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Old 23rd June 2015, 02:16 AM   #1
hifu is offline hifu  United States
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Default Noob question about power supplies for bi-amped system

Hi, I'm planning a 2-way bi-amped system using a mini-dsp. The amp box will contain a mini-dsp, preamp/tone control board, power supply(ies) and amp(s). I was advised to avoid running two different amp boards from one power supply. I'm expecting a crossover frequency around 500 Hz, so I'll need a bigger amp for the bass drivers than the midtweeters. Can I use two different power supplies, one for each amp, and use only one a/c input? How does that go together? I don't want to have to plug it in twice...

Sorry if my question is too basic--this is my first project involving electronics.
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Old 23rd June 2015, 02:39 AM   #2
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Yes, you can use just one ac line cord. Just keep safety in mind - fuse each amp, don't leave hot connections exposed, etc.
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Old 23rd June 2015, 12:03 PM   #3
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The approach that I used in my first chip amp was to use terminal blocks.

I'm also quite fond of heat shrink tubing.

Have a look in the sticky thread at the top of this forum, there are many good example of how to wire correctly.

Dave
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Old 23rd June 2015, 03:37 PM   #4
hifu is offline hifu  United States
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Ok thanks!
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Old 23rd June 2015, 06:04 PM   #5
frank1 is offline frank1  United Kingdom
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I have done exactly what you propose with 2x LM3886 per channel, all fed by one PSU.
Its fine.
The main problem is powering the MiniDSP which needs a 24v (max) supply.

The MiniDSP can also produce a really nasty switch-off noise before the amp smoothing discharge.

Frank
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Old 24th June 2015, 04:24 PM   #6
AndrewT is online now AndrewT  Scotland
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A circuit that gives you delayed ON and instant OFF does the job.
Since you know it is the source that is misbehaving you can use a mute/unmute between source and power amp to give silence at and during start up and instantly mutes at power OFF.
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Old 24th June 2015, 05:06 PM   #7
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For better crosstalk supression you should use two PSUs.
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Old 24th June 2015, 05:30 PM   #8
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You really don't need two complete separate power supplies. Using a single transformer of adequate power with one bridge rectifier and filter caps for each amplifier channel works just fine. Minimizing crosstalk is usually determined more by the wiring and layout than anything else.

Mike

Last edited by Michael Bean; 24th June 2015 at 05:33 PM.
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Old 24th June 2015, 06:50 PM   #9
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well..maybe a set of rectifier for every board.
i hazard anything more is just not worth it.
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Old 24th June 2015, 06:56 PM   #10
frank1 is offline frank1  United Kingdom
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Quote:
Originally Posted by Keruskerfuerst View Post
For better crosstalk supression you should use two PSUs.
Have you measured this?
How much is the crosstalk improved by having separate PSU's?

I would really like to know.

Allowing for the very high power supply rejection ratio, the "improvement" will be at best minimal and then only at very low frequencies where crosstalk is irrelevant.
I don't have any "noticeable" crosstalk due to a common power supply in my amp.

Frank
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