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Old 14th December 2011, 09:59 AM   #1
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Default Power supply for balanced input stereo amplifier

I am currently working on a stereo balanced input amplifier project and wanted to share with you an idea I had about power supply.
It is based on following assumption:
- most of the power if used to produce low frequencies
- low frequency signals are mainly the same on two channels
So the idea is to cross the input and output of one of the amplifiers and use the same power supply for both, so that when an amplifier drags current on one supply rail the other drags current on the other rail.
The result is:
- smaller caps
- smaller tranformer
- smaller ripple
- smaller radiation

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Old 14th December 2011, 11:57 AM   #2
AndrewT is offline AndrewT  Scotland
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A properly designed balanced amplifier will have a constant current draw on the power supply.
Look up EUVL's F5x for an example.
This constant current draw is very rare among all the various topologies used for amplification.
This constant current draw does give significant performance improvements.

A balanced input for an amplifier does not approach the specification requirements for a constant current draw amplifier.
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Old 14th December 2011, 12:20 PM   #3
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Constant current ? That could be possible, even for balanced input, only in case of class A amplifier. My purpose was more generaly about class AB/B amplifiers.
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Old 14th December 2011, 12:35 PM   #4
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AndrewT View Post
.............This constant current draw does give significant performance improvements.

A balanced input for an amplifier does not approach the specification requirements for a constant current draw amplifier.
Quote:
Originally Posted by SMourareau View Post
... My purpose was more generally about class AB/B amplifiers.
then you are chasing ghosts as another Member puts it.
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Old 14th December 2011, 12:43 PM   #5
CBS240 is offline CBS240  United States
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A balanced output class AB amplifier has a constant current draw...like this one.
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Old 14th December 2011, 12:53 PM   #6
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You can take it all ways you want. balancing input or output or both you will never have a constant draw current with something else than a pure class A amplifier.

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Old 14th December 2011, 12:54 PM   #7
godfrey is offline godfrey  South Africa
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Quote:
Originally Posted by SMourareau View Post
...So the idea is to cross the input and output of one of the amplifiers and use the same power supply for both, so that when an amplifier drags current on one supply rail the other drags current on the other rail.
The result is:
- smaller caps
- smaller tranformer
- smaller ripple
- smaller radiation
Yes, that should give less supply ripple especially with low bass notes. I seem to remember this being done in some commercial amp, might have been NAD?

Starting with balanced inputs certainly makes it easier to reverse one channel.
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Old 14th December 2011, 01:13 PM   #8
AndrewT is offline AndrewT  Scotland
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Originally Posted by CBS240 View Post
this one.
"this" took me to post66 & the zip in the next.
Where is the schematic?
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Old 15th December 2011, 12:31 AM   #9
CBS240 is offline CBS240  United States
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I misspoke about constant current draw, I meant equal current draw resulting in a zero difference in current flowing from zero volt node (gnd) to each PS cap bank. this is the VAS section, each +/-10V output is for two seperate output followers for BAL output.
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Old 15th December 2011, 04:40 AM   #10
ontoaba is offline ontoaba  Indonesia
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Quote:
Originally Posted by SMourareau View Post
So the idea is to cross the input and output of one of the amplifiers and use the same power supply for both, "so that when an amplifier drags current on one supply rail the other drags current on the other rail".
The result is:
- smaller caps
- smaller tranformer
- smaller ripple
- smaller radiation

Regards
That was bridged amplifier.

-smaller transformer = not really. The power drawn is just same, even bigger because more drop voltages on amplifier (less efficiency). You may get fewer copper needed (smaller secondary cables for winding, because for same power, Vout is doubled, current is half, but power is same.
-smaller caps = yes, for half current like above.
-smaller ripple = no, because the capacitor is also smaller.
-smaller radiation = ??? what radiation.

Remember, with same current, same voltages, same power, the load resistance is 4:1 for series and paralelled.
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