As promised, here's my review. For this review I had two goals: compare the performance of the Yulong’s various inputs against each other, and compare the Yulong against the DV337 amp. The following equipment was involved:
Yulong DAH-1 Mark Amp/D/A converter (Yulong)
Darkvoice 337 amp with stock tubes (DV337)
Musical Fidelity 192Khz upsampling DAC (MF DAC)
Laptop (for USB)
Sony MDR-CD3000 headphones
For phase 1, I created a setup where the Yulong was simultaneously connected to all 4 types of input, Any music that was played was synchronized across all inputs. The Yulong has a relay when switching inputs, so when pressing “mode” the switch is done physically and is instantaneous. This is a good thing. The configuration is as follows:
Laptop --USB--> Yulong
Squeezebox --Optical--> Yulong
Squeezebox --Coax--> MF DAC --Coax--> Yulong
Squeezebox --Coax--> MF DAC --RCA--> Yulong
The first thing I tested was the noise floor. When disconnected from its inputs, the USB and optical sources make a quiet digital static-like noise. When connected, all inputs are virtually silent. There is some white noise that can be heard, but only in a quiet room with no music playing.
Next, I played a variety of music and switched back and forth between all the inputs. Perhaps I don’t have the golden ears of some of the people here, but there is no noticeable difference in sound between any of the digital inputs. There is, however, some difference between the analog and the digital inputs, most likely due to the difference in DACs. The Yulong’s DAC is a touch brighter than the MF DAC. My guess is that this is due to the interpolation/curve smoothing that the up-sampling DAC is doing at higher frequencies. Which sounds better? It’s probably up to personal preference.
Overall, the Yulong is a very capable device. It blows away my external USB soundblaster card and my iPod in all aspects. My primary complaint with it is that the display is way too dark. In dark lighting, it’s clearly visible, but in daylight, it’s unreadable. I wish it had a brightness adjustment of some sort.
For phase 2, I hooked up the DV337. It has separate analog volume controls for each channel. To eliminate volume bias, I put a 2khz sine wave through both amps and matched all output voltages (to about 30mV AC+DC) using a Fluke multimeter. Interesting observation: the output voltage on the DV337 fluctuated quite significantly compared to the Yulong (+-2mV vs +-.01mV). This didn’t seem to have any effect on my perception of the sound though. The following two configuations were compared:
Laptop --USB--> Yulong
Laptop --USB--> Yulong --RCA--> DV337
The differences between the Yulong and DV337 are rather subtle. The main difference in the sound between these two is the DV337 seems to project better separation. I was more aware of what was coming out of each channel than on the Yulong. The DV337 also seems to have slightly more powerful bass. If I wasn’t doing an A/B comparison, and only listened to the two on separate occasions, I doubt I would be able to say which one sounded better. I had my parents over for dinner that night and I let them compare the two. My dad couldn’t tell any difference. My mom made note that instruments could be slightly more clearly distinguished on the DV337, but the differences were very small.
One other observation: I tested the power draw on the two amps at idle. The Yulong used 7W and the DV337 used 137W. The DV337 is quite the heater.