The unique centre tap switch allows the transformers' centre tap to be connected to either the devices' input ground, output ground or isolated from both. The number of channels range from 1 to 10 and the channel types can be bidirectional, unidirectional, or both. The technology types are capacitive coupling, giant magnetoresistive (GMR), or magnetic coupling. Glensound's solution was to design a transformer isolating unit starting with a very good quality audio transformer from Lundal and adding a unique feature of a variable centre tap switch. Digital Isolators electrically separate circuits but still allow for digital signals to be transferred between them. An LM324 op amp is used here to drive the LED input of the 4N25.
AUDIO ISOLATOR CIRCUIT PROFESSIONAL
The input circuits of a professional audio device should of course be able to handle this situation but as our customer was a freelance contractor for the OB company he wasn't in the situation that he could tell his employer that their multi million pound OB truck had a rubbish audio desk. 5.3.4, adapted from a design in Newnes Electronic Circuits Pocket Book by Ray Marston (ISBN 10:1-4832-9192-8) uses the 4N25 connected as a phototransistor to pass audio signals whilst isolating the input and output circuits. This customer was providing audio facilities in a venue away from the OB truck and there was sometimes hum being received at the OB truck on his output circuits. The isolator itsel is build around the ADUM4160 chip from Analog Devices. He Glensound GS-ET2 (External Transformer) was designed to help a specific outside broadcast customer who was having no luck in curing hum problems with cheap DI boxes.
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