ALLEN AVIONICS ANALOGUE AUDIO GROUND LOOP HUM ELIMINATORS AND ISOLATORS
The Allen Avionics AGL Series employ fully-shielded, 1:1 ratio, true isolation transformers, designed for 'low distortion, linear phase-response and excellent pulse fidelity'. This is accomplished by extending the bandwidth to over 300kHz, 10-15 times the normal 20kHz bandwidth.
Hum in audio systems is usually the result of a ground loop in the system. Common-mode alternating currents or EMI will flow in a ground loop created by an electrical system that has grounds at different voltage potentials, usually as a result of connecting equipment, racks or vehicles powered, unavoidably, from different supplies. The result is 50 or 60Hz hum at equipment outputs. These effects are often seen where signals are fed from floor to floor within buildings and can be very significant when they are passed from building to building. Probably the worst environment is the outside broadcast, where multiple generators or AC power supplies are used. In audio installations, signals have a frequency bandwidth which contains all the hum component frequencies and these cannot be removed without adversely affecting the audio signal itself. Hum may however be eliminated by inserting an isolation transformer.
The AGL-600 and AGL-600-2 include a three-position ground-lift switch for the XLR connectors, offering audio ground and chassis ground disconnection options.
Switch position 1: Chassis shield connected, audio ground not connected. Acts as a balanced line transformer to break ground loops. Eliminates hum and buzz.
Switch position 2: Chassis shield and audio ground connected. Corrects balance on audio lines.
Switch position 3: Chassis shield and audio ground not connected. Breaks ground loops and provides audio isolation.
AGL-600 - Single Channel - XLR connection - Earth lift switch
Impedance (input and output): 600 ohms balanced. Bandwidth: 300kHz. Line isolation: 100Mohm minimum. Insertion loss: Less than 0.5dB. Connection: 3-pin XLR. Housing: High impact ABS. Dimensions: 67(w) x 38(d) x 95(h) mm.
AGL-600-2 - Dual Channel - XLR and 1/4inch B gauge connection - Earth lift switch for each channel
Impedance (input and output): 600 ohms balanced. Bandwidth: 300kHz. Line isolation: 100Mohm min. Insertion loss: less than 0.5dB. Isolation between channels: 100dB min. Connection (each channel): 3 pin XLR and 6.35mm B-gauge. Housing: High impact ABS. Dimensions: 102(w) x 51(d) x 137(h) mm.
Impedance (input and output): 10k ohms. Bandwidth: 300kHz. Line isolation: 100M ohms minimum. Insertion loss: Less than 0.5dB. Connection: 6.25mm A-gauge. Housing: High impact ABS. Dimensions: 67(w) x 38(d) x 95(h) mm.
In a multiple device system where hum is present, it is very important to determine which two pieces of equipment are causing the problem. Disconnect one piece of equipment at a time until the hum stops. When the combination causing the hum is found, insert a ground loop eliminator between them.
Many other hum blockers, isolators, transformers, video noise eliminators, attenuators and delay lines are available from Allen Avionics to assist with the removal of unwanted interference, synchronisation and equalisation in video and audio systems. Formats include SDI-HD, Component and composite video, CATV, S-VHS and analogue audio. Packaging options include stand-alone modules, card and rack frame enclosures and discrete PCB mounting components.