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Lower chipamp distortion through PCB routing
Lower chipamp distortion through PCB routing
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Old 23rd June 2018, 12:06 AM   #21
alexcp is offline alexcp  United States
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Lower chipamp distortion through PCB routing
Quote:
Originally Posted by 00940 View Post
I attach a pic of my amp at the same output (25vp, 50vpp) to give you an idea of what could be hiding under the noise floor. But it's so down under...
What is you measurement setup?
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Old 23rd June 2018, 01:34 AM   #22
00940 is offline 00940  Belgium
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A focusrite 18i8 and a dedicated load. It's very similar to your setup actually, the load is kind of a simplified version of the Millet interface.

I use a scope to check the amp output levels. Most measurements are made so that the input going into the 18i8 is at -5dbfs (knowing that the 18i8 inputs max out at +16dbu).
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File Type: jpg IMG_20180608_163106930.jpg (114.8 KB, 134 views)
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Old 23rd June 2018, 11:38 PM   #23
alexcp is offline alexcp  United States
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Lower chipamp distortion through PCB routing
Quote:
Originally Posted by 00940 View Post
A focusrite 18i8 and a dedicated load. It's very similar to your setup actually, the load is kind of a simplified version of the Millet interface.

I use a scope to check the amp output levels. Most measurements are made so that the input going into the 18i8 is at -5dbfs (knowing that the 18i8 inputs max out at +16dbu).
Thank you.

The setup is indeed quite similar, as are the specs of the soundcards, yet your noise floor in the spectrum atatched to your post above is 10 to 20dB better than I can get from my soundcard connected to itself, without the interface. Curious.
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Old 24th June 2018, 12:21 AM   #24
00940 is offline 00940  Belgium
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Are you certain your soundcard is operating in 24 bits ? Windows can be tricky...
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Old 24th June 2018, 02:33 AM   #25
alexcp is offline alexcp  United States
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Lower chipamp distortion through PCB routing
Quote:
Originally Posted by 00940 View Post
Are you certain your soundcard is operating in 24 bits ? Windows can be tricky...
Thank you - for the second time, you point me in the right direction

The card used 24 bits, but ARTA used 16-bit dithering. With 20 bit dithering, the picture is somewhat better - see attached. This is just the soundcard by itself.
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Last edited by alexcp; 24th June 2018 at 02:50 AM.
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Old 30th June 2018, 04:10 PM   #26
alexcp is offline alexcp  United States
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Lower chipamp distortion through PCB routing
And here are the spectra of the amplifier as before: simple unregulated power supply, 18.5Vrms (about 43W) into a 8ohm resistor.

Here I am using Pete Millett's soundcard interface, but switched from ARTA to SpectraPLUS for FFT processing.
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File Type: png 2018-06-30 (5).png (349.3 KB, 68 views)
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