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Old 20th May 2006, 10:46 PM   #1
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Question Lm3886t

Hi there! I got two LM3886 and was wondering were can i find a schemtaic for a good audio amp. Since im a beginner and pretty much dont have a clue , any advice is highly appreciated!! Thank you !

Mike
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Old 20th May 2006, 10:56 PM   #2
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Try the Chipamp forum @ diyaudio.com

You could start with the reference design in the spec sheet to get your feet wet. Decibel Dungeon also has a lot of info together.
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Old 21st May 2006, 04:49 PM   #3
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Just biult a pair of these lasr Saturday. Point to point took about 3 hours. Works great!!! The schematic is right out of BrianGT's manual.

Note: I did not use the Zobel network or
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Old 21st May 2006, 05:00 PM   #4
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PS. I also did not use Cm or switch. Just wired Rm striaght to V-.
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Old 21st May 2006, 05:10 PM   #5
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Quote:
Originally posted by davidlzimmer
PS. I also did not use Cm or switch. Just wired Rm striaght to V-.
Hi,
I would like to ask , what is purpose of R1, R2 in the circuit ? Seems of no use to me.

Regards,
Lukas.
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Old 21st May 2006, 09:44 PM   #6
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Disclaimer: I don't know. Hopefully the more knowledgeable will jump in.

As far as R1, I was curious myself. While bench testing, I temporally bypassed R1 and noticed no difference.

R2 is in every chimpamp circuit. I've always assumed it set up a reference voltage like bias.
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Old 21st May 2006, 10:00 PM   #7
Bazukaz is offline Bazukaz  Lithuania
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Hi,
I think that something is missing here (probably DC blocking cap).In that case , R2 would make a sense. Now it is just a paralell resistor to volume control potentiometer. However , this should change anything at all...

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Lukas.
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Old 22nd May 2006, 01:17 AM   #8
dfdye is offline dfdye  United States
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Coupling/input caps aren't necessiary for these circuits in my experience. If you want to add one in, be sure to make it pretty high quality since it can make a substantial impact on the sound of the amp.

It makes sense to me that R1 and R2 are there to set up an input voltage divider. R1+Rin makes the first stage, but on looking at it again, it is a little wierd. . .
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Old 22nd May 2006, 01:29 AM   #9
dfdye is offline dfdye  United States
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Oh yea, back on topic, in addition to the gainclone-esque circuits, I like the Linkwitz LM3886 implementation(attached). I am powering mine with +/-30V rails with 4,400uf per rail using a dual mono unregulated PSU. This is probably a little overkill, and the amps definitely work with 2,200uf/rail/chip, but I had a surplus of 2,200uf caps laying around, and one thing led to another. . .
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Old 22nd May 2006, 01:37 AM   #10
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Determination of whether the input coupling (DC blocking) cap is needed depends on the DC offset (or lack thereof) from the prior stage.

Prior stage is commonly the source, or a buffer/pre/etc. Many have coupling caps on their outputs already, in which case another coupling cap on the power amp stage input is redundant. Some (especially DIY), "might" not have that output coupler cap, so before one goes amplifying the signal to power amp levels it is important to measure for the DC offset (L to Gnd, and R to Gnd) if there is any uncertainty.
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