Onkyo TX-NR797 Internals

The Onkyo TX-NR797 is the top receiver in Onkyo's middle range NR receiver line-up for 2019/2020. This receiver has the following advertised specs:

9-channel amplifier

100 watts per channel into 8 ohms (20-20,000 Hz) at .08% THD, with 2 channels driven

https://www.onkyousa.com/product/tx-nr797/

https://www.zkelectronics.com/receiver/onkyo-tx-nr797/north-america/

After "auditioning" a few different Onkyo amps/receivers I finally landed on this one because of its price/feature ratio. Currently I am actually just using it for 4-channel audio, not movies etc. I could have got the previous years model cheaper, but it would not have supported Amazon Music/Alexa which I wanted since I am a Prime member. But it turns out that Amazon Music is not supported on these devices in Canada (but is in the US - go figure)! I can get around this using Alexa and streaming to the receiver though (but not ideal).

One pet peeve I have about the budget receiver manufacturers including Onkyo is that they only do firmware upgrades for about one year or two, thus forcing you to upgrade if you really feel you need whatever new whiz-bang software feature they have added. Too bad!

I was interested in how this receiver differs internally from the higher range RZ line-up, but I was not able to find any pictures online, so I took the cover off mine and took these pictures (using phone), just in case someone else wants this information as well.

One oddity is that the RZ models and European version of the NR797 support a "Pure Audio" mode, whereas the North American version of the NR797 do not (has "Music Optimizer" instead"). Not sure what kind of market research guides those kind of decisions!

Fig 1: Onkyo TX-NR797 top view

There are four main boards inside. At the bottom is the front panel board. At the back is the Audio/Video pre-amplifier board. Below that is the power amplifier board. At the left back is the standby power board. You can see the solid aluminium heatsink and also the automatic fan, just like the RZ models. The lower NR models have thin folded aluminium heatsinks and no fan. In typical audio use I have not seen the unit get hotter than about 40C so far. Older Onkyo receivers were apparently notorious for failures with the HDMI chip as it heated up (witness all the Youtube HDMI reflow videos). The chips here all use pins/legs instead of an BGA, so I am not anticipating any similar problems - but just in case I have added small heatsinks to all the larger chips (not shown).

Fig 2: Onkyo TX-NR797 HDMI board detail

Detail of the HDMI board (new design for 2019 models). The larger chips are:

• Panasonic MN864777 / MN864787 HDMI chips
• Texas Instruments TI D808K013DPTP3 DTS chip (not much information out there on this one)
• Cirrus Logic CS49844A-CQZ DSP chip
• Unknown ASIC
• Somewhere in there is also an AK4458 DAC chip

Fig 3: Onkyo TX-NR797 HDMI board detail 

Above you can see the Bluetooth/WiFi board with the antenna connectors. This receiver has lots of streaming support, which is the main reason I purchased it.

Fig 4: Onkyo TX-NR797 driver transistors

The amplifier section has 9 channels. The front two channels are "special" and are mounted on separate boards bolted to the heatsink. The chips here are Toshiba A1962 / C5242 bipolar power transistors. These retail for about $2 a pair on ebay, but I dont know how that relates to performance/quality. They are rated for 80W nominal / 130W max output.

Fig 6: Onkyo TX-NR797 filter capacitors

Above you can see the two power supply filter capacitors rated at 10,000uF. Ok, but not brilliant when compared to more expensive power amps I suppose.

Fig 7: Onkyo TX-NR797 transformer

Above is the main transformer , which is rated at 750W, and the standby power supply. Not much more to say here.

Anyhow, I really like this receiver and its not really missing much for my needs, other than a preamp out for the main channels (but I can live without that for now). Sound quality is excellent to my ears, and the AccuEQ room correction is a bonus when using multi-channel.

Cheers!