This is another affordable measuring system, though not totally cheap. DAC used is Topping DX5 (both XLR and RCA output) and the digital input for the DAC is via Toslink optical cable. This is to avoid USB ground loops that destroy the measurement (both S/N and THD+N). ADC is E1DA Cosmos. Topping D10s is used as a USB/Toslink bridge to feed the DX5 with bit perfect digital signal.
Balanced inputs and outputs are used, measuring bandwidth used is 20Hz-45kHz if not stated different. Cosmos input range set to 4.5V.
Some graphs below:
Noise density
Total system noise 22Hz-22kHz is 4.243uV
Noise in dBFS
Total noise level is -120.5dBFS (22Hz-22kHz), -122.8dBFS A-weighted
THD and THD+N at 1kHz
THD+N = 0.00017% at @BW45kHz. Distortion components all below -130dBr.
Photo
When measuring power amplifiers, I use balanced dividers in front of the E1DA Cosmos ADC.
Balanced inputs and outputs are used, measuring bandwidth used is 20Hz-45kHz if not stated different. Cosmos input range set to 4.5V.
Some graphs below:
Noise density
Total system noise 22Hz-22kHz is 4.243uV
Noise in dBFS
Total noise level is -120.5dBFS (22Hz-22kHz), -122.8dBFS A-weighted
THD and THD+N at 1kHz
THD+N = 0.00017% at @BW45kHz. Distortion components all below -130dBr.
Photo
When measuring power amplifiers, I use balanced dividers in front of the E1DA Cosmos ADC.
It is truly better than most commercial HiFi gear I work on. I recently bought a second QA403 unit for a portable station, along with the programmable load (QA-451B).
A QA forum member who is also a very talented programmer, has produced a rapidly evolving independent piece of software which is a joy to use.
https://github.com/MZachmann/QA40xPlot
Example:
Related to what full scale voltage? Loop or ADC only? These questions must be asked to know what is the usable SNR and dynamic range. That is why I would like to see the FS 1kHz as well. In case of measurements we must be very specific, to get meaningful and comparable numbers.
Sure Pavel 🙂 But full scale with respect to what? The QA403 can output 18dBV balanced (7.94/15.88V) max. With several hardware output attenuators/gain. Bear in mind the software in a hardware analyzer is driving the D/A in its sweet spot for both noise and THD and using the hardware attenuators/gain stages to produce the best outcome. I can't send it a xdBFS request. I send it a dBV, dBu or Vrms request.
Example:
Best noise floor is on the 0dBV input range, best THD is on the 12dBV and 18dBV ranges with hardware gain/attenuators.
But your settings above are at -1.14dBFS, not "full scale". What is the output from the Topping DX-5 in volts at -1.14dBFS?
The software written by MarkZ does have drop downs for various units, but I haven't confirmed what does what as the software is evolving so fast. I do not claim this software is 100% accurate, but neither do I claim any software is. The results align very well with the official Quantasylum QA40x software which also is continuously evolving.
This is the alternative QA40x Plot software A/D noise floor with shorted inputs (Fs 192kHz)
This is the same, except the outputs from the generator (set to zero) are connected to the inputs. Note, the generator does not isolate/mute itself with relays at zero output, so the comparison with your DX-5 is fair.
This is a 2V (4V bal) loopback on the alternative software
As you say, there are so many variables to consider. The QA403 also has the benefit of using cross-correlation (in the QA40x software) to push the noise floor down to ~450nV for absolute noise floor measurements. Truly it's an incredible time for affordable test gear.
Your system appears to have a ~9dB advantage on THD which is amazing. 🙂 But not when it comes to N. That's because you run into the converter noise at low levels when using a designed for HiFi D/A.
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A really nice feauture to the UPV (and a modest one, albeit not seen on other AAs to my knowledge?) is the encoder wheel. You can click on any menu parameter box and increase / decrease by whatever increment you've parked the cursor in, i.e. 1V / 0.1V or 1KHz / 0.1KHz. It means you can find out info such as clipping points or specific frequencies of interest in a few seconds. Likewise, the random noise FR feature scans 20Hz to 20KHz in real time, with >0.1dB accuracy (you can centre a balance control knob in seconds). These are just 2 reasons that make the UPV such a workhorse. If another AA offered such practical features I'd be interested in knowing (R+S still service the UPV btw).
edit - what about a hardware remote controller for other AAs? Can anyone think of one? A small box that gives basic parameters for an AP or QA, with a handul of knobs and basic display would be a seriously cool addition to the bench (a little like those programmer boxes that came out in the 90s for synthesisers, which otherwise felt akin to painting your living room through the letterbox due to being purely menu and button-based).
edit - what about a hardware remote controller for other AAs? Can anyone think of one? A small box that gives basic parameters for an AP or QA, with a handul of knobs and basic display would be a seriously cool addition to the bench (a little like those programmer boxes that came out in the 90s for synthesisers, which otherwise felt akin to painting your living room through the letterbox due to being purely menu and button-based).
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