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Old 2nd March 2011, 12:37 AM   #1
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Default LM3886 four channel amp transformer?

Hi, I'm using two stereo chipamp.com kits to build a four channel amp. Is there any reason I cannot use a single transformer to power both stereo kits?
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Old 13th March 2011, 05:49 AM   #2
Francec is offline Francec  Australia
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No. Just make sure the VA of the transformer is, more than, enough.
From my calculations, 4 x 70 = 280W so I would go for a 400 or 500 VA Tranny, bigger IS better.

Having said that, you probably won't ever use full power BUT bigger is better for regulation.

Frank

Last edited by Francec; 13th March 2011 at 05:50 AM. Reason: Correction
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Old 13th March 2011, 01:38 PM   #3
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Frank, thanks for the reply. I asked because I originally assumed this would be OK but blew fuses when I tried to power it up (and eventually blew rectifiers and ruined the one power supply). I still haven't figured out what went wrong, but I know that one side of the kit worked fine once disconnected the other side. This is probably because of a short somewhere, its just that I can't find it to save my life.

The xformer is a robust 330VA so, in theory, it should be plenty. I figure, one amp will be driving frequencies above 300Hz and the other will handle the rest (biamp setup). It's unlikely that I'll be running full power on both amps at any point in time. Even if I do, 330 should still cover it. I'll have to check voltages during power testing just to see.

Brian

Quote:
Originally Posted by Francec View Post
No. Just make sure the VA of the transformer is, more than, enough.
From my calculations, 4 x 70 = 280W so I would go for a 400 or 500 VA Tranny, bigger IS better.

Having said that, you probably won't ever use full power BUT bigger is better for regulation.

Frank
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Old 14th March 2011, 12:03 AM   #4
Francec is offline Francec  Australia
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Brian,
I'm using a 160VA transformer for a tri-amp setup, ie, driving three LM3886 amps. It does it without any problems but I will get bigger toroidal when funds permit.

I certainly would go over the PCB meticulously because one misplaced component is all you need. Are the rectifier connections correct?

Frank
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Old 21st March 2011, 12:00 AM   #5
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Frank, thanks for the reply. I checked everything and found nothing wrong. I ended up buying another stereo kit and built it this weekend. All four channels are working now...

...but, I have a bad hum I need to track down. It only occurs when I have all four input channels connected. If I only connect two inputs, it's quiet as it should be. I have some sort of ground loop but haven't been able to track it down as of yet. A MiniDSP is upstream.

Brian
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Old 21st March 2011, 12:15 AM   #6
krips is offline krips  Canada
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Hey there. I have a 800VA 20v transformer that i believe is suitible for that chip from Antek if you are interested.
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Old 21st March 2011, 12:24 AM   #7
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Wow, that's probably a bit more than I need but thanks for asking
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