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Old 29th March 2010, 08:06 PM   #1
srinath is offline srinath  United States
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Default Power supply for lm3886 chip amp

I bought this chip amp recently.
Excellent 2 X LM3886+6N11Tube Audio Amplifier Board - eBay (item 200449560702 end time Mar-22-10 19:52:08 PDT)

Now it asks for a +28V - 0 -28V and I am not finding that 28V exactly. Where do I get that type of transformer/power supply. Or will a higher voltage one work. If I were to buy a power supply and open it and mod it, what would be a good starting point ?

Now it also asks for a 6.3-8V ac in the pre amp board I guess for the tube stage. Is that simply a AC transformer into it, or do I still need to put it through a rectifier bridge ?

Thanks for all the help.

Cool.
Srinath.
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Old 29th March 2010, 08:14 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
a dual secondary 20+20Vac transformer or a centre tapped 40Vac transformer will give you about +-28Vdc dual polarity power supply.
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Old 29th March 2010, 08:24 PM   #3
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Quote:
Originally Posted by srinath View Post
I bought this chip amp recently.
Excellent 2 X LM3886+6N11Tube Audio Amplifier Board - eBay (item 200449560702 end time Mar-22-10 19:52:08 PDT)

Now it asks for a +28V - 0 -28V and I am not finding that 28V exactly. Where do I get that type of transformer/power supply. Or will a higher voltage one work. If I were to buy a power supply and open it and mod it, what would be a good starting point ?

Now it also asks for a 6.3-8V ac in the pre amp board I guess for the tube stage. Is that simply a AC transformer into it, or do I still need to put it through a rectifier bridge ?

Thanks for all the help.

Cool.
Srinath.
This, Antek - AN-4228 , should work for your 28-0-28 transformer.

The 6.3 VAC transformer is for the heaters in the tube. You should find something suitable here: Low Voltage Transformers - 6v to 7v
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Old 29th March 2010, 08:39 PM   #4
AndrewT is offline AndrewT  Scotland
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antek 4228 is a 28Vac transformer.
That will give about +-40Vdc to the chipamp. Far too high if the manufacturer is recommending +-28Vdc.
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Old 29th March 2010, 10:54 PM   #5
Bill_P is offline Bill_P  United States
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Quote:
Originally Posted by AndrewT View Post
antek 4228 is a 28Vac transformer.
That will give about +-40Vdc to the chipamp. Far too high if the manufacturer is recommending +-28Vdc.
The auction says that the DC supply is on the board, just connect AC 28v-0-28v to the board from a transformer.
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Old 29th March 2010, 11:52 PM   #6
srinath is offline srinath  United States
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Oh that is what that means ?
Great ... thanks no need for rectifier bridge then ? whooo whooo.

Then the 6.3-8V ac I guess another transformer.

Cool.
Srinath.
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Old 30th March 2010, 12:14 AM   #7
Bill_P is offline Bill_P  United States
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The text in the auction says just connect a transformer. When I looked at the auction, most of the pictures did not load so I didn't see where the rectifier is on the board. Check your board to see if the rectifier is there.
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Old 30th March 2010, 01:08 AM   #8
srinath is offline srinath  United States
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Default Too much $

Quote:
Originally Posted by Bill_P View Post
The auction says that the DC supply is on the board, just connect AC 28v-0-28v to the board from a transformer.
OK say I was a bigger cheapskate ... and wanted to yank the transformer out of some sorta trash pile ... what would contain such a transformer ? desktop PC ?

Now would it have to be a toroidal transformer, what about the, rectangular ones with that laminated steel core and what not ? yea a flyback type.

I can put it in a separate box if the vibrations will be bad for the chip amp.

Cool.
Srinath.
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Old 30th March 2010, 01:18 AM   #9
srinath is offline srinath  United States
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Default Assuming

Quote:
Originally Posted by Bill_P View Post
The text in the auction says just connect a transformer. When I looked at the auction, most of the pictures did not load so I didn't see where the rectifier is on the board. Check your board to see if the rectifier is there.
You give me too much credit ... like I can identify a rectifier if it jumped off the board and bit me in the nose.

Seriously I shouldn't be allowed within 100 ft of an amplifier and shouldn't be allowed to own a soldering iron, but hey, we're in a free country ... so here goes ... 2 min.

Cool.
Srinath.
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Old 30th March 2010, 01:25 AM   #10
srinath is offline srinath  United States
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OK there is a pair of massive capacitors - 50V 10,000 Uf caps, and what I would bet is some sorta rectifier bridge - 4 pin flat chip about 1 inch X 1.5 inch with 4 pins that are +, ~, ~ and - ...
The whole chip amp with the exception of the massive capacitors and that part of the board would fit in a small cigarette box size box. Like my other chip amp.
My bet, its a power supply ... bingo, thanks.
Cool.
Srinath.
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