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-   -   Smaller transformer for lm3886 amp? (http://www.diyaudio.com/forums/solid-state/13404-smaller-transformer-lm3886-amp.html)

ted 5th April 2003 04:30 PM

Smaller transformer for lm3886 amp?
 
OK, I made an LM3886 amplifier and worked out the bugs, and is powered by a large transformer, 400watts, making the whole thing big and heavy. So I was thinking it may be interesting to reduce the size/weight by doing something like what Carver did since for a lot of power, the transformer sure seems small when I compare a Carver 1.5 with something like a Phase Linear 400 transformer.

So the question is. Is there something special about a Carver type transformer? Since a triac is used before the transformer, to switch power on/off, can the transformer be connected directly to the mains? Additionally, and most important, can an off the shelf transformer be tricked to have similar properties, if there are any special properties?

Just an idea....
Thanks.

Dj BASS AMP 5th April 2003 08:09 PM

u can us in a switched transformer....

very small

ted 13th April 2003 12:00 AM

I assume that when you say "switched transformer", that it's a "flyback" or buck-boost derived switchmode converter technique?

The thing that sent me down the trail was that most switchmode converters run from a ~20Khz->50Khz oscillator, and not 60Hz as I assume that a Carver does since I do not find the typical forementioned switching frequency? But obviously Carver got it to work.

Since I have little desire to design a switchmode supply running at 60Hz, Iíll just have to find a better way to optimize the power supply requirements of my lm3886 amplifier.

Thanks for the information.
:)

trwh 13th April 2003 09:46 AM

Ted, have a read through of this thread:

http://www.diyvideo.com/forums/showt...5&pagenumber=1

I think 400W is overkill for a 2xLM3886 amp.

Nisbeth 13th April 2003 05:20 PM

If you look at the datasheet for the 3886, i think you'll find that the max. consumption is ~150-160W (per chip), so a 300VA should be acceptable for all practical purposes. Since you're (presumably, hehe) only playing music and not test tones at full amplitude, I think you can get away with a bit less than that, say 220-250 VA. You might run out of power a bit earlier, but for normal listening levels it should be OK.

/U.

ted 13th April 2003 10:58 PM

I use a 400 watt transformer since it's powering 5 X lm3886 where the rail voltage is ~38+/- volts. I get about 50watts/ch into 8 ohms with all 5 channels running. I know the transformer is to small if I were to use 4-ohm speakers, a.k.a. why I was thinking of a smarter power tub.

I have been sufficiently discouraged in constructing a 60hz switchmode supply, so I am now thinking of attacking the weigh / size by reducing heat sinking. The reduced heat sinking would be theoretically possible if I use an unused tap on the transformer (30vac / ct [20vdc +/-]]). Then feed the ln3886's with the lower supply, then if let's say there is 5v on the output, kick in the presently used 38+- volt rails. To keep things really simple, any one of the lm3886's, that exceed 5v's, would cause all the others to see the larger supply voltage also.

I know lots of amplifiers that use this trick, but I am not sure how much a lm3886 would like the dynamic voltage switch.

Thanks for all the advice.

Christian 14th April 2003 02:41 PM

Quote:

Originally posted by ted
I use a 400 watt transformer since it's powering 5 X lm3886 where the rail voltage is ~38+/- volts. I get about 50watts/ch into 8 ohms with all 5 channels running. I know the transformer is to small if I were to use 4-ohm speakers, a.k.a. why I was thinking of a smarter power tub.

I have been sufficiently discouraged in constructing a 60hz switchmode supply, so I am now thinking of attacking the weigh / size by reducing heat sinking. The reduced heat sinking would be theoretically possible if I use an unused tap on the transformer (30vac / ct [20vdc +/-]]). Then feed the ln3886's with the lower supply, then if let's say there is 5v on the output, kick in the presently used 38+- volt rails. To keep things really simple, any one of the lm3886's, that exceed 5v's, would cause all the others to see the larger supply voltage also.

I know lots of amplifiers that use this trick, but I am not sure how much a lm3886 would like the dynamic voltage switch.

Thanks for all the advice.


Hi Ted!
I'm building a 5 channel power amp using the LM3886 chips to! Do you have any pics or more info on your'e amp?
Are you using it in a surround system?

/Chris


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