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

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

  1. restorer-john

    restorer-john Addicted Member

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    It wasn't really ahead of its time with the 'jitter' thing. There was a serious issue with early toslink receivers and transmitters unable to maintain an even duty cycle and practically all the external two box or transport/dac combos used a simple circuit like this switchable one to fix that issue. All digital input amplifiers from the late 80s had similar circuits after the toslink receiver to do exactly the same. Jitter has come to mean something else these days, in this case, it was for consistent duty cycle correction- nothing more.
     
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  2. Audioraven

    Audioraven Active Member

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    The Jitter Free circuit is a jitter elimination (it works on toslink and coaxial) clock circuit in the SH-X1000. When it is engaged the digital stream is fed into a memory buffer and is then fed to an internal reclocking circuit eliminating any jitter present in the data stream before being converted to analog. When the Jitter Free circuit it is not engaged (your choice via front panel switch) the X1000 uses a PLL clock circuit. In either mode it has no problem maintaining a lock on the data stream.
     
  3. crooner

    crooner Tube Marantzed

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    Tested the power supply tonight with a couple of vitreous enamel resistors as loads, and the ground temporarily floated from chassis. Got 197 V DC on my Fluke. The target was 200V, so it has been met. The 3V difference is negligible and probably caused by the CL-90 thermistor in series with the toroid's primary. I like using them as soft start devices.

    Tomorrow I will start wiring up the tube circuit turret board...

    IMG_1173.JPG IMG_1174.JPG IMG_1175.JPG
     
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  4. GD70

    GD70 AK Subscriber Subscriber

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    Very enjoyable read for a Sunday morning and coffee! Impressive work here.
    Glenn
     
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  5. crooner

    crooner Tube Marantzed

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    Thank you Glenn. I'm a big fan of turret boards in tube amps so it was a natural choice. I am glad the Cree SiC Schottky's worked well. Never used them before. Supposedly they sound as good as tube rectifier. We'll see...
     
  6. GD70

    GD70 AK Subscriber Subscriber

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    Reading this thread made me realize I had never considered modding a CD player. This has sure opened a door to a lot of us. I don't have the necessary electronic know how you have, but your work is inspirational, and a tube buffer sounds like a great way to tame the sometimes overly bright aspect of CD playback.
     

     

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  7. crooner

    crooner Tube Marantzed

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    I had never realized it either until I started reading Lampizator's blog. I knew about Luxman "Brid" CD players and Carver's in the late 80's, early 90's but that was about it.

    Most high-end digital during the 1990's was solid state. My reference Sony CDP-XA7ES is like this, all discrete solid-state, but very smooth sounding. Complex as heck though...
    The beauty of the tube approach is the simplicity which makes relatively easy for a fan like me to attempt to do it.
     
  8. crooner

    crooner Tube Marantzed

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    Ok. So after a day long marathon session, I finished the player. Wired the tube turret board first. Tried to be as symmetrical as possible .Used some very fancy parts in there. The Arizona "Cactus" caps are a leftover from a Marantz tube restoration and are worth more than $30 each! Lots of vintage Allen Bradley carbons as I like the sonic flavor of them. Used more stable Ohmite vitreous enamels in high voltage areas. I also used a vintage Sprague black beauty from the pin 9 (electrostatic shield) to ground. No high voltage here so it should be fine.

    Had to experiment a bit with standoff height due to the 6CG7 tube sticking past the top cover of the player. I am using a 1950's vintage RCA black plate with shield.

    The Mundorf's can also be seen as final coupling caps going to the RCA's. The RCA's are new chrome plated types. Not a fan of gold in RCA's.

    I also devised a star grounding scheme which can be seen right in front of the tube turret board.

    In all, I think it looks pretty clean. Gonna fire it up shortly and report back on my impressions!

    IMG_1176.JPG IMG_1177.JPG IMG_1179.JPG IMG_1182.JPG IMG_1183.JPG IMG_1184.JPG IMG_1186.JPG
     
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  9. Bert 1100

    Bert 1100 Super Member

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    Wow !
     
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  10. crooner

    crooner Tube Marantzed

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    Well of course, I am getting some digital "whine" noise on both channels. Could be a grounding issue.
    I also added 300K resistors from each output to ground, and this was not on the original Lampizator schematic.
    This was done to minimize thumps when connecting to a preamp. But I may have to remove them first to see if this is what's causing the problem.
    Otherwise, there is output from both channels.
    Tired so I'll continue tomorrow or Tuesday...
     
    Last edited: Feb 6, 2017
  11. Bert 1100

    Bert 1100 Super Member

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    Good luck on debugging this !
     
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  12. crooner

    crooner Tube Marantzed

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    Thanks. At least the thing didn't go up in smoke!
    I was very careful with my wiring, specially the HV lines.
    I also added a 0.5 amp fast acting fuse that protects the whole player.
    These players came with no glass fuses, which is strange. I am sure there are thermal fuses in the original transformer though...
     
  13. crooner

    crooner Tube Marantzed

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    Here is the modified schematic of the audio signal path of the player. The lines in red represent the current signal path. The lines in yellow the original path going to the Op-amps.

    The negative differential signal from the DAC is jumpered to C809 (left) and C810 (right), effectively bypassing IC802, IC803 and IC804. The signal then goes to the LPF/De-emphasis network. The output from this filter is fed into the new triode buffer stage, effectively bypassing IC805 and IC806. The output from the buffer stage is then taken to the RCA jacks. The muting transistors are bypassed as well and the headphone input is connected to the outputs at this point....

    SL-P555 output circuit MODIFIED.jpg
     
  14. Dandy

    Dandy Super Member

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    Still eating popcorn while following this. Good luck with the debugging.
     
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  15. crooner

    crooner Tube Marantzed

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    Thanks man. I have some ideas on what is causing the problem. Here's the final schematic of the output stage...

    schematic tube stage final.JPG
     
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  16. crooner

    crooner Tube Marantzed

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    Duplicate Post
     

     

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  17. GD70

    GD70 AK Subscriber Subscriber

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    Looks great! Are you considering some kind of venting for the tube heat?
     
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  18. crooner

    crooner Tube Marantzed

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    Thanks! the single 6CG7 inside should not require any ventilation. We'll see when I have it running with the cover on for a while.

    In regards to the noise issue, I've done some investigation and it appears it's common mode noise from the DAC's differential outputs.
    I mistakenly took the negative signal directly from the DAC chip, bypassing the common mode noise filter composed of a 47K resistor in series and a cap across both positive and negative legs on each channel.

    So I need to pull out the motherboard again and rewire the outputs. Will report after everything is put back together....
     
    Last edited: Feb 7, 2017
  19. Dandy

    Dandy Super Member

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    Great troubleshooting. How did you determine this?
     
  20. crooner

    crooner Tube Marantzed

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    Well. the DAC chip voltage output uses a differential mode with two signals per channel, one positive phase and another negative. These signals are not referenced to ground. Any digital hash they carry is common mode noise embedded in the audio signal which is AC, of course. The series resistor and parallel cap act as a filter for this noise and prepares the differential signals for the next OP-AMP stage which combines them into a conventional single ended signal referenced to ground.
     
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