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<blockquote data-quote="Geoff Doane" data-source="post: 58284" data-attributes="member: 1155">Re: Phanton power destroying outputs ?The SSM 2142 line driver, a very common line driver in the &#039;90s and perhaps later, does not tolerate phantom voltage on its output.&nbsp; I once worked on a Crest console that had been used to feed a BetaCam (with phantom turned on, of course :roll<img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":)" title="Smile&nbsp; &nbsp; :)"&nbsp; data-smilie="1"data-shortname=":)" /> from a matrix output, and it had let the smoke out.&nbsp; The funny thing was that the smoke came out of the power supply decoupling resistors feeding that part of the console, not the output driver itself.&nbsp; As far as I could tell, the SSM 2142 still worked once phantom was removed, although I replaced it anyway.&nbsp; Here&#039;s the link to the SSM 2142:<a href="http://www.analog.com/static/imported-files/data_sheets/SSM2142.pdf" target="_blank">http://www.analog.com/static/imported-files/data_sheets/SSM2142.pdf</a>Crest built in provision for output transformers on the PC boards, but I&#039;ve never seen a console (Century Series) that had that option.&nbsp; Has anybody?BTW, here&#039;s a tip for you console designers out there :razz: :&nbsp; Metal film resistors might be great for audio, but aren&#039;t so great for power supply decoupling.&nbsp; When you exceed the power dissipation on a metal film resistor, its value goes down, increasing the current draw (The resistors in the Crest started off at 10Ω.&nbsp; By the time I got to look at it, the value was down to about 5Ω each).&nbsp; Traditional carbon film resistors behave like a fuse, and open up once they&#039;ve smoked a bit.&nbsp; I&#039;ve run into this problem a few more times in other gear, when tantalum power supply bypass capacitors shorted.&nbsp; The current draw wasn&#039;t enough to blow the line fuse, but it did cook the custom $100 toroidal power transformers (I guess Rupert made his name designing audio circuits, not power supplies).GTD</blockquote>

[QUOTE="Geoff Doane, post: 58284, member: 1155"] Re: Phanton power destroying outputs ? The SSM 2142 line driver, a very common line driver in the '90s and perhaps later, does not tolerate phantom voltage on its output. I once worked on a Crest console that had been used to feed a BetaCam (with phantom turned on, of course :roll:) from a matrix output, and it had let the smoke out. The funny thing was that the smoke came out of the power supply decoupling resistors feeding that part of the console, not the output driver itself. As far as I could tell, the SSM 2142 still worked once phantom was removed, although I replaced it anyway. Here's the link to the SSM 2142: [url]http://www.analog.com/static/imported-files/data_sheets/SSM2142.pdf[/url] Crest built in provision for output transformers on the PC boards, but I've never seen a console (Century Series) that had that option. Has anybody? BTW, here's a tip for you console designers out there :razz: : Metal film resistors might be great for audio, but aren't so great for power supply decoupling. When you exceed the power dissipation on a metal film resistor, its value goes down, increasing the current draw (The resistors in the Crest started off at 10Ω. By the time I got to look at it, the value was down to about 5Ω each). Traditional carbon film resistors behave like a fuse, and open up once they've smoked a bit. I've run into this problem a few more times in other gear, when tantalum power supply bypass capacitors shorted. The current draw wasn't enough to blow the line fuse, but it did cook the custom $100 toroidal power transformers (I guess Rupert made his name designing audio circuits, not power supplies). GTD [/QUOTE]

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