Mikhail Naganov

Marantz AV7704 As An Audio Hub

I have a Marantz AV7704 A/V receiver that I was using for some of my work projects. I know Marantz well for their classic “Hi-Fi” equipment: CD players and receivers. Originally an American company, it was acquired by its Japanese competitor Denon, forming a “D&M” holding. Then the holding was bought by “Sound United” which now owns “Classé”, “Denon”, “Marantz”, and “Polk” brands. We can only hope that all these corporate games didn’t degrade the quality of the products.

Up until the last month I was considering this receiver for work usage only but lately I decided to give it a bit more use and hook it up for my daily listening. My goals were:

So let’s see how this receiver performs. The documentation on its technical capabilities is quite scarce, it will be useful to fill up missing information on measurements.

First Look

This is quite a versatile receiver. If you look at its back panel there is no shortage of inputs and outputs:

AV7704 supports 3 audio zones, and its remote has 14 buttons for selecting an input. The inputs utilize a range of technologies from good old analog to digital wireless. This is somewhat overwhelming. I decided to wear a consumer hat first and see what functions I can utilize.

Inputs

My usage of AV7704 is 95% for audio playback. I have the following “use cases”:

Currently I have a stereo setup but nevertheless I enjoy listening surround re-issues of famous albums downmixed into stereo for headphones (binaural). Sometimes surround remixes reveal background details that I missed on the original stereo mixes.

What AV7704 can offer to me? It has a built-in HEOS player which supports some streaming services and Internet radios, however Play Music is absent from the list. Not a big problem—I have a Chromecast HDMI dongle and NVidia Shield TV Pro set-top box that I can connect to HDMI inputs.

Playing local stereo is of course supported by HEOS, and the most convenient way for making files from a local server to be accessible to HEOS seems to be via a Plex server. In theory HEOS can connect to network shares directly, but I couldn’t make it work.

Unfortunately, HEOS doesn’t support surround audio files and neither does Chromecast. Shield comes to the rescue offering a Plex client and VLC apps. Both support “pass-thru” mode for sending encoded surround audio to the HDMI output of Shield directly.

AV7704 also has support for Bluetooth and AirPlay. However, Bluetooth is obviously lossy and limited to stereo, and AirPlay requires using a computer or an iOS device—not my option.

Outputs

Here I’ve got somewhat atypical demands. I need optical output to feed the miniBox for LXminis and the subwoofer, with volume control! I need parametric equalizers for interfacing SPL Phonitor mini headphone amplifiers.

This is where AV7704 falls short for me—it only offers HDMI outputs and analog outputs (line and headphone), no SPDIF. Also, the EQ on this unit is a classic “Graphic EQ” with fixed bands and no adjustment for the “Q” value of filters. It’s good that this receiver at least offers tone controls, I will need to use them when playing some records.

It is possible to split off SPDIF from an HDMI output by using one of numerous “HDMI Splitter” boxes. I was considering that until I discovered that AV7704 only offers volume control on its analog outputs—not when sending audio via HDMI.

Failure? Not really—I have a trump in my sleeve—MOTU Ultra Lite AVB card which I was previously using for my surround setup. This card has 6 high quality line inputs, DSP, and both analog and digital outputs. So I can use to complete the HDMI receiver and Dolby / DTS processing functions of AV7704, great! And MOTU AVB can work on its own, without a computer, thus my initial requirement is still fulfilled.

The remote control requirement is fulfilled by AV7704, the companion HEOS app for Android, and obviously other apps on Android that can work with Chromecast.

Configuration

This is how I hooked things up:

I decided to use Zone 1 output for headphones (driven by SPL Phonitor minis). XLR outputs of AV7704 connected to inputs of MOTU AVB for headphone equalization. Since the headphones are connected to Phonitors which have volume controls, I don’t need to control volume on AV7704. So potentially I could send audio to HDMI, split it out as SPDIF and send that to MOTU optical input. I considered that option but found it inconvenient because first, this will require adding yet another electronic box to the configuration, and second, this will force MOTU AVB to be clocked at the same sampling rate as HDMI audio, which is normally 48 kHz. So using the analog XLR output is more robust, although it adds an extra D/A->A/D conversion.

Specifically for surround downmixes I would prefer to use the headphone output of AV7704 (HPH on the diagram) because typically there are differences in how Dolby and DTS downmix to speakers vs. headphones since the latter offer much better channel separation.

And Zone 2 output (only RCA is offered for it) is used for LXminis. Since the miniBox is about two meters away from AV7704 and is powered from a different outlet I decided to use optical connection between AV7704 and miniDSP in miniBox for full isolation and less noise. For the speakers I have to use the volume control of the AVR so the analog output is the only option here. In order to convert analog into TOSLink I also use MOTU AVB.

With all these extra D/A and A/D conversions and use of analog outputs on AV7704 it is important to verify that there is no signal quality degradation due to noise, output or input overload, or any other issue. Also, AV7704 offers options like “direct” output which clams to provide “purer” output and I’m curious to validate these claims.

Verification

Digital Inputs

Need to recall two issues that can happen with digital recordings that do not leave enough headroom due to aggressive mastering. The first is clipping of intersample peaks during resampling. The problem illustrated below:

If a record is digitally mastered in a way that puts non-peak values of waveforms to maximum (or minimum) values of a particular integer representation (16-bit or 24-bit integers), then resampling can yield values that are outside of the domain of the integer representation, which means clipping. This is what I have encountered with Google Nexus Player with its mandatory resampling of 44.1 kHz content to 48 kHz.

Presence of this problem can be detected purely in digital domain by capturing the digital output of the player. I decided to check Chromecast, HEOS, and Shield whether they have this issue. For that I used the same test files as back in 2017: a sine wave phase shifted by 45° and “normalized” to 0 dBFS digitally.

Recall that this isn’t just a DSP geekery but rather a real issue encontered in commercial CD recordings that were engineered to sound “louder”.

This is the test setup I used:

I was capturing the digital output digitally by sending audio to HDMI and using a splitter. The optical output from the splitter was captured by MOTU AVB. What I’ve found is that Chromecast and HEOS do not attempt to resample the input signal and hence do not clip it, whereas Shield Pro always opens the HDMI output at 48 kHz and resamples 44.1 kHz inputs to 48 kHz with clipping. Thus, the conclusion is—avoid using Shield Pro for music playback except for encoded surround audio which is sent to the AVR directly for further decoding, or if you are sure the audio is at 48 kHz already.

I also checked if I can ditch HEOS in favor of Chromecast for local playback too, but quickly discovered that VLC can glitch when casting to Chromecast, while HEOS always plays flawlessly.

AV7704 Analog Outputs

What I wanted to verify is whether the quality of the XLR, RCA, and the headphone output of AV7704 are on par with each other. I used Cambridge Audio DacMagic Plus as a reference. I verified that its XLR and RCA outputs in fact have the same linearity and I was expecting the same from AV7704.

However, as I started measuring I found that the RCA output of AV7704 is much noisier than XLR. The fact that the noise was fluctuating as I was touching the unit’s screws at the back lead me to the conclusion that it is missing proper grounding. Indeed, the power input of AV7704 is two-pronged so the enclosure if “floating”. I can understand why the manufacturer has done that—it’s in fact typical for consumer equipment which normally uses unbalanced connections and thus there is a high chance of creating a ground loop. However, instead of simply not grounding the enclosure I would prefer to have a “ground lift” switch as the last resort for solving ground loop issues.

After I grounded the box by connecting a copper wire to one of the screws on the back with one end and to the power strip enclosure on the other, the noise situation has become much better and indeed XLR and RCA started showing similar performance. It seems that Cambridge Audio DAC is engineered better than AV7704 since it performs great without requiring to be grounded.

As for the headphone output, I measured its output impedance and found that it’s quite high—39 Ohm which means it can only damp well headphones with high input impedance—300 Ohm or higher. Recall that I plan use the headphone output for surround renderings, and my preference is to use IEMs in this case, as they have less interaction with my ear pinnaes. Since IEMs typically have very low impedance, I ended up connecting the headphone output of AV7704 to the line input of MOTU AVB which constitutes a perfect load for this headphone output.

Yet another thing to consider is what is the optimal output level from AV7704. This receiver in fact provides several options here:

  1. Attenuated output: 0 dB down to -79.5 dB.

  2. Amplified output: 0 dB up to +18 dB in case if the digital program level is too low.

  3. Pure Direct output mode which bypasses processing circuitry and turns off all analog video circuits in an attempt to lower the noise.

The hardware test setup was essentially my playback setup. I only added one extra connection: TOSLink output from MOTU into AV7704 “CD” input. Here is how XLR, RCA (Zone 2), and the headphone output are seen by MOTU AVB when the output level on AV7704 is set to -6 dBFS. I was using REW tone generator to produce a sine tone of 1 kHz at maximum dBFS:

As we can see, the headphone output (red) has the highest output level and also the highest level of noise and harmonics. It’s interesting that only the headphone output has a small spike around 60 Hz which didn’t went away after I grounded the receiver.

The most linear output is XLR (green). It seems that -6 dBFS is the sweet spot for it, as reducing attenuation to 0 dBFS significantly degrades its linearity and in “amplifying” modes performance is unacceptable.

I was curious whether “Pure Direct” mode can deliver better performance for Zone 1 outputs, however the results practically didn’t change at all. However, I don’t use analog video inputs and outputs (I’m curious who would these days), so perhaps there is no interference from them in the first place. To me, the “Pure Direct” mode looks like a heritage of the old days, and I would prefer Marantz to remove the analog video I/O at all rather than adding this mode.

In contrast, the Zone 2 RCA output (red) provides better S/N ratio when amplified (at the cost of a slightly higher distortion), but only up to a certain point. For it, +9 dBFS is the frontier of linear behavior.

The summary of THD and noise for different outputs of AV7704 is in the table below. Note that I ran MOTU at 96 kHz sampling rate and didn’t use a low-pass filter, thus the THD and noise figures are across the whole range up to 48 kHz.

Output, mode 1 kHz RMS (Z) THD Noise THD+N
Z1 XLR, -6 dB -13.2 dBFS 0.0019% 0.0021% 0.0029%
Z1 HPH, -6 dB -9.2 dBFS 0.0018% 0.0027% 0.0033%
Z2 RCA, -6 dB -21.8 dBFS 0.0034% 0.0063% 0.0072%
Z1 XLR, 0 dB -7.2 dBFS 0.012% 0.0044% 0.013%
Z2 RCA, +9 dB -6.7 dBFS 0.0047% 0.0036% 0.0059%

The official specs of AV7704 specify distorion at 0.005% over 20 Hz–20 kHz range (not specifying signal level), so it seems that my measurements are in the same ballpark.

Yet another problem that can be encountered with DACs is lack of headroom for intersample peaks. Even if there is no resampling involved, DAC still can clip intersample peaks on aggressively mastered tracks. As we can see below, putting non-peak values of waveforms to maximum / minimum integer values can result in having the peaks between samples to reach +2.6 dBFS:

Presence of this problem is checked by using the same files that I used to detect intersample peaks clipping in digital domain. I checked AV7704 and it doesn’t have this problem, good!

AV7704 Tone Controls

Tone controls are available for Zone 1 only and offer modification of bass and treble in the range from -6 dB to +6 dB. I was also interested in their operating frequency range and slope. Below are the graphs of the transfer function for the tone controls:

The slopes of the tone controls are gentle, which is good. There is some phase distortion which indicates that the tone controls are implemented as recursive (IIR) filters, however due to gentle nature of the phase changes the resulting group delay is zero.

I’m pretty sure the tone controls are implemented in a DSP as they are very precise (unlike JDS Labs Subjective 3), and it seems strange to me that the control steps are 1 dB. I would like to have a better precision, at least by half of a dB.

Conclusions

All in all, Marantz AV7704 offers good quality analog outputs. Even the secondary zone offers good performance. From my experience, this receiver works reliably and predictably. I haven’t encountered any serious glitches during a couple of months I was using it. The built-in HEOS player is useful and offers good quality playback.

Being a “consumer-oriented” (not a pro device), this receiver has some useless extras, like the analog video I/O and “Pure Direct” mode. These are seemingly relics from past models, and Marantz, being a part of a big consortium isn’t very good at trimming extra functionality. I would gladly trade these “features” for a digital audio output with digital volume control which I could use for connecting LXminis.

Some annoyances that I have noticed with AV7704:

Note that I haven’t covered here capabilities of AV7704 in decoding surround audio and downmixing it into 2 channels, I hope to do that later. Also I haven’t coverted the built in room correction module (Audissey) partly because I do it externally on miniDSP units, and it only applies to Zone 1 which I use for headphone playback only.