Using the LM3886/LM3875/LM1875 for a HT amp set up - diyAudio
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Old 31st March 2006, 01:51 PM   #1
diarav is offline diarav  India
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Default Using the LM3886/LM3875/LM1875 for a HT amp set up

Hi,
I am planning to make a Home Theatre set up complete with Satellite speakers and subwoofers. Deciding to start with the amp, I am planning to use either of the LM3876 / LM1875 / LM3886 for the Power Amp for each of the 5 channels + 1 subwoofer. Most of the designs would be from the ESP site.

Which (LM3886 / LM1875 / LM3875) in your opinion is good for subwoofer / satellite power amp ?

Can I use the power amps directly without having any preamps - my input would be from my PC soundcard. Or is it not recommended ?

How much transformers would I need for 6 channels? 3 TFRs with 6 rectifier units?

For two channel inputs, I am planning to use Rod Elliotts Surround sound decoder.

Any opinions / ideas are welcome.

Thanks in advance.

Din
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Old 31st March 2006, 08:18 PM   #2
enter is offline enter  Greece
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Have a look at my amp: My "audiophile" LM3886 approach

and : My "audiophile" LM3886 approach

I think the rev c or rev a is perfect for the front-center channels.
For the rear some gainclones will do the job
You can see my subwoofer and amp here: Project Sub+Plateamp Finished

I am very pleased, espesialy with movies
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Old 31st March 2006, 09:24 PM   #3
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Well for simplicity you can't beat the LM1875, sounds pretty darn good too, but you had better have some really efficient speakers as it doesn't have the output you need to get the true theater dynamics. The Lm3875 on the other hand is a pretty nice chip, it is what I have used in my own setup, easy to design around and good output power, but watch your load impedances.
The LM3886 IMHO might be the best choice though, as it has very similar sound to the 3875, but can handle lower impedance loads, making it a bit more compatible with a range of speakers. As for a preamp, you really shouldn't need one if you are powering it from a PC soundcard, but you might want to buffer the inputs with something simple like a BUF634 from Texas Instruments. Just give yourself enough gain in the amp section and you'll be perfectly happy. For the subwoofer section consider paralleling or bridging a pair of LM3886's (or use an LM4780) this will give you plenty of thump. As for a transformer I am using a 750VA 24-0-24 for the five channels and a seperate 160 VA 20-0-20 for the the sub amp (220VA would probably be a better choice for this). I haven't found it lacking in the output department. You can get as fancy as you like with the power supply. The "snubberized" supplies seem to be the flavour of the month, I've listened to regulated, unregulated and the snubberized...I really don't have a favourite...but it is probably best to start really simple a power supply is really easy to replace/tweak.

Have fun building!

G.
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Old 1st April 2006, 04:29 PM   #4
diarav is offline diarav  India
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Thank you for your inputs.

enter:
Thanks for sharing the thread and pictures. What exactly is rev a, rev c? I get a lot of threads while doing a search, I find it difficult to pin down the actual answer.

Gcollier:
Thanks for the tips. Yes, as you suggested I was also considing constructing the sub amp separately.
As for the transformer, from your answer I assume one could use a single high VA transformer for 5 channels (with separate rectifier units). Considering its size, I could house it separately, if required.
And yes, I might stick to the LM3886, as I had almost decided that before posting the original thread.

I post any progress I make on this.

Regards
Din
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Old 2nd April 2006, 10:33 AM   #5
enter is offline enter  Greece
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Hi

Rev a and rev c is basically the same design from maurapenasa.
Russ White made the rev a modification to rev c which is 2 mono boards.Russ white also sells some very nice kits of this amp, you can see here: http://www.twistedpearaudio.com/
Go and read as many posts as you can from this thread ( My "audiophile" LM3886 approach ) and you will find everything about this cheapamp.
I can give you the schematics-layaouts if you like which i have in pdfs but if you search the thread you will find them and learn about it
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Old 2nd April 2006, 04:43 PM   #6
diarav is offline diarav  India
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Thanks for the reply, enter.

I will take a look at the thread.

Thanks
Din
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