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Old 28th January 2007, 07:08 PM   #1
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Default Questions on building 3 channel LM3886 chipamp

Hi all,

About 6months ago I put together a LM3886 stereo chipamp and it sounds awesome. Now I want to build a 3 channel monoblock amp. I would like to put all channels into one divided chassis. I am going to use 1 transformer for each amp. What would like to know is what size tor. transformer to use? On DD it was stated that a min. of 80VA would be Ok. I was thinking either 120VA or 160VA, but I'm not sure. Would it be better to use the 160VA over the 120VA?

Now since I'm building 3 separate amps into one chassis and using 3 separate power supplies, should each one have it's own plug going to the wall socket? Is there a way that I can connect all 3 and have one plug going to the wall? I really would like to have one power switch to turn on all 3 amps. Is that possible to do?

Lastly, since all 3 amps are in on chassis, is it better to use heatsinks to cool the chips or would a nice thick piece of copper or aluminum do the job? I have searched many threads, and can't really seem to find the info I'm looking for.


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Chevy
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Old 28th January 2007, 07:14 PM   #2
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If you tie the primaries of all the transformer mains to the Pwr switch you will have a tripple mono-bloc amp with a single common input cable, fuse, and switch. VERY common and routine.

If the chassis is heavy enough you can use that as the heat sink, but if your going to play it loud a good portion of the time your better off using a heat sink.. Metal bar is ok for coupling, but for extended loud volumes even it heats up unless it is tied to another cooling source.
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Old 28th January 2007, 09:07 PM   #3
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Sounds like that is what I will do.

As for transformer size what do you all recommend?



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Chevy
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Old 29th January 2007, 12:57 AM   #4
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Avel-Lindberg Inc
*
Input: 2 X 120Vac 50-60 Hz
3 3/4" Dia X 1 1/2" Tall
Output: 2 X 28.4V @ 2.67Amps over 150Va
$22.00ea


http://www.apexjr.com/miscellaneous.html

Plenty for all but commercial use...
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Old 29th January 2007, 11:42 AM   #5
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Is there any difference between the stereo power supply PCB and the mono block version?


Chevy
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Old 29th January 2007, 11:59 AM   #6
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Quote:
Originally posted by troystg
If you tie the primaries of all the transformer mains to the Pwr switch you will have a tripple mono-bloc amp with a single common input cable, fuse, and switch.
I'd fuse the traffos separately.
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Old 29th January 2007, 08:57 PM   #7
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Quote:
I'd fuse the traffos separately.
Then just have one wire to the switch.

What about PS PCB? Are the stereo version the same as the mono block version?


Chevy
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Old 29th January 2007, 11:42 PM   #8
troystg is online now troystg  United States
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For me personally I'd have a 6 position terminal strip with three lugs from the FUSED IEC, the hot lead out to the switch, and returning to feed the transformers.

| grnd | ntrl | empty | hot frm fuse | empty | Hot from switch|

| chs grnd | x-frmr neturals | empty | hot to switch | empty | X-fromr hots|


Now lets see how this looks posted..

Edit:

It didn't take any spaces... Oh well.. Try to visualize a 6 position barrier strip...
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Old 30th January 2007, 12:06 AM   #9
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Ok I'm trying to figure this out. I'm going to have 3 trannys and I should tie all the nuetrals together and all hot together of the 3 trannys? Then run a single wire, hot to hot on the switch and nuetral to nuetral. Now I want to put a fuse into the mix. What would be the amp to use? I currently am using a 3amp slo-blow in my 2channel Lm3886 setup. Would I be looking to get a 6amp for this setup?


Thanks so much,
Chevy
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Old 30th January 2007, 03:01 AM   #10
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Size of the fuse depends on the size of the trannys.. Inrush current will likely blow the fuse before SPL volume.

I will see if I can draw a wiring diagram..
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