Questions on building 3 channel LM3886 chipamp

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chevy2410

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Joined 2005
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.


Cheers,
Chevy
 
troystg

troystg

Member
Joined 2004
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.
 
troystg

troystg

Member
Joined 2004
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.. :xeye:

Edit:

It didn't take any spaces... Oh well.. Try to visualize a 6 position barrier strip... :D
 
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chevy2410

Member
Joined 2005
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
 
troystg

troystg

Member
Joined 2004
Fuses are in Yellow boxes...

I think it is MANDATORY to have a fuse immediately after chassis entry..

I do not disagree with Al but think individual tranny fuses are optional..

Wiring colors are standard US colors.. UK uses some crazy messed up colors like Yellow / green for ground, Blue for netrual, and Brown for hot.. :D :cool: :clown:

That was a JOKE!!!!

We will not have any cheap amp imitations here.. So... No flames.. :hot: :rolleyes:

I guess my ex-wife was right, I'm NOT funny.
 

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troystg

troystg

Member
Joined 2004
Dotted green line is OPTIONAL and it is to tie the chassis ground with the power supply ground. Again optional and I would NOT do it unless you actually used the CL60 in series..

Fuse for 3 x 120va = 3-5 amp slo-blo and 5-8 amp fast blo. If your using LM38xx chips you can delay the unmute to allow the pwr supply to fully charge before the amp starts playing.

Also you might add a small value high voltage cap accross the switch to help with arching and possible surges. .001uF 250volt ish...

I PERSONALLY do not fuse the individual transformers.. If ANYTHING develops problems the main fuse will blow. As it was intended.. Of course the whole amp will be down, but in MY OPINION if there is a problem in the amp I want it out of service anyway..
 
troystg

troystg

Member
Joined 2004
pinkmouse said:
Just an ordinary panel mount fuse, accessible from the outside of the case.
Click to expand...


Ah.. Just an ordinary fuse holder...

http://www.apexjr.com/images/APEXFUSEHOLDER.jpg

That's what my mains fuse is... The entire diagram is connectivity in IN the amp, but the components can be mounted anywhere.

And if you want to get "fancy" we can dual rectify and snub the pwr supply, add inline noise filter, and add CLC filters..
 
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chevy2410

Member
Joined 2005
That's what I'm currently using in my LM3886 2channel stereo setup. I bought that kit from Brian GT @ chipamp.com. Power supply is "snubbed". I do get a bit of humming when you put your ear right up against the loudspeaker. I don't hear it when music is playing, only when it's dead quite. Power is on, but no music. Now I'm kinda thinking it's because my P\S and tranny are not enlcosed away from the 2 amp chips. Any thoughts??


Chevy
 
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