A Clean Audio Installation Guide™

1.0 INTRODUCTION
The problems encountered in achieving clean audio are ones that each of us involved in professional audio must face with renewed interest. Initially, with the advent of inexpensive quality receiving equipment from Japan, the FM world was forced to "get it together". Now with AM and TV stereo, HI-FI video tape, DVD systems in home theaters, the Compact Disk, R-DAT, Compact Digital Cassette, recordable disc systems, etc., creating an ever increasing public awareness of very high quality audio, we have no choice but to get it together as well!

Fortunately for us, the tools are available, and the price to be paid is usually that of time, some technical knowledge, occasionally some new test equipment, but most importantly, greater than average care with our installations. This paper will deal only with analog audio systems.

1.1 Overview
After choosing our quality audio equipment, there are five major areas, that must be properly addressed to achieve truly outstanding audio:

proper power systems installation;
inter-connection system methods;
RF immunity;
proper headroom and signal-to-noise ratios; and
correct operation within the limits of the system.

2.0 POWER SYSTEM INSTALLATION
If all of the lighting and equipment in this world ran on DC as Edison had wanted, then the only concerns that we as audio professionals would face with our installations would be those of RF immunity, very low noise, low distortion levels, and wide bandwidth in our equipment. As we all well know, that is not the case. Probably the largest single source of audio "interference" we face is that of power line related voltages being added to the desired signals within our systems. Most of this problem is a result of normal 50 or 60 Hz voltage differences that exist between the chassis of equipment. (See figure 1)

Figure 1 - TYPICAL VOLTAGE DIFFERENCE SITUATION BETWEEN CHASSIS

These differences are a result of the different electro-magnetic environments experienced by each piece of equipment. They come from nearby AC power lines and transformers, lighting equipment, etc., and from internal power transformer magnetic leakage. Additionally, higher frequency audio trash may be conducted into the equipment via the power line. Our objective, of course, is to reduce these potential interference sources to, or near to, zero volts.

Therefore, the following generally accepted guidelines should be observed in relation to power system installation:

2.1 Separate Feeders
The most ideal power installation uses a separate dedicated feeder for the audio equipment, where a separate transformer (if required) and panel are installed as close as possible to the equipment in use. This separate feeder should originate, if possible, at the point of power entry into the building. This will provide the lowest possible source impedance to the equipment. Likewise, the equipment grounding conductor should also originate from the "cleanest possible source." (see details under INTERCONNECT Section 5.0)

2.2 Noise Generators
Keep all high power switching equipment off of the separate feeder (or phase) used for your quality audio. SCR lighting controls, motor switching, high power vapor lamps, etc., even fluorescent lights, generate a lot of Electromagnetic Interference. (EMI)

2.3 Quality Transformers
Use equipment that has input line filters, if possible, and quality power transformers to minimize conducted and leakage coupling. Occasionally a high isolation transformer, such as those made by Topaz and others, with ultra low coupling capacitance from winding to winding, may be necessary to eliminate high frequency conducted interference from the power line. The installation of high isolation transformers requires some careful thought to achieve the degree of isolation to which they are capable.

2.4 Separate Conduit
Provide individual, separate, steel (rigid, IMC or EMT) conduit runs for power and audio lines, separated physically as much as possible to avoid induced power related signals. Be sure to use ferrous metals for magnetic shielding effectiveness - that is, preferably not aluminum. If you find yourself in a situation where it is impossible to use conduit and virtually impossible to have a separate space for audio and power lines, such as on stage, where audio and power lines must cross, do so at 90 degree angles rather than letting them cross obliquely.

2.5 Safety or System Ground and Technical Ground
Tie all equipment together in a star configuration with insulated ground wires (to prevent random connections to other grounded objects) to reduce any potential differences between pieces of equipment to a minimum. We will discuss this in more detail under the subject of INTERCONNECT.
(Section 5.0)

Go to: Section 3.0