Audio T Verdict
The Audio Note DAC 2.1x Signature is a Level 2 digital-to-analogue converter built around an 18-bit Analog Devices AD1865N converter and a twin-valve analogue output stage.
The Signature model adds upgraded Audio Note components and a 6X5 valve-rectified power supply to the fundamental DAC 2.1x design. It accepts coaxial S/PDIF and professional AES/EBU digital sources without adding conventional oversampling, noise shaping, jitter reduction or re-clocking.
Connectivity is focused and the 3.2V output is fixed, so source and amplifier matching should be considered carefully. Within a suitable system, it provides a clearly defined step beyond the more compact DAC 0.1x.
Audio Note DAC 2.1x Signature Valve Digital-to-Analogue Converter
The Audio Note DAC 2.1x Signature converts compatible digital audio from a CD transport, streamer or other digital source into a stereo analogue signal.
It uses an Analog Devices AD1865N 18-bit converter, two 6DJ8 valves in its analogue output stage and a 6X5 valve rectifier in the power supply.
One 75O RCA coaxial S/PDIF input and one 110O XLR AES/EBU input allow it to accept two established digital connection formats.
This Is the DAC 2.1x Signature
This page describes the Signature version rather than the standard DAC 2.1x or the larger DAC 2.1x/II Balanced.
The Signature model adds upgraded Audio Note components and a 6X5 valve-rectified power supply. It retains single-ended RCA analogue outputs and should not be confused with the separate Balanced model.
What Does a Digital-to-Analogue Converter Do?
A CD transport, digital streamer or other source supplies music as digital data. A conventional amplifier requires an analogue electrical signal, so a DAC must perform the conversion before the music reaches the amplifier.
The DAC 2.1x Signature receives compatible PCM audio through its coaxial S/PDIF or AES/EBU input, converts it into analogue form and sends a fixed-level stereo signal to a preamplifier or integrated amplifier.
It does not contain a power amplifier, loudspeaker output or user-adjustable volume control.
Typical Signal Path
- CD transport or digital streamer
- Coaxial S/PDIF or AES/EBU cable
- Audio Note DAC 2.1x Signature
- Stereo RCA analogue interconnects
- Preamplifier or integrated amplifier
- Power amplifier and loudspeakers
Not Included
- CD transport or disc mechanism
- Network music streaming
- USB digital input
- Optical digital input
- Bluetooth connectivity
- Volume or headphone control
Audio Note Level 2 Design
The DAC 2.1x Signature is part of Audio Note's Level 2 range.
For this model, the Level 2 specification includes a valve-rectified power supply and a higher-grade selection of internal materials and components.
The level designation describes Audio Note's internal design hierarchy rather than the number or type of digital inputs.
Audio Note Non-Oversampling Architecture
Audio Note takes a different approach from digital converters that use oversampling filters and extensive corrective signal processing.
The DAC 2.1x Signature does not apply conventional oversampling, noise shaping, jitter-reduction processing or re-clocking. The incoming digital data is reformatted for the converter without multiplying the original sample rate.
This architecture is fixed and cannot be changed through filters, menus or selectable listening modes.
No Selectable Digital Filters
Many contemporary converters allow the listener to select between several digital-filter responses.
The DAC 2.1x Signature does not provide adjustable filters. Audio Note uses one predetermined conversion and analogue-filter arrangement throughout.
This makes operation straightforward, but it also means the DAC is not intended for listeners who require selectable upsampling or digital-filter controls.
Analog Devices AD1865N Converter
Digital-to-analogue conversion is performed by an Analog Devices AD1865N stereo converter.
The AD1865N is an 18-bit converter and forms the centre of Audio Note's non-oversampling digital circuit.
Audio Note specifies input capability at 44.1kHz, 48kHz and 96kHz. The connected source must be configured to supply a compatible signal.
18-Bit Conversion and 96kHz Input Capability
The internal AD1865N is an 18-bit converter, while the digital input circuitry can accept the published sample rates of 44.1kHz, 48kHz and 96kHz.
These figures describe different aspects of the design. The ability to receive a 96kHz signal does not make the converter itself a native 24-bit DAC.
Designed for Compatible PCM Audio
The manufacturer specifies conventional PCM sample rates rather than universal compatibility with every digital format.
The connected source should provide a compatible stereo PCM signal at 44.1kHz, 48kHz or 96kHz.
Native DSD, multichannel soundtracks and other unsupported formats may need to be converted by the source before transmission. When connecting a multipurpose player or television interface, stereo PCM provides the appropriate starting point.
75O RCA Coaxial S/PDIF Input
The RCA digital input has a specified impedance of 75O and accepts a coaxial S/PDIF signal.
It can be used with a compatible CD transport, digital streamer or another source equipped with a coaxial digital output.
Use a purpose-designed 75O digital coaxial cable rather than a conventional analogue RCA interconnect.
The
Audio Note CDT Three
provides one possible dedicated CD source for the DAC.
110O XLR AES/EBU Input
A second digital input is provided on a three-pin XLR socket and accepts the professional 110O AES/EBU digital format.
This connection requires a source with a compatible AES/EBU digital output and a correctly specified 110O digital cable.
A standard balanced analogue interconnect may use the same style of XLR connector, but it is not necessarily constructed to the required 110O digital specification.
The XLR Socket Is a Digital Input
The XLR connection on the DAC 2.1x Signature is a 110O AES/EBU digital input. It is not a balanced analogue output.
The Signature model supplies its analogue audio through single-ended RCA outputs. Customers requiring balanced analogue outputs should consider the separate DAC 2.1x/II Balanced.
No USB or Optical Input
The DAC 2.1x Signature does not provide direct USB or Toslink optical connectivity.
A computer, television or streamer equipped only with USB or optical output will require a suitable external digital interface capable of producing coaxial S/PDIF or AES/EBU.
A source with a native coaxial or AES/EBU output will generally provide the most straightforward connection.
Custom Filter-Interface Components
Audio Note uses custom filter-interface coils and transformers between the digital conversion circuitry and the analogue stage.
These components are designed and manufactured in-house for the required circuit rather than being selected as generic off-the-shelf filters.
They form part of the DAC's analogue filtering arrangement after the conventional digital oversampling filter has been removed.
Filter-Interface Transformers, Not Output Transformers
The DAC 2.1x Signature uses custom filter-interface coils and transformers within its conversion circuit.
This should not be confused with the separate DAC 2.1x/II Balanced, which adds dedicated analogue output transformers and balanced XLR analogue outputs.
Twin 6DJ8 Valve Output Stage
The analogue output stage uses two 6DJ8 double-triode valves.
These valves handle the converted analogue signal before it reaches the fixed-level RCA outputs.
They are internal parts of the circuit rather than exposed valves mounted on top of the chassis. Inspection, testing and replacement should be carried out by suitably qualified personnel.
6X5 Valve Rectification
The Signature model adds a 6X5 valve rectifier to its power supply.
Rectification converts incoming alternating current into the direct-current supply required by the internal circuits.
This is one of the principal differences between the Signature version and the standard DAC 2.1x, which uses solid-state rectification.
Signature-Grade Components
Audio Note equips the Signature version with upgraded internal components when compared with the standard model.
These include Audio Note tantalum resistors and selected Audio Note copper capacitors in key parts of the circuit.
The component upgrades and valve-rectified power supply should be considered as part of the complete Signature circuit rather than as isolated additions.
Standard, Signature and Balanced Versions
DAC 2.1x Signature
- Model described on this page
- Two 6DJ8 output-stage valves
- 6X5 valve rectifier
- Upgraded Signature components
- Single-ended RCA analogue outputs
Other DAC 2.1x Models
- Standard version uses solid-state rectification
- Balanced version uses a different valve stage
- Balanced version adds output transformers
- Balanced version provides XLR analogue outputs
- Each is a distinct model rather than an option
Fixed 3.2V Line-Level Output
The DAC 2.1x Signature has a published reference output of 3.2V RMS.
This is a fixed line-level output rather than a variable preamplifier output. Volume must be controlled by the connected preamplifier or integrated amplifier.
The 3.2V reference level is higher than the 2V output commonly associated with many CD players. It may therefore sound louder than another source when compared at the same amplifier-volume setting.
Do Not Treat the DAC as a Preamplifier
The DAC 2.1x Signature does not include a volume control and should not normally be connected directly to a power amplifier.
Direct connection could cause the system to play at full output. Use a suitable preamplifier, integrated amplifier or another properly controlled line-level input.
600O Output Impedance
Audio Note specifies an output impedance of 600O for the DAC 2.1x Signature.
This provides a relatively low source impedance for connection to a suitable preamplifier or integrated-amplifier line input.
Analogue interconnect lengths should remain practical, and compatibility should be checked when using equipment with an unusually low input impedance.
Compact but Deep Chassis
The DAC measures 145mm high, 300mm wide and 415mm deep.
Its 300mm width is narrower than many conventional full-width components, but its 415mm depth requires a suitably deep shelf with additional space for cables.
The unit weighs 5.1kg and should be placed on a stable, level support.
Ventilation and Warm-Up
Three internal valves and the power-supply components produce heat during normal operation.
Allow air to circulate around the chassis and avoid placing the DAC directly on top of a power amplifier or another component that generates substantial heat.
The DAC may take a short period after switch-on to reach stable operating conditions. It does not need to be left powered continuously when it is not in use.
Anodised Aluminium or Black Acrylic Fascia
The Audio T product options currently list anodised aluminium and black versions.
The anodised aluminium option provides the silver appearance, while the black version uses a black acrylic fascia.
The internal Signature specification remains the same, so the choice is primarily visual. Finish availability and current build lead times should be confirmed when ordering.
Key Features
- Audio Note Level 2 digital-to-analogue converter
- Signature version of the DAC 2.1x
- Audio Note non-oversampling conversion architecture
- No conventional digital oversampling
- No noise shaping
- No jitter-reduction processing
- No signal re-clocking
- Analog Devices AD1865N 18-bit stereo converter
- 44.1kHz, 48kHz and 96kHz input capability
- 75O RCA coaxial S/PDIF input
- 110O XLR AES/EBU digital input
- Custom Audio Note filter-interface coils and transformers
- Two 6DJ8 analogue output-stage valves
- 6X5 valve-rectified power supply
- Audio Note tantalum resistors
- Selected Audio Note copper capacitors
- 3.2V RMS fixed reference output
- 600O output impedance
- Single-ended RCA analogue outputs
- Anodised aluminium or black acrylic fascia
Frequently Asked Questions
How is the Signature different from the standard DAC 2.1x?
The Signature adds a 6X5 valve-rectified power supply and upgraded Audio Note components. The standard version uses solid-state rectification.
Is this the DAC 2.1x/II Balanced?
No. The Balanced version is a separate model with a different valve output stage, dedicated output transformers and balanced analogue outputs.
Is the XLR socket a balanced analogue output?
No. The XLR socket is a 110O AES/EBU digital input. Analogue output is supplied through stereo RCA sockets.
Does it contain a CD transport?
No. A separate CD transport or another compatible digital source is required.
Can it be used with a network streamer?
Yes, provided that the streamer supplies compatible PCM audio through coaxial S/PDIF or AES/EBU.
Does it have a USB input?
No. A computer or source equipped only with USB output requires a suitable USB-to-S/PDIF or USB-to-AES/EBU interface.
Does it have an optical input?
No. Its digital inputs are 75O RCA coaxial S/PDIF and 110O XLR AES/EBU.
Does it support 96kHz audio?
Audio Note specifies input capability at 44.1kHz, 48kHz and 96kHz. The internal AD1865N remains an 18-bit converter.
Does it oversample the signal?
No conventional oversampling is applied. The DAC also avoids noise shaping, jitter-reduction processing and signal re-clocking.
Does it include a volume control?
No. It provides a fixed 3.2V RMS reference output and should connect to a preamplifier or integrated amplifier with volume control.
Can it connect directly to a power amplifier?
It should not normally be connected directly because it has no volume control. Direct connection could cause the system to play at full output.
What valves does it use?
The Signature uses two 6DJ8 valves in its analogue output stage and one 6X5 rectifier valve in its power supply.
Will the valves eventually require replacement?
Valves have a finite operating life. Testing and replacement should be undertaken by suitably qualified service personnel.
Which cable should be used with the RCA digital input?
Use a purpose-designed 75O digital coaxial cable rather than a conventional analogue RCA interconnect.
Which cable should be used with the AES/EBU input?
Use a correctly specified 110O AES/EBU digital cable fitted with XLR connectors.
What finish options are available?
The fascia is available in anodised aluminium or black acrylic, subject to current production and availability.
Why Buy From Audio T?
- Experienced Audio Note digital-system specialists
- CD transport and streamer compatibility advice
- Coaxial S/PDIF and AES/EBU connection guidance
- Digital source-output configuration support
- Amplifier and preamplifier matching advice
- Digital and analogue cable recommendations
- In-store demonstrations through participating branches
- Ongoing valve servicing and system support
Contact your nearest Audio T store
to discuss source compatibility, finish availability and demonstration options.