Power amp measurement system

I have good experience with SSR speaker protection. The simulation is attached.
 

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I finished and measured the 10k passive notch filter. Depth is 60dB, pretty good.
 

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I tried to compensate the notch1k filter in ARTA. The compensation file was generated by STEPS.

green trace - soundcard loopback
black trace - loopback with notch + compensation (*.mic file)
blue trace - green black difference

H1 diff -0.8dB
H2 diff +1.37dB
H3 diff -0.04dB
 

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preamp quick test

the chain : Viktor1K -> Notch1k -> PreampK4v3 -> XFi

Viktor1K output: +4.4dBv
Notch attenuation: H1 -55dB, H2 -9dB, H3 -5dB
Preamp : +40dB
X-Fi input: -10dBv

After correction:
H1 = -10+55 = +45dB
H2 = -114+9 = -105dB (at least)
H3 = -117+5 = -112dB (at least)

I hope I am correct ... THD < -145dB
 

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Yeh, some form of total test setup Faraday cage (with all equipment inside, including batteries and interconnecting cables), with only USB cable exit, can often supress local stray hum ingress.

I do the same with my EMU0404 when testing an amp on the bench - the EMU sits in an aluminium tray, with exit hole for 100:1 probe to go to bench DUT, and exit hole for line output lead, and another for USB. Battery powering for EMU (and if needed also for USB isolator) sits in tray as well. A ground clip link from line input BNC cover to tray also seems to help sometimes, as does inverting a tray over the top to make a total cage.
 
I have used a ADuM4160 based pcb that was on ebay years ago - it has a 'full speed' data rate setting, so I can get 48kHz sampling rate from the EMU if needed. I typically used the USB isolator for cheap USB soundcards I was checking out, as I was keeping the EMU for reference measurements back then. I haven't had to use it for the EMU now I think about it - and use a battery power interface for the EMU when checking for hum loop parasitics.