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Line Level Isolation Transformers
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<blockquote data-quote="John Roberts" data-source="post: 49445" data-attributes="member: 126"><p>Re: Line Level Isolation Transformers</p><p></p><p>In an ideal world there wouldn't be much need for a line level isolation transformer, so the implication is this will be applied to mitigate some ground problem. </p><p></p><p>Modern properly designed gear should handle pin 1 currents without corrupting the audio signal integrity, but there is enough legacy gear still in use to worry about. IMO the chassis should be hard tied to pin 1 on either the input or output. A ground lift switch can open the connection between Pin 1 input and Pin 1 output. I also like the small cap always in circuit to provide a low Z RF shield ground path, and even a high value resistor to drain off static charge, if present. If no charge is present the high value resistor will not conduct enough current to be a problem. </p><p></p><p>JR</p><p></p><p>edit/ back in the early '80s I experimented with using back to back diodes between signal ground and chassis ground, to ignore low voltage ground potential differences, while still providing a low impedance path for larger voltages/currents (I used power rectifiers that were quite robust.). </p><p></p><p>For a "fixer" Isolation transformer, it might be nice to add a LED and resistor across the switch open position that could light up to indicate if a large voltage potential exists across the grounds, something that would be useful to know for human safety. /edit</p></blockquote><p></p>
[QUOTE="John Roberts, post: 49445, member: 126"] Re: Line Level Isolation Transformers In an ideal world there wouldn't be much need for a line level isolation transformer, so the implication is this will be applied to mitigate some ground problem. Modern properly designed gear should handle pin 1 currents without corrupting the audio signal integrity, but there is enough legacy gear still in use to worry about. IMO the chassis should be hard tied to pin 1 on either the input or output. A ground lift switch can open the connection between Pin 1 input and Pin 1 output. I also like the small cap always in circuit to provide a low Z RF shield ground path, and even a high value resistor to drain off static charge, if present. If no charge is present the high value resistor will not conduct enough current to be a problem. JR edit/ back in the early '80s I experimented with using back to back diodes between signal ground and chassis ground, to ignore low voltage ground potential differences, while still providing a low impedance path for larger voltages/currents (I used power rectifiers that were quite robust.). For a "fixer" Isolation transformer, it might be nice to add a LED and resistor across the switch open position that could light up to indicate if a large voltage potential exists across the grounds, something that would be useful to know for human safety. /edit [/QUOTE]
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