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Help with measurements in ARTA
Help with measurements in ARTA
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Old 6th September 2019, 02:41 AM   #1
itsikhefez is offline itsikhefez  United States
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Help with measurements in ARTA
Default Help with measurements in ARTA

Disclaimer: I am only interested in pointers for ARTA since I've found it easier to use and I've purchased a license.

Hi, I'm interested in measuring a SE tube amp with different output tubes and load resistors. I'll be doing the tests initially on my SS amp until I'm confident with the testing process.

My setup consists of a PC with E-MU 0404 PCIe card, pmillett SC interface, Windows 7 (for driver compatibility) and ARTA.

I've done calibration and run the SPA FFT measurement and I _think_ it is working as expected.

Things I'm unsure of: 1) How to set the amp volume - I've been setting the amp volume so that the output voltage matches the input voltage, i.e, if the generated signals is -3dbFS, that is where I set the volume pot on the amp. Is this the correct way?

2) Frequency Response - I've done this both through FR1, and though IMP. In FR1, the response is almost ruler flat. When running the IMP test and marking a region, rolloff can be observed below 40hz. What is the proper way to measure this?

3) Power output - This part confuses me. With signal generator set to -3db FS, that is about 2.8V output. Due to matching the amp volume to input (as described in #1), the output is always 2.8V RMS or ~4V pk-pk. To measure output, I am doing V^2/R (R is the resistance of the dummy load). Doing it this way basically results in the same power output for anything I measure. Opening the pot all the way causes significant distortion, so what is the correct procedure here?

4) Output Z - is it possible to compute with ARTA?

Sorry for the long post, tips for any of the questions would help me greatly
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Old 6th September 2019, 11:04 AM   #2
ergo is offline ergo  Estonia
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Take a look at STEPS (part of ARTA package) and the Help for that. For amplifier testing the stepped sine method can be more reliable.

You can also take a look at a document I once did about ARTA calibrations. Thats for speaker measurements but perhaps helps to understand how the cal fields and values work in ARTA
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Old 6th September 2019, 11:47 AM   #3
voltwide is online now voltwide  Ireland
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I would recommend an 30dB-attenuator between output and soundcard input. This keeps ADC modulation in the range -10 ~ -20dBFS where its own THD is at minimum.
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Old 10th September 2019, 03:35 PM   #4
itsikhefez is offline itsikhefez  United States
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Help with measurements in ARTA
@ergo, thanks for the tip about STEPS.. I've used it and found the graphs useful.

Can anyone else comment on questions 1, 3 & 4 ?
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Old 10th September 2019, 05:52 PM   #5
ergo is offline ergo  Estonia
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Have you tried the method from ARTa handbook
http://www.artalabs.hr/AppNotes/ARTA...%20English.pdf

And for power see the handbook for LIMP
http://www.artalabs.hr/AppNotes/STEP..._4_English.pdf
and the
3.3. Voltage- or power-related measurements with STEPS
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