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Old 2nd August 2013, 05:10 AM   #2471
Ulis is offline Ulis  Russian Federation
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bottom side PCB

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Old 2nd August 2013, 06:15 AM   #2472
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Quote:
Originally Posted by Rainwulf View Post
35 volt caps? What rails are you running to the lm3886?
Supply voltage +/-28 Volt
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Old 2nd August 2013, 06:20 AM   #2473
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Why not the full amount for the chip? 37+-

I know with the lm3875 with driving 4 ohms load you have to drop the rails otherwise the protection kicks in, but i didnt think the lm3886 had that issue.
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Old 2nd August 2013, 07:16 AM   #2474
Ulis is offline Ulis  Russian Federation
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Supply voltage +/-25~28 Volt - empirically identified for better sound

Sorry for my bad English
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Old 2nd August 2013, 07:54 AM   #2475
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Quote:
Originally Posted by tommy_o View Post
Sorry, I'm probably just dim, but where is the buffer on that PCB? Nice looking boards though. If you have a thread with other info, can you just link that so I dont pollute the photo gallery?

Cheers!
I could see no buffer also??? but after a re-look at the underside and wondering why so many electros on the top side... ... yes some sort of chip buffer for a chip amp??? Does a chip amp need a buffer??

Last edited by mhouston; 2nd August 2013 at 07:56 AM.
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Old 3rd August 2013, 04:19 PM   #2476
tommy_o is offline tommy_o  United States
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Quote:
Originally Posted by mhouston View Post
I could see no buffer also??? but after a re-look at the underside and wondering why so many electros on the top side... ... yes some sort of chip buffer for a chip amp??? Does a chip amp need a buffer??
It's probably too subjective to say yes or no, but my LM1785 sounded much better when I built a economical B1 Buffer (B1 buffer --> volume pot --> LM1785) driving a pair of BR Mark Audio CHR70s. A B1 buffer clone is so cheap, you might as well build one and see This is the one I built, which includes toner transfer images. PM me if you want more info (or start a new thread).
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Old 3rd August 2013, 05:28 PM   #2477
Ulis is offline Ulis  Russian Federation
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Quote:
Originally Posted by tommy_o View Post
It's probably too subjective to say yes or no, but my LM1785......
Maybe LM1875?
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Old 3rd August 2013, 11:08 PM   #2478
benb is offline benb  United States
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I think another part of the secret is the (inverted) part here:
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Originally Posted by Ulis View Post
LT1122(buffer)+LM3886 (inverted)
Using a chip amp (or op amp) in inverted mode (the positive input goes to ground, and the signal is put at the resistor going to the negative input that would otherwise go to ground (through an electrolytic cap). There's been discussion that this runs with lower distortion than non-inverting mode. It certainly seems reasonable, as the LTP input transistors don't have a varying voltage on them in inverting mode (or it's orders of magnitude less), and thus don't add any distortion that might be added from them moving up and down with the input signal in the noninverting mode.

The input and feedback resistors mush be fairly low to keep noise down, so the inverting mode has a much lower impedance than noninverting mode. Thus a buffer is needed to drive the circuit from most audio sources, which expect a higher input impedance.

This makes the whole amplifier inverting, but that can be fixed by swapping the speaker wires.
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Old 4th August 2013, 05:34 AM   #2479
tommy_o is offline tommy_o  United States
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Quote:
Originally Posted by Ulis View Post
Maybe LM1875?
Youch, I fat-fingered that one. 'LM1875' it should have read.
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Old 6th August 2013, 12:09 AM   #2480
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Just a little stereo amp using 4 tda2030a chips. Powered by an old 2.5 amp radio shack 12v power supply. Sounds pretty good.


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