Stello's upsampling DAC
It features coax, Toslink, AES-EBU and USB inputs and also I2S digital transmission via a mini-DIN connector to receive I2S signals from the matching CDT 100 transport (see http://hi-fi-avenue.blogspot.com/2010/05/stello-transport-affordable-way-to-good.html). I2S means separate signals are transmitted on individual conductors for master clock, word clock, bit clock and audio data.
The DAC offers both single-ended and fully-balanced analogue outputs. Stello states that it has a jitter-free timing circuit, a 6th order digital filter, discrete Class A analogue output stage and audiophile-quality components like 1% tolerance metal film resistors, WIMA polypropylene capacitors, Cardas RCA connectors and Neutrik balanced connectors.
Though the power switch is at the rear, you still have to press the standby switch on the front panel to power up the unit.
On the front panel, there is an upsampling button - which works for AES/EBU, coax, optical and USB inputs. When upsampling is set at 24/192kHz the light is green; at 24/96kHz it is red and when it is in bypass mode there is no light. 'Bypass' means the digital output is exactly the same as the input up to 24/96. Upsampling can be changed on the fly and April Music, the South Korean manufacturer of Stello products, recommends 192kHz upsampling.
There is another knob to select the input and a green LED lights up to indicate that the input digital signal has been detected by the DAC.
The DA 100 Signature DAC does not support an ASIO driver and it is essentially a plug-and-play component and when the USB is plugged in, the laptop will say "USB device connected" and then it will say that the USB device can be used.
I2S vs coax/toslink
Despite all the hype about the superiority of I2S, there was just a minor difference detected after much switching back and forth between inputs using the Stello transport and DAC to drive the Benchmark DAC1 Pre (used as preamp), the Bryston 4B SST power amp and the ATC SCM40 floorstanders.
And it was only when I played an Eva Cassidy CD which had lots of ambient acoustics and high frequency sounds that I could hear that the I2S input sounded more open and extended in the treble region.
Upsample or bypass mode?
If you want to upsample, the 192kHz sounds better than the 96kHz setting. There is greater clarity, but it comes with more sibilance. This was very apparent when I played Paul Simon's Diamonds On The Soles Of Her Shoes from his Graceland album.
When I played a Frank Sinatra CD that had lots of horns, the horns gained a metallic edge that was jarring when upsampled to 192kHz. This CD sounded better on bypass mode.
When using the USB input, MP3 songs generally sounded better upsampled to 192kHz, but again the trade-off was more sibilance on some songs. I played a Carrie Underwood MP3 song and there was more sibilance. Listening to Internet radio was better with 192kHz upsampling,.
When playing 24/88.2 or 24/96 files through the Stello U2 24/96 USB Link, they sounded better on bypass mode.
I played one native 24/192 file and it sounded better when upsampled to 24/192 (since the DAC received 24/96 signals via the U2).
On most songs, I preferred the bypass mode while other songs sounded better upsampled to 192kHz. Songs upsampled to 96kHz tended to sound congested.
Thus it seems as if you will have to experiment with the upsampling as different songs and different files sound different when upsampled.
The Stello DAC is bright and forward sounding. It tends to 'push' the soundstage a bit more forward than the resident Benchmark DAC1 Pre.
This may sound impressive at first, but when I heard Handel's Messiah (Linn's 24/88.2 Studio Master FLAC download) through the Stello DA 100 Signature DAC's USB input, I realised that the forward-sounding nature of the DAC affected the soundstage.
Through the Benchmark and even the Wadia 381i's DAC section, the chorus had the singers standing in a curved row behind the speakers.
Through the Stello DAC, this depth was flattened. This effect was more apparent through the USB input than the other digital inputs.
Using the Toshiba laptop and WinAmp, I played a selection of songs ripped with EAC into FLAC files, downloaded MP3 files and the Handel's Messiah Studio Master files from Linn Music at 24/88.2.
Along the way, I tried the J. River music player which was very smooth sounding.
Like I mentioned above, the forward-sounding nature of the DAC was emphasised through the USB input.
I sent an e-mail to April Music asking if a 24/192 signal would be downsampled through the USB input and the reply was that the USB input of the Stello DA 100 Signature DAC only accepts up to 48kHz sampling rate and the USB DAC chip is the Burr-Brown PCM2704 from Texas Instruments.
A quick check of the manual revealed that it is a 16 bit chip that accepts 32kHz, 44.1kHz and 48kHz sampling rates.
Thus when you use the Stello DA 100 Signature DAC's USB input, a native 24/96 or 24/88.2 signal is reduced to 16/48.
The USB input of the Stello DA 100 Signature DAC, in my view, is the weakest of its digital inputs.
And this has led me to opine that the Stello U2 24/96 USB Link is a must-buy component.
The essential U2
If you buy the RM3,300 DA 100 Signature DAC, it is essential for you to spend another RM950 to buy the cigarette-box sized U2 24/96 USB Link.
The U2, an active component that draws power from the USB connection, converts the USB to I2S and coax outputs and it can be used with any DAC that lacks a USB input. It also converts the signals to 24/96 SPDIF.
When you connect the laptop to the U2 with a USB cable and then to the DAC, you will feed the DAC with 24/96 signals.
Playing Handel's Messiah 24/88.2 files through the U2 resulted in a sound quality that equalled the Benchmark DAC1 Pre. The singers were reproduced standing in a curved row behind the speakers. The soundstage was placed more naturally behind the speakers and it was large and deep while the tonal balance became less bright and more neutral.
Most songs played via the laptop through the U2 sounded better on bypass mode since the DAC was already receiving 24/96 signals.
For the heck of it, I tested the U2's output into the Benchmark to check if there was any difference between a signal that went through the U2 and a signal that went direct to the Benchmark's USB input. After a few songs, I felt that there was no difference.
The DAC is sensitive to power cords. When I used a DIY power cord, it sounded brighter and harsher and on 96kHz upsampling, the soundstage was very narrow. I switched to the DH Labs Power Plus and the sound was overall better.
Related post: http://hi-fi-avenue.blogspot.com/2010/05/stello-transport-affordable-way-to-good.html
Stello is distributed in Malaysia by Rave Systems, Level 1, PNB Darby Park, Jalan Binjai, Kuala Lumpur. Tel: 03-21632818