Technics SL-P555 CD Player - Circa 1989 - MASH DAC - Restoration Thread

Discussion in 'Digital Sources' started by crooner, Dec 9, 2016.

  1. crooner

    crooner Tube Marantzed

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    Hi guys and gals,

    I have always had a soft spot for Technics CD players, specially those from the late 80's, early 90's with their unique MASH 1 bit DAC and colorful FL displays.
    I recently discovered their 1989 line was actually the first to feature MASH technology but it was disguised as "18 Bit Linear" due to marketing reasons. The public had the perception that more bits were "better" in a high resolution DAC, and 1 bit technology required some reeducation.
    The first CD players marked as such appeared a year later in 1990.

    The Technics SL-P555 seems to fit the bill to be a good representative of the breed. It has enough bells and whistles to scream "I am from the 80s!", it has a very nice handsome appearance with the "jog dial" style knob and it features a MASH DAC inside: the MN6471. It was launched in japan in late 1988 but it was available worldwide in 1989.

    It was a mid range model sitting just below the SL-P777, which sported a larger chassis but very similar circuitry. It is interesting to note, the Technics home CD player line for this year shared the exact same transport: the SOAD70A. This is a linear tracking mechanism with a magnetic rail, which is very fast and reliable. It is therefore possible to swap transports among the line with no issues.

    This particular era of Technics also showcases Matsushita's expertise in mass production techniques. All players share the same transport and very similar power supplies. The integration in their PCB's is also very impressive, allowing them to offer a lot of features and performance for the money. On the larger players, though they seem to have a lot of empty space inside. This is actually a boon for modders as a tube output stage and power supply can be easily added to a player.

    I have been recently reading a lot about CD player modifications after purchasing a Lampizator Atlantic DAC. I have heard of the Lampizator before but never paid attention to his early CD player mod adventures until now.

    He makes very valid points on the value of adding a tube output stage to a classic CD player.

    The Technics SL-P555 with it's MASH DAC is already reputed to sound good. And the larger chassis is perfect for this type of modification.

    I purchased a SL-P555 off Yahoo Japan via Buyee. A 100V model. It was really cheap but shipping was steep. Still, it is cool to own a Japanese domestic model and it should be arriving today in the mail.

    The player will be converted to 120V using parts from another Technics player, a SL-P150, a lower end model from this era that shares the same power supply and transport.

    I am now studying different tube topologies and approaches. I will probably go point to point using a turret board. I will add a nice size transformer and possibly schottky diodes for the power supply.

    The dilemma I am facing right now is where to take or "steal" the signal going to the tube output stage input grids. Lampizator and others take the signal directly off the DAC chip, bypassing the different OP-AMP buffers and muting transistors. This seems to work fine as the sound quality obtained is described as excellent and a step above stock performance.

    However, I think the low pass filtering should remain to filter out- of- band noise from the D/A process. And also I would like to preserve the de-emphasis circuit which is activated by a flag in the data stream of many early CD's recorded using the emphasis process. So my approach will be different.. I am studying the Carver 490T circuit for ideas and I will look at other tube based commercial CD players to see how they deal with de emphasis.
    One thing I like about the Technics is that it features an "emphasis" light on the front panel display to indicate a CD recorded with it is being played. Very cool feature that seems to have disappeared shortly thereafter.

    Stay tuned for more pictures and details as I go along with my restoration.

    Any thoughts and input greatly appreciated!

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  2. Dr Tinear

    Dr Tinear AK Subscriber Subscriber

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    Let me offer a huge +1 on your decision to leave the post-conversion analog reconstruction filter in place. You don't need or want all that ultrasonic noise driving your downstream gain stages into nonlinearity and adding distortion to your CD playback.

    You might want to consider purchasing an add-on tube buffer that goes between your CD player and your preamp rather than building a tube output stage into the CD player. The changes to the sonic signature will be the same -- a little added warmth and perhaps a slight rolloff in the top octave -- and you'd be able to use the buffer with any CD player. You could, in fact, use a buffer of this type with any line-level source by hooking it into a tape loop or external processor loop on your preamp.
     
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  3. crooner

    crooner Tube Marantzed

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    Agreed on the buffer. But i am a tinkerer at heart and I think it would be cool to make this into a sleeper. Looking like a regular Technics job on the outside and packing a wallop inside!
     
  4. Dandy

    Dandy Super Member

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    With a bunch of CD players on my floor all requiring tinkering to keep them going (Nakamichi CDP3A, NAD 5425, etc) I picked up a Panasonic SL-PJ324A today. It's got a smaller footprint and is marked Made in Germany. Nice build quality and similar to the pics of the Technics unit modified by Lampizator. Transport is a CDM 4/19 and it plays everything you put into it, including scratched CD-Rs. Chips similar too, includig the MN6625. So, I'll be watching over your shoulder.

    Pic here: http://www.hifidatabase.com/static/gallery/8/2298-SL-PJ324A.jpg
     
    Last edited: Jan 7, 2017
  5. crooner

    crooner Tube Marantzed

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    Cool! Those were product of a joint collaboration between Matsushita and Philips, which actually went back to the 1950's when the latter helped setup a tube factory in Japan. I almost got the same player as the one modified by Lampizator, but I really liked the design of these late 80's disguised MASH players. And the player I got from Japan has an aluminum faceplate which is quite nice. Their domestic market stuff apparently was made a little better.
    So far I have converted the player to run on 120V by using a transformer salvaged from a US spec lower end Technics player. Looks totally stock.
    Next is to add a tube output stage but I will add a de-emphasis circuit which will be switched in and out by the logic of the player. Stay tuned!
     
    Last edited: Jan 7, 2017
  6. Dandy

    Dandy Super Member

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    I'll be interested to follow your tube output stage here. I got my Nak partly inspired by Lampizator's comments on it, and I like it very much, but I think it needs a new laser.
     

     

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  7. crooner

    crooner Tube Marantzed

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    I have just powered on the Technics. Will probably be working on it tonight. I think I'll start by recapping the main circuit board with Nichicon Muse caps and the like. Except for the output stage, of course, which will be replaced with the tubed circuit. I detect some background hum in the headphone circuit. I will probably recap that also.

    The Nakamichi Lampizator is talking about is the CDP-2A/2E, which uses the Philips TDA-1541 DAC along with a Sony digital filter. I happen to have purchased a NOS example from a forgotten warehouse in Texas. Time capsule of sorts. Works beautifully. Cool to have a brand new CD player from almost 30 years ago! Nakamichi was my dream brand when I was a kid back in the day!
     
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  8. Dandy

    Dandy Super Member

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    My Nakamichi is the CDP-2A model. The 3A above us a typo. It is quite rare here. My unit had been messed with because of the well documented issues with the transport sticking. I've sorted that out, but it is still temperamental and doesn't read CD-Rs or even some clean commercial CDs reliably.
     
  9. SoNic67

    SoNic67 Well-Known Member

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    There is no comparison between a true multibit DAC like TDA1541 and the MASH garbage.
     
  10. crooner

    crooner Tube Marantzed

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    Nice thread crap!

    MASH never claimed to be multi-bit, and it is actually a very clever implementation of PWM to overcome low level linearity which was known issue with multi-bit converters at the time.
    No DAC is perfect and the TDA-1541 had it's own set of issues. The "A" version was developed for this reason. And of course, they had to be "graded", to weed out the poor performing ones.
     
  11. crooner

    crooner Tube Marantzed

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    Have you recapped the main board? If you have done so and it's still acting up, then the laser could be on it's way out. My NOS CDP-2A reads all CD's flawlessly, even CD-R's.
     
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  12. Dandy

    Dandy Super Member

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    I've not recapped the main board of the CDP-2A. I will if you think this might have a bearing on my disk reading issue. Regarding replacing the laser: is this a drop in job, or is there always alignment and focusing to do as well?

    SoNic67, I have a number of CDPs with the TDA-1541A DAC (e.g. a Marantz CD60, a reclocked Rotel RCD 965BX as well as the Nak CDP-2A that I particularly like). But if you take the trouble to read Lampizator's page on the Technics SL-PS700 you might see that he is surprised at how good the MASH chip can sound.
     
  13. onwardjames

    onwardjames Hoardimus Maximus Subscriber

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    I have had many cd players come thru my home, and studio (worked in FM radio for decades, and we used the MASH Technics units exclusively) and I found them to be very non-fatiguing, pleasant and full.
    Your results may vary.

    To Crooner - That thing looks evil! Love it. Will follow with interest. I have a SL-PS700 that the radio station was going to toss. Cleaned the lens, lubed it up, and it works to this day. Must have about a million hours on it. It stayed on 24/7 for probably 7 years. Works flawlessly.
     
    Last edited: Jan 8, 2017
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  14. crooner

    crooner Tube Marantzed

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    Depends on the player. Replacing the actual laser requires alignment including a scope. However, some players allow hot swapping of either the laser mechanism or the complete transport including tray. The SOAD-70 used by Technics in 1989 and 1990 is like this.

    My SL-P555 was not reading discs when I got it and the tray had a bad belt. I simply hot swapped the whole mechanism from a working bottom of the line SL-P170 (1990) and in minutes I was in business. No adjustments of any kind needed. Truly plug and play! You just swap the decorative tray trim piece, fasten 4 screws and connect two ribbon cables. That's it!

    Here are pictures of the player with the 120V power supply but otherwise still stock. This was originally made for the Japanese domestic market with a 100V transformer. The red caps in the analog output stage are actually Elna Cerafines which is a nice touch!

    The player is also really black in color and not "Technics dark grey" like US market models, and the aluminum faceplate is a nice touch as well.

    IMG_0948.JPG IMG_0939.JPG IMG_0942.JPG
    IMG_0951.JPG IMG_0934.JPG
     
    Last edited: Jan 8, 2017
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  15. crooner

    crooner Tube Marantzed

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    Thanks! I think these CD players are real sleepers. The fact that the parts count is so low probably helps with reliability. Other CD players of this period often had many circuit boards inside, all densely populated.

    Upon first opening this thing, you ask yourself, where's the rest of the stuff, as it appears half empty. Looks can be deceiving though, as the design is very well thought out and engineered for reliability.
     
    Last edited: Jan 9, 2017
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  16. Audioraven

    Audioraven Active Member

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    HPIM0212 (6).jpg "MASH garbage." Really? My Technics SH-X1000 D/A converter would beg to differ.
     
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  17. crooner

    crooner Tube Marantzed

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    Beautiful MASH standalone DAC!!
    Was it ever sold in the US? Looks like a Japan only unit!
     
  18. Audioraven

    Audioraven Active Member

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    Thanks, crooner! Indeed, my X1000 is an 100 volt Japanese market unit. I have a Canadian audio magazine review of the SL-Z1000/ SH-X1000 Transport/DAC combo, so I know they made it into Canada. My Orion Audio Bluebook indicates that they were also sold here in the US, but I have never seen a 120 volt version for sale.
     
    Last edited: Jan 9, 2017
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  19. onwardjames

    onwardjames Hoardimus Maximus Subscriber

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    Sweet DAC, Audioraven.
     
  20. Audioraven

    Audioraven Active Member

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    Thanks, Onwardjames!
     

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