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Old 2nd August 2013, 02:18 PM   #1
davym is offline davym  Scotland
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Default Chipamp lm3886

Hi all, I'm waiting for a stereo kit to arrive from chipamp and have been reading the build instructions again.

I now have a 300VA 2x22v transformer and hope to order a case on Monday, my plan is to follow the build plans to the letter and make a small power amp from the kit.

One thing puzzles me though, according to the build instructions the feedback capacitor is optional but shows it fitted to the boards in the picture. Is the lower DC offset this is supposed to achieve worth compromising sound quality and what is the possible consequences of leaving it out. Could its absence cause speaker damage?

Also I am considering using the tocos cosmos 20k pot with a source selector switch in a separate case with a very short interconnect to the power amp. My sources are MF - V-DAC & V-LPS which have low output impedance, can anyone see any problems with this arrangement and is there anything else I should consider before I start.

Cheers

Davy
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Old 2nd August 2013, 06:58 PM   #2
AndrewT is offline AndrewT  Scotland
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download the National datasheet.
Read from cover to cover twice.
Then ask about everything you don't completely understand.

Note:
National describe some components as optional.
In my view all these "optional" components are compulsory, especially for a beginner.
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Old 2nd August 2013, 10:08 PM   #3
davym is offline davym  Scotland
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lol, that's quite a paper and it doesn't answer my question. Anyway I don't need to bother with most of it as I am buying a kit and rely on someone else to design the circuit properly, I have confidence in the designer.

I'll fit the feedback cap, can't see it causing much loss in sound quality and if it does, I doubt i'll notice.

The data sheet shows a 10k pot, chipamp's build sheet shows a 25k. I could try to do the maths involved but i'm not good with maths so i'm going to fit a 20k pot and hope it's good enough. The last half decent power amp I built was a World Audio Design kel84 tube amp kit. Not one shock - electrically speaking anyway.
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Old 4th August 2013, 06:29 AM   #4
Mihkus is offline Mihkus  Estonia
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But check this thread
LM3886 without electrolytic feedback capacitor and (hardly) no DC offset voltage

He still needed a capacitor in hes feedback circuit, or else amp may go full retard (motorboating, oscillating)
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Old 4th August 2013, 12:39 PM   #5
davym is offline davym  Scotland
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Thanks Mihkus, if the boards ever turn up I will fit the cap, I am shocked it took five days to go from Atlanta to Miami! I'm going to go ahead and order the case tomorrow anyway, it's coming from China so I might get a working chipamp by Christmas at this rate!
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