“After 8 years of research we have finally created a stand-alone music player that brings back the vintage music exprerience from before the digital era.”
Because most of the music available in the world today is only available in a digital format, we set out to try and re-produce this vintage music experience using the digital CD data as our source.
How hard could it be ?
After 8 years we can say that it was much harder than we could ever have imagined…
Thanks to numerous people that listened, contributed to and influenced the direction of our final music player design, we are confident that this music player reproduces the music in such a natural, clear and refined way that at last we can again sit down and enjoy our music like we once did from our vinyl record player.
The SD1 music player
- Stand-alone player, all music is read from the SD card inserted into the player
- Can read upto 999 CDs from a single SD card
- Includes software to remotely control the SD1
- Includes software to create and write CD lists onto SD card
- Includes build-in webapp to remotely control SD1 from phone/pad
- Included non-regulated/non-switched power adapter (important !)
- Integrated passive volume control with extra analogue input
- Optional IR remote control
- Playback: 44.1 / 16 only
- Storage: SDcard, max. 999 CDs in WAV format
- Output signal amplitude: 2.5Vpp (0.88V rms)
- Volume control: 0 … -48dB in -3dB steps
- Power supply: external 12V DC, polarity protected
- Supply current: average 200mA @ 12V
- Interface: RS232, full galvanic insulation (slotted IR sensors)
- IR remote control (based on RS232)
We are convinced that our hearing is much more sensitive to time domain variations than to distortion. The last decades most of the effort in audio development was targeted toward minimizing distortion and not minimizing time domain variations. Increasing the sample rate would imply less time domain variation, but if the source (clock) is not significantly improved this will introduce even more time domain variations over all. Increasing bit depth is only useful if this resolution can accurately be reproduced in the analog domain (amplifier/speakers). This is why we chose to only support uncompressed 44.1 KHz 16 Bit stereo PCM.
To attain the minimal level of time variation required to accurately reproduce the vintage music experience we eventually realized that we need to eliminate as much interference from the player as possible.
This means that using a PC as (streaming) source is not good enough because a PC generates interference and jitter that cannot be fully blocked. Also harddisk, SSD drives and USB drives cannot be used for similar reasons. This leaves “passive” storage devices as the only option. We chose the SD card as storage device because the SD storage device uses external clocks that can run in sync with the DAC clock, this prevents unwanted cross-talk between multiple clocks. The SD1-player runs on one single clock source and the SD-transport is slaved by this single clock source. But even this low jitter concept still isn’t good enough, as cross pollution between clock source and connected loads can still degrade overall performance.
This problem that exists in every digital audio source was fixed by using a novel electronic tuning fork circuit. Similar to a tuning fork that is used to tune musical instruments, the electronic tuning fork will resonate at one frequency (fundamental) when brought into resonance. This electronic tuning fork was designed such way that only one frequency can travel between clock source and connected clock loads, blocking all other frequencies thus preventing cross-pollution. The result is an exceptional clean clock signal that turned out to be essential for obtaining sound quality comparable with vinyl and tape.
Apart from this clean clock signal, the microcontroller reads WAV files from the SD-card and converts these to an I2S stream using on-chip hardware rather than software routines. Since no conversion is required like with FLAC or Apple Lossless for example, and the I2S conversion is handled by on-chip hardware, processor load remains very low. This in turn is essential to maintain low interference levels and provide guaranteed bit-perfect playback. Increased processor load and higher processor system clock rates lead to increased interference levels that indirectly degrade perceived sound quality, that’s why we used lowest possible system clock rate and lowest possible processor load.
The only interaction between the SD1 and any remote controller is either by IR or low speed slotted IR transponder. The IR transponder drives the external USB or Bluetooth interface while providing perfect galvanic insulation. The USB / Bluetooth interfaces are not built-in as they would pollute the SD1-player electronics.