harman/kardon Rabco ST-7

The United States was a vibrant market for turntables, with a number of specialist tonearm manufacturers. One such company was Maryland-based Rabco, which sold its complex SL-8 and SL-8E tangential-tracking tonearms from the late sixties onwards. Powered by two small electric motors, they built up small but dedicated followings and this caused the company to branch out into turntable making. The ST-4 was the result, and the success of this attracted Sidney Harman, who duly decided to buy the company for Harman International Industries, Inc. By the time the sale went through, Rabco had replaced it with the ST-6 and ST-8 turntables, and then refined these to produce the ST-7, which had just entered production. This was then sold as a harman/kardon product, with the only trace of its parentage being the ‘RABCO’ legend on top of the arm bearing assembly. By 1975 the deck that you see here was on sale in the USA, Europe and Japan for nearly £200 – twice as much as a Linn LP12.

The ST-7 was designed by Jacob Rabinow (January 8, 1910 – September 11, 1999), an engineer and inventor who held no less than 229 U.S. patents on a variety of mechanical, optical and electrical devices. He was born in Kharkiv, Ukraine, only to move to China and then the US where he got a Master’s Degree in Electrical Engineering. He worked on defence projects at the US National Institute of Standards and Technology, then went on to set up his own company. It is Radinow that the world can thank for the first disc-shaped magnetic storage media for computers (1954), the first straight-line phonograph (1959) and the first self-regulating clock (1960) among various other marvels. He formed Rabco in 1968, but left after selling it to Harman. During this time, he picked up a string of awards and published a book called Inventing for Fun and Profit, in 1989.

Several things strike you when you see an ST-7 in the flesh – it’s a beautifully elegant and simple design from the outside, with a striking ‘mid century futurist’ look to it. The plinth is made from thin planes of brushed aluminium, and there are barely any plastic parts anywhere. The deck sports touch controls, which were the stuff of sci-fi dreams back in the early seventies. There’s a variable speed facility, aided by a recessed stroboscope cut into the underside of the 2.4kg aluminium platter. Compared to most Japanese designs of the day, it’s a wonderfully elegant thing with excellent ergonomics – indeed it looks more like a ruggedised Bang and Olufsen than a typical American turntable. The parallel tracking arm works in a simple, fuss-free way and even has detachable arm wands to make cartridge swapping easy. General build quality is high – but not, as we shall see, flawless. The deck itself measures 157x419x413mm and weighs 10kg.

Inside, it’s a different story. It’s a belt drive design, but there the simplicity ends. The tonearm is an elaborate affair, supported on a two-axis gimbal mount with optical end-of-side sensing. It is driven across the surface of the record by a belt turned from the underside of the inner platter – itself of course driven from the turntable’s motor by another rubber belt – which drives the tracking shaft. The latter turns a tracking roller. When the arm is at zero degrees, the roller is angled enough to move the tonearm at the correct speed for the arm to traverse an LP – approximately 0.17 inches per minute.

Although far more complex than a conventional turntable, the system is simpler than earlier Rabco decks which used electric motors. It’s still a pain to service and for this reason many ST-7s were scrapped over the years, simply because people didn’t know how to fix them. The same criticism can be levelled at many Japanese direct drive decks from this period of course, with the difference being that the ST-7 is largely a mechanical engineering challenge, and not an electronic one.

Perhaps the biggest flaw in the design is the fact that the tonearm is in effect mechanically connected to the brushless DC turntable drive motor. Although this is a decently quiet thing with sophisticated electronic speed control, all that separates it is the long drive belt to the tracking shaft pulley, which duly sends vibrations down the tracking shaft with only the tracking roller as the last line of decoupling. This is a rubber item and of course, over the years and with extended use, degrades like a cassette deck pinch roller. In other words, there is plenty of potential for the deck to sound less than optimal as it ages. Of course this is fixable, but not by most non-mechanically minded users. The other downside is that the plinth is a largely hollow structure made of aluminium panels, which aren’t exactly the least resonant material it’s possible to find. As such, many examples have been modified over the years with damping panels applied inside.

In a nineteen seventies world where published specifications were very important, the ST-7’s motor unit measured pretty well but was no great shakes compared the influx of high end Japanese direct drives of the day. Wow and flutter was quoted at a respectable 0.04%, with rumble at a decent -68dB. Its tonearm specs were more impressive though – with tracking error, vertical friction and lateral friction quoted as zero. Effective mass was said to be 6g, which was very low for the day. Tracking an Ortofon OM-10 – perfectly suited for this application – the deck worked smoothly, showing glitch-free operation.

A well maintained, fully serviced ST-7 is an interesting thing to hear. Someone’s vision of the vinyl state-of-the-art in 1975, it’s actually quite impressive in a number of ways – although it would be too kind to say that it’s flawless. What you get is a clean, smooth and quite unflustered sound, with an even and balanced nature that resembles open reel in some respects. One is certainly aware that you’re listening to a deck with a tangential tracking tonearm; it sounds well seated, stable and has an impressive stereo soundstage that keeps on impressing you, whatever record you play.

In other respects, things aren’t quite so impressive. Bass is a little warm and boomy – although some might like that – and there’s a slight tonal coloration to the midband too. It’s not one of those turntables that instantly whisks you from one recording studio to another, as you run the gamut of your LP collection.

The deck has its own sound and although pleasantly soft and warm, isn’t neutral. Treble is very pleasing though; it’s clean and crisp, like all turntables running good parallel tracking arms, and there’s pretty much no end of side distortion. The main bugbears of the Rabco are its very subtle speed instability – really only audible if you’ve just been listening to a good quartz-locked direct drive deck – and its susceptibility to external vibrations. It needs to be mounted well away from loudspeakers and on a dead-level surface.

“Flawed genius” is the best way of describing the harman/kardon Rabco ST-7. It’s a bit bonkers compared to its rivals, using a radical solution to a problem that many would argue was more of an academic issue than a practical one. It’s still an amazing deck to have and to use, and a great talking point among your hi-fi friends. In truth it was questionable value for money back when new, but nowadays they can be picked up for almost nothing if in need of a rebuild, or up to a £1,000 for a mint example. As we drift ever further away from those heady days of the nineteen seventies, expect prices to rise.

Buying secondhand
Anyone who’s owned a basic belt-drive like a Pioneer PL-12D and thinks they can ‘set up a turntable’, may think again when they see the number of parts, and indeed adjustments, inside the ST-7. The upside to this however is that any decent DIY-er should be able to get one going, and there are plenty of decks that need sorting around on sale for pennies. As a result, when you do find a Rabco in the classifieds, take it as you find it and pay low unless it’s in really good, fully working condition. Decks in top condition are beginning to command serious money now. There’s a good deal of info about the ST-7 online, including a download of the original user manual which goes into great detail about how to set it up and service it. It may be very fiddly, but it’s not rocket science.

One comment

  1. David Aldridge

    Excellent article. Thank you for publishing this. I acquired a ST-7 about 6 months ago. I performed complete maintenance on it. I replaced the main electrolytic capacitor and also installed a better course speed pot on top of the PCB to make adjustment easier. Then I installed Dynamat {sound deadening material used in automotive applications} anywhere possible on the insides, even the motor mount. It weighs 3-4 lbs more than it did I’m sure.
    The arm has a AT 440 MLb cartridge, carefully set up.
    I am in the business of buying/restoring things of this nature. Also recently I acquired a LINN Axis with the Akito arm/Linn K9 cartridge, which I went ahead and installed a ATML stylus.

    I have been comparing both, trying to decide which basically sounds better, to me. I am in the business to sell, not to keep everything.

    They both sound very good. After many listening sessions I have determined the LINN is going to be sold. The ST-7 is that good. BTW setup is very simple. No, it’s not a plug and play, but any good table shouldn’t be.

    In my system I had no complaints about the bass. It was not boomy or flabby, and I am running NHT 2.9’s with a stereo pair of 15″ powered subs that sit by their sides. I did carefully set the room up.

    I guess what I trying to relay here is the ST-7 is an Excellent table. I’m 60, and have been in the audio game since I was 15. My older Dr. brother has a nice 6 figure system. He is the one that introduced me to audio at q young age. He agrees that this Rabco model is an excellent machine.

    I bought a new JNB heavy dust cover for it. Stunning is a good word for this table with it’s very unique design and impressive looks.

    Thanks again,

    David in TX.

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