Recently I won a Mytek Stereo192 DSD DAC from Positive Feedback Online & Mytek, which is way cool, big props to Mytek for giving away a killer DAC.
It arrived this week and given my proclivity for poking at things, I put it on the test bench last night just to have a quick look. I was interested in the output level, which seemed very high and from what I read in the Mytek design philosophy I didn't seem to be imagining this but their write up was slightly unclear, so measurement was in order.
I fed it via S/PDIF from the Prism dScope III's digital outputs and of course measured the analog output into the dScope using a balanced connection. The dScope does have a current calibration.
With the output level jumpers in the factory position I recorded the following: (H2, H3 and H4 refer to 2nd, 3rd and 4th order harmonic distortion).
0dBFS = 10.33v RMS on balanced outputs, .00102% THD+N, H2 = .00036%, H3 = .00082%, H4 = .00004%
-18dBFS = 1.3009V RMS balanced, .00295% THD+N, H2 = .0001%, H3 = .00036%, H4 = .00005%
Note the design doc shows 9.79VRMS as maximum output, mine is a little hotter (.46dB).
With the jumpers engaged the output is 6dB lower as it should be. The levels were:
0dBFS = 5.1568v RMS on balanced outputs, .00105% THD+N, H2 = .00021%, H3 = .00032%, H4 = .000006%
-18dBFS = 649.25mV RMS balanced, .0065% THD+N, H2 = .0006%, H3 = .0004%, H4 = .000015%
With the lower level, the THD+N is a little higher, since noise is part of the measurement. The dScope has the ability to make THD measurements without noise, so the H2,3 and 4 are more indicative of the actual harmonic distortion, not that any of them are very high and lower order HD isn't offensive anyway. I found I preferred the sound with the jumpers on and the level lower, it appears the jumpers control the I/V portion of the circuit, they are certainly before the bypass relay and the output stage, so the Zout should not change but I didn't measure it. Looking at the board there are only resistors between the jacks and the output op amp, so the Zout can't change, a good thing IMO, I much prefer that to adding some type of attenuation network after the output.
The RCA jacks would be exactly half those levels as it does have a fully differential output, I connected two channels of the scope and the balanced outputs are differential.
The graphs that follow are mostly FFT shots that show the distribution of the harmonics. Interestingly there are some spikes that appear at about 12,24 and 36kHz, regardless of whether there is any input or not, something is making some low level noise. The highest of these is at about -92dB, so I suspect inaudible. The stray noise was not changed when moving the jumpers. Each graph has a caption at the bottom saying what it is.
There are also two shots showing the squarewave response with the default "slow" and optional "sharp" filters. The slow version exhibits less pre-ringing, a good thing based on other DAC's I've heard with this type of filter.
Before anyone asks, I don't have any way to generate a DSD signal, the dScope only operates in PCM.
Hope someone besides me finds these interesting. This is by no means a comprehensive set of measurements, just what I had time for last night and enough to satisfy my curiosity about the output levels. If anyone wishes to reuse the images, that is OK but please say where you got them.
Mike
