LM3886 Single Supply Rail Transformer Setup - diyAudio
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Old 6th January 2006, 08:53 PM   #1
john65b is offline john65b  United States
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Default LM3886 Single Supply Rail Transformer Setup

I have a 600VA Transformer with dual secondaries (40V - 0V, 40V - 0V). Would like to conect 4 LM3886 (2 paralleled per channel) to this transformer, as it has 600VA.

With single full wave bridge rectifier at each seconday pair (40 - 0), and after 12,000uF caps, I should have around 55V - 0V.

Now, can I use the 55V - 0V to connect to the LM3886 in a single supply rail fashion instead of the +/-30V dual supply rail? In this way, I am not exceeding the 84V max, right?

I do not want to unwind/reverse wind the windings on the transformer to get a reduced DC voltage, as it would be easier just to get the correct transformer.

But thought this single supply rail setup may work...
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Old 7th January 2006, 03:13 AM   #2
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Single supply scheme will work...U need a midpoint voltage for biasing i/p stages as well as an output capacitor to isolate DC getting into speakers...Pls Refer data sheets..
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Old 7th January 2006, 12:04 PM   #3
minder is offline minder  China
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Old 7th January 2006, 02:00 PM   #4
john65b is offline john65b  United States
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Default Good deal, but...

The datasheet doesn't give a whole lot of info - unless I am not looking at the correct datasheet...a simple schematic is shown, and no indication of what the V+ range could be (I guessed it to be < 84 Volts)

At far as midpoint voltgae for biasing input, could you elaborate a bit more? Are you referring to the components off of Pin 7 (usually grounded for dual voltage operation?)

Looks to be a few more components for the single rail setup...anyone have any experience on how it sounds compared to dual rails?
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Old 7th January 2006, 03:27 PM   #5
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Default single supply

Your voltage will become the maximum figure specified by LM , if 84V it will be 84V/0 ground. The chip will loose a great deal of performance, single supply will tripple components add an out put capacitor to block DC and create a mid voltage point for bias, and the ability to parellel the chips effectivley will be lost.
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Old 8th January 2006, 11:08 PM   #6
Bazukaz is offline Bazukaz  Lithuania
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I prefer you modifying transformer , if it is possible , to get a dual supply one.
Electrolytic caps at output are bad for quality.
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Old 9th January 2006, 01:17 AM   #7
john65b is offline john65b  United States
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Default Forget Single Supply, how 'bout a Voltage Divider?

I am ready to deep six the Single supply idea, but what about a two - resistor voltage divider? I would have approximately (recified) 27V with a 55V input... I know it's a waste of energy, but hey...why not try...

Any dealings/opinions on this route? I can't see a reason as to why not...

I would really like to use these transformers, and +/- 27V and 300VA/channel would still work out fine.
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Old 9th January 2006, 01:31 AM   #8
lineup is offline lineup  Sweden
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Go ahead.
Single supply can be just as good as dual supply.

I think people are afraid of single supply for no valid reason.
Like they see some ghost .....
Single supply is better in some parameters than dual supply.
With several rails, there are more paths for garbage to enter circuit.

Was not long ago best amplifiers in world were single supply
with output electrolytic capacitors.
Designed by some wellknown world famous amplifier constructors.
And those electrolyts was not of the quality we have today.

I have built a super sounding headphone amplifier
with 12 volt single supply and using an 1.000uF axial ROE for output.
It is the best sound I have ever heard.
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Old 9th January 2006, 02:00 AM   #9
john65b is offline john65b  United States
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Default Voltage Regulator

I was looking into the LM317/337 voltage regulator setup and I have exceeded the Amp limit (1A) and the LM350 is only marginally better at 3A...

Oh well, looks like I need to get another transformer, as +/-55VDC won't work...

Any other thoughts before I go purchase another toroidal transformer?
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Old 9th January 2006, 02:22 AM   #10
Nordic is offline Nordic  South Africa
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Well, the voltage you are after depends on what the load of your speakers will be ...i.e. 4 ohm or 8 ohm....
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