Pioneer "Legato Link" Appreciation Thread

Lately I've been enjoying the sound of an oldie but a goodie. "Legato Link" is Pioneer's version of single-bit digital-to-analog conversion, which appeared in their CD players around 10 years ago and can still be found in their latest DVD gear. The PD-S801 is a CD player:-

This player also features Pioneer's "Stable Platter" mechanism, which basically consists of an aluminium disk topped with a vibration absorbing rubber mat, forming a "turntable" integral to the sliding drawer.



CD's must be inverted and placed label-downwards on the turntable, a minor inconvenience necessitated by the Stable Platter. The laser shines onto the disc from above, with the added advantage that it is highly unlikely that dust could ever settle on the lens. By coincidence there is also a long-term disadvantage to having the laser mechanism upside-down, which the designers could hardly have predicted...

One day a screeching sound emits from the mechanism. This is more than slightly disconcerting as the Pioneer is not mine - it has been kindly loaned to me! I carefully remove the cover and I have to admit it is exciting to see the mechanism and the vaunted "Legato Link" circuitry for the first time.



More about that later though. First I have to find out if there really is a tortured rat inside somewhere with its tail tangled in the gears while the laser brings heat to its unspeakables.

I remove the 3 locating screws from the rubber bushings and lift the mechanism up to 90 degrees.

Everything looks fine and naturally the lens is spotless but lacking any better ideas I clean it anyway.



(The clear plastic wheel to the right is the main spindle which rotates the CD between 200-500 rpm. To the left of that is the laser lens in a red plastic housing called the "sled" because it slides smoothly along the long stainless steel pin above. The sliding motion is provided by the copper-coloured worm drive (parallel to the pin), which is in turn belt-driven by the silver motor at top. The lens itself is attached to the sled by flimsy springs and is surrounded by two sets of electromagnetic coils, one of which provides fine tracking control, the other providing focus by adjusting the vertical distance to the CD.)

A quick test and it seems to be working fine with no squeaks. With more than a tinge of suspicion I refix the locating screws. Intermittent faults may be the worst, but even so I'm not at all pleased when halfway through the next CD the thing starts skipping tracks and then dies completely! Now it won't even spin up the disc, just makes a solitary *TICK* sound when I press the play button, as if there is no disc inserted.

I start wondering how you explain to someone that their years-old CD player has keeled over just days after lending it to me. I can see I'm going to end up owning this thing after all... I get visions of salvaging the Legato Link converter as an external DAC. Yikes.

There are numerous potentiometers on the boards near the mechanism, with labels like "TR.GAN" (tracking gain) and "FO.OFS" (focus offset). Couldn't one of these have gotten dirty or absorbed some moisture? I tweak them all, carefully returning them to their exact positions.

*TICK* The Pioneer now has the entertainment value of half a pair of castanets.

I undo the screws for another seemingly pointless inspection of the mechanism and - "Hello, where's the flippin' lens"!? Within a minute I've located it and retrieved it from a deep plastic well inside the player. Close inspection of the sled reveals heat-hardened glue which has become brittle and cracked, with gravity taking over from there. In the standard (non-inverted) design, this might never have become a problem, although the fault is certainly with the glue, not the design. I mix up some 2-part epoxy, making sure to get the lens in the right way around.

Since then it has been working perfectly again, with no adjustments necessary. It turns out I am not the first person to discover the displaced lens problem. Many consumer products have one or two particular flaws which cut them short before their time. If you are in the habit of fiddling around and fixing equipment you can save time by doing an internet search or by ringing a service centre and asking them "Hey, what usually goes wrong with an XYZ model?".
Here's a great link about servicing CD players.

Now to the fun part. Let's trace the signal through a Legato Link player:-



The signals from the laser pickup come along the grey ribbon cable on the left and are fed to a Sony CXA1372S (pdf) RF signal processor and sled/tracking/focus servo driver chip (the big one at the bottom). To the right of that and mostly hidden undder the board is a surface mount chip which presumably decodes the disc data to PCM and applies the CIRC error correction. From there it's on to the top level via a 15-wire ribbon cable (at the right) to a Pioneer PD0116A chip which I think is just a multiplexer breaking out the left and right channel digital info.

The two PULSEFLOW Pioneer PD2028B single-bit DAC's are the medium sized chips symmetrically placed with a 74HCU04 Toshiba chip inbetween them providing some logical glue. Behind it is the timing crystal. The differential outputs of the Pulseflow chips go to JRC 5532DD op-amps which are surrounded by analog filter components, and also appear to be getting some buffer assistance from 6 transistors per channel (three C3068's, two C124's and an A124). Output impedance is fairly low, 100 ohms or so with enough oomph to drive a pair of high impedance headphones.

Voltage regulators abound. Top left are the +/-12V pair. Behind the crystal (centre) is a pair of 5V reg's, must be one for each DAC. To the left is another 5V reg, presumably for the multiplexer.

If you buy a cheaper (non-Legato-Link) version you don't get the upper analog board at all, and all the empty real estate on the lower board will be filled up, probably with a single multi-bit DAC.

Here's a closeup of a single channel, viewed from the right.



Some people like the Pulseflow DAC but can't bear the thought of an op-amp in the signal path. I saw a website where someone had modified a player, taking the DAC outputs to drive a valve amp. How crazy is that? [I'd love to be able to provide a link but unfortunately can't find the website again].

Hey, one more quip like that and next week you'll be looking at a Yamaha multi-bit player... with "4X Oversampling"!!
Unless of course, you'd care to show us the insides of the Marantz.


And a big shout-out to lini! (and any Legato Link lurkers out there).