Full expert review and laboratory test of the Marantz PM6005 Amplifier  by Australian Hi-Fi Magazine.

The following review consists of a full subjective evaluation of the Marantz PM6005 Amplifier  written by Greg Borrowmant, as published in Australian Hi-Fi Magazine, October/November 2015. At the end of the review is a link to a complete set of independent laboratory tests conducted on the PM6005 by Newport Test Labs and a report about those tests written by Steve Holding. There is also a link where you can download the review as it originally appeared in the magazine, in pdf format.

 

Founded by Saul Marantz in the USA in 1953, Marantz has changed ownership a number of times over the years, being managed in turn by Superscope, Philips, and Marantz Japan. It now operates under the auspices of D+M Group, a company created in 2002 when Denon (Japan) merged with Marantz Japan. One thing that hasn’t changed over those years is Marantz’s commitment to manufacturing high-quality hi-fi equipment, and setting the pace in audio technology. The PM 6005 is a perfect example of this focus, with some innovative circuitry on board, as well as a nice blend of ‘classic’ and ‘new’ technologies. One example of the ‘new’ is that the PM6005 has an on-board DAC, so you can directly input digital sources

The Equipment

In many ways, the front-panel layout of the Marantz PM6005 harks back to the early days of Marantz, when all amplifiers had bass and treble tone controls and balance controls, because they’re right there on the front panel. These days, those controls are often not provided at all, or buried deep in an electronic menu. The PM6005 even has a source-switching knob, so you can switch from one source to another manually, rather than by using a touch-screen. (And also by using the remote control, about which more later.) One thing that’s certainly ‘classic’ is the circuitry inside the PM6005, because Marantz is using a traditional passive power transformer and large-value smoothing/storage capacitors in its power supply, rather than a switch-mode supply, and its output stage is a conventional analogue Class-AB type, not one of the newer digital Class-D modules.

One thing that’s not ‘classic’ about the PM6005’s circuitry is that it employs current feedback—rather than voltage feedback—architecture. Although current feedback had been used in high-frequency amplifiers for many years, it was first proposed for use in audio amplifiers only in 1990 in a circuit topology invented by Mark Alexander and assigned to US semiconductor manufacturer Analog Devices in 1992 (US Patent #5097223). The reasons for its previous exclusive use in high-frequency amplifiers include the fact that current feedback has significant disadvantages at low frequencies. Alexander didn’t exactly solve these significant disadvantages, but he did come up with a novel solution that uses current feedback at high frequencies and voltage feedback at low frequencies, effectively getting the best of both worlds. Using current feedback in an audio amplifier enables extremely wide bandwidth and an ultra-fast slew-rate. So why isn’t everyone using it? Because it’s difficult to implement. As the inventor himself noted in his ‘White Paper’ on the subject: ‘when proper attention is paid to all the details (and some of them are nontrivial indeed) current feedback amplifiers can offer superior sonic performance to all known topologies.’

Also almost unique to Marantz is its use of HDAMs where most other manufacturers use integrated operational amplifiers (opamps). An HDAM is functionally identical to an operational amplifier but is made using discrete circuit boards and discrete surface-mount components rather than as an integrated circuit. Although Marantz’s HDAMs perform exactly the same electronic function as ordinary mass-produced op-amps, Marantz says they have faster slew rates and lower noise levels, which enables much more dynamic, accurate and detailed sound quality. Marantz builds several different types of HDAM, and the ones used inside the PM6005 are two steps up from its basic versions, with HDAM3s being used throughout.

A circuit that’s new to the PM6005—but one that not everyone likes!—is an automatic standby mode that switches the amplifier into standby when you haven’t been using it for a while. I now number myself amongst those who like this feature (initially I wasn’t keen on it, but I am now a fan), but if you don’t like the automatic on/off switching, and would prefer to switch the amplifier on and off manually yourself, you can, simply by disabling the automatic circuitry using the simple process outlined in the manual. The advantage of the automatic circuit is that you can’t accidentally leave the amplifier on, which will shorten its operational life and rack up unnecessary power bills. The standby circuit draws less than half a watt, and means that the amplifier is always ready for instant use… no warm-up required.

The PM6005 has four analogue line-level inputs, plus a phono stage so you can connect a turntable. As mentioned in the introduction, it also has two digital inputs, one coaxial and the other optical. The input it doesn’t have is a USB input. USB is not only the best way to connect your computer to your audio system, it’s also the method most people use, and are most comfortable with, so I think its omission on the PM6005 is a definite oversight. (An additional 3.5mm input on the front panel might have been nice too, to allow you to quickly and easily plug in a mobile phone or portable music player.) On the output side, the PM6005 has a line-level output (associated with the record/play loop) and two switchable speaker outputs. It has a ‘Source Direct’ switch so you can bypass the tone controls, plus there’s a ‘Mute’ switch on the remote control.

The PM6005 isn’t overly powerful (Marantz rates the power output at 45-watts per channel into 8Ω and 60-watts per channel into 4Ω), but this will be sufficient if the amplifier is used with efficient speakers in an ordinary-sized room. And, for the record, the PM6005 actually delivers a little more than its rated power under normal operating conditions (as demonstrated by the test results gained by Newport Test Labs).

The rear panel is nicely laid out, with plenty of room, and the speaker terminals are very high quality. The Marantz PM6005 measures 440×371×104mm (WDH) and weighs 7.6kg. One curious feature is a tag that’s affixed to the ventilation holes at the top of the amplifier. I have no idea what it’s for and, at the time of going to press, neither did anyone else I asked!

In Use and Listening Sessions

There’s no doubt the Marantz PM6005 is a classy-looking little amplifier, looking equally good in its swanky champagne gold livery or its basic black finish. That feeling of quality is further enhanced when you switch the unit on and the small LEDs on the various controls and the display illuminate. Then that feeling of quality gets even greater when you turn the input selector and find it’s actually a rotary encoder and, as you turn it, small blue LEDs in the long thin display cycle through the available inputs—Phono, Tuner, CD, Network, Recorder, Coaxial, Optical. Because it’s an encoder, if you keep turning it to the right after you’ve reached Optical, it just starts again at Phono. Alternatively, you can just rotate it in the other direction… whichever you think will get to you the input you want the fastest. If you’ve set either the ‘Source Direct’ or ‘Loudness’ options to ‘On’, these settings get carried from one input to the other. Muting, however, if selected, is cancelled whenever you switch inputs.

If your computer does not have a coaxial or optical digital output, you’ll have to buy a USB to SPDIF converter if you want to connect it to the PM6005. There are a few cheap ones available, the better ones being the Pro.2 DAC32 for $75 from Radio Parts, or the Matrix Audio for $69 from Noisy Motel. (If you want a really high-quality converter, another option would be a full-fledged DAC with a USB input, which will also have analogue outputs, so you could bypass the DAC inside the PM6005, but this would be expensive and kind of defeats the purpose of having a DAC inside the PM6005.) If you keep your music files on a desktop computer, another alternative would be to fit it with a soundcard equipped a coaxial digital output.

The most likely reason Marantz fitted the PM6005 with a coaxial/optical digital input is so that anyone who owns an older CD player with a digital output can improve its sound quality by connecting it to the PM6005 digitally, rather than via its analogue outputs. This in itself is laudable, so Marantz should get some Brownie points for it. It should get even more Brownie points for fitting a very good DAC (Cirrus Logic’s CS4398 24/192) and putting it inside an isolated, fully-shielded cage so it can’t affect the analogue signals.

The volume control on the PM6005 is motorised, but doesn’t have the ‘dead’ tactile feel when it’s manually rotated that some motorised controls have. It also doesn’t have any ‘lash-back’, so it’s very easy to set accurate playback levels. Although you can use the front panel control to adjust volume, it’s better to use the Up/Down volume buttons on the remote, because if you’ve muted the signal using the muting button, the muting circuit doesn’t cancel if you move the front-panel volume control, whereas it does cancel if you use the remote.

The remote is one made by Marantz, rather than an ‘OEM’ one, but it’s not one of the metal ones Marantz reserves for use with its top-ranked products, rather a plastic one. It’s a decent size and the buttons on it duplicate all the front-panel functions except for bass, treble and balance. It doesn’t add any features to the PM6005 that aren’t available on the front panel, with the exception of manual standby mode (enter/exit), but it can be used to control other Marantz components, for example Marantz’s matching CD6005 CD player.

Connected to a pair of large, low-efficiency floor-standing speakers, the Marantz PM6005 immediately proved itself to be capable of outstanding control over the bass drivers, because the bass was powerful and driving, but without any blurriness. The volume levels I was able to achieve without hearing any distortion whatsoever were impressive for such a low-powered amplifier, but I eventually did run into the amplifier’s limits, where I could hear the output stage go into clipping. However so long as I stayed below this level, the sound was highly dynamic, so the PM6005 obviously had some reserves of power available for transients, even at high playback levels. By way of example, I was playing the 30th anniversary reissue of Tears For Fears’ classic album ‘The Hurting’ at very high volume and on Mad World the Marantz didn’t miss a beat at the kick drum entry, reproducing it full-force and with accurate tonality.

Midrange sound was completely smooth and had a nice sense of warmth to it while at the same time being completely balanced against the bass and the treble. I was also impressed by the way all sounds in the midrange were treated even-handedly, whether instrumental or vocal. So although I continued to hear a slight warmth to the sound no matter what I played, it was always the same for every sound the PM6005 reproduced… it wasn’t as if one instrument or voice type sounded warmer than any other. The detailing in the midrange was outstanding. Listening to Lisa Gerrard’s Now We Are Free, which is very complex and multilayered, I could relax and enjoy the soundscape as a whole, or instead concentrate on any one strand and hear it perfectly.

I could not fault the high-frequency reproduction of the PM6005. It was clean, spacious, airy… and beautifully detailed. And whereas the high treble of some amplifiers begins to cloud over and become less transparent when the amplifier is working hard due to there being lots going on with a rhythm section, the high-frequency sound of the Marantz remained pure no matter what was going on elsewhere in the audio spectrum.

When I switched over to a smaller pair of higher-efficiency stand-mount speakers, I was gratified to hear that the although the overall sound changed due to the use of different speakers, the sound of the Marantz itself remained identical, so this is an amplifier that is quite unfussy about which loudspeakers you use with it, which will greatly increase your choices when buying loudspeakers. The smaller speakers had less bass response than the floor-standers, so my immediate thought was to put that bass tone control to good use. As I started to turn it, my first thought was that the circuit wasn’t working, because I didn’t hear the immediate bass lift I’m used to hearing. ‘This can’t be right’, I thought to myself. ‘Am I accidentally in Source Direct mode?’ Nope. So I tried the bass tone control again, this time listening more carefully, and the penny dropped. Yep, the bass was being boosted, but only the very lowest frequencies… and the same was true for the treble: it too was affecting only very highest frequencies. Both controls were leaving the midrange virtually untouched.

It didn’t take long for me to realise that because the midrange wasn’t being boosted, I could turn up the bass quite high, which lifted and extended the level of bass from the stand-mount speakers to a level I could not have done with an ordinary bass control. The action of the treble control, on the other hand, seemed fairly conventional, but since I didn’t need to use it, I left it at its detent position. (It subsequently turned out that the treble control isn’t conventional, because its boost rolls off above 15kHz rather than shelving, presumably to protect tweeters against excessive treble boost).

Conclusion

Yes, I have expressed my disappointment at the lack of a USB input, and the lack of a 3.5mm front-panel jack, but overall I was so impressed by the performance, build quality and classy appearance that I am more than happy to forgive those slight failings. Its performance as an integrated amplifier is exceptionally good, plus you’re also getting a brilliant on-board DAC into the bargain. The kicker, of course, is the price tag, which makes the Marantz PM6005 amplifier superb value for money. # greg borrowman

Readers interested in a full technical appraisal of the performance of the Marantz PM6005 Integrated Amplifier should read the LABORATORY REPORT HERE which includes full tests on the MP6005's frequency response, power output, distortion, channel separation and more. 

If you'd prefer to see the review exactly as it first appeared in Australian Hi-Fi Magazine, including the laboratory test report, click HERE or on the graphic below: