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Chip Amps Amplifiers based on integrated circuits

Neurochrome LM3886DR Build
Neurochrome LM3886DR Build
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Old 3rd September 2017, 08:31 AM   #251
Mixi is offline Mixi  Europe
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So i can attach the ground to the baseplate, right? It doesnt have to go to one of the outer panels as the baseplate will be connected to them anyways.
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Old 3rd September 2017, 09:10 AM   #252
scottjoplin is offline scottjoplin  Wales
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Not the best, on back panel close to inlet is recommended. What enclosure are you using?
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Old 3rd September 2017, 10:42 AM   #253
Mixi is offline Mixi  Europe
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ok, i can take it to the back panel right next / above the mains inlet. thanks of the advice!

i'm using a galaxy 2u chassis with additional base plate:

Galaxy 2U

Base Plate
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Old 3rd September 2017, 01:14 PM   #254
jan.didden is offline jan.didden  Europe
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Originally Posted by Mixi View Post
thanks tom for the debugging suggestion. I'll try to finish the enclosure as soon as possible and if the noise is not gone by then i'll try further debugging.

my build process has slowed down a bit due to a shoulder injury but i'll eventually get there....
If you can hear it, it is probably not rf interference ;-)

Another thing to realise is that with just a few mV input your S/N ratio is relatively low giving the impression of highish noise, which will disappear with 'normal' listening levels.

Jan
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Old 3rd September 2017, 04:32 PM   #255
tomchr is offline tomchr  Canada
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If you can hear it, it is probably not rf interference ;-)
Unless the RF is demodulated by a diode junction somewhere and turned into bouncing DC. Happens all the time with GSM cell phones. The RF bursts of the GSM signal can cause the DC offset of an input stage to bounce which results in the BRRZT-BRRZT that you hear in the speaker as a result. That's one of the many reasons I put the RF filter on the input of the LM3886DR.

I recall the design review for the LMV851 EMI hardened opamp to be rather interesting. The applications team had fun trying to "break" the chip. You can see the results, including the cell phone call I mentioned above, on page 16-17 of the LMV85x data sheet.

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Another thing to realise is that with just a few mV input your S/N ratio is relatively low giving the impression of highish noise, which will disappear with 'normal' listening levels.
True. You can't move electrons without causing noise. That said, with a medium-efficiency speaker (say 85-87 dB) an LM3886 amp should not generate enough noise to be bothersome at the listening position. I measure 43 uV RMS 20Hz-20kHz (unweighted) on the output of the LM3886DR.

Tom
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Old 10th September 2017, 06:27 PM   #256
Mixi is offline Mixi  Europe
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i finally finished the enclosure for my 3886dr project last night. to my great satisfaction the noise problem i had earlier disappeared almost entirely once the enclosure was finished and the ground was securely connected. what remains is tiny amount of white noise which is only audible if i hold my ear against the tweeter and listen very hard.

i'll post more later - for now i am very happy the way it turned out.
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Old 10th September 2017, 06:35 PM   #257
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Congratulations Have you ever held a shell to your ear and heard the sea?......
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Old 10th September 2017, 06:38 PM   #258
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uhm .... ok, i'll shut up about noise now :-)
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Old 10th September 2017, 06:41 PM   #259
scottjoplin is offline scottjoplin  Wales
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How about some pictures, we like pictures too
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Old 10th September 2017, 08:20 PM   #260
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by Mixi View Post
i finally finished the enclosure for my 3886dr project last night. to my great satisfaction the noise problem i had earlier disappeared almost entirely once the enclosure was finished and the ground was securely connected. what remains is tiny amount of white noise which is only audible if i hold my ear against the tweeter and listen very hard.

i'll post more later - for now i am very happy the way it turned out.
Awesome! Yep. That noise you're hearing is the 40 uV RMS (unweighted) of the LM3886 along with whatever acoustical noise is in your head. It's normal.

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uhm .... ok, i'll shut up about noise now :-)
Sounds like a plan. I'm glad the amp worked out well for you.

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Originally Posted by scottjoplin View Post
How about some pictures, we like pictures too
Yes, please. I'm curious what you ended up with.

Tom
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