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Old 20th June 2008, 06:56 AM   #1
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Default Power supply for LM3886

Hi,

Seems that I did something silly when purchasing my transformer. I seemed to have purchased a transformer rated at 35Vrms when I though it was 35Vpeak...oops. Anyways, just curious what you guys think I should to do bring down the 50Vdc I'm getting to the 35V that I want. Figure since the max the LM3886 can take is between 80 and 90 volts...100 might be a bit too much.

I was thinking of just using some high value resistors to step it down, or should I suck it up and get the correct rated transformer at 25Vrms? This is my first chip amp so I figure someone may have run into the same silly mistake and have a suggestion

Thanks!

Blair
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Old 20th June 2008, 07:29 AM   #2
frank1 is offline frank1  United Kingdom
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Default Re: Power supply for LM3886

Quote:
Originally posted by brconner
Hi,

Seems that I did something silly when purchasing my transformer. I seemed to have purchased a transformer rated at 35Vrms when I though it was 35Vpeak...oops. Anyways, just curious what you guys think I should to do bring down the 50Vdc I'm getting to the 35V that I want. Figure since the max the LM3886 can take is between 80 and 90 volts...100 might be a bit too much.

I was thinking of just using some high value resistors to step it down, or should I suck it up and get the correct rated transformer at 25Vrms? This is my first chip amp so I figure someone may have run into the same silly mistake and have a suggestion

Thanks!

Blair
Best thing is to return it if you can and swap for 25v.
Forget resistors... just not an option.

Last resort, take some turns off the secondaries. Torroidals are very easy to do in this respect.

Frank
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Old 20th June 2008, 09:35 AM   #3
owen is offline owen  United Kingdom
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How about a nice lightbulb or two...

Seriously though, dropping the necessary 15V is not a trivial matter. It can be done, using a fully regulated supply, but having tried one on a chip amp, personally, I didnt like the sound.

You can also 'adjust' the voltage out of a PSU using a CRC section at input, but again, the R will get hot - hence the lamp suggestion...

The primary problem is that as this is an AB amp (mainly B actually) the PSU draw is not constant.

A long winded way of saying, get the other thransformers....


Owen
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Old 20th June 2008, 01:44 PM   #4
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Yea, I figured the resistor thing probably wouldn't be the way to go. So I'll get the correctly rated transformer. Also random question, should I use a fuse or a circuit breaker?

Thanks for the help!

Peace,

Blair
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Old 21st June 2008, 07:57 AM   #5
eketehe is offline eketehe  Indonesia
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Hi Blair,
I got a same problem,
Maybe someone have knows if we can use LM338?
Brgds.
Eka
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Old 23rd June 2008, 06:46 AM   #6
thitis is offline thitis  Thailand
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Sell it awayr or keep this one for the other projects. Then, buy the right one for GC.

This is not your last DIY project, isn't it?

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Old 23rd June 2008, 06:52 AM   #7
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2 x 28 VAC is max healthy voltage and this will create around 2 x 40 VDC at low load.

35 VAC => forget it.
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Old 23rd June 2008, 01:48 PM   #8
eketehe is offline eketehe  Indonesia
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Quote:
Originally posted by eketehe
Hi Blair,
I got a same problem,
Maybe someone have knows if we can use LM338?
Brgds.
Eka
I mean something like shows here :

http://www.pedjarogic.com/gc/supplies.htm
and here?

http://www.tcaas.btinternet.co.uk/jlhnewps.htm

yes i have them from Nordic's.

Brgds.
Eka
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