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The Korf Blog

The inside story: our research,
development and opinions

26 June 2021
Sony PUA-7 Tonearm
People often ask, what are the most historically important tonearms? Which designs influenced the industry most?

Chronologically, I will probably start with Gray fluid suspension unipivots. Then the Ortofon RS/SKG/SMG series, the first ones with the removeable headshell that became today's standard. SME 3009 and its many derivatives that defined the 1970s. Rabco linear tracker. Breuer Dynamic Tonearm. Rega RB300.

But what about Japan? Micro Seiki's dynamic balancing mechanism? Acos Lustre GST-801's fluxvalve antiskating? Pioneer PL-L1000's linear tonearm motor? The innovations and the design language they pioneered stayed home, with the obvious exception of Technics SL-1200's tonearm's looks .
I would single out the Sony PUA-7/9 series though. Technically, they were pretty advanced yet, again, very little of what they did influenced others. But visually... I think the PUA-7/9 series set the standard on what a quality tonearm should look like. The mix of materials, textures, subtle colour variations, detail — everything is in its place and contributes to the harmonious whole. PUA-7/9 are an aesthetic benchmark.


But does it perform?
That's a much harder question than it seems. There are huge internal differences between similar-looking Sony tonearms. Leaving the high end nearly unobtainable PUA-9 aside and focusing on PUA-7, here's the (probably incomplete) list of its versions:
Although it looks like PUA-7 (and -9) use a typical SME/Ortofon headshell connector, it isn't really so. These Sony arms have a collet clamping the round part of the headshell. The headshell pin is not loaded and is used for location only. As far as I know, nobody ever did anything similar. Probably because making this collet is economically ruinous, unless you are a multi-billion industrial conglomerate.

From Sony sales literature

We have a pristine Sony PS-X50 in our collection, and this is the PUA-7 version we measured the way we described in the post about the typical tonearm resonance measurements.

The accelerometer is attached to the top front of the headshell, and the vertically modulated 0 to 20 kHz sweep recording is played. The output from the accelerometer is conditioned, amplified and converted to g. We're keeping our tradition of using the Audio Technica AT7V cartridge for the vibration measurements and for listening.
We have used the Sony headshell that originally came with the tonearm. Yes I know there is considerable controversy whether the junior PUA-7 came with a SH-165 or a SH-155... but I have no way of telling one from the other. I'll refer to it as a SH-165 for convenience's sake.

How does Sony PUA-7 compare to the typical tonearms such as RB300 or Jelco?
The Sony's original SH-165 headshell is of the high damping kind. 17 gram (!!!) of aluminium/carbon mix, if Sony's marketing literature is to be believed (its top part looks like normal carbon-less thermoplastic to me). The combination of high mass and polymers very effectively suppresses high frequency resonances, but how would it sound?

I have actually re-measured this arm 4 times, because I could not believe that the low frequency resonance situation could be so bad. Sony took pride in selecting the best alloy for the armtube — and this is the result?

It took a while to understand what is happening. As I suspected, it had nothing to do with the armtube itself. The nylon cylinder connecting the counterweight stub to the main arm assembly has fallen apart. Time is not kind to plastic parts.

For a quick hack, I replaced the ruined nylon connector with a 3D printed one. It still wobbled a bit, but the comb of low frequency resonances went away, and a single peak appeared just below 400 Hz (not shown). Once we have some time, I will make a nylon counterweight stub connector. There are many thousands of PUA-7's around, and most if not all will benefit from a new one.

Subjective Evaluation
We have first listened to PUA-7 with its original SH-165 headshell, and then repeated the evaluation with our own HS-A02 in its place. The listening was done with a 3D printed ABS counterweight stub connector in place of the ruined nylon original.

With the Sony headshell, the subjective performance was good rather than outstanding. As the measured lack of high frequency peaks predicted, the sound is a bit on the warm-and-dark side. It's hi-fi at its best, with excellent readability and clarity. But the decays are cut short, some of the spatial information is lost, and the timbres tend to be a bit boring.

Swapping the SH-165 for Korf HS-A02 shows the true potential of this arm. Hi-fi sound? Not a hint of it. This is a thoroughbred that can hold its own against any of today's mass-market tonearms. What really impressed me was lack of the arm's own sonic signature. Not necessarily a bad thing (SME V has one), but I personally prefer tonearms that don't constantly remind me of their existence.
With bookshelf speakers, PUA-7 might be all the tonearm you need
Can the PUA-7 play in today's premier league? Sadly not.

In the last decades, vinyl reproduction became a lot better in one key area: the quality (and often the quantity) of low frequencies, the viscerality of the bass tracks. PUA-7 hints at what's there; today's top tonearms give it to you like it is. If your system is full-range, you'll notice at once. But with bookshelf speakers, PUA-7 might be all the tonearm you need.

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