HARMAN/KARDON PM665: The Power Station

Submitted on: 27 Dec 22

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Category: Amplifiers

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Founded in 1953 in the USA, the company Harman/Kardon is one of the pioneers of HiFi.

They made some of the best tape decks ever :). But I won’t talk about that here. Their first product was an FM tuner. Considering that the company turns 70 next year, it’s really worth respecting that they’ve survived for so many decades.

On the other hand, this had its price in difficult commercialization, occasional poor quality of some components, some bad devices… and personally, I have the impression that they ruined all the other companies they got their hands on – for example, AKG (now owned by Samsung).

Nevertheless, with years of work, effort, and obviously great engineering teams, HK has produced many nice products. They rarely ventured into high-end, focusing more on the lower, middle, and upper categories, and they did a masterful job there.

Walking through a flea market one Saturday, I didn’t find anything interesting, as I expected. I don’t know what got into me, but I decided to visit the first part of the market again. And… in one place, there’s a guy selling a Harman/Kardon PM665 amplifier. I knew that model, but I never had it, I had its predecessor – the PM660. The PM665 model was a beast in its time, with a price of 1,800 DEM (900 EUR) if I’m not mistaken. The guy said the amplifier works, the switches interrupt a bit, the aluminum knobs come off the plastic caps, but he uses it as a powerhouse. We quickly agreed on the price.

I started carrying the amplifier, completely forgetting about my heartache and the intervention I had some time ago, so I shouldn’t be carrying 13.5 kilograms of amplifier in my life. I had to take breaks to the car, good thing Harman didn’t cost me my life :). That’s passion for you. I somehow dragged it home, how will I explain to my wife what an idiot I am?

At home, I first took a screwdriver and removed the cover, convinced that the amplifier had burned countless times and that there was no trace of original transistors on the outputs. How surprised I was when I saw that the original parts were there and that the amplifier had never been serviced. Great, I’ll have something to write about :).

I glued the knobs very carefully – they don’t have a central pin for the cap so it can be wrong, I used epoxy two-component glue. The buttons started working, I planned to clean them with contact spray – Harman is known for weak switches on its devices from the 80s.

The PM665 model first appeared in 1985 and lasted only that and the next year – the fight with Japanese competition was ruthless, the Japanese were like a tank that crushed everything in its path. Harman even moved production to Japan, as they later did with China, so the PM665 was also made in the Land of the Rising Sun.

 

Description:

This amplifier is a beast in the true sense of the word, although it weighs “only” 13.5 kilograms. When you open it up, there are two separate transformers inside, a battery of large electrolytics of 10,000 uF, vertical boards with driver stages, phono section, and other amplifier parts. All packed just like that and, of course, inconvenient to approach and service. The output power is 2×100 W at eight ohms, with a solid (at that time) damping factor of 65 and a great frequency range from 0.2 Hz to 150 kHz.

The PM665 is entirely made of discrete components, meaning it doesn’t have a single integrated circuit. Some designers believe that this approach provides greater flexibility in designing the circuits themselves rather than using ready-made chips. Others, for example, the German T+A, do just the opposite in all sections of some of their amplifiers except the output.

A digression: in the 1970s, at the University of Oulu in Finland, Dr. Matti Otala taught electronics. Interested in audio amplifiers, he made a discovery that can be summarized in the frequent occurrence that amplifiers that are far better on paper than others have a noticeably inferior sound compared to the mentioned (on paper weaker) amplifiers. His research led to the discovery of what is called TIM – Transient Intermodular Distortion. In short, this distortion occurs when the physical limitation of the amplifier in terms of rapid voltage changes in this case (slew rate) and time domain delays lead to sound distortion, mostly at high frequencies. The distortion was particularly noticeable in amplifiers with a high degree of feedback. This phenomenon would literally cause the amplifier to “stumble” in the sense that it would not be able to reproduce transients in a faithful manner. The mentioned feedback was very popular at that time to reduce harmonic distortions and increase the frequency range.

Because of this, Dr. Matti Otala proposed a different amplifier concept, with a much lower degree of feedback, and Harman/Kardon is one of the companies that widely accepted this solution.

In addition, Harman has been pushing the concept called HCC – High Current Capability for years, which starts from the assumption that the amplifier, precisely because of transients, needs the ability to deliver a large amount of current “at its peak”, so the PM665 can deliver up to 60 A of current, which was a respectable figure in its time, and still is today. Additionally, Harman made amplifiers with a very wide frequency range.

Harman/Kardon PM665 doesn’t have a case designed to withstand a meteor strike: classic sheets, front panel, but the cast aluminum knobs do the job. What’s nice is the amount of options: the PM665 is a classic analog amplifier that practically has everything: from an excellent phono section for MM and MC cartridges with capacitance trimming for the MM section and connections for two turntables, to connections for two analog recorders. There’s also a bass contour control which is a version of physiological sound correction, and tone controls can be set with a central frequency of 200 or 400 Hz for bass and 2 or 6 kHz for high frequencies. It’s generally delightful :).

This amplifier uses the known 2SA1302 and 2SC3281 output transistors, four per channel. Most interesting is the protective circuit of the amplifier, which does not use relays but turns off the output signal section, but leaving it active and connected to the speakers. With this system, all problems related to the output relay are avoided, but there is a danger that the amplifier will burn the speaker in case of output transistor breakdown because the output section still receives voltage and remains physically connected to the speaker. Perhaps the designers thought that it was practically impossible for this to happen, so they implemented the mentioned solution.

Unfortunately, I forgot to take pictures of what the PM665 looks like when it’s opened…

 

Sound:

After so many years, Harman still sounds decent. I must mention that after I sold it, the amplifier was taken to a competent technician for inspection, and the assessment was that the replacement of electrolytics is still not necessary. I really don’t know how that would affect the sound because the procedure of refreshing is a double-edged sword: in a good number of cases, the sound can be better, but I’ve also seen the opposite examples.

Anyway, the PM665 has incredible power, it seems stronger┬áthan its 100 W per channel and is a muscular bodybuilder. The bass of this amplifier is one of the best I’ve ever heard in my life, let’s say it’s among the top 10 amplifiers out of hundreds that I’ve had the opportunity to hear or test. It’s truly incredible: powerful, precise, hitting the listener directly, born for rock and pop lovers. For me, that’s the biggest advantage of this amplifier. For the money on the market (I sold it for 200 EUR), I can’t imagine there’s anything similar with such low tones.

The sound itself is agile, quite dynamic, on harder or neutral speakers or headphones, the mentioned bass works wonders. I didn’t use Loudness, it seemed too strong to me.

On the other hand, as you go up, the situation changes: the voices are good, but they are withdrawn in the scene and are not even close to being as clear as in some newer amplifiers, and the device struggles a bit with sibilants, especially in male performers. This gives me one flaw in reproduction that I couldn’t overlook. There is a slight, but really slight, blurring of the entire sound scene.

The high tones have details that are correct but not fascinating. I wouldn’t characterize the sound of PM665 as rough at any moment, the details it reproduces are completely correct but, believe me, some of them are completely missing or so withdrawn that you have to “hunt” for them in a way that you know which one will come, so you expect it, instead of noticing it by itself. Comparing it with, for example, the excellent (rare in our country) and much younger Astin Trew AT2000 Plus amplifier, Harman PM665 has a more receptive and stronger, I could say even more defined bass, but Astin beats it in all other areas with one hand behind its back.

The mentioned sound defects of PM665 also affect the stage, whose width goes only between the speakers, no more.

Maybe I’m too harsh on the old powerhouse – if there weren’t problems with sibilants in the voice, I could get used to it and live with it. I belong to bass lovers, and PM665 always put a smile on my face when I turned it on and started listening. I spent many hours using it as a headphone amplifier (AKG K601, K550, Sennheiser 580S) and I can say it sounded great, and the flaws I noticed through speakers (Elac FS210 Anniversary) were almost imperceptible. I didn’t test it with a turntable.

 

Conclusion:

Buying old, used amplifiers is a big risk for the buyer, as is everything else used. I was lucky with the PM665 – I watched a detailed video about one unit that didn’t work and even some factory flaws regarding the printed circuit boards. But my unit worked as it should and showed what Harman could do at that time.

What is Harman like today compared to new amplifiers? It’s emotional, powerful, good but lacks that finesse, spatiality, micro-detailing that new amplifiers have – of course, technology has progressed in 37 years – read my text about the Astin Trew AT2000 Plus amplifier and its comparison with Harman. But can the PM665 be listened to? Definitely, it will provide a lot of enjoyment, and for someone, it would be the end of the story in terms of not needing to invest more in a HiFi system. Others would go further. The decision depends on the lover of good sound.

 

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