Why do I need a USB DAC? If you like music and have it stored or streamed on a computer, a USB DAC will sound a lot better than the analog output of your computer. A USB DAC is plugged into your computer with a USB cable and into your stereo system with an analog (RCA/Phono) cable. If you are fond of open source projects, this DAC in particular is something for you.
The AB-1.2 USB DAC from QNKTC does three different things at the same time:
The AB-1.2 lets you play high-resolution audio (up to 24 bits at 192kHz) from Windows, Linux and OS X computers. It is a hardware implementation of the Audio Widget
open source project. The project was started by an online group who wanted to develop a good solution for a USB DAC. So that's what we did! AB-1.2 simply happens to be the third (counting from 1.0) Analog Board
for the project.
This is what people say about its sound character:
A few technical details:
The AB-1.2 is sold with the help of PayPal. USD prices are for international customers. Norwegian customers must use the right-hand menu for prices which include tax (MVA).
With Free International
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Here is what the press writes about the QNKTC AB-1.2:
HiFi Pig 2013-11-12 (English)
A spectacular review of the AB-1.2. Read the full text for a listening experience described in great detail.
Watt Magazine 2013-02-28 (Norwegian)
En anmeldelse av DAC’en og en teknisk artikkel. Firmware-problemene anmelderen hadde, er for lengst løst.
Teknisk Ukeblad 2013-09-05 (Norwegian)
En teknisk artikkel om prosjektet som ligger bak AB-1.2. Det er også et bilde fra lab’en og en god forklaring på asynkron USB. Bildet viser et reelt debug-signal fra firmware i DAC’ens prosessor.
Oslo Audio Society 2012-10-29 (Norwegian)
Aller første ordentlige test av AB-1.2. Egil Erlandsen i Oslo Audio Society liker det han hører.
Oslo Audio Society 2012-10-29 (English-ish)
The very first proper test of the AB-1.2. Egil Erlandsen of the Oslo Audio Society likes what he hears.
Click the thumbnails below to get larger pictures and full schematics.
AB-1.2 Schematics with AK4430
USB-I2S Module Schematics
USB-I2S Module Mechanics
The AB-1.2 will operate in both USB Audio Class 1 (UAC1) and UAC2. In UAC1 it supports more than CD quality, 24bit/48ksps. In UAC2 it uses up to 32bit/192ksps for high quality audio.
The actual DAC chip receives 24-bit samples. The USB audio protocol is asynchronous with both UAC1 and UAC2. That means the analog part of the AB-1.2 minimizes jitter errors.
UAC1 is available with built-in drivers on Windows, Mac and Linux. UAC2 is available in Mac and Linux. For UAC2 on Windows you must install a driver. The driver is recommended even if you don't need UAC2 playback qualities. The Windows driver will let you play back high quality audio using ASIO capable players such as JRiver Media Center and foobar2000. Windows UAC2 will not work in generic Windows programs like web browsers. For that you will have to use UAC1. The good news about that is that "Pling - You Got Mail" will also not play on Windows UAC2. So with the listed players you can listen to music on Windows UAC2 without such interruptions.
UAC1 is indicated by a green light at the front of the AB-1.2. UAC2 is indicated by a red light. To switch between the two modes do as follows:
What does asynchronous USB mean? It means the DAC is the timing master. In typical digital audio based on S/PDIF (coax) and TOSLINK (optical) cables the audio data and the clock are synchronous. Both travel from the same source. This source is typically a CD drive. Such a drive may be made with a good clock circuit. Synchronous digital audio is also common over USB. Then the timing reference is derived inside the computer. That clock is often very noisy. With synchronous digital audio the DAC is responsible for extracting the clock signal. Instead, with an asynchronous protocol, the source of the audio data becomes the timing slave. Commands are sent on the USB cable from the DAC to tell the computer to speed up or slow down. This enables the DAC to use precision crystal oscillators instead of a complex clock regenerator. The audible result is that many of the typically digital artefacts are significantly reduced.
The open source Audio Widget project and its origin, the SDR Widget project, use various webpages to stay in touch and store project data. You are very welcome to join the project. Important web pages are found here:
Q: Do I have to be a programmer to use the USB-I2S module and AB-1.2?
A: No, you don't. It plays music right out of the box. But in the future you may perhaps want to install new firmware. That pretty much means following a very well documented routine of 13 simple steps.
Q: Do I have to be an analog hacker to use the USB-I2S module and AB-1.2?
A: No. But if you have a soldering iron you can tweak it. Although it works very well, it is designed as a starting point for DIYers.
Q: I am a programmer. Where do I start?
A: Visit the project links at the top of this page and join both SDR-Widget and Audio-Widget mailing lists. There is very little cross-posting. The SDR-Widget Wiki is a good starting point. It explais the git repository and other details.
Q: Which coding efforts are wanted?
A: We're always trying to improve on the MCU firmware. Our most pressing issue right now is Windows driver support. If you're familiar with Audio processing / USB / Windows drivers / Linux drivers, or related things, please join our efforts.
Q: I like analog tweaking. Where do I start?
A: It is very possible for you to design your very own Analog Board and fit the USB-I2S module on it. Such a board must include DAC, clocks and PSU. But if you don't want to make the whole thing from scratch, feel free to download the AB-1.2 schematics and see if there are areas where your knowledge can improve on things. Oh, and please feed your knowledge back to the group members.
Q: I'd like to reuse the PCB designs for a commercial project. What do I do?
A: Contact me at firstname.lastname@example.org. I have years of experience in commercial PCB design and manufacturing. We'll sort something out!
Q: The diyaudio thread is huge. Where do I look?
Linux player posts 758-759, 800
Layout, back panel posts 819, 825, 831
Test results post 819 currently evolving...
Jtest posts 761, 776, 781 currently evolving...
Feel free to suggest other highlights!!
Q N K T C enk. Børge Strand-Bergesen
ASIO is a trademark and software of Steinberg Media Technologies GmbH
The predecessors of the AB-1.2 are called AB-1 and AB-1.1. These kits are no longer for sale. If you own one, consult these web pages for information about your system. If you don't own one you may ignore these links. AB-1 AB-1.1