the power circuits end up at a point in one box in the middle of the equipment ensemble. Very often, this middle point would be in the floor trench under the tabletop of the producer’s table equipment cabinet behind where the engineer/producer sits.

Install as many circuits as you think you need. What this scheme buys you is that by bringing all circuits into one multi-gang outlet box, all of the associated equipment ground conductors (one per circuit) also end up in the same box, all bonded together as prescribed by code. This star point becomes your one connection back to building ground, with the added advantage that now you have a demonstrably lower impedance path back to building ground by virtue of having X paralleled equipment ground conductors.

From this central box, 3-wire branch circuits are then run out to each grouping of equipment. If at all possible, all of these circuits should be in one continuous raceway/conduit, so that the associated equipment ground conductors are daisy-chained throughout the facility. This ensures that the total length of the equipment ground conductors between different equipment locations within the room is as short as possible. For only a few circuits, series-connected power bars are acceptable for this application, but use good ones and try to stay away from conventional “Surge Protected” ones, which employ Metal Oxide Varistors (MOVs) – they have been known to start fires when they ultimately outlive their service life. This ensures that the total length of the equipment ground conductors between different equipment locations within the room is as short as possible. As simple as this seems, this approach may eliminate enough residual noise so as to end the effort to go any further.

“OK wise guy, so what happens when I then run shielded audio cables all over the place?” you ask. “Don’t I end up with a big bunch of ground loops anyway?” Yes you do. Minimize the areas of the resulting ground loops by selectively cutting cable shields at one end or the other, the One-End-Only (OEO) approach. This is a simple way of smothering the symptoms of Pin-1 problems, and while in larger systems it may be required for other reasons, it’s usually not necessary in a small installation – besides which, it’s a pain in the ass and you can’t do it anyway in unbalanced single-conductor shielded cable installations for reasons which should be obvious. What you can do to minimize these loop areas is to simply run all of the low-level audio cables parallel and adjacent to your new branch power cables.

Be sure to pick up the October issue of PS where Muncy delves into the Pin-1 problem and other RFI solutions.

Neil Muncy has been around since the days when recorded sound was analog mono and vacuum tubes ruled the audio landscape. He has been a consultant in the audio field for many years, and can be contacted by e-mail at: nmuncy@allstream.net.

Everything Is An Amplifier Part II by Bryan Martin

Sunday, August 19th, 2007

Once all of the requirements of a gain stage are met [as outlined in the June issue], the designer will then select the ideal requirements for a specific stage, but achieving these requirements rarely happens in the real world. Attaining one design goal is often at the expense of another. There will be limitations imposed by the characteristics of the gain device chosen, economics, physics, and a host of other factors. And as the number of stages increase, so does the difficulty in bringing them all into an optimum specification.

Great sounding amplifiers require high-quality components. Transformers used in power supplies and for audio I/O are both large and expensive. Quality coupling capacitors, gain devices, and hardware all drive up equipment costs. The classic and highly sought after Neve modules have large, expensive power supplies, plenty of transformers, and build quality of impeccable craftsmanship. You will also notice that these Neve consoles have a far simpler layout and less options than the later generation Neve V Series, SSLs, and the like. Generally, a very well-implemented, simple gain path will always out perform a complex one – and negates the need for further processing.

Bryan Martin owns Sonosphere Mastering. Over his 20+ year career he has worked with David Byrne, Rufus Wainwright, Max Roach, Run DMC, and White Zombie. He can be contacted via e-mail at bryan@sonosphere.ca or on the web at www.sonosphere.ca.

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