The AB-1.2 now fulfills and requirements!

QNKTC AB-1.2 USB Digital-to-Analog Converter

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:

It is a good sounding USB DAC 100% ready to use.

Although you don't have to, it allows you to experiment with audio
hardware. The schematics are open source.

Likewise, if you wish to, it allows you to experiment with open
source firmware and drivers.

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:

“It sounds annoyingly close to my own reference converter in my Bladelius
Embla player” - Watt Magazine

“Far more airy, dissolved, detailed and three-dimensional in 24/192 Flac
than the regular CD.” - Egil Erlandsen OAS

“Wav files into 96kHz from Blue Coast Records impressed with very natural
sound.” - Egil Erlandsen OAS

“I am surprised how well it plays right out of the box. Much too close to
my approximately 30 times as expensive CD player.” - DIY Audio forum
member

A few technical details:

Regardless of your type of computer read the Windows
Driver Installation Guide.

Asynchronous USB Audio powered by Golledge high-quality crystal
oscillators at 22.5792 and 24.576MHz

Supports the common sample rates of 44.1, 48, 88.2, 96, 176.4 and
192ksps

RCA (phono) stereo outputs

Asahi Kasei AKM4430 DAC

Atmel AVR32 general-purpose MCU programmed in open source C

ASIO driver for Windows programmed in open source C

Low-noise 3.3V LDOs powered from USB

The AB-1.2 is modular. An USB-I2S Module is plugged into an Analog
Board.

The option of experimenting with the power supply.

Lots of internal headers for experimenting.

You must provide a USB 2.0 mini-B cable. It is not included. Use a cable
shorter than 3m.

Purchasing

The AB-1.2 is sold with the help of PayPal. It is may be
via ordinary mail to Europe and Northern America. Delivery to Asia, Russia,
South America, Africa and Oceanea must use Shipping with Tracking
Number. Norwegian customers must use the right-hand menu for prices which
include tax (MVA).

International Mail
(EU, US, CA):

Shipping with
Tracking Number:

With Norwegian Shipping
and MVA:

1x AB-1.2 $170.00 USD 2x
AB-1.2 $340.00 USD 3x AB-1.2 $500.00
USD

1x AB-1.2 $220.00 USD TRK 2x AB-1.2 $440.00 USD TRK 3x
AB-1.2 $600.00 USD TRK

1x AB-1.2 inkl.mva 1,200.00
NOK 2x AB-1.2 inkl.mva
2,400.00 NOK 3x AB-1.2
inkl.mva 3,500.00 NOK

Press

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.

“The Q DAC pushed the
track into the room with fantastic top end and mid range transparency...”

“I haven’t heard a DAC even triple it’s price that comes close.”

Watt
Magazine 2013-02-28 (Norwegian)

En anmeldelse av DAC’en og en teknisk artikkel. Firmware-problemene
anmelderen hadde, er for lengst løst.

“I bruk er konverteren
en fest.”

“Fantastisk lydkvalitet til en utrolig lav pris. Mer er
det nesten ikke å si. Bortsett fra ‘løp og kjøp’.”

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.

“Notatene sier blant annet ‘tett,
veldefinert bass, nøytral klangkarakter, veloppløst og detaljert uten tegn
til skarphet. Kjapp, dynamisk spillestil’.”

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.

“Among other things the
notes say ‘tight, well-defined bass, neutral character, well-defined and
detailed without a sign of shartpness. Quick and dynamic playing style’.”

Pictures and Schematics

Click the thumbnails below to get larger pictures and full
schematics.

AB-1.2 Back

AB-1.2
Internals
AB-1.2 Schematics
with AK4430
USB-I2S
Module Schematics
USB-I2S Module
Mechanics

USB Audio Class 1 and 2

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:

Press the rear Prog button until the light changes

Keep pressing Prog until the light goes dark

Press and release Reset

The AB-1.2 should now be up and running in the new mode

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.

Links and Resources

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:

A large collection of technical information: Audio
Widget Readme file

Windows 7 instructions for Driver Cleanup and Driver
Installation

SDR-Widget Homepage,
Wiki and Project
Downloads

Audio-Widget Mail
Archive

Firmware
Source Code

Windows ASIO Driver Download
and Source ode

diyAudio
Discussion Thread (English)

HifiSentralen
Discussion Thread (Norwegian)

Audiofaidate
Discussion Thread (Italian)

AUDIO
PLANET Discussion Thread (Spanish)

FAQ

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 mailto:[email-masked]. 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?

Capacitors posts 670,
756,
763,
854,
867

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!!

Contact Information

Q N K T C enk. Børge Strand-Bergesen
Hvalstadlia 4,
1395
Hvalstad
Norway

[email-masked]
Tel: +47 90639918

Norwegian company registration number (org.nr):
986 023 739 MVA

Why “QNKTC”? Well, on a dark and misty
night in an electronics lab deep underground, a young electronics engineering
student (me) was soldering together what he thought would be a revolutionary DA
converter. The sound was very nice, gentle piano notes came out with clarity and
brilliance. But the thing also said "BLUHHHA" and "WHAHAHAHA" completely on its
own accord. Stunned by this surprise observation I walked home, dissapointed,
wet and cold. It was only the day after that I realized that the particular
combination of digital and analog filters in this DAC would give the
low-frequency quantization noise an enormous gain. Hence the odd behaviour in
the bass. And then out of the blue it struck me that, indeed, Quantization
Noise Killed The Cat. It's a true story!

Oh, and it has nothing to do
with the pop group Curiousity Killed The Cat.

ASIO is a trademark and software of Steinberg Media Technologies GmbH

Obsolete Kits

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