Yamaha RX-A6A 9.2CH 8K AV Receiver Bench Test Results!

Yamaha RX-A6A Introduction

The Yamaha RX-A6A is a 9.2CH 8K ready Atmos/DTS:X Receiver that retails for $2,200 and is one step down from their new flagship the RX-A8A. The RX-A6A has 11 channels of processing with 9 channels of built-in amplification rated at 150wpc. In this test report, I put the RX-A6A through our standard Audioholics bench tests and dig a little deeper to uncover the reasons for some of the performance issues I've discovered. I full written review with YPAO tests will come in early 2022 and will be linked up to this report.

All measurements were conducted using our Audio Precision APx585 8 Channel HDMI Audio Analyzer.  The Yamaha RX-A6A was defaulted to high-impedance (High Z) mode (8-ohms or more) and ECO Off unless otherwise stated.

For more information about how we measure power amplifiers, please see: Basic Amplifier Measurement Techniques

Yamaha RX-A6A Preamplifier Measurements

The RXA-6A is capable of outputting > 4Vrms unclipped from the multi-ch preamp outputs which is more than 2X voltage drive needed to make most external amplifiers reach full unclipped power. This unit has 2CH XLR outputs that yield 8Vrms unclipped output. That’s the good news.

Analog Preamp

In fact, with an analog input signal, the RX-A6A produced some of the cleanest preamp outputs we’ve seen in an AV receiver. The analog preamp section is ruler flat to the limits of my test gear (80kHz) and the distortion is incredibly low (.001% THD+N) or 100dB SINAD.

Yamaha RX-A6A Frequency Response Analog Pure Direct

For those wondering if “Straight” vs “Pure Direct” makes a measurable difference, it does!

Yamaha RX-A6A “Straight” vs “Pure Direct” Analog Preamp

In “Straight” mode, the distortion went up slightly from .001% to .005% THD+N and the bandwidth limited to 48kHz or ½ the 96kHz sampling rate of the unit’s DSP.

Note: While this distortion difference is measurable, it’s unlikely to be audible.

Yamaha RX-A6A SNR Pure Direct Analog

The Signal to Noise Ratio was much better (+24dB) on the analog preamp in “Pure Direct” (106dB A-wt @ 2Vrms with 410mVrms input) than in “Straight Mode” (82dB A-wt @ 2Vrms with 410mVrms input). This is of no surprise since the DSP is engaged  in “Straight” mode and the ADCs Yamaha uses are the culprit for the increased noise. I would use “Pure Direct” when feeding the RX-A6A analog input signals unless you absolutely want to engage bass management or you wish to upmix your 2CH music to German Bathtub DSP mode that Yamaha is so well known for.

HDMI Digital Source

And now the not so great news. With the RX-A6A engaged in “Pure Direct”, and HDMI input being fed a test signal from my APx585, I did a 1kHz sweep of multi-ch preouts (FL, C, FR, SurL, SurR, SBL, SBR) vs distortion. As you can see the Yamaha was able to output 4Vrms for all channels unclipped. However, I identified the C, Sur L and Sur R channels produced higher distortion than the rest of the channels tested once the output level exceeded 650Vrms. Please note, the distortion never went above 0.05% THD+N and likely inaudible, however.

Yamaha RX-A6A Vsweep vs Distortion (HDMI In, Preout)

Even with a digital source, “Pure Direct” still showed a measurable improvement in distortion as you can see with the lowest vertical traces in the graph above.

To illustrate the distortion differences between the problematic (Center, Sur L and Sur R) channels vs the better performing channels, I graphed all channels output voltage on the horizontal X-axis vs %THD+N on the left vertical Y-axis and SINAD on the right vertical Y-axis.

Yamaha RX-A6A Vsweep vs Distortion (HDMI In, Preout)

You can see the "good" channels produced > 90dB SINAD (.002% THD) while the "Center, Sur L and Sur R" channels produced < 70dB SINAD (but never exceeded .05% THD).

Yamaha RX-A6A HDMI Input Level vs Output Distortion

I determined that this unusual behavior was happening with an HDMI input that exceeded -9dBFS (this threshold changed a bit depending on the # of channels driven). You can see the distortion performance of the C, Sur L and Sur R channels drop about 22dB at that point. What this means is if you get an input signal greater than about -9dBFs below digital fullscale (0 dBFS), the distortion goes up on those channels 22dB, again likely inaudible but Yamaha could do better.

With a -10dBFS input signal, the FFT distortion from the unbalanced and balanced 2CH outputs was about the same (1dB better for unbalanced). At 2Vrms output, this is an extremely clean output with no ground hum or DC offset and the 3^rd harmonic down 102dB below the 1kHz fundamental. That’s superb performance not just for an AV receiver but for a high end digital preamp too.

 

Yamaha RX-A6A FFT Preout (2Vrms out, -10dBFS input)

Yamaha RX-A6A FFT Preout (2Vrms out, 0dbFS input)

 

Yamaha RX-A6A FFT Preout Center Channel (2Vrms, -10dBFS input)

The same test conditions were repeated on the main Left/Right channels this time with a digital full-scale input (0dBFS) and the volume adjusted to 2Vrms. You can see the distortion spikes went up about 6dB which is still an excellent measurement.  However, even with a -10dBFS input, the Center, Sur L/R channels still exhibited relatively high distortion harmonics (3^rd harmonic @ -70dB) which was about 25dB higher than the main channels under the same test conditions.

    

Yamaha RX-A6A Signal to Noise Ratio: DSP Engaged (Left) ; Pure Direct (right)

Note: Ignore CH 4 which is the subwoofer channel in this case.

With 0dBFs HDMI input, I measured the SNR at 2Vrms from the preouts. The left measurement is in “decode”  (106dB A-at) mode while the right measurement is in “Pure Direct” mode (112dB A-wt). There is about a 6dB lower noise floor if you run this receiver in “Pure Direct” mode. This is a good measurement and means you likely won’t hear hissing from your speakers during quiet passages.

Bass Management

With all channels set small, the HPF is correct 12dB/oct and LPF is correct 24dB/oct. This is what you would get from a THX certified product and is textbook good performance. If you set the main speakers large, the response is ruler flat up to 48kHz. “Extra Bass” (with mains set large) works as expected, copying bass from main speakers to the sub. You will want to use this mode if you still want the subs active for 2CH music when the mains are set to “Large”.

   

Yamaha RX-A6A Bass Management (fc = 80Hz)

 

Yamaha RX-A6A “Extra Bass” with Mains set Small

If you set the mains “small” and accidentally engage the “Extra Bass” feature, some weirdness happens as you can see in the graph above. Yamaha claims this is deliberate and was initially developed for small speaker systems without the capability of reproducing below 80-100 Hz. The processes emphasizes the second harmonic of the frequencies that the speaker is unable to reproduce. The theory is, by hearing the harmonics of a low frequency in the proper proportions, your brain interprets hearing the lower fundamental which is not necessarily present in the room. I haven’t confirmed this claim with small speakers but you’re welcome to try it for yourself. Though if you’re a purest like me, you’ll probably just want to not engage the “Extra Bass” feature if you set your speakers to “small”.

Yamaha’s manual PEQ function is perhaps my favorite tweak they offer. In their latest AVR’s, they’ve increased the resolution to allow for finer increments of adjustments of the center frequency. In the measurement below, I set Fc to 32Hz with a Q of 1.6 with a -8dB cut and that’s roughly what I measured.

Yamaha RX-A6A PEQ Manual Filter Engaged

HDMI PLL Mode and DAC Settings

I briefly watched a Youtube influencer review of this product and the reviewer gushed over how the sound changed with the various DAC settings so I was curious if I could measure what he was hearing.

Yamaha RX-A6A Jitter Setting Options

 

Yamaha RX-A6A Frequency Response & Distortion Comparison for Jitter Settings

There was virtually no measurable change when selecting the different level options for the HDMI Jitter PLL Mode. I could barely measure a slight shift in the LPF response above  50Khz and the resultant distortion was very similar for high sample rate (192kHz) test signals.

Yamaha RX-A6A DAC Settings

Yamaha RX-A6A Frequency Response & Distortion Comparison for DAC Settings

Measuring the amplitude response changes for the various DAC setting options was a bit tricky. I had to first lower the test signal sampling rate to 44.1kHz to better gauge the differences within the audio band. Then I had to increase the resolution of the measurement and zoom in on the vertical axis to see the response changes. As you can see above, the different DAC settings slightly impact the LPF response at 1/2 the sampling rate (22kHz). The "slow" DAC setting begins to roll off the high frequencies at around 18kHz with "short" and "sharp" exhibiting slightly more bandwidth out to 20kHz, respectively.

Yamaha RX-A6A Square Wave Response Various DAC Settings

I compared the time domain behavior of these different DAC settings by using a 1kHz square wave to observe the over/under shoot behavior. The "short latency" exhibited the most asymmetric response and most overshoot of the 3 settings for the leading edge of the signal. The "sharp" and "slow"settings were most symmetric with the "sharp" being slightly better. From a measurements standpoint, I would recommend using the "Sharp roll-off" setting to best preserve the bandwidth.

These measurement differences are quite minuscule and mostly academic. It's possible the reviewer heard a difference due to expectation bias, not based on the minor physical differences in the output caused by changing these settings. Alternatively, it could also be his HDMI source had lots of jitter that my test gear didn’t and the Yamaha was resolving that issue for him in this case. It's pretty cool that Yamaha offers so much customization of the DAC and HDMI jitter control. You can try the various settings to see if you hear a difference but if you don’t, leave them alone and don’t hassle it man. 

Power Measurements

Using our Audio Precision APx585 8-channel HDMI analyzer, we conducted a full barrage of multi-channel amplifier tests on Yamaha RX-A6A per our Amplifier Measurement Protocol. We tested power using three methods all of which were taken at < 0.1% THD + N:

• Continuous Full Power Bandwidth (CFP-BW) from 20Hz to 20kHz into 8 and 4-ohm loads (up to two-channels)

• 1kHz Power Sweep vs. Distortion (1kHz PSweep) - popularized by the print magazines, this is an instantaneous power vs. distortion test at 1kHz. The problem with this test is it often masks slew-related and/or frequency response problems some amplifiers exhibit at the frequency extremes, and thus inflates the measured power results. It does provide an instant gratification number for consumers to argue over on the forums, so we are now incorporating this test to please the masses.

• Dynamic PWR - 1kHz CEA-2006 Burst Method testing. This is a dynamic power measurement adopted from the car industry similar to IHF method only a bit more difficult for an amplifier and more representative of real musical content.

Keep in mind most review publications don't do continuous power measurements and they usually publish power measurements into clipping at 1% THD + N. Our measurements are very conservative as we use a dedicated 20A line with no Variac to regulate line voltage.  We constantly monitor the line to ensure it never drops more than 2Vrms from nominal, which in our case was 120Vrms. 

For more info on amplifier measurements, see:  The All Channels Driven (ACD) Test

Yamaha RX-A6A Frequency Response @ Speaker Output

The RX-A6A exhibited ruler flat frequency response from the power amp all the way out to 48kHz when driving an 8 ohm at 10Vrms.

The Yamaha RX-A6A put out some impressive power numbers IF you disable the dreaded nannies (ie. Eco and Low Impedance switch).

With two-channels driven, the 150 watt/ch rated RX-A6A delivered > 150 watts/ch for full bandwidth 20Hz to 20kHz at under 0.1% THD+N into 8 ohm load. It was able to muster 186 watts/ch at 8 ohms and 282 watts/ch for 4 ohms at 1% THD+N with 2CH driven for our 1kHz sweep test.

Yamaha RX-A6A 1kHz PSweep (2CH) - 4 ohms

 

Yamaha RX-A6A 1kHz PSweep (4CH) – 8 ohms

Even with the nannies turned off, Yamaha has built in protection to limit power with multiple channels driven as you can see the distortion rise to 10% (hard clipping) with 4 channels driven. I’ve seen this type of behavior before on other Yamaha receivers we’ve tested.

Yamaha RX-A6A 1kHz PSweep (7CH) – 8 ohms

With 7CH driven, the RX-A6A limits power to 52 watts. This is not surprising as Yamaha has always set their limiters very conservatively. It’s unlikely you would trip this limiter with real program material, however.

Yamaha RX-A6A ECO Mode

Sadly, Yamaha doesn’t have an ECO “Auto” mode like Denon/Marantz which switches to lower rails at lower power usage for increased efficiency and goes to the higher rails on demand to allow for maximum output when needed.

Hold the Nannies

I can say this till I’m blue in the face, but there will still be readers that will email me asking if they should set the impedance switch to the “low” setting since they are running 4 ohm speakers. If you want to severely limit the power of this receiver when driving more than 2 channels, be my guest. But, if you want the power you paid for, DON’T Do it. Here’s why:

With 2CH driven, the Low Z setting didn’t affect the power output much for 4 ohm loads but we did see a slight reduction of power into 8 ohm loads (168 watts/ch to 146 watts/ch @ 0.1%, and 186 watts/ch to 168 watts/ch @ 1%) since the amplifiers are pulling power off the reduced rail voltage from this setting. Eco mode did however greatly reduce the available output power as you can see below.

Yamaha RX-A6A  Power Test Eco On vs Low Z - 2CH, 8 ohms

The "Eco On" setting reduced the 2CH, 4 ohm available power from 282 watts/ch to 105 watts/ch. 

So far the Low Z setting doesn’t look that bad….or does it?

Yamaha RX-A6A  Power Test vs Low Z - 4CH, 8 ohms 

The Low Z setting completely neutered the power with 4CH driven from 152 watts/ch to 54 watts/ch at 1% THD+N.  With 7CH driven, in the Low Z setting, the power drops to a measly 24 watts/CH.  Keep the switch on the default high setting!

By comparison, leaving the receiver in the high Z setting but turning Eco On didn’t drop the power much in this case since the Yamaha already power limits with 7 channels driven to about 50 watts/ch anyway.

Bottom line: Keep the impedance setting at the default "8 ohms min" regardless of speaker impedance and keep Eco to "OFF".

  

Yamaha Dreaded Impedance Speaker Impedance Switch
Damn you Yamaha for populating this switch in the most visible menu of the GUI

Editorial Note: Impedance Selector Switch - No matter how tempted you may be to do so, DO NOT change the default "8 ohm min" impedance setting of ANY AV receiver.  All this does is starve your speakers of power, simply so Yamaha could get 4-ohm certification (at a reduced power level) without making the receiver get too hot during their power tests. We have tested this 'feature' on virtually every receiver that offered it in the past and the results were always the same: the low impedance setting robs your speakers of power. 

For more information, see:  Setting the AV Receiver Impedance Switch

Editorial Note About Dynamic Power Testing: The Yamaha RX-A6A is the first receiver I’ve been unable to perform CEA 2006 short dynamic burst testing since the nannies prevented the receiver to be driven into the distortion threshold for high dynamic transients.

# of CH	Test Type	Power	Load	THD + N
2	CFP-BW	150 watts	8-ohms	0.1%
1	1kHz Psweep	200 watts	8-ohms	1%
1	1kHz Psweep	175 watts	8-ohms	0.1%
2	1kHz Psweep	186 watts	8-ohms	1%
2	1kHz Psweep	168 watts	8-ohms	0.1%
2	1kHz Psweep	282 watts	4-ohms	1%
2	1kHz Psweep	241 watts	4-ohms	0.1%
4	1kHz Psweep	152 watts	8-ohms	1%
4	1kHz Psweep	136 watts	8-ohms	0.1%
5	1kHz Psweep	81 watts	8-ohms	1%
5	1kHz Psweep	71 watts	8-ohms	0.1%
7	1kHz Psweep	52 watts	8-ohms	1%
7	1kHz Psweep	52 watts	8-ohms	0.1%

Yamaha RX-A6A Power Measurement Table

The RX-A6A has similar continuous power output of the Marantz SR8015 with 2ch driven, but with power sweeps, the Yamaha had a bit more output (282 watts/ch, 2ch 4ohms vs 251 watts/ch on the Marantz). However, the SR8015 didn’t limit power like the Yamaha did with 7CH driven as it was able to deliver 101 watts/ch whereas the Yamaha only put out 52 watts/ch under the same test conditions.

Yamaha FFT Distortion Analysis (1 watt, 8 ohms)

Unfortunately the Yamaha RX-A6A did NOT produce SOTA distortion measurements like we’ve seen from its Marantz competitor. The FFT spectra is about 20dB higher at 1 watt than I measured on the SR8015.  Again, likely inaudible but academic nonetheless.

Yamaha RX-A6A Power vs Distortion (2CH, 8 ohms)

SINAD results are about 70dB for this amplifier. Which isn’t at that magic > 90dB number we see in truly SOTA performing amplifiers but it’s important to keep this into perspective. 70dB SINAD is still .03% THD+N which is below the audible threshold for most mere mortals.

 

Yamaha RX-A6A CH-CH Crosstalk (1CH, Undriven) @ 1 watt

The channel-channel crosstalk was excellent for a multi-ch receiver, especially one packing 9 channels of amplification. With ACD except for the one under test, the RX-A6A provided > -60dB of CH-CH isolation out to 20kHz. This measurement was taken from the HDMI input all the way to the speaker outputs. The preamp output section has even better results at -80dB ch-ch isolation. 

Summary

The Yamaha RX-A6A produced some truly state of the art measurements via the analog inputs and available output power with up to 2CH driven and some rather ho-hum measurements when driven with a digital input at levels near digital full scale, especially on some of the channels as previously noted. I don’t think any of the measurements I’ve shown here should be a showstopper if you’re a Yamaha fan, however. This unit has some impressive output reserves (if you disable the nannies) and should be able to drive a high quality 9CH speaker system with satisfying results. I will be conducting critical listening tests in the formal review process coming next. 

Unless otherwise indicated, this is a preview article for the featured product. A formal review may or may not follow in the future.