Cheap DAC working well

[roclite]

Hi all,

I have been following this thread with interest and hope i can contribute something to the discussion.

I purchased my first SMSL SD1955+ over a year ago and intended to use it in USB INPUT mode with a Samsung NC10 netbook (Windows XP)/external HDD as a music server. I experienced lots of problems connecting the SD1955+ USB to the netbook,
it was not reliable and would often crash when I was using my preferred audio player WINAMP. When it did work, it sounded really good and I agree with other reviewers comments here that for £70 ($100) it is very good value and has a sound quality that is worthy of a DAC several times the price. Anyway, the regular system crashes finally got to me and I moth-balled the SD1955+ until I could upgrade my netbook.

Fast forward a year later and I have finally replaced the Samsung with an Acer Aspire One running Windows 7 Ultimate. Even better, the Windows 7 has a proper device driver and the SMSL is recognised as "SMSL SD1955+" and works perfectly! No unexplained audio drop-outs and computer crashes!

OK, the tweaker in me got the better of me and I did a bit of op-amp substitution, replacing the JRC5532 output buffer with a selection before finally choosing the LM4562. It sounded better - better sound stage, top-end and tighter bass. I kept the other two I/V converter op-amps (OP275) the same. Intrigued by this apparent beneficial change, I looked more closely at the DAC to see if there was room for further improvement. An obvious area is the +9V SMPSU. Why would the manufacturer of a high quality DAC compromise its quality with a cheap, noisy switching power supply? To answer that question, I coupled a linear +12V DC supply to a very basic hand-made LM317K linear regulator, output DC adjusted to 9V. The results were very impressive sound-wise, and I can only agree with other reviewers that the SD1955+ sound is much improved, mostly by the marked reduction in digital "hash" appearing on the analogue output signals.

At about the same time, I was trawling on eBay and spotted an SMSL SD1955 (the original, first version) starting at £28 in auction. No-one else bid, so I got it for that price :-) . The specification of the original SD1955 looks better on paper (more dynamic range and lower distortion) but there is another significant difference - it comes complete with a linear 24VDC supply instead of the cheap, nasty 9V supply provided with the SD1955+. On listening tests, it did sound very good but not markedly better than the SD1955+. I popped open the lid and found there were 3 off OP275 fitted (not sure if it was tweaked by previous owner or if that was factory build) and so I substituted the output buffer for an LM4562, so I could compare the two DAC's in the same configuration. The result was pretty impressive - before the op-amp swap, the bass had been quite boomy and the top-end very muted and thin. After the swap, it sounded more like the SD1955+ but to my ears so much cleaner and musical. I could not resist opening up the SD1955 power supply case and not surprisingly found a hefty transformer, PSU capacitor and an LM317T regulator on a heatsink - quelle surpris! So, the moral of the story (if there is one) is that it would appear that SMSL manufacturer has probably compromised the performance of this lovely little DAC over the past few years for purely commercial reasons, cheap (and lightweight!) SMPSU versus low noise linear regulator (heavy, so increased overseas postal charges) and cheap, low-cost (even by Chinese standards) op-amps.

I hope I have added something informative to this thread. Keep on listening to that lovely (when sympathetically modded!) DAC. :-)

roclite