Onkyo TX-SR806 THX Ultra2 Plus 7.1 A/V Receiver


On the Bench

Here we found some, well, interesting numbers.

In terms of line level performance, within the audio band, the Onkyo exhibits a measured frequency response of 20 Hz - 20 kHz, + 0, - 1 dB. Inter-modulation distortion at the line level was actually below what our equipment can measure, while THD+N came in at a respectably low 0.00822%.

Next we confirmed Onkyo's published spec of 130W per channel, two channels driven.  We loaded two channels with 8 ohms (with the hardware set to the default >6ohm setting) and brought two channels up to 130W output where we measured THD+N at only 0.01944.  Simply excellent.

Next we moved on to the "cooking" tests.

As we've talked about in past reviews and articles, in all common amplifier topologies low-impedance loads have the inherent consequence of increased heat as the greater current (as opposed to voltage) is delivered.  Make no mistake: no matter how "good" a receiver is (no matter how much it costs), it cannot compete with separate power amplifiers for this reason.  There is simply too much crammed into one box.  Elaborate means of dissipating heat are possible, but they are expensive to the point of making the pursuit futile (i.e., you might as well just go the way of separates).

The 806 has what is common in any decent (and safe to use) receiver: a setting for low impedance speaker loads.  Specifically, in this case, you must set the receiver for either >6ohm loads or >4ohm loads.  Because of this we test the receiver's performance in both settings.

First we left the 806 in its 6 ohm setting, brought the output up to 1% THD (popularly accepted as the point of clipping), and measured the output with an 8ohm load.  We then loaded it with 4 ohms on each channel and measured again.  Switching the 806 to its  4 ohm setting we again measured with 8 and 4 ohm loads.  The results are tabulated as follows.

>6 ohm setting (default) >4 ohm setting
8 ohm load 144 Watts 36 Watts
4 ohm load 217 Watts* 56 Watts

* Time limited test under controlled laboratory conditions.

The results in the >6ohm setting are more than commendable for a receiver at this price point, with a special nod to the power delivered into 4ohms, demonstrating that the unit can swing some serious current, at least transiently.  The results when the unit was set of >4ohm load are disturbing to say the least, so much so that we must take a bit of a tangent to talk about exactly what that setting does and why it is there.

In a nutshell, it biases the power supply for less voltage and limits output as such.  The unit is prevented from dumping any significant amount of current, protecting it from ever going into a thermal meltdown, but consequently (in this case at least) putting the speakers at serious risk of damage from amplifier clipping.

The setting is there for safety reasons: when the governing bodies test an AVR for safety, included in what they do are amplifier tests involving steady state signals driven into test loads.  Under such conditions any amplifier gets hot, and when driving a low impedance load it gets even hotter.  In the case of just about every AVR on the market it gets too hot to be considered safe so the infamous speaker impedance setting is required: instead of getting hot, the amp's output is limited.  The consequences are that the unit is "safe", but underpowered in that setting (grossly so in the case of the 806).

Indeed one wonders how THX configured the unit during their tests as many THX speakers are 4ohm designs, yet in it's 4ohm setting the 806 is basically useless as an amplifier.

Now there have been some in the industry who will say, always "off the record" mind you, that using an AVR like the 806 in its default setting of >6ohms with speakers which are rated as 4ohm is just fine because no one actually plays steady state test signals all evening long.  They play movie soundtracks and music, neither of which taxes an amp the way steady state test signals do.  These people feel that the governing bodies' test methods are out of date and not indicative of real world usage.

On the flip side there are those who argue that what matters when it comes to safety is not what an AVR does "typically", but rather what is technically possible.  This seems a little extreme since it is technically possible for any automobile to be driven faster than is safe (by any standard) yet none are limited as such.

Safety is important and we at Secrets cannot endorse circumnavigating or disregarding safety functions, yet it seems clear a call must be made for a review of how CE AVRs are tested and what safety systems are mandated, perhaps with some consultation from manufacturers, people like THX, and other industry professionals.

Electrical Consumption

We also look at an AVRs idle power consumption since electricity use, especially as it relates to something "just sitting there" is of increasing importance to people.  Not surprisingly the numbers are slightly lower than last year's model:  the power-on consumption with no audio signal hovers right around 88 Watts in the default >6ohm speaker setting.  In the standby state its consumption is below what our equipment can measure so it can be assumed to be less than 2 Watts which is excellent!  As we expect, when switched to the >4ohm speaker setting idle consumption drops to just 56 Watts.  At first it may seem point moot since that setting is all but useless, however if using the 806 as a preamp/processor coupled to an outboard power amp, placing it in the >4ohm setting might shave a couple kWh off your power bill at the end of the year (or make you feel just a little less guilty if you leave it on by accident when not in use), and the unit gives off marginally less heat.

Please note and be aware though that if HDMI-Control is enabled, the 806 consumes no less than 50 Watts when in standby....all day, everyday.  The feature allows the 806 to "control" compatible equipment (say, turn on a TV for example), but would you really leave an incandescent lamp on 24/7 just for the convenience of not having to reach for its switch?