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The very last release of REW, v5.20.9, even allows to display the frequency range taken into account for the fundamental. That's genious !) One "controversial" characteristic to this design which I need to add here (as you can see in the comments, I had neglected to do so in the first release of this article), is that this device does not incorporate an input buffer which results in variable and relatively low input impedance. Here's how it looks like depending on the voltage dip switch settings: 1.7V (6.83dBu) = 640Ω2.7V (10.85dBu) = 1kΩ This warranty extends only to personal use & does not extend to any product that has been used for commercial use, rental use, or use that is not intended. There are no warranties other than expressly set forth herein.
Regarding the grading, each Cosmos ADC unit is individually calibrated for the minimal distortions at level -0.5dbfs 1kHz with the typical THD <0.00003% or to say shorter .3-.2PPM. The typical level of 2nd, 3rd, and other harmonics between -135.. -145db for all grades from A to C. Grades are only about the noise, and each unit has a grade mark on the left side of the front panel. In most cases, SNR/Dynamic_Range in the MONO mode is within 127+/-1db(A) it is grade-B Cosmos ADC. Less than 126db(A) means grade-C, from 128db(A) and better grade-A, 129db(A) and better grade-0(very rare grade, and probably redundant, just in case). The MONO mode improves the SNR/DR for 3db, so a grade-A unit typically has SNR 125db(A) in STEREO mode. MONO/STEREO modes are switchable by the UAC2 volume commands, for example, if your Windows volume slider position is less than 50%(0 to 49%) the device works as 2 channel ADC, if more than 50% it is a MONO ADC with summed Left+Right inputs mapped on the Left channel(Right input is always mapped to the Right channel). In the MONO mode, both channels need to be tied together L+ to R+, L- to L-. And if you can't afford the full zoom set, you probably will be able to earn enough to live with just this one, if it fits your needs. I ask you please, not only Ivan but the many experienced participants of this forum if you can help me with this problem, to know if it can be solved with some adjustment or firmware (although after writing down the factory parameters I have already tried almost all the combinations from the tweak and I also installed the latest firmware, without success…). Right Channel Stereo Mode: Almost 10 dB more noise at 1KHz, 30 dB more noise at 100 Hz and almost 40 dB more noise at 20 Hz As indicated on the enclosure, one can change the input level for each left and right channel. If you've measured DACs before, you've probably seen that many balanced outputs are 4Vrms so the 4.5Vrms configuration would be a good one to use that optimizes potential dynamic range for such devices.
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A-weighted noise is -128.6dBFS, matching the specs for an A-grade unit. I get the same value with the input set to 10V or 1.7V. At the 1.7V setting this corresponds to noise below 1µVrms. The noise floor being below -126dBFS at all input levels rivals the APx555. Unlike the APx555, the Cosmos cannot autorange, so for measurements like sweeps the APx555 still has superior performance. Over the years, I've gradually improved my measurement capabilities with updates to the ADC; this being the first time I've added an analogue processor to the measurement chain. As you noted, what's happening here is that the graph shows a +60dB gain applied to the noise floor. So if we look at 17kHz and that -89dB noise, it's actually -89-60dB=-149dB. The output of the test generator is exactly the same. The output of the Scaler is exactly the same. Those weren't touched. But, by running the output of the Scaler through the notch filter of the Cosmos APU, the level of the 1 KHz fundamental tone into the ADC is reduced, with the harmonics mostly unaffected. That minimizes the distortion added by the ADC, so we just see the distortion coming from the generator. This applies for most countries. However, large items such as headphones and desktop DAC/AMPs (e.g. HarmonicDyne G200, MUSICIAN MDP-2, and etc.) are excluded.Any item returned incomplete or with physical damage such as scratches etc., excessive signs of use, or abuse will not be accepted for return.
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