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FFT and 60 Notch filter software

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nali:

--- Quote from: loop123 on March 15, 2024, 12:57:07 am ---Did it. The error is 0.001  or about 0.1%.. from   0.926 (5V)  to 0.0922 (0.5V).   

Why, does other ADC or typical sound card show more error? The E1DA was marketed to measure distortions (not for general playing music) so it is super accurate. And their technical team said it hasn't got any form of automatic gain control or clipping protection.

--- End quote ---

It might be super-high resoludion and linearity, but that's not the same as accuracy.

I can't see any refernce to it above, but have you tried terminating the ADC input to characterise its noise? If you don't know the characteristics of your measuring device then everything else is academic.

Out of interest are you making differential measurements all along the line, or are you feeding single-ended inputs into the diff amp somehow?

WatchfulEye:

--- Quote from: loop123 on March 15, 2024, 02:33:58 am ---So the broadband noises don't come from the Netech simulator because the resistor also made those noises. So what do you think is the origin of the broadband noise at your estimated 100-150nV/Sqrt (Hz)? I have 2 units BMA and it can't be both AMP01 were damaged. Or maybe they are? What is your other theory WatchfulEye?  I am clueless now. Thanks.

--- End quote ---

Well it must be the measurement setup somewhere. The most likely point is the input the amplifier. I've looked at some of the photos again, and it looks like there is an additional amplifier or head stage before the BMA? What is that? If it is before the BMA, then it will be contributing to noise, potentially more than the BMA.

Isolated amplifiers may sacrifice noise and bandwidth performance in order to achieve isolation.

loop123:

--- Quote from: WatchfulEye on March 15, 2024, 11:55:31 am ---
--- Quote from: loop123 on March 15, 2024, 02:33:58 am ---So the broadband noises don't come from the Netech simulator because the resistor also made those noises. So what do you think is the origin of the broadband noise at your estimated 100-150nV/Sqrt (Hz)? I have 2 units BMA and it can't be both AMP01 were damaged. Or maybe they are? What is your other theory WatchfulEye?  I am clueless now. Thanks.

--- End quote ---

Well it must be the measurement setup somewhere. The most likely point is the input the amplifier. I've looked at some of the photos again, and it looks like there is an additional amplifier or head stage before the BMA? What is that? If it is before the BMA, then it will be contributing to noise, potentially more than the BMA.

Isolated amplifiers may sacrifice noise and bandwidth performance in order to achieve isolation.

--- End quote ---

The small box is just empty (see below). It used to be the chassis of the ISO122 isolator but I found out at 1mV and 1000Hz and above, it has ripple noises and we traced it to the ISO122. So I removed the isolator pcb and just used the chassis as connector box for the 1.5mm touchproof sockets.



The Netech has differential outputs. I'm still asking the designer if his E1DA ADC could cause the noises and asking about the inputs shorted way of testing noises.



In the BMA. I traced the following and found out it has clamping protection, and the inputs didn't go directly to the AMP01. Instead it goes to the LF412CP CHIP (the left is 1In-, 1In+) and detours elsewhere before going to the AMP01. Can I just bypass the inputs directly to the AMP01? I plan to remove the chip, and put another empty socket with the +IN, -IN not connected to the pcb but instead directly to Netech, this would work?  I don't want to damage the board irreversibly because I plan to use the 2 pcs of BMA for 2 channels.


WatchfulEye:
Can you provide wav files for the resistor and new measurements. The files I had have very low signal - looks like gain was set wrong, and this may cause errors in the noise calculation (the wrong gain setting may mean the ADC/quantisation noise is contributing excessively in the earlier files).

I've looked at the photos of the BMA-200. Looks like the input stage is the LF412C, which conditions the signal before going to the AMP01. The LF412C is quite a low noise op amp, but still a lot higher than the AMP01. There are also a lot of resistors in the signal path, which can also add noise. I can't read the values off the resistors near the LF412C, so don't know if these are contributing much. It might be interesting to know these, to calculate the noise contribution of teh individual components before any modifications are made.

loop123:

--- Quote from: WatchfulEye on March 15, 2024, 03:48:57 pm ---Can you provide wav files for the resistor and new measurements. The files I had have very low signal - looks like gain was set wrong, and this may cause errors in the noise calculation (the wrong gain setting may mean the ADC/quantisation noise is contributing excessively in the earlier files).

I've looked at the photos of the BMA-200. Looks like the input stage is the LF412C, which conditions the signal before going to the AMP01. The LF412C is quite a low noise op amp, but still a lot higher than the AMP01. There are also a lot of resistors in the signal path, which can also add noise. I can't read the values off the resistors near the LF412C, so don't know if these are contributing much. It might be interesting to know these, to calculate the noise contribution of teh individual components before any modifications are made.

--- End quote ---

The IN- for example is connected to the blue Bourn variable resistor and many resistors (didn't do complete trace of the portion before because I thought it was not necessary but now there seems no other choice but to do full trace to know the source of the dreaded noise at 10uv 1000Hz up). Here are the front photo without using Inkscape transparent mode.






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