Description

Here is a convenient, compact, and tidy way to implement an “Earth-Loop Breaker” circuit in your amplifier or other device.

An earth-loop breaker works to reduce noise in a system, by inserting a buffering impedance between a device’s signal ground, and its earthed chassis, to reduce currents circulating between them.

The metal-oxide resistor provides the buffered impedance at low frequencies, and the polypropylene capacitor—in parallel—gives a low impedance at RF. A bi-directional diode clamp—also in parallel with the resistor and capacitor—does nothing in normal operation, as there is 0VDC across it. In case of a fault, such as a DC power rail coming in contact with the chassis, or AC power being shorted into the device’s signal ground, the voltage across the diodes will rise above 0.6V, it will clamp, and the fuse should blow.

Recommended reading: Rod Elliot has a terrific article on the subject of “Earthing your Hi-Fi” wherein he describes the use of earth-loop breaker circuits, and gives invaluable advice on the subject of making electrically safe, and quiet audio equipment.

Installation:

SAFETY WARNING: An earth-loop breaker circuit should never be used between safety earth ground and chassis.

This is not a “Ground lift” or “Earth Lift” circuit. Safety earth ground should always be connected directly to the chassis of your device, using wire at least as thick as the power wire, with its own ring terminal, on its own, dedicated bolt through the chassis. Use star-tooth lock-washers on both sides.

Connection to the chassis is made through the brass stand-offs on which the board mounts. For lowest noise, the earth-loop breaker should be mounted near the point on the chassis where the safety-earth connection is bolted. Avoid mounting the earth-loop breaker in a place where there are eddy currents or magnetic fields between it and the earth ground point. (Such as on opposite sides of a transformer.)

The board’s dimensions are 34x20mm, and 38mm tall. Drill two 1/8″ mounting holes, 25mm apart. Optionally, scrape some paint off the chassis around where the screw heads make electrical contact. Remove any burrs from the mounting holes.

Connection to the device’s signal ground (usually the star-point) is made through a 2.0mm terminal, accepting up to 14ga stranded wire.

Caveats and disclaimers:

I cannot guarantee the suitability of this product to any particular amplifier or other device. Issues surrounding ground loops, shielding, stability, noise pickup, etc, are vast and complicated. Every device is different, and so I cannot guaranteed your device will benefit, or indeed, even be stable with an earth-loop breaker installed.

I do know that they work great on Adcom GFA-5×5 amplifiers, and I have used them in several audio projects with great results. The board is designed to have as little inductance as possible.

Kit is supplied with a 47Ω metal-oxide resistor, and a 0.47µF Panasonic polypropylene capacitor. These values are chosen because, in my experience, they work well for a wide variety of equipment. These values may not be ideal for your particular application, and that is up to you to determine. Common values for this type of circuit range from 0.1µF to 1µF, and 10Ω to 100Ω. Metal oxide 1/2W resistors and polypropylene capacitors are recommended for their high-frequency performance. Footprints for the resistor and capacitor are 10mm lead spacing.