Onkyo TX-NR646

Onkyo TX-NR646 was introduced in 2015. It is equipped with 7 channel amplifier with 100 W (8 Ω, 20 Hz - 20 kHz, 2 channel driven) power per channel and is capable of 7.1 maximum channel processing. It supports Dolby Atmos and DTS:X, passes 4K/60Hz video signal.

We evaluated the a/v receiver and gave 82 overall score out of 100. Our ranking system is based on the amplifier specifications, audio and video features, connectivity, multizone capabilities, radio and many other details.

For more details about the ranking please go to    Evaluation section.

Here is a history of the series, where you can view and compare the main specifications of the receivers.

You can view their side-by-side comparison here: Onkyo TX-NR696 vs TX-NR686 vs TX-NR676E vs TX-NR656 vs TX-NR646 vs TX-NR636.

In this section we present pros and cons of Onkyo TX-NR646.

In 2015 Onkyo released 7 new receivers. Here is the lineup:

You can view their side-by-side comparison here: Onkyo TX-RZ900 vs TX-RZ800 vs TX-NR747 vs TX-NR646 vs TX-NR545 vs TX-SR444.

Onkyo TX-NR646 has replaced TX-NR636. Here we present differences between these two models.

UPGRADES	Onkyo TX-NR646	vs	Onkyo TX-NR636
Higher Power Output	100 W (8 Ω, 20 Hz - 20 kHz, 2 channel driven)	vs	95 W (8 Ω, 20 Hz - 20 kHz, 2 channel driven)
Higher DAC Specs	384 kHz/32 Bit	vs	192 kHz/24 Bit
DTS:X	up to 5.1.2 after firmware update	vs
DTS Dialog Control		vs
Dialog Level Adjustment	DTS:X only	vs
More Advanced Auto Speaker Calibration System	AccuEQ Advance	vs	AccuEQ
HDR10		vs
AirPlay	AirPlay	vs	AirPlay via optional Onkyo RI Dock DS-A5 (sold separately)
More HDMI Inputs	8 (1 front)	vs	7 (1 front)
More Optical Inputs	2	vs	1
More RCA Line Inputs	7	vs	6
More RCA Line Outputs	1	vs
More Component Video Inputs	2	vs	1
Deezer		vs
Higher Power Output (8 Ω, 20 Hz - 20 kHz, 2 channel driven, FTC)	100 W (0.08% THD)	vs	95 W (0.08% THD)

DOWNGRADES	Onkyo TX-NR646	vs	Onkyo TX-NR636
3-Stage Inverted Darlington Circuitry		vs	Front & Center Channels
Surround EX		vs	also known as Dolby Digital Surround EX
Video Signal Upscaling		vs	up to 4K/30p (Marvell Qdeo)
Component Video Maximum Resolution	480i/576i	vs	1080p
MHL Input		vs	Front HDMI
Less Coaxial Inputs/Outputs	1	vs	2
Less Composite Video Outputs		vs	1
Less Component Video Outputs		vs	1
Front A/V Inputs	HDMI	vs	HDMI/MHL, USB
Color-Coded Speaker Terminals		vs
Lower S/N Ratio (Line, IHF-A)	100 dB	vs	106 dB

For more detailed comparison between the models please visit Onkyo TX-NR646 vs TX-NR636.

Onkyo TX-NR646's 7 channel amplifier can be assigned for different speaker configurations.

• Dolby Atmos Configurations: The following speaker configurations are supported for Dolby Atmos:
5.2.2 with internal amplifier.
• DTS:X Configurations: The speaker configurations for DTS:X are the same as for Dolby Atmos:
5.2.2 with internal amplifier.
• Configurations without height channels: There are also other speaker configurations available which do not include height channels:
5.2, 7.2 with internal amplifier.
• 2-ch Bi-Amp: Onkyo TX-NR646 allows you to bi-amp up to 2 main channels simultaneously. During bi-amplification two amplifiers are used for one speaker. One amplifier powers the midrange and tweeter section of the speaker and another amplifier powers the low frequency woofers. Each amplifier is less loaded and performs better. In order to use this feature speakers must have 2 pairs of connectors.

Dolby Atmos

Onkyo TX-NR646 supports Dolby Atmos with Surround Upmixer.

• Surround Upmixer: If the content is not mixed in Dolby Atmos then the Dolby surround upmixer will expand the audio to all channels including ceiling speakers. The upmixer has replaced the Dolby Pro Logic II family with improved upmixing algorithms.

DTS:X

Onkyo TX-NR646 supports DTS:X .

• DTS Dialog Control: This function adjusts the dialog levels during playback of the DTS:X stream. It allows you to separately increase the dialog levels in contrast with the background sound and hear dialog easily even under noisy circumstances.

DECODING
Dolby Atmos	up to 5.1.2 after firmware update
Dolby Atmos Height Virtualization
Dolby Atmos Music
Dolby TrueHD
Dolby Digital Plus
Dolby Surround Upmixer
Dolby Pro Logic
Surround EX
DTS:X	up to 5.1.2 after firmware update
DTS Neural:X	after firmware update
DTS Virtual:X
DTS Neo	Neo:6 until firmware update
DTS-HD Master Audio
DTS-HD High Resolution Audio
DTS 96/24
DTS Express
DTS-ES
IMAX Enhanced
Auro 3D with Auro-Matic Upmixer

Onkyo TX-NR646 features 8 HDMI inputs. It has 2 outputs which work parallelly and output the same signal.

• 4K/60Hz Passthrough: All inputs pass up to 4K/60p (RGB/YCbCr4:4:4/YCbCr4:2:2, 24 bit) video signal.
• Analog To HDMI Upconversion: The a/v receiver supports video upconversion, so you can connect your analog Component and Composite video sources and Onkyo TX-NR646 will output them via HDMI. This means that you will need only one HDMI cable to connect to your TV.
• HDCP 2.2 Copy Protection: 3 inputs and 2 outputs are HDCP 2.2 compliant which is a requirement for 4K/HDR copy-protected content transmission.
• 3D Ready: Onkyo TX-NR646 is able to pass 3D video through HDMI.

andh3>HDR (High Dynamic Range)

Onkyo TX-NR646 supports HDR (high dynamic range) video formats such as HDR10 via HDMI ports. High dynamic range video has greater dynamic range than standard dynamic range (SDR) video with brighter whites and deeper blacks. The result is greater contrast and more details in dark and bright areas, better color and depth.

VIDEO FEATURES
HDR10
HDR10+
Dynamic HDR
BT.2020 color space
Dolby Vision
HLG (Hybrid Log Gamma)
HDBaseT Compatible
Enhanced Audio Return Channel (eARC)
HDCP Version	2.2 (3 inputs / 2 outputs)
QMS (Quick Media Switching)
ALLM (Auto Low Latency Mode)
VRR (Variable Refresh Rate)
QFT (Quick Frame transport)
3-D Ready
Video Signal Passthrough	up to 4K/60p (RGB/YCbCr4:4:4/YCbCr4:2:2, 24 bit)
Video Signal Upscaling

Onkyo TX-NR646 comes with AccuEQ Advance room correction system and includes the calibration microphone.

• AccuEQ: First, AccuEQ detects the presence of speakers and evaluates the impedance of each. Next, it pinpoints their distance relative to the main listening position using the mic and sets suitable sound-pressure levels. Then it selects the optimal crossover frequency so that deeper bass rolls smoothly off to the subwoofer. Finally, AccuEQ performs frequency response equalization based on room-acoustic and speaker data collected via microphone. The sound-field is now tailored around the listening position, resulting in a more immersive and realistic in-film experience.

Onkyo TX-NR646 offers multi-zone playback which allows you to play different input sources in 2 different rooms.

Zone 2

• Powered Zone 2: You can use the unit's 2 amplifier channels by connecting Zone 2 speakers directly to the speaker terminals. The remaining 5 channels will be left for main zone amplification.
• Audio Line Output: If you have a dedicated integrated amplifier for Zone 2 you can connect it to the a/v receiver via line outs by sending fixed signal and then control volume on the Zone 2 amplifier.

Audio

• Phono Input: There is an MM phono input with built-in phono stage for connecting the moving magnet cartridge output of the turntable directly to the a/v receiver.
• Analog Line Inputs and Outputs: There are 7 line inputs and 1 line output for analog audio connection.
• Digital Inputs: 2 optical inputs and 1 coaxial input are available for digital audio connection.
• Headphone Output: There is a 6.3 mm (1/4") headphone output jack on the front panel.

Video

• HDMI:
Inputs: 8 (1 front)   Outputs: 2 (simultaneous)
8K Inputs: 0
• Composite Video: Connect you VCR, Laserdisc player and other old video equipment with composite video cables.
Inputs: 3   Outputs: 0
• Component Video: Component video connection gives you the higher quality video compared to the composite video connection. So in case your old DVD player and other equipment do not have an HDMI output but have Component video output use this connection over the composite one. Onkyo TX-NR646 supports up to 480i/576i resolution on Component video connectors.
Inputs: 2   Outputs: 0

Front A/V Inputs

• HDMI

In 2016 Onkyo TX-NR646 was replaced by Onkyo TX-NR656. Let us now have a look at some important differences between Onkyo TX-NR646 and its successor.

UPGRADES	Onkyo TX-NR656	vs	Onkyo TX-NR646
VLSC (Vector Linear Shaping Circuitry)	Front L/R channels	vs
DTS Neural:X	after firmware update	vs	after firmware update
Higher Resolution Music Playback via USB	up to 192 kHz	vs	up to 96 kHz
High Resolution Audio Formats via USB	FLAC, WAV, Apple Lossless, DSD, AIFF, AAC, Dolby TrueHD	vs	FLAC, WAV, WMA Lossless, Apple Lossless, DSD, AAC
Dialog Normalization		vs
BT.2020 color space		vs
Dolby Vision		vs
Video Signal Upscaling	1080p to 4K	vs
Chromecast Built-In		vs
Front A/V Inputs	HDMI, Mini-Jack	vs	HDMI
Tidal		vs
Higher S/N Ratio (Line, IHF-A)	106 dB	vs	100 dB
Higher DSD Sampling Rate via USB	2.8 MHz, 5.6 MHz	vs	2.8 MHz, 5.6 MHz
Wi-Fi Standard	IEEE 802.11 a/b/g/n	vs	IEEE 802.11 b/g/n
Wi-Fi Terminal Frequency	5 GHz, 2.4 GHz	vs	2.4 GHz
Newer Bluetooth Version	4․1 + LE	vs	2․1 + EDR

DOWNGRADES	Onkyo TX-NR656	vs	Onkyo TX-NR646
Music Playback via USB	FLAC, WAV, Apple Lossless, WMA, MP3, DSD, AIFF, AAC, Dolby TrueHD	vs	FLAC, WAV, Apple Lossless, WMA, WMA Lossless, Ogg, MP3, DSD, AAC, LPCM, Dolby TrueHD
InstaPrevue Input Source Prevue		vs
Less RCA Line Outputs		vs	1
Less Composite Video Inputs	2	vs	3
ONKYO-RI System Control		vs
Pre-Pro/Learning Remote	/	vs	/
Pandora		vs
Independent Power Supply		vs	2
Lower DSD Sampling Rate via HDMI	2.8 MHz	vs	2.8 MHz, 5.6 MHz
Narrower AM Frequency Range	530 kHz - 1710 kHz	vs	522/530 kHz - 1611/1710 kHz

For more detailed comparison between the models please visit Onkyo TX-NR646 vs TX-NR656.

GENERAL
Brand	Onkyo
Model	TX-NR646
Type	A/V Receiver
Country	Taiwan
Release Year	2015
Predecessor	Onkyo TX-NR636
Successor	Onkyo TX-NR656

AMPLIFIER
Channels	7.2
Power Output	100 W (8 Ω, 20 Hz - 20 kHz, 2 channel driven)
Front Wide Channel Support
WRAT (Wide Range Amplifier Technology)
VLSC (Vector Linear Shaping Circuitry)
Optimum Gain Volume Circuitry
THX™ Certification
Continuous 6 Ω Rated
Certified 4 Ω Performance
Discrete Output Stage Circuitry
3-Stage Inverted Darlington Circuitry
PUSH-PULL Design
Independent Block Construction (Amp/Preprocessor)
Bi-amp Capability
BTL (Bridged Transless or Bridging)

AUDIO FEATURES
Digital Signal Processing (DSP) Engine	Dual 32-bit DSP for Powerful Advanced Processing
DAC	Asahi Kasei AK4458
DAC Specs	384 kHz/32 Bit
Maximum Channel Processing	7.1
Air Studios Monitor Certification
Dolby Atmos	up to 5.1.2 after firmware update
Dolby Atmos Height Virtualization
Dolby Atmos Music
Dolby TrueHD
Dolby Digital Plus
Dolby Surround Upmixer
Dolby Pro Logic
Surround EX
DTS:X	up to 5.1.2 after firmware update
DTS Neural:X	after firmware update
DTS Virtual:X
DTS Neo	Neo:6 until firmware update
DTS-HD Master Audio
DTS-HD High Resolution Audio
DTS 96/24
DTS Express
DTS-ES
IMAX Enhanced
Auro 3D with Auro-Matic Upmixer
PCM	2-ch/Multi-ch Input
Music Playback via USB	FLAC, WAV, Apple Lossless, WMA, WMA Lossless, Ogg, MP3, DSD, AAC, LPCM, Dolby TrueHD
High Resolution Music Playback via USB and/or Network	up to 96 kHz
High Resolution Audio Formats via USB	FLAC, WAV, WMA Lossless, Apple Lossless, DSD, AAC
Gapless Playback
DSD via HDMI	2-ch/Multi-ch Input
DSD via USB	2-ch Input
DSD to PCM Converter
USB DAC
Jitter Reduction	PLL (Phase Locked Loop) Jitter-Cleaning Circuit Technology for S/PDIF Audio
DTS Dialogue Control
Dialog Enhancement
Dialog Level Adjustment	DTS:X only
Dialog normalization
Dialogue Lift
Tone Control	Front L/R Channels
Compressed Music Enhancer	Advanced Music Optimizer (bluetooth included)
High-resolution Music Enhancer
THX Processing Mode
Audyssey Dynamic EQ
Audyssey Dynamic Volume
Audyssey LFC
Audyssey Sub EQ HT
Audyssey DSX
Phase-Matching Bass Boost	for Deep Bass and Clear Mid-Range
Direct Mode
Pure Audio Mode
Pure Direct Analog Path Mode
Virtual Speakers	T-D (Theater-Dimensional)
Independent Subwoofer Outputs

CALIBRATION
Auto Speaker Calibration System with Mic.	AccuEQ Advance

VIDEO FEATURES
HDR10
HDR10+
Dynamic HDR
BT.2020 color space
Dolby Vision
HLG (Hybrid Log Gamma)
HDBaseT Compatible
Enhanced Audio Return Channel (eARC)
HDCP Version	2.2 (3 inputs / 2 outputs)
QMS (Quick Media Switching)
ALLM (Auto Low Latency Mode)
VRR (Variable Refresh Rate)
QFT (Quick Frame transport)
3-D Ready
Video Signal Passthrough	up to 4K/60p (RGB/YCbCr4:4:4/YCbCr4:2:2, 24 bit)
Video Signal Upscaling
Analog To HDMI Upconversion	Component**, Composite
Component Video Upscaling
Analog to Analog Video conversion
Component Video Maximum Resolution	480i/576i
isf Certified Calibration Control

CONNECTIVITY
Wi-Fi
Bluetooth
Works with Amazon Alexa
Chromecast Built-In
Works with SonoS
DTS Play-Fi
MHL Input
DLNA 1.5
AirPlay	AirPlay
Apple Product Connection	iPod, iPhone and iPad
Remote App	Onkyo Remote App for iPod touch/iPhone and Android-Powered Devices
InstaPrevue Input Source Prevue

TERMINALS
HDMI Inputs	8 (1 front)
HDMI Outputs	2 (simultaneous)
8K Inputs
USB Input	1 (Rear)
USB DC Out Port
Optical Inputs	2
Optical Outputs
Coaxial Inputs	1
RCA Line Inputs	7
RCA Line Outputs	1
XLR Line Inputs
Phono Input
Multi-Channel Input
RCA Pre-Outs	0.2
XLR Pre-outs
Composite Video Inputs	3
Composite Video Outputs
S-Video Inputs
S-Video Outputs
Component Video Inputs	2
Component Video Outputs
Ethernet
Ethernet Switch
PC In
Front A/V Inputs	HDMI
Speaker A/B
Headphone Out	6.3 mm (1/4")
Detachable Power Cord
uport

ZONES
Number of Zones	2
Powered Zones	2
Zone 2 Outs	RCA Line Out
Whole House Mode
RS-232C Interface
+12V Trigger Output	0
Remote (IR) Input/Output	0 / 0

MISCELLANEOUS
On-Screen Display	Graphical Overlaid On-Screen Display (OSD) via HDMI with Quick Set-Up
ONKYO-RI System Control
RIHD (Remote Interactive Over HDMI)
Pre-Pro/Learning Remote	/
On Screen Remote Programming
Bi-directional Remote Setup via GUI
Smart Grid-Ready

RADIO
Analog Tuner	FM/AM
Presets	40
Digital Radio
Internet Radio	TuneIn
Pandora
Spotify
Tidal
Deezer
Napster
SiriusXM

CONSTRUCTION
Solid Aluminum Front
Speaker Terminals	9
Large Speaker Terminals	9
Color-Coded Speaker Terminals
Transparent High-Grade Speaker Terminals
Gold plated RCA terminals

POWER
Power Supply	AC 120 V, 60 Hz
Independent Power Supply	2
H.C.P.S. (High Current Power Supply)	Massive High Power Transformer
Toroidal Transformer
Power Consumption	6.4 A
No Sound Power	70 W
Standby Power	0.1 W
Capacitor Bank	8,200 µF
ECO Mode / Hybrid Standby Function

PHYSICAL
Dimensions (W x H x D)	435 mm x 173.5 mm x 329 mm 17-1/8" x 6-13/16" x 12-15/16"
Weight	9.4 kg (20.7 lbs)

SPECIFICATIONS
Power Output (8 Ω, 20 Hz - 20 kHz, 2 channel driven, FTC)	100 W (0.08% THD)
Power Output (6 Ω, 1 kHz, 1 channel driven, FTC)	170 W (0.9% THD)
Maximum Effective Power Output (6 Ω, 1 kHz, 1 channel driven, JEITA or IEC)	175 W
Rated Power Output (6 Ω, 1 kHz, 1 channel driven, IEC)	160 W (1% THD)
Dynamic Power per Channel (3 Ω, Front)	240 W
Dynamic Power per Channel (4 Ω, Front)	210 W
Dynamic Power per Channel (8 Ω, Front)	120 W
THD	0.08% (20 Hz - 20 kHz, Half power)
Damping Factor	60 (Front, 1 kHz, 8 Ω)
Input Sensitivity and Impedance (Line)	200 mV/47 kΩ (Line)
Input Sensitivity and Impedance (Phono MM)	3.5 mV/47 kΩ (Phono mm)
Phono Overload	70 mV (MM, 1 kHz 0.5% Direct)
S/N Ratio (Line, IHF-A)	100 dB
S/N Ratio (Phono MM, IHF-A)	80 dB
Frequency Response (Analog In)	10 Hz - 100 kHz/+1 dB, -3 dB (Direct mode)
DSD Sampling Rates via HDMI	2.8 MHz, 5.6 MHz
DSD Sampling Rates via USB	2.8 MHz, 5.6 MHz
Video Input Sensitivity/Output Level and Impedance	1 Vp-p/75 Ω (Component Y) 0.7 Vp-p/75 Ω (Component PB/CB, PR/CR) 1 Vp-p/75 Ω (Composite)
Video Frequency Response	5 Hz - 100 MHz/+0 dB, -3 dB (Component)
Ethernet Standard	10BASE-T/100BASE-TX
Wi-Fi Standard	IEEE 802.11 b/g/n
Wi-Fi Terminal Frequency	2.4 GHz
Bluetooth Version	2․1 + EDR
Bluetooth Frequency	2.4 GHz
USB Terminal	5 V, 1 A
FM Frequency	87.5 MHz - 107.9 MHz
AM Frequency	522/530 kHz - 1611/1710 kHz
Warranty	2 Years

* - 480i/576i and 480p/576p only
** - 480i/576i only
*** - no 1080p/24 upconversion
**** - 1080p signal is not converted