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Old 13th January 2019, 06:20 AM   #1
Evenharmonics is offline Evenharmonics  United States
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Default Amp Kit from ebay

I just finished a UPC1342V + NJW0302G/NJW0281G stereo class AB power amplifier board from ebay. It's all in one board (power supply, speaker protection & amp). It was cheap so I decided to build it for my surround sound speakers. It works but FFT measurement (yellow graph) looks odd.

Is anyone familiar with the distortions shown between harmonics and what's causing it? My other amp from ebay (LJM L20SE kit, class AB) shown in red doesn't have it so I'm wondering. Thanks in advance.
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File Type: jpg R-FFT.jpg (363.6 KB, 466 views)
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Old 1st June 2019, 07:13 PM   #2
Tournesol is online now Tournesol  Belgium
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Quote:
Originally Posted by Evenharmonics View Post
I just finished a UPC1342V + NJW0302G/NJW0281G stereo class AB power amplifier board from ebay. It's all in one board (power supply, speaker protection & amp). It was cheap so I decided to build it for my surround sound speakers. It works but FFT measurement (yellow graph) looks odd.

Is anyone familiar with the distortions shown between harmonics and what's causing it? My other amp from ebay (LJM L20SE kit, class AB) shown in red doesn't have it so I'm wondering. Thanks in advance.
You, who on another thread, spend your time giving lessons endlessly to seasoned professionals in the most aggressive of ways, really, you do not know the source of odd harmonics in amplifiers ?
It is something teached in first year of any electronic schools.
You, who spend your time shouting that only the measures have a meaning in audio, you do not know how to interpret them and act accordingly ?
Fortunately, ridicule do not kill !

The solution is childish, and I would have helped you if my mother had not forbidden me to feed the trolls
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Last edited by Tournesol; 1st June 2019 at 07:26 PM.
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Old 1st June 2019, 07:33 PM   #3
Mark Tillotson is online now Mark Tillotson
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Quote:
Originally Posted by Evenharmonics View Post
I just finished a UPC1342V + NJW0302G/NJW0281G stereo class AB power amplifier board from ebay. It's all in one board (power supply, speaker protection & amp). It was cheap so I decided to build it for my surround sound speakers. It works but FFT measurement (yellow graph) looks odd.

Is anyone familiar with the distortions shown between harmonics and what's causing it?
Think its all power supply harmonics, multiples of 120Hz?
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My other amp from ebay (LJM L20SE kit, class AB) shown in red doesn't have it so I'm wondering. Thanks in advance.
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Old 1st June 2019, 08:42 PM   #4
Evenharmonics is offline Evenharmonics  United States
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Quote:
Originally Posted by Tournesol View Post
You, who on another thread, spend your time giving lessons endlessly to seasoned professionals in the most aggressive of ways, really, you do not know the source of odd harmonics in amplifiers ?
It is something teached in first year of any electronic schools.
You, who spend your time shouting that only the measures have a meaning in audio, you do not know how to interpret them and act accordingly ?
Fortunately, ridicule do not kill !

The solution is childish, and I would have helped you if my mother had not forbidden me to feed the trolls
I thought I was happy to be on your ignore list. I wonder how my post was visible to you. Also, you must not understand the phrase "distortions shown between harmonics"
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Old 1st June 2019, 08:43 PM   #5
rayma is offline rayma  United States
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Originally Posted by Tournesol View Post
The solution is childish, and I would have helped you
if my mother had not forbidden me to feed the trolls
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Old 2nd June 2019, 05:43 AM   #6
Ian Finch is online now Ian Finch  Australia
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There are several kits meeting the description. One that I found may not be the same as yours but its clear that this one will have problems with rectifier harmonics anyway, as yours does, since the power supply and its switching AC currents are so close to the input stage in the uPC1342.

It's not a good design and probably was never measured critically for performance. The DIY market in China is intensely competitive and underhanded - so buyer beware.
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File Type: jpg UPC1342 kit.jpg (90.7 KB, 315 views)
File Type: png uPC1342A.PNG (762.0 KB, 279 views)
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Last edited by Ian Finch; 2nd June 2019 at 06:07 AM. Reason: add 2nd pic
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Old 2nd June 2019, 07:31 AM   #7
scottjoplin is offline scottjoplin  Wales
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I bought a cheap stereo chip amp from China, the bridge and smoothing caps were between the chips, moved them off board, vast improvement
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Old 2nd June 2019, 09:31 AM   #8
huggygood is offline huggygood  France
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Old 2nd June 2019, 03:36 PM   #9
N101N is offline N101N
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Quote:
Is anyone familiar with the distortions shown between harmonics and what's causing it? My other amp from ebay (LJM L20SE kit, class AB) shown in red doesn't have it so I'm wondering. Thanks in advance.
I keep asking myself the same question. That moiety shown in yellow is almost certainly an algorithmic freak. It should definitely not be there. Very confusing indeed.
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Old 2nd June 2019, 03:56 PM   #10
Evenharmonics is offline Evenharmonics  United States
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Quote:
Originally Posted by Ian Finch View Post
There are several kits meeting the description. One that I found may not be the same as yours but its clear that this one will have problems with rectifier harmonics anyway, as yours does, since the power supply and its switching AC currents are so close to the input stage in the uPC1342.

It's not a good design and probably was never measured critically for performance. The DIY market in China is intensely competitive and underhanded - so buyer beware.
Thanks for the technical input. It's the one on the right. It was very cheap and I bought it as an experiment.
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