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Marantz PM-90 Review (Vintage Amplifier)

amirm

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This is a review and detailed measurements of the Marantz PM-90 Vintage stereo integrated amplifier. It was purchased by a member from japan and drop shipped to me for testing. It came out in 1991 with a price of 160,000 Yen (about $1,500 in today's exchange rate). I looked online and I can only find one for US $950 but it is more beat up than this unit.

I must say, this is one nice looking amplifier with a look that would fit in even today:

Marantz PM-90 Review Integrated Balanced Vintage Stereo Amplifier.jpg


The feel of the controls is excellent other than volume control which I found a bit loose. A flip down door gives you additional control including switching between Class AB and Class A mode of operation! Sadly it requires the unit to be powered down to change so no opportunity for instant switching and comparison.

I was pleasantly surprised to see modern, beefy speaker terminals as well:

Marantz PM-90 Review Integrated Balanced Vintage back panel Stereo Amplifier.jpg


Even more interesting is the inclusion of XLR balanced inputs for CD.

This amplifier is back breakingly heavy due to use of two massive transformers. It is at the limit of what I could lift and carry up two flight of stairs for testing. Sitting here, my back aches just thinking about the reverse trip to pack the darn thing! Speaking of packing, it was immaculately double boxed by Hifi-Do with zero impact to it despite the long journey. Apparently it even came with one year warranty although you have to ship it back to Japan for that.

Speaking of Japan, the unit is made for that market and hence 100 volt rating as opposed to 120 volts we have here in US. If it were mine, I would go ahead and use it at 120 but being that of someone else's and hard to replace, I powered it by both my Lab AC generator and a Variac set to 100 volts. This may have caused some measurement issues as I noted below.

Marantz PM-90 Amplifier Measurements
There is a lot here to test due to dual mode of operation and dual type of input. Let's start with Class A operation with RCA and then XLR:

Marantz PM-90 Measurements RCA Vintage Stereo Amplifier.png


Marantz PM-90 Measurements XLR Balanced Vintage Stereo Amplifier.png


Unfortunately our measurements are polluted by high mains noise and harmonics. I tried every which way but could not reduce that impact much. Whether this is due design of the amplifier or longer AC mains connection due to use of lab AC gen or Variac, I can't tell. As is SINAD doesn't appear to be better than modern AVRs with Marantz on their front plate:

Best vintage stereo amplifier review.png


However, if we look at the FFT, we see only two harmonics and then it disappears into noise. Here is the performance of Marantz SR7015 as a reference:

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Noise from power supply is lower there which aids it in getting similar SINAD.

Switching to Class AB mode has no penalty:
Marantz PM-90 Measurements Class A vs Class B THD XLR Balanced Vintage Stereo Amplifier.png


If anything distortion harmonics go a bit lower although that was not reliable.

To see if there is a difference at all between Class AB and Class A, I turned on the residual mode of Audio Precision in the scope display. This shows us the difference between input and output waveforms. If there is zero crossing error due to class AB operation, we should see more difference around that part of the waveform but we don't:

Marantz PM-90 Measurements Class A vs Class B XLR Balanced Vintage Stereo Amplifier.png


What is there is mostly power supply noise. I changed frequencies, power level down to 1 watt and still saw nothing that would correlate with zero crossing distortion which class A is supposed to solve. Feedback and class AB operation seem to have cured that ailment leaving little room for Class A to do better.

Here is the comparison between Class AB and Class A again with respect to signal to noise ratio:

Marantz PM-90 Measurements Class AB SNR XLR Balanced Vintage Stereo Amplifier.png


Marantz PM-90 Measurements Class A SNR XLR Balanced Vintage Stereo Amplifier.png


Class AB pulls ahead in full power mode because it can create more power. At baseline 5 watts they are similar likely limited by power supply noise.

Crosstalk showed a tiny improvement in favor of class A but it is not material:
Marantz PM-90 Measurements Crosstalk XLR Balanced Vintage Stereo Amplifier.png


Bandwidth is good but not exceptional:

Marantz PM-90 Measurements Frequency Response Class A vs Class AB XLR Balanced Vintage Stereo ...png


Notice how amplifier gain changes as you switch modes so for any listening tests, you may have to compensate for that.

Class AB of course has tons more power:

Marantz PM-90 Measurements Power into 4 ohm class A vs Class AB  XLR Balanced Vintage Stereo A...png


Marantz PM-90 Measurements Power into 8 ohm class A vs Class AB  XLR Balanced Vintage Stereo A...png


Overall shape of the graph is average. Wanting to see the impact of the pre-amp vs power amp, I separated the two and fed the unit with my analyzer direct using RCA:

Marantz PM-90 Measurements Power into 4 ohm vs frequency class AB  RCA direct Vintage Stereo A...png


As expected, my analyzer is cleaner but impact is on distortion, not noise which is a bit surprising. As is one channel being worse than the other. SINAD reaches almost 100 dB now near full power, good channel, which is very nice.

There is a lot of headroom when using class AB vs Class A:

Marantz PM-90 Measurements Power into 4 ohm Peak and Max Class AB  XLR Balanced Vintage Stereo...png


Marantz PM-90 Measurements Power into 4 ohm Peak and Max Class A  XLR Balanced Vintage Stereo ...png


Testing amplifier linearity vs frequency we get:
Marantz PM-90 Measurements Power into 4 ohm vs frequency class AB  Balanced Vintage Stereo Amp...png


Marantz PM-90 Measurements Power into 4 ohm vs frequency class A  Balanced Vintage Stereo Ampl...png


Class A power limits more at 20 Hz than Class AB. Both show very predictable and smooth responses which is great.

Multitone tests shows slightly lower distortion at higher frequencies in favor of Class A:

Marantz PM-90 Measurements Class A vs Class AB Multitone  XLR Balanced Vintage Stereo Amplifier.png


Effectiveness of feedback lowers at higher frequencies and likely this is the reason class A does better there.

Marantz PM-90 Phono Input Measurements
It was hard to figure out a fair way to measure the performance of its phono stage to compare to stand-alone devices. At first I used tape output but that didn't produce great response. Best was from pre-amp tap to power amp:
Marantz PM-90 Measurements Phono MM Vintage Stereo Amplifier.png


Sadly the mains noise is there and dwarfs SINAD. There is no sign of harmonic distortion so that is very good. Same situation exists for MC mode:

Marantz PM-90 Measurements Phono MC Vintage Stereo Amplifier.png


RIAA equalization is probably the best I have measured:
Marantz PM-90 Measurements Frequency response RIAA Phono MM Vintage Stereo Amplifier.png


That story continues into headroom measurements:

Marantz PM-90 Measurements Phono MM MC headroom Vintage Stereo Amplifier.png


You get almost 12 volts of output before it starts to clip! So pops and clicks should be much less noticeable.

Conclusions
The PM-90 does NOT show its age. It produces above average performance compared to today's amplifiers. It does so while running very cool and comfortable. Not once did it get warm to touch or go into protection. Push it hard and it just pulls back on the output but keeps going. Clearly this is a very robust implementation. Can it compete with state of the art amplification today in the form of Benchmark THX and Hypex/Purifi Class D amps? No. There is real innovation there to push down distortion and noise. But we also have a lot of terrible amplifiers today which the PM-90 easily outperforms and does it with so much style.

There is nothing to apologize for and a lot to praise for Marantz PM-90. I hope the company goes back to these roots rather than horrible looks and performance of much of their AV line.

On class A mode, I see no reason to recommend it and many reasons to avoid it. If you run out of power there, you will certainly create audible distortion. Whereas any benefit it might have is literally lost in the noise.

I am happy to recommend the Marantz PM-90.

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As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

restorer-john

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nyxnyxnyx

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Great review as always!

Nowadays this is not considered SOTA but I assume that back when it was first released it must have been quite something right? I love how some old amplifiers from Marantz and Denon still go so well with age - both in performance and durability.
 

Matias

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Very nice review!
 

Doodski

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Chrispy

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So how would one cope with the 100V thing here in the US for best results?
 

Doodski

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So how would one cope with the 100V thing here in the US for best results?
Hmmz good question.

"The frequency of electric current is 50 Hertz in Eastern Japan (Tokyo, Yokohama and other northern area), 60 Hertz in Western Japan (Nagoya, Osaka, Kyoto, Hiroshima and other southern area)"

Considering the fluctuation in the voltage delivery in North America through the days and having monitored the mains voltage for a couple of years and noticing that it dipped down to ~105VAC and peaked at ~128VAC I think it would be safe to run the Marantz on the lower voltage but the higher voltage is questionable.
 

restorer-john

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So how would one cope with the 100V thing here in the US for best results?

A large (min 1KVA) stepdown (120:100V). Running a big 100V Japanese model on 120V is not a good idea, especially in Class A where they run hot enough as it is. They have no regulation for the main amp rails and the extra 20% voltage may well push the main filter caps outside their WV. The heatsinks are marginal in Class A as it is.

My PM-95 is a 220V and 240V switchable. They felt it important enough to provide twin primary taps for both Europe 220V and UK/Aust 240V at the time.
 
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amirm

amirm

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GXAlan

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Thanks for the wonderfully detailed review! Any chance you can run a quick test on the standard RCA input?
 

sarumbear

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"The frequency of electric current is 50 Hertz in Eastern Japan (Tokyo, Yokohama and other northern area), 60 Hertz in Western Japan (Nagoya, Osaka, Kyoto, Hiroshima and other southern area)"
Wow! Japan has two power system networks! I’m shocked!
 

sam_adams

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It is interesting that a vintage audio device of this age—from a Japanese manufacturer—does not have some type of metering on the front as we talked about over in the Douk discussion.
 
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