Okto Research DAC8 PRO User manual

dac8 PRO
A versatile, high-performance 8-channel D/A converter
Owner’s Manual

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Contents
Specifications ..............................................................................................................................................................................................................3
Mechanical drawings................................................................................................................................................................................................5
Back panel overview.................................................................................................................................................................................................6
Package contents ......................................................................................................................................................................................................6
Digital connections....................................................................................................................................................................................................7
USB...........................................................................................................................................................................................................................7
Drivers.............................................................................................................................................................................................................7
AES/EBU inputs.....................................................................................................................................................................................................9
Signal integrity.............................................................................................................................................................................................9
SPDIF compatibility................................................................................................................................................................................... 10
AES/EBU output ................................................................................................................................................................................................. 10
Analog Connections............................................................................................................................................................................................... 10
Main outputs....................................................................................................................................................................................................... 10
Driving power amplifiers directly......................................................................................................................................................... 10
Volume operation......................................................................................................................................................................................11
Interfacing with legacy devices with single-ended inputs only...................................................................................................11
Headphone output ........................................................................................................................................................................................... 12
Input modes.............................................................................................................................................................................................................. 13
Pure USB............................................................................................................................................................................................................... 13
USB / AES............................................................................................................................................................................................................. 13
Pure AES............................................................................................................................................................................................................... 14
Controls ...................................................................................................................................................................................................................... 15
Rotary control ..................................................................................................................................................................................................... 15
Remote control................................................................................................................................................................................................... 15
User interface and menu system........................................................................................................................................................................ 16
Main screen, left................................................................................................................................................................................................. 16
Main screen, right.............................................................................................................................................................................................. 17
Main menu........................................................................................................................................................................................................... 17
Volume submenu.............................................................................................................................................................................................. 18
Routing submenu.............................................................................................................................................................................................. 18
System submenu................................................................................................................................................................................................ 19
Displays submenu..............................................................................................................................................................................................20
Filters submenu..................................................................................................................................................................................................20
Status submenu..................................................................................................................................................................................................23
Advanced submenu..........................................................................................................................................................................................24
Mains voltage selection.........................................................................................................................................................................................24
Troubleshooting.......................................................................................................................................................................................................25
Issue 1: USB input not recognized................................................................................................................................................................25
Issue 2: Dropouts during AES/EBU playback............................................................................................................................................25
Service and warranty..............................................................................................................................................................................................26
Manual revisions......................................................................................................................................................................................................27

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Specifications
Digital inputs / outputs:
-USB
-8 output and 8 input channels
-asynchronous, UAC 2.0 compliant
-playback data formats
-PCM, up to 192kHz / 32-bit
-native DSD, 64x / 128x
-DSD over PCM (DoP), 64x
-recording data format
-PCM, up to 192kHz / 32-bit
-AES/EBU
-4 AES/EBU inputs (SPDIF compatible)
-up to 192 kHz / 24-bit
-resampling-free (i.e. requiring a single signal source)
-unique USB/AES input mode ensures a bit-perfect data flow from
AES/EBU to USB, allowing for a real-time signal processing or
simultaneous recording & playback with no resampling applied
-1 AES/EBU output
-fixed to playback channels 1 and 2 (of USB or AES/EBU, depending on
the selected input)
Analog outputs:
-Main outputs (back side)
-8 x Neutrik gold-plated XLR connector
-output level: 4.2 V RMS differential full-scale
-output impedance: 200 Ohm (differential) or 100 Ohm (SE)
-capable of directly driving power amplifiers
-Headphone output (front side)
-6.3 mm (1/4”) TRS connector
-Output level: 4.2 V RMS full-scale
-120 mA linear output current
-fixed to output channels 1 and 2
-output impedance <100 mOhm

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Analog performance
-0.000032 % / -130 dB THD (Total Harmonic Distortion) full-scale, 1kHz
-0.00011 % / -119 dB THD+N (Total Harmonic Distortion + Noise) or 119 dB SINAD
(full-scale, 1kHz)
-125 dB of dynamic range
-0.000224 % / -113 dB THD+N @ 100 mW into 32 Ohm headphone output
Menu functions
-Individual volume for each of the 8 output channels (relative to the master volume)
-Routing matrix (any input channel to a specific output channel)
-Upper volume limit
-Remote control learning
-Choice between 7 PCM reconstruction FIR filters
-Configurable display timer to dim or turn off the displays
-Configurable Auto on / Auto off with non-zero audio data detection
-Adjustable 2nd and 3rd order THD compensation
Other features
-Trigger output
-5 V voltage level (works with most 12 V trigger inputs)
-short-circuit proof with 15 mA maximum current
-pulse or continuous
-Full control with either rotary or remote control
-Rack-mountable with optional 2U, 19” rack mounting brackets
Dimensions
-446 x 183 x 50 mm, (17.56 x 7.2 x 1.97 in), excluding removable feet
-Weight: 4.5 kg (10 lbs)
Power
-Mains voltage: 120 V AC or 230 V AC, according to the mains voltage of the country
from which the order was placed, unless requested otherwise
-Standard 3-pin IEC 60320 power connector
-Power rating: 15 W
-Fuse: F400mA

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Mechanical drawings

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Back panel overview
Package contents
-dac8 PRO (silver or black depending on your choice, 120 V or 230 V according to the
mains voltage of the country from which the order was placed, unless requested
otherwise
-rack mounting brackets (optional)
In an effort to reduce electronic waste, we've decided not to include the standard disposable
USB and power cables in the package. We understand that audio enthusiasts often already
own their preferred cables.

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Digital connections
USB
The dac8 PRO is compliant with USB Audio Class 2 (UAC2), a widely used digital audio
interface standard that enables asynchronous operation. This feature allows the DAC to
control data flow according to its own high-precision oscillator, bypassing any requirements
for the precision of the clock in the source device or cables.
Drivers
The UAC2 standard also enables operation with Mac OS and Linux without the need for
installing additional drivers. The dac8 PRO will be recognized as an 8-channel playback
device and an 8-channel recording device. The only action required by the user is to select
the dac8 PRO in your operating system's audio control panel.
This also applies to Windows 10 and newer; however, we strongly recommend installing the
Okto Research ASIO driver to bypass the Windows sound mixer and enable exclusive access
to the device for bit-perfect, low-latency operation. The driver can be downloaded from the
following link:
https://oktoresearch.com/assets/OktoResearchUsbDriver.zip
To install it, extract the executable file from the archive, run it and go through the steps.

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After a successful installation, the Okto Research icon will appear in your system tray. If the
unit is connected to the computer, it will be recognized by the driver, as shown in the
following image.
Please note: this driver will only work with units running firmware 1.5 and newer. Units with
older firmware have different USB identifiers and will not be recognized. Please contact us
to receive an ASIO driver compatible with older firmware versions.
Once the installation is complete, the "Okto Research USB device" will become available in
any ASIO-capable playback software. The following image shows the output device setting
in JRiver:
To reduce latency, navigate to the USB driver's control panel, select the "Buffer Settings"
tab, and change the buffer size in the dropdown menu. The dac8 PRO is tested to work with
1.5 ms output latency for playback and 1.67 ms for recording; however, the host computer
must be able to provide data in a timely manner to avoid buffer underruns and dropouts
during playback.

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Warning: The USB input of the dac8 PRO may not work correctly when connected to a USB
hub or a legacy USB 1.0 port. Be sure to use a USB 2.0 (or newer) port when connecting the
unit.
AES/EBU inputs
The dac8 PRO offers four AES/EBU inputs that are free of resampling. This allows for bit-
perfect playback, as well as recording at the USB host side. However, it also requires the
inputs to be mutually synchronized and carry signals with matching sample rates.
Due to the device's design, there is a specific order in which individual AES/EBU inputs must
be connected. If only one input is used, it must be the first input; if two are used, they must
be inputs 1 and 2. There are no further requirements for inputs 3 and 4.
Signal integrity
AES/EBU (as well as SPDIF and TOSLINK) is a synchronous connection, meaning that the
signal source device also serves as a clock source. Moreover, the clock signal is encoded
into a single bitstream with audio data using biphase mark code. This places the
responsibility of reconstructing the clock signal on the receiving device, and in the case of a
D/A converter, deviations can lead to undesirable noise or spurious signals at the output.
Although the dac8 PRO employs the highly effective Sabre jitter elimination algorithm, it is
recommended to ensure the best signal integrity possible. One important and commonly
overlooked factor is cable impedance. The source and termination impedance for AES/EBU
is 110 Ohms, and while reception will likely work with a line cable, using a dedicated cable
with 110 Ohm impedance is highly recommended.

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SPDIF compatibility
The AES/EBU inputs of the dac8 PRO will also accept a signal with the SPDIF voltage level
of 0.5V peak-to-peak. The termination impedance requirements differ between the two
standards, and while the SPDIF signal will generally be received correctly, it is recommended
to either employ an impedance-matching transformer or use a 75 Ohm RCA –XLR cable
and solder a 240 Ohm resistor to the XLR connector on the receiving side, effectively
decreasing the termination impedance from 110 Ohms to 75 Ohms.
AES/EBU output
The AES/EBU output is always active, transmitting channels 1 and 2 of the audio data
currently being played by the dac8 PRO, with the master volume applied. The per-channel
volume value is not taken into account.
Analog Connections
Main outputs
The main analog outputs provide 8 channels that represent 8 signals from the selected
digital input, converted to the analog domain with extremely high precision.
The main outputs are not muted when the headphone jack is plugged in. The reason for
this is that the operational amplifiers driving the main outputs are also responsible for driving
the headphone amplifier.
Driving power amplifiers directly
Low output impedance allows the unit to directly drive inputs of power amplifiers without
the need for a pre-amplifier. In such a setup, the full-scale output voltage of the DAC, which
is 4.2 V RMS in the case of the dac8, and the input sensitivity (voltage required for full power)
of the power amplifier should ideally match to optimally utilize the dynamic range of the
devices. Below are two examples of how the dynamic range can be negatively impacted if
there is a significant difference between the two values: