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2017 : TA-AX7

PostPosted: Sun Oct 01, 2017 12:12 pm
by Axel
At last restored, installed and working : the magnificent TA-AX7 !
Found in Japan in 2010 (#20 3341) with an added part (the gain knob) sourced from another Japanese AX7 (#20 2764, beyond repair that one), this gem was restored, upgraded and modded last august by Pat66 with circuit help from Ozzy.

Restoration :
Recap' of the PLPS, change of all diodes and caps, most resistors, thermal insulation of the output transistors, relays cleaned, DC offset, bias - etc. Also a grey compound was found pretty much everywhere to mechanically dampen parts and resistors ; this compound, however, with age, corrodes everything down to the core - get rid of it and replace all parts touched by it.

Mods :
> Replacement of all lamps with large-beam LEDs - 120°, they work ; after some hesitation, the color scheme was finally kept as devised by Shigeo Takahashi in 1980 (red, green and yellowish orange for the muting switch).
> Lowering of the -20dB muting switch to c. -6,5dB : far more useful even if the AX7's linear pot's resistance doesn't rise over the adjustment range. Still a little loss of transparency and dynamics when in use but really nothing compared to that useless -20dB range.
> Phono MC stage : componentry upgraded with 1% Vishays and much better parts throughout plus boosting of the 3 Ohm position to a 200 Ohm value to load the XL-44L a bit more than the normal 100 Ohm (of the 40 Ohm position). So the 40 Ohm position still is an actual 100 Ohm loading but the 3 Ohm position is now a 200 Ohm loading ; the difference between the two is slight but 200 seems better indeed - a bit more "juice" mostly.
This was the crucial part of the restoration as I mostly needed an excellent MC stage to transfer about a third of my favorite music on LP to DAT ; my previous efforts were marred by tired hardware (TA-E86B), limited hardware (Precise P7, Wega 42V), prissy hardware (TA-F55) or a not as good-sounding turntable (PS-X800 - yes the 8750 beats the pants off it, especially bass- and low-mid wise).

Still pending :
The balance pot is partly dead and leaks one side or another when used - I don't use it it anyway but, still...
Some better use could be made of the subsonic switch and said balance pot but I can't think of what :)
I had to ground the amp as there was a huge eddy current leak - JP components have no grounding terminals : one cable hooked to one underside chassis screw forked into the grounding post of the big Airlink 100/230V transformer (https://airlinktransformers.com/product/japan-europe-voltage-converter-eu-ja0750) - no more eddy current.


The results, sonically.
The phono stage itself justifies everything : extremely low noise floor, dynamic, wide, no saturation or nasties, it is magnificent. Whatever noise is left is also much lower in frequency than the usual "hiss" of a phono stage : take the "ss" out of the word, the "i" as well and you've got a word sounding like what it does, a very discrete "hhhhhh" at about -65dB. Headphones and volume much UP are necessary to hear it. With the PS-8750 and XL-44L it's a match made in heaven.

The rest of the amp far surpass the Precise P7 and TA-F55 and even, yes, the TA-E86 / N86 combo : transparency, dynamics, stereo spread, highs and low extension, overall cleanliness and depth. The linear gain pot is very easy and precise to use (no quirky F55 pads here) and heat production, although consequent, doesn't reach F55 levels - luckily. Of the amps I still have around (but not for long), probably only the Victor A-X9 would beat it but it isn't as enthusing, live, as the TA-AX7 - the latter makes moving MUSIC.

However, not all is always perfect and as it happens the AX7 does NOT like the SS-A1L, at all. To be fair neither did the F55 nor, to a lesser extent, strangely, the Precise P7. They are very demanding speakers and the PLPS apparently doesn't like that... The Wega 42V with its regular toroidal trafo likes them A1Ls a lot but doesn't sound nearly as good as the AX7. So a change of speakers is planned as my APM-77W are much too big now - books can do that to an apartment, they can and they did it to mine : they expand your mind but shrink available space to do so. Probably a pair of APM-33W.


The results, visually.
This is the object that got me into design back in '82, alongwith the APM-77, and undoubtedly Shigeo Takahashi's absolute masterpiece.
Straight, cutting yet absolutely not "cold", some of its design echo parts of the Falcons (front+top angle and proportion), the Precise series (two-tone/structure enclosure, frosty/shiny oppositions) and the pre-Esprit (bare surfaces & elegance), and part of the overall organization goes as far back as 1975 when the pre-Esprit were underway (play/rec structure, linear slider). The AX7 is where it takes shape, all in one, extended yet as controlled as it has to be.
This is my amp forever : it took me 35 years to get it - I ain't budging' no more.

(ctrl + click & "open in new window" all images for full-size)
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And a few closeups to grasp the finesse, the attention to detail, edges, anodization, proportions, surface vs. texture, depth alterations, colors and textures variations, shiny strips added for definition of the different volumes - etc.
In the later TA-AX6, the "ACT" scripting was lighter and blue (not sure it was better - a bit too light), the tone knobs circled in green (so that "green = tone" just as here "red = rec out") and the entire strip separating the gain slider and source/rec selector lowered to a 50% grey (interesting but not good - unless the entire amp was also made darker). Mostly, the AX6 lost the two-piece / two-tone /two-anodization top plate to a standard pressed metal enclosure : it was was a cheaper version to try and sell more because the AX7 and AX8 didn't sell, at all, mostly because of their looks.

(ctrl + click "open in new window" all images for full-size)
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ps. this is my final post on TVK.