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SamV 
Old Croc 
Joined: 21 October 2008 Location: London Status: Offline Points: 8711 |
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 Posted: 20 November 2017 at 10:07pm |
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Right so I need the following:
+18V @ 5A DC -18V @ 5A DC +12V @ 4A DC +48V @ 0.75A DC I have found an A&H PSU that will do + / - 17.5V = 16A +48V 1.6A +12V 6.3A Reckon that will work fine or will the the 0.5v make a noticeable difference?
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kedwardsleisure
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Joined: 20 January 2009 Location: Staffordshire Status: Offline Points: 4947 |
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Posted: 20 November 2017 at 10:56pm |
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I doubt it, though some desks have sense wires running from the desk to the PSU to take care of any volt drop in the cable and/or improve ripple rejection, if a desk proves susceptible. Something to look out for.
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Kevin
North Staffordshire |
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SamV
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Joined: 21 October 2008 Location: London Status: Offline Points: 8711 |
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Posted: 20 November 2017 at 11:09pm |
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Ah good to know :)
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studio45
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Joined: 16 October 2007 Location: United Kingdom Status: Offline Points: 3864 |
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Posted: 21 November 2017 at 4:00pm |
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I'm sure it will be just fine. The +/- rails are to feed opamp chips. Modern opamps are highly standardised in terms of power needs, and will usually operate safely from anything between +/6v and +/-17.5v. The maximum voltage they can withstand between power pins without damage is usually quoted as 40v, with maximum recommended supply being 35v. The more voltage you can supply them with, the more output swing they can provide. Given that in a desk they are not normally required to swing more than about 1.4v RMS, you can see that variation of 1v on a nominal 18v supply won't really be a factor.
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Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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Earplug
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Joined: 03 January 2012 Location: Europe Status: Offline Points: 7216 |
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Posted: 21 November 2017 at 6:48pm |
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The +/- 18V is most probably dropped to +/- 15V inside the desk via zeners or linear regulators. I´ve been working on a lovely old Soundtracs Quartz and they have zeners + 'protection resistors' on every channel.
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Earplugs Are For Wimps!
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tonysparks69
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Joined: 27 October 2017 Location: Doncaster Status: Offline Points: 16 |
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Posted: 21 November 2017 at 9:20pm |
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The Allen & Heath PSU will work fine. The = & - supplies at 17.5V 16A are running at 8A per rail and if you measure the voltage it is unlikely to be exactly 17.5V anyway.
You will need a connecting plug though to match your desk, and double check the wiring before plugging it in. |
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SamV
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Joined: 21 October 2008 Location: London Status: Offline Points: 8711 |
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Posted: 21 November 2017 at 11:14pm |
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Yep thats a deffo
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