I promised some time ago that I would show some measurements showing Mojo's performance. My reasoning for this was that Mojo does things that no other (non Chord) DAC does at any price; I was kind of annoyed that some people were comparing it to $100 DACs when the true competitors were $100K - and I kind of get that, its difficult to take Mojo seriously given its size and price. But if you could see the design complexity that goes inside Mojo then one could appreciate how much better it is; it really is vastly more complex than other DAC's, and this complexity is needed to recreate the original analogue signal accurately.
But I can show you that something special is going on from measurements. Take a look at this plot. This is a FFT of a 1kHz output at 2.5v RMS into a 300 ohm load (blue trace) and then with no signal (red trace):
Now what is very interesting is the noise floor at -175dB - it does not change at all with 2.5v or nothing which indicates a complete absence of measurable noise floor modulation. Noise floor modulation is extremely important subjectively - you perceive the slightest amount as a brightness or hardness to the sound. When it gets bad, you hear glare or grain in the treble. All DAC's (apart from Chord DAC's) suffer from measurable noise floor modulation - typically the noise floor would be -160 dB with no signal, and -140 dB at 2.5v RMS. Some Class D amps are awful with noise floor at -120 dB (one reason why Class D often sounds so bad).
To get this measurement is a massive challenge, as ADC's themselves have large amounts of noise floor modulation, way bigger than my DAC's. The only test instrument that has noise floor modulation that can actually measure Mojo's performance is the APX555. This uses a novel approach to solving the issue - 4 ADC's and an analogue notch filters. The outputs are combined in the digital domain, so this means one ADC is handling the fundamental sine wave, another ADC looks at the noise via the notch filter. So you will only be able to measure Mojo's true performance using the APX555.
Many posters have commented on how smooth and musical sounding Mojo is - and its in part down to the absence of measurable noise floor modulation. Actually getting this performance is very complicated, as within the DAC there are a enormous number of mechanisms to create noise floor modulation. One reason why its taken me 20 years of DAC development to do it!
Rob
