signalyst dsc1 (dsc2) DAC review

DIY OPEN SOURCE BUILD WIPES FLOOR WITH MORE EXPENSIVE COMMERCIAL DSD DACS

I received a coveted not easy to find product recently.  It is a Signalyst (HQPlayer) true DSD DAC.  Click here for description. Or, perhaps Converter is simply the best thing to call it, since, it really has no DAC in it, which is one of the points in DSD's favor; simplicity of conversion.  IF one choses to make it simple.  That tends NOT to be the case with many DSD DAC's, with their digital volume controls, so called 'DSD-Domain' processing, re-modulation, etc.  

I recently made a blog post on how pure DSD works. (Click here to read the post).  The purest DSD conversion is still something of a holy grail, involving only an analog filter, such as a RC filter, and never having more than the 1 bit bitstream.  The more realistic, and better performing pure DSD conversion still uses just an analog filter, but it's a FIR filter, which is more complex than the RC and other analog alternatives.  But a FIR filter, which is usually implemented via digital means, can be done 100 percent in the analog realm, either on silicon or via discrete analog components.  The beauty of the Signalyst DSC DAC is it is made of all discrete analog components once you are past the USB input stage.  

The DSC DAC is the hardware version of what we call 'open source' software, so its design is open to some tinkering and modifications.  My version is known as the DSC2, and is a fully differential balanced output that uses output transformers for final analog stage.  Output transformers are a bit controversial in modern solid state equipment, because they have higher harmonic distortion than many find unacceptable, nor are they perfectly linear.  The worst distortion is found at the low frequencies, and it lessens as frequency increases.  The output transformer will impart something of a tube like sound.  However, this does not have to be the analog output stage for this DAC.  Going back to the 'open source' nature, it could be anything of the designer's choosing.  

Anyone read the current controversy regarding the uber expensive PSAudio Directstream DSD DAC MK2?  And its 'high' noise levels and 'high' distortion levels?  Well, most of its measurement issues center around the use of output transformers. 

I am making NO statement whatsoever on the efficacy of the PSAudio implementation or its actual sound.  I have never heard it.  What I DO know, is my DSC2 Converter, which costs a tenth as much (that is, if you can find one or the parts to build it.  It is unfortunately NOT a commercial product.)  significantly outperforms the Directstream in every measurement of the DSC2 I have made, while only needing a simple software such as Roon to listen to PCM files, and needing NO conversion to listen to native DSD files. (HQPlayer, though, is recommended as it and the DSC2 converter are designed to work in tandem.)  It is bitperfect with DSD, something the Directstream cannot claim.  

The 'worst' measurements will be the THD+N, which inverted is called SINAD.  Anything over 90db SINAD is certainly decent enough performance, and 100db SINAD is probably more than good enough for most ears.  All of this, however, is the consequence of the use of output transformers at the output stage in the DSC2.  I can gladly report, though, that the transformers used are quite linear, for transformers.  It stays above 90db SINAD from approx. 50hz to over 15khz.  Not only that, the NOISE floor is well below -120db at virtually all frequencies.  The low level amplitude linearity is ASTONISHINGLY good for a 1 bit DAC.  And jitter?  Not even a factor.  Less than 20 picoseconds.  The worst thing the the lower SINAD will do is impart a sweet, tube like sound, which is exactly what it does, but NEVER at the expense of treble extension, detail or transient response.  It shifts a little to the warm side of neutral, and as is the case with many a piece of kit, will need careful equipment matching.   Yet overall its sound is both state of the art digital and beguilingly 'analog like' at the same time.  Its a beautiful sound that you will just want to listen to all night long, and not feel guilty about the internet mob mocking the noise floor, low linearity, or jitter while you fall asleep, because there is nothing there for the absolutist zealots to mock.  

Yet, I am still hesitant to post too many measurements, by experience I have become acutely aware of how important clean power is.  I am currently running the DSC2 on a variable output Switch Mode Power Supply that is of unknown noise quality. I will be more comfortable when the XPower 9 volt arrives.  Apparently it was out of stock on Amazon and is delayed to a Saturday delivery.  More refined measurements and graphs to come.  

UPDATE 7/2/2023-   I now have a 9v iFi Xpower SMPS powering the DSC2 DAC.  It did exactly as expected, lowered the 'hash' and anomalous 'stuff' in the noise floor.  See the new graphs below.  

The resolution of the DSC2 is exceptional.  Both the noise floor, and the linearity.  (Both of these are required for true high resolution.  Often we focus on the excellent in-band noise floor of DSD, but ignore the low level resolution that is exposed in a linearity test) 

No worries here. As I said, the linearity of the DSC2 is truly first class.  


All these measurements are at DSD256.  

At -100db, linearity is virtually perfect.  deviations are LESS than 0.1db.  Much less.  

At -110db, we are STILL at <0.1db deviation.  This beats out some DACs and come close to others made by that other company with the letters DSC in it, lol.  

At -115db, we finally hit some loss of resolution, with a deviation of an 'entire' lol -0.5db.  Wow.  

-119db we finally have a deviation of -2.5db.

So with my measurements we have practically perfect 18 bits of resolution, still very, very linear to 19 bits of resolution.   Linearity doesn't quite make it to a 'perfect' 20 bits, but for a 1 bit converter this is exceptional.  Heck, for any converter it is impressive. 

Couple that with the actual noise floor that is lower than -120db, I cannot help but be impressed by the measured performance here.  

SINAD (THD+N) in my latest, better calibrated measurements stays in the mid 90db range, approaching 100db at times. 

Even deep into the low frequencies, it only drops once you get under 50hz, and more like 30hz.  Our ears are not as sensitive to the distortion that low anyway.  Once again, I am thinking of a $8000 DSD transformer DAC that does not come close to this level of performance.  

And on jitter... my final measurements at DSD256, with a 48khz base rate, (48k x 256 or 12,288,000hz),  I got a low result of a mere 18 picosecond jitter.  


I will remeasure everything once I get the XPower 9V power supply.  I am not sure the numbers will change much; I do expect the FFT noise floor to be cleaner however, in my graphs.  

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looks like some SMPS noise in the low level hash. Will be remedied with a much higher quality external power supply soon. What is DOES show is how good the internal power noise regulation really is.

Again, I expect the low level 'hash' and spurious tones to clean up with the new PSU

The THD+N stays very linear for a transformer output. It stays below -90db from approx 50hz as mentioned before, to around 17 or 18khz. Only at 25hz does it increase to -80db and up. EXCELLENT performance for a transformer output.

J-test measurement is the same, but note the much cleaner noise floor when the iFi XPower 9v supply is used instead of the generic SMPS. The results still say approx a very very low 18 picoseconds of jitter, however, I can't help but be influenced in my assessment by the much, much cleaner graph.