External pins. Portable DAC review: Hi-Fi for the long haul Not the most transparent sound
There is no music without a DAC if your music files are stored digitally. You may not know how they work, but most of us use at least one digital-to-analog converter, better known as a DAC or DAC (Digital to Analogue Converter), on a daily basis.
They are built into devices such as computers, tablets, smartphones. The DAC is the fundamental basis for decoding familiar digital music, turning it back into an analog signal that the human ear can hear.
Any device that is a source of digital signal - be it a CD or Blu-ray player, DAB (digital radio), set-top box, game console or music player - requires a DAC to convert the sequence of zeros and ones back to an analog signal before sending it for playback.
Traditional amplifiers don't amplify and loudspeakers don't reproduce the digital signal and your ears can't hear it. They only hear sound waves. Without a DAC, your digital music collection is worthless. This is a simple set of "0" and "1", which is only necessary for the operation of digital devices. In short, DACs play a big role in digital music playback.
However, a serious problem is that the DAC chips built into most of the above devices may often not be of a sufficiently high level and may not always provide the highest possible quality of a digital original. In this connection, the thought arises of the need to replace the DAC in order to transform the music archive of digital music and really get the most out of your audio system.
The sounds we hear on a daily basis, whether it be music, speech, the noise of a big city or the murmur of a stream, are transmitted as sound waves and enter our ears in the form of a continuously changing analog signal.
One of the earliest ways to store analog recordings was in the early days of today's vinyl records, and later tapes, but the unwanted noise and fragility of these formats required something new. And that novelty was the compact disc (CD), invented by Sony and Philips in the 80s of the last century and made a digital revolution in the process of storing music recordings.
Digital audio is very different from analog. Digital music files are typically created using Pulse Code Modulation (PCM) or PCM as the English abbreviation, and are created by continuously, strictly periodically measuring the amplitude of an analog signal.
Then, the amplitude value is encoded as a binary number (a set of 1s and 0s), and the bit depth of this number is often referred to as bit depth. The time interval between measurements is determined by the sampling frequency.
When recording a standard CD, measurements are taken 44,100 times per second (44.1 kHz). Each measurement is recorded for storage in binary format with 16-bit precision. When recording high-resolution audio tracks, up to 24-bit bit depth is used, with a sampling rate of 192 kHz or higher.
Generally speaking, digital audio data can be encoded at different bit depths and sampling rates, and then into different file formats with different compression ratios to reduce the volume. But no matter how they are created, the DAC's job is to recognize it all and translate as accurately as possible from the binary format in order to get as close (as possible) to the analog original.
Why do you need a separate DAC?
In fact, almost every modern digital audio device has a built-in DAC, but it is also obvious that not all DACs are the same. Low-end converters may introduce unwanted noise due to the limited capabilities of the microcircuit used. They cannot support all data rates, not to mention additional distortion due to loss of synchronization (jitter effect or jitter).
Loss of synchronization is defined as a time delay. Precise timings are extremely important in receiving a digital music stream and if they are not kept (usually due to a poorly designed digital clock circuit) sound quality suffers.
Loss of sync problems can occur when transmitting a digital signal and are especially dangerous when the signal is being transmitted between two devices. Therefore, in recent years, asynchronous DACs have become widespread, which use their own clock source.
The clocks in most high-end DACs tend to be more stable than those found in mid-range PCs, so the sound will be correspondingly better (ceteris paribus).
The raw material determines the quality
Of course, to get the most out of your new DAC, you need to start with good source material. Don't expect miracles if you send music in MP3 format, 128 Kbps to the converter. In fact, improved decoding of such an overly compressed audio signal can make any audio imperfections even more apparent.
Optimal results, with CD quality or better, can be obtained when playing lossless compressed FLAC, WAV or ALAC (Mac) files in PCM or DSD format.
DSD or PCM?
The DSD or Direct Stream Digital format is an alternative to PCM and was originally developed for Super Audio CDs (SACD discs) by Sony and Philips in the late 90s.
This much rarer format differs significantly from PCM (pulse code modulation). Here, pulse-width modulation (PWM) is used for coding, only single-bit coding is used, but with a significantly higher sampling rate - 2.8 MHz for DSD64 and 5.6 MHz for DSD128.
The debate about which coding systems are best continues to rage to this day. So it's easy enough to note that if you're a die hard DSD music fan, it's worth making sure the DAC you choose supports DSD, which isn't always the case.
Which DAC to choose?
DACs come in different shapes and sizes, differ in functionality and interface capabilities. So you need to first understand how you will use it. And choose according to the cost you want to meet.
Compact USB DACs are portable, reasonably priced, and easy to use. Sizes range from a standard plug-in USB module to a pocket-sized unit that connects via a separate USB cable.
Most often, such DACs do not require a separate power supply, receiving the necessary electricity from the USB port. Such DACs have, to a large extent, a simple set of interfaces. There is a headphone jack and, perhaps, there will be a line output for connecting active speakers or other Hi-Fi class audio equipment.
If you want more connectivity options and don't need a wearable converter, the desktop unit should be your go-to. They tend to be larger and require a separate power supply, but often offer several additional digital and analog audio inputs, along with USB for connecting to a computer. Look out for a headphone amp if you need one, as not all transducers have one.
Finally, there are DACs that are specifically designed for use in large home audio systems. They tend to have even more inputs, including underused ones like AES/EBU, and feature more features, support the full range of hi-res music formats, or provide a Bluetooth connection to stream music from your smartphone or tablet.
And some even have their own volume control so they can be used as a preamp as well.
Conclusion
Despite the seeming absurdity of double conversion from analog to digital and from digital back to analog, we will not wait for the vinyl revolution and will have to be content with digital sound. The digital form of storage and transmission of audio recordings is too convenient, both for home use and in professional equipment.
Of course, digital audio is just a copy of the analog original. A copy that even in the last century seemed imperfect and was used for purely utilitarian, narrowly professional purposes. But the sound quality of the best samples of today's audio equipment, even to the ear of a music lover, approaches the best analog samples. Not the last role in this is played by digital-to-analogue converters, which allow you to get the most out of high-resolution music recordings.
In recent years, the use of the interface has become more widespread. USB to output sound from the computer. The undeniable convenience of this method of connecting a computer to a sound system via an external DAC is reinforced by the expanding production of digital-to-analog converters equipped with the so-called "asynchronous USB".
And this is not just a fashionable hobby for digital sound lovers, but a really serious way to get a decent digital source (even high-quality, under certain conditions) in the form of a computer + DAC bundle.
True, the question introduces some uncertainty: why do manufacturers of high-end music servers / digital players install S / PDIF (RCA, BNC, optical) and AES / EBU (XLR) digital outputs on their products, and do not use the capabilities of the popular USB interface ? Let's try to clarify the answer to this question.
The main difference between the standards for connecting a computer and a DAC, S / PDIF and AES / EBU, on the one hand, and USB, on the other, lies in the method of data transfer. In the first case, data from the computer, using the appropriate interface, is transmitted to the DAC in the form of a continuous stream, that is, in the form that they acquire after the software player. In the second case, in accordance with the USB data transfer protocol, the data stream is first divided into packets, and then transferred to the USB DAC input, in which it must again acquire the form of a continuous stream before digital-to-analog conversion.
In addition to the data corresponding to audio information, the data packets transmitted via the USB connection also contain configuration, control and status information.
The Universal Serial Bus specification defines various types of timing when transferring information from a host (computer) to a peripheral device (in this case, a DAC). At the initial stage of using USB for sound output from a PC, the so-called adaptive type became widespread, technically related to the company's PCM270x series chips. Burr Brown (Texas Instruments) from USA.
However, this type of USB connection could not provide high quality sound, as it caused an increased level of jitter. In addition, converters with a USB input based on the PCM270x chip operating in adaptive mode could work with sampling rates no higher than 48 kHz and bit depth up to 16 bits, that is, they could provide CD-level quality, but not high resolution.
After several stages of development of digital audio transmission technology via USB in 2004 by the company Wavelength Audio(USA) was released the first DAC using asynchronous type of data transfer. The converter and the software needed to make it work, called Streamlength, were developed by Gordon Rankin. Since then, the asynchronous USB interface has established itself as the go-to for transferring a music signal from a computer to a DAC, and Streamlength's asynchronous USB software is used in many high-end DACs, including from companies such as Ayre, Aesthetix, grace design, Berkeley Audio design and others. Currently, most of the produced digital-to-analog converters, which are equipped with a USB interface for connecting to a computer, work on this principle.
Unlike adaptive, the asynchronous type of operation of the USB interface for sound transmission is technically more advanced, because. when implemented, not only data packets are transferred from the computer to the DAC, but feedback is also provided to the computer in such a way as to control the process of this data transfer. The computer and the DAC work in this case in concert, as connected devices.
Interestingly, asynchronous USB was based on the TAS1020B chip, which was released simultaneously with the mentioned PCM270x. The TAS1020B USB controller is an integrated circuit with a USB transceiver, a microprocessor, a memory buffer and an I 2 S interface for connecting to a digital-to-analog converter chip. As an example, in fig. Figure 1 shows a block diagram of a DAC based on the TAS1020B USB controller.
In this asynchronous USB DAC circuit, the sample rate clock is placed in the optimal location, right next to the digital-to-analog converter chip. This allows the converter to be powered by a potentially more accurate oscillator without relying on an unstable clock signal from the computer. Indeed, such a high-precision oscillator layout, along with other features of the asynchronous USB connection type, provides the lowest level of jitter and, accordingly, the best sound quality. Compared to the adaptive type, jitter is reduced by two orders of magnitude (100 times!) in asynchronous USB.
In addition, a special driver is required to operate the asynchronous USB converter with signals above 96kHz/24bit from a Windows PC. For computers Apple that support the USB Audio Class 2.0 specification, such a driver is not needed.
First DACs Wavelength Audio with asynchronous USB, they could convert VR signals with a sampling rate of up to 96 kHz and a bit depth of up to 24 bits. Currently, digital-to-analog converters are being produced, including those for domestic use, which support frequencies up to 384 kHz and bit depth up to 32 bits, which corresponds to the highest format of professional digital audio recording. In addition, DSD digital music recordings have recently become more widespread, the signals of which can also be fed to the DAC via the USB port. Not so long ago, in 2012, the open standard DoP (DSD over PCM) was developed specifically for this purpose - a method for transmitting DSD audio using PCM frames. Description of the latest version 1.1 of this standard in English. lang. can be found.
DAC manufacturers offer a wide range of devices with asynchronous USB costing from 3 thousand rubles. to astronomical seven-figure prices. In order to somehow navigate this variety of converters of various technical and price levels, let's try to determine what requirements the DAC must meet, so that we can say that it produces sound of really high fidelity. Here are some of the characteristics associated with the USB input interface:
- High quality USB controller chip.
- Use of galvanic isolation.
- USB Audio Class 2.0 specification compliant.
- High precision, low jitter clock.
- Use of high quality drivers.
- Perfect power plan. Separate stabilized power lines for the USB controller, converter and analog circuits, or better - with a separate transformer for each of them.
- High quality digital-to-analogue converter chip.
Vinyl, of course, is now a fashionable thing, friends, but it will never have to overcome the digital distribution of music. For more than a decade and a half, digital sound sources have firmly held a dominant position in both the professional and consumer electronics sectors. Let's talk about how to squeeze the most Hi-Fi juice out of a range of fruits - from Internet radio stations to 24-bit audio.
Once upon a time, a CD player was the only solution, and generally considered cool High End at first, but today this topic seems to be considered morally exhausted. Yes, in the old fashioned way, many still keep CDs in their collections, but as a physical medium, it loses to vinyl, which looks tritely beautiful, and is technically inferior in terms of HD audio parameters, which are already being sold on the Internet not only by audiophiles, but also by major labels. Thus, instead of a CD player, we need a more versatile device with external inputs that can convert the binary code from zeros and ones to an analog signal, which would then be fed to the amplifier and speakers in the end.
DACs are everywhere
A block with a digital-to-analog converter (DAC, converter, DAC) is equipped with both an AV receiver, and a CD, and, in principle, any media player. As a standalone device, DACs appeared as a high-end upgrade to an existing CD player. The designers believed that it would be more reasonable to separate the player into separate blocks with their own power supply.
One of the first Sony DAS-R1 external DACs, released in late 1987 In the first, the actual mechanical part was installed with a reading optical system and a digital output. It was called CD transport. There were no moving nodes in the second block - only the DAC board, the value of which has now grown to the title of a digital hub. By the way, it often happens that a modern CD player has a couple of digital inputs for connecting external sources.
The life cycle of sound from the source, subsequent recording and digitization, processing, and the reverse cycle - digital-to-analog conversion A modern converter interacts with a number of signal sources - the main thing is that there is an appropriate switching for everyone. An old DVD player can also be a source - they are usually connected via an optical TosLink or a coaxial cable. The latter looks like an ordinary "tulip" from a stereo pair. Expensive models may still use XLR connectors. Using the USB input, you can connect a computer or portable audio source to the DAC.
In addition, portable DACs are made compatible with sources based on iOS or Android phones, iPods, tablets and other gadgets. In fact, in all these cases, the converter becomes an external sound module with a separate power supply and good stuffing, which could not be dreamed of in regular multimedia technology. And modern DACs are often equipped with a headphone amplifier.
Multi-bit and single-bit DACs
Until the 21st century, digital-to-analog converters only handled 16-bit audio, according to the Red Book CD format. There was simply no other. The CD sample rate was 44kHz, the professional DAT recorders were slightly higher at 48kHz. At first, all DACs worked on a "parallel" principle - all 16-bits were "weighted" on an R-2R matrix (ladder-type resistor circuit).
R/2R DAC Example Schematic Connoisseurs know by heart and appreciate chip brands such as Burr-Brown PCM63 or Philips TDA1541. However, R-2R matrices turned out to be expensive and not very technological pleasure. An accurate laser adjustment of all resistance values was required. Otherwise, during operation, inaccurate sampling of bits led to a violation of the linearity of the signal.
Therefore, the R-2R was replaced by DACs with a 1-bit conversion, called "delta-sigma". If the multibits gave out the signal voltage directly, based on all the 16-bit data received by the matrix, then in the delta sigma the voltage fluctuated depending on whether “zero” came to the receiver or “one”. 1 meant an increase in the voltage of the analog signal, and 0 meant a decrease.
Burr-Brown PCM63 multi-bit DAC chip Old audiophiles no, and they will remember the musicality of R-2R chips, but there is nowhere to go. Delta-sigma proved to be both more practical to set up and cheaper to manufacture. And the quality of the SACD format has proven that 1-bit conversion can handle High-End tasks very well. The sampling frequency of SACD is no longer measured in kilohertz, but in megahertz, so the circuit can do with very simple analog filters.
In classical PCM-based circuits, one still has to digitally filter quantization noise - there are several of them, and some DAC models provide the opportunity to choose one of them.
The delta sigma itself progressed towards hybrid circuits, where the stream was processed in cascades, both in 1-bit and in parallel circuits. But most importantly, the size of the digital word grew in them first to 24, and then to 32 bits. In addition, field-programmable gate array (FPGA) DACs are a promising area, where there are no traditional converters at all.
Modern Mytek Manhattan DAC works with PCM streams 32 bit / 384 kHz, DXD, DSD-DS-DSD256 (11.2 MHz) Why such extended capacity? For authenticity. The professional industry today uses 24-bit recording to provide a more accurate description of the original signal. As already mentioned, a number of music publications are already available in high-definition format. So you can, of course, listen to a stripped-down version on CD or MP3, but you must admit, it's more interesting to get one step closer to the sound engineers who fiddled with your favorite album. And therefore, your DAC must be fully prepared to receive high-definition content - both via USB and other data transfer protocols.
- Supported modes: 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz and 96 kHz, 16 and 24 bits
- Entrance: USB
- Outputs: audio 3.5 mm combined with optical
- Output level: 2.1 Vrms at 4.7 kΩ load, 1 Vrms at 30 Ω load
- Dynamic Range: 112 dB
Design
The appearance of the U2 is incredibly minimalistic. It fully justifies its name in the sense that the developers managed with small-scale production. The U2 does not come with a box, it comes in a regular bubble bag. The case is a small rectangular parallelepiped, on one end of which there is a short USB cable for connecting to a computer, on the other - a 3.5 mm output for an audio signal. The same connector serves as an optical output jack, allowing the U2 to be used as a USB to optical converter. In the corner of the device there is an LED for indicating operation.
In general, the design is simple, without frills, but given the marginal price and compact size, it’s stupid to find fault here. Moreover, it is worth noting that the internal design of the DAC is at a fairly high level, the soldering is of high quality, no savings were made on details (within the budget of the device, of course).
Sound
The following equipment was used for listening:
- Apple MacBook Pro 15″ early 2011
- Decibel as player
- Recordings in lossless formats
- Audio-GD NFB-6 as amplifier
- Headphones: Fischer Audio TBA-04, VSonic GR01
ESS Saber 9023 is an almost self-sufficient chip. It does not require complex binding (although it does not exclude it if the developers wish), therefore, in creating DACs on it, the main thing is not to spoil it. The developers of U2 succeeded in this to the fullest. They used the SA9023 chip from SAVITECH as a USB interface (despite the coincidence of the indexes, this chip has nothing to do with the DAC chip itself). A 27 MHz resonator with a PLL1705 chip is used as a generator. The design of the DAC uses a circuit without coupling capacitors at the output, which also has a beneficial effect on the sound. 
Windows users can use ASIO drivers developed by SAVITECH.
The funniest thing about this device is that it performs as well as many much more expensive solutions, and even outperforms some. First of all, this is the merit of a good DAC and controller, and secondly, in a competent circuit design.
Out of the box, the sound of the U2 is detailed, rather cold, but without an annoying excess of highs. There is a lot of air and lightness in the sound, although the bass also plays well. Sibilants are weak, background noise depends on the quality of your USB output (see below about the filter). The headroom is sufficient for most non-tight headphones. This DAC is well combined with various amplifiers, due to its "transparency" it practically does not introduce distortion into the sound image.
Modification
To unleash the full potential of U2, I sent it to a familiar master for revision. During the finalization of the DAC has undergone many changes:
- removed tantalum capacitors from the analog path and replaced with larger electrolytic ones
- the filter has been recalculated and its components have been replaced with higher quality ones, and the amplitude of the output signal has been slightly reduced to achieve greater detail
- implemented a separate power supply for the DAC chip
- some of the capacitors are shunted with ceramics
Since this modification could not fit in the original case, holes were cut in the cover for the capacitors and the entire DAC was shrink-wrapped. The view turned out to be a little artisanal, but the increase in sound quality more than justifies it.
After modification, the sound of the player becomes not so pronounced-cold, the bass drive is added, which makes the sound of the DAC more musical. The sound becomes "multidimensional", the imaginary scene becomes more voluminous, the separation of instruments improves.
USB filter
Since the U2 is powered by USB, and the small size does not allow for a serious power filter, the sound of the DAC depends on the quality of the implementation of the USB bus in your computer. To solve this problem, HiFiMeDIY offers a simple but effective isolator. It is made in the same form factor as the U2, but instead of an audio jack, it has a USB connector. By enabling it in front of the DAC (it doesn't have to be U2), you can noticeably improve USB power quality and sound. 
conclusions
Very inexpensive device with huge potential. Don't let the very simple appearance fool you, for its modest price this little DAC is able to please the owner with a very good sound.
These reviews are written real buyers external DACs in our store. We do not publish the names of customers for reasons of safety of personal data. Buying from us this or that product, you also have the opportunity to add your review.
Gorgeous cap. Switched to it from TEAC UD 501. Compared to 505m, the 501m has noticeably raised edges of the range, too thick bass and bright treble. This one is all right. The bass is tight and textured, the treble is accurate. With the same cabling (DH LABS RED WAVE power cable) the 501 would "whistle" on vocals on bright recordings. When listening to a calarature soprano, the 501st smelled of frank synthetics. The 505, on the other hand, sounds natural at the same moments. Very detailed and comfortable, which absolutely corresponds to its class. Has a great headphone amp. I tried the refurbished SENNHEISER HD 650 (300 ohm) It swings quite well, and there is still a margin for volume. I compared the sound with TEAC HA 501, according to the sensations, without taking into account the various power cables installed on them and connecting the interconnect, they sound about the same. But there is a separate analog device operating in class A, and here, adjacent digital circuits .... In general, with headphones, too, "test"! The only, I think, big minus is that when the jack is inserted, both line outputs are automatically turned off. And to switch listening to acoustics and back in headphones, you will have to constantly insert and remove the jack from the socket, which will quickly lead to wear of the socket itself and erasure of the metallization of the expensive jack. So I continue to use the HA 501 as a headphone amplifier.
I bought it to connect headphones to a Samsung TV, because. It only has an optical audio output. DAC with optical cable came up perfectly headphones work. True, when you go to Youtub, the blue light goes out at the DAC and the headphones do not work. For me, this is not critical, maybe I'll deal with it later. But the rating is excellent.
The DAC will noticeably improve the signal quality compared to any built-in sound card. Done minimalistically. No buttons, no settings. It just works. It is inexpensive compared to alternatives.
The purchased external DAC Cambridge Audio DacMagic 100 Silver was connected to my player Onkyo C-7030 via optical cable Kennerton MOF-010 1.5 m. Amplifier Onkyo A-9110, acoustics Polk T-50. The DAC is great, works great. Fascinating sound, lays out a piece of music by instruments while maintaining volume and scene. Amazing detail. Favorite compositions have acquired a new depth and clarity. Honestly, I did not expect such a agility from a small device ... Of the shortcomings, perhaps one is sensitive to temperature. This is also stated in the instructions. Initially, the DAC was installed in a small volume of an equipment rack. After 50 minutes of work, he just turned off. Looks like the protection worked. After eliminating the surrounding small space, drove it for almost 6 hours, everything works fine. Good CAP. I recommend.
