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

Interesting to see the space inside your SL-P555. That enabled them to make my midi sized player without sacrificing anything. The PCB looks pretty much the same. I noted a Technics SL-P770 for sale on the 'bay here today, with a disk skipping problem. Looks nice otherwise, but my amateur bench is now full, with not much movement in the winter months.

Re my CDP-2A, I'd like to get a 240V transformer, but there aren't as many cheaper donor units here. But I could get a new laser mechanism, and will when funds allow.
 
SoNic67, ...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.
I am very aware of the polish guy work. I consider him a medium/low-end electronic technician that is interested (obsessed) in destroying good players by adding tube stages. His workmanship looks like the work of a 14 year old that just started to dabble in electronics. His opinions about audio/sound "quality" of certain devices mean very little to me.
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.
I was impressed by MASH first time when they arrived on the market, but now, listening with a different experience, I realised that they are not in the top tier at all. DAC manufacturers moved further from the the first generation, simple, delta-sigma (PWM) long time ago, because they heard the same things and they tried to "fix" them.

Disclaimer:
I had read over and over a very good book about electronics and tubes when I was 12 year old, did my first solid state amp at 13 and repair/recondition my first tube amp when I was 14 year old, I was enamored by tubes at that stage... but that was a very long time ago.
 
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I am very aware of the polish guy work. I consider him a medium/low-end electronic technician that is interested (obsessed) in destroying good players by adding tube stages. His workmanship looks like the work of a 14 year old that just started to dabble in electronics. His opinions about audio/sound "quality" of certain devices mean very little to me.

I was impressed by MASH first time when they arrived on the market, but now, listening with a different experience, I realised that they are not in the top tier at all. DAC manufacturers moved further from the the first generation, simple, delta-sigma (PWM) long time ago, because they heard the same things and they tried to "fix" them.

Disclaimer:
I had read over and over a very good book about electronics and tubes when I was 12 year old, did my first solid state amp at 13 and repair/recondition my first tube amp when I was 14 year old, I was enamored by tubes at that stage... but that was a very long time ago.

You do realize that this hobby isn't some type of potato-sack race, right? There's no finish line.

You clearly have technical know-how. That's unarguable. But I wonder if your social skills might be improved somewhat with that old line we've all heard, the one about "if you can't say something nice...."

C'mon, man. You can easily get your point across without being so aggressive about it. We're all friends here.
 
I noted a Technics SL-P770 for sale on the 'bay here today, with a disk skipping problem.

Had 2 of those as well. Same situation - my radio station throwing them out. After a lens cleaning and lube, worked perfectly. They sound identical to my SL-P700.

I enjoyed their sound.
 
Thanks for your thoughts SoNic67. Your comments about your preference for SS over tubes shows your different audio preference. Me, I've lost interest in SS, though I have some restored SS classics and I usually prefer listening to vinyl on a quality turntable.

I find Lampizator's work entertaining and he's certainly listened to more CD brands than most of us. As crooner said in his first post, he's not going to copy his approach anyway.

No harm in disagreeing, but (as rock critic Robert Christgau once said), maybe we'd better not have lunch.

(Post written just before Onwardjames' last couple of posts.)
 
C'mon, man. You can easily get your point across without being so aggressive about it. We're all friends here.
What was aggressive in what I said? Sorry if you perceived that way.
I am stating my personal opinions, that might not be in line with yours. To me that's fine, since they are just that... personal opinions on a public forum. We don't have to agree on everything.
Tubes and the first order delta-sigma DAC's where replaced by something else for a reason. Or for no reason at all...
 
Calling MASH garbage in a dedicated MASH thread wasn't nice at all. I don't go on other member's restoration threads calling their equipment trash. Forum etiquette I suppose. Perhaps soNic67 should start a MASH bashing thread of his own or express his opinions on a general thread about CD players and their perceived sound quality...

As for Lampizator, his CD player blog was started almost a decade ago. And given he had so many players and so little time, I guess he went as fast as he could without regards to neatness.
He has since come a long way and his manufacturing operation nowadays is CE certified and very high quality. But many of his early CD blog statements still hold water today.
 
Interesting to see the space inside your SL-P555. That enabled them to make my midi sized player without sacrificing anything. The PCB looks pretty much the same. I noted a Technics SL-P770 for sale on the 'bay here today, with a disk skipping problem. Looks nice otherwise, but my amateur bench is now full, with not much movement in the winter months.

Re my CDP-2A, I'd like to get a 240V transformer, but there aren't as many cheaper donor units here. But I could get a new laser mechanism, and will when funds allow.

yes, this thing is a miracle of miniaturization. If you compare the innards of the SL-P550 from the year before, they cleaned up things quite nicely. As you can see, everything plugs in, only minimal amount of cables. The boards are the usual thin phenolic which was typical of mass produced Japanese goods back then. And this went all the way back to the original transistor radio days of the electronics industry in Japan.

The SL-P770 and the SL-P777 although similar in cosmetics are two different animals inside. The former is Burr Brown based and true 18 bit. The latter is MASH based like my SL-P555.

As for your Nakamichi, I think the "E" 240V version is probably harder to find over there. Nakamichi was a premium brand with limited distribution and most folks went with Sony, Technics, and the like. Have you downloaded the free service manual from Hi-Fi engine? Maybe the transformer has 240V primary windings and can be rewired...
 
I am attaching the block and schematic diagrams of the SL-P555's output stage.

I will probably be placing the tubed buffer stage in place of the "comparator" OP-amps, preserving the player's low pass filtering/de-emphasis circuit. The output from this filter will go directly to the RCA jacks bypassing the "Class AA" buffer and muting transistors.

Alternatively, I could bypass the comparator stage and have the DAC voltage output go directly to the low pass filter circuit and then add the tube buffer stage in place of the Class AA op-amps...

I want to preserve the player's headphone amplifier circuit, so I will tap the signal before the RCA jacks to feed it.

SL-P555 output block diagram.JPG SL-P555 Output Stage.JPG
 
Is there a way of deciding which would be the better of the two options? Either on sonic or practical grounds?

P.s. Thanks for referring me to the Nak service manual. I'll need to check the transformer in mine to see if it can be connected for 240V, but the manual is great for laser assy replacement.
 
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Is there a way of deciding which would be the better of the two options? Either on sonic or practical grounds?
It's hard to say, I think either approach will work as the signal is already 2V at the DAC output pins. Notice this DAC chip has a differential output with positive and negative signals. It is then converted to singled ended by the buffers, hence the "4DAC" designation...
 
After careful deliberation I decided to go for the classic anode follower circuit for this CD player as described by Lampizator on his Yamaha and Technics projects. Makes total sense since the MASH chip outputs a healthy 2V and this super simple circuit should suffice.

I will be using the best quality reasonably priced parts I can source along with some vintage Allen Bradley carbon resistors, as I like how these sound in my Marantz tube gear.

I have already ordered the toroidal transformer which is small enough to fit in between the original power transformer and the SOAD70 mechanism.

Instead of going for the octal based 6SN7, I will be using the 9 pin 6CG7, of which I have plenty of spares. It is identical in specs and should yield great results.

The complete circuit will be laid out on turret boards to give it a nice vintage look.

Will post more pictures when I start putting everything together.

This will be the first phase of the modification. The second phase will involve upgrading the clock to a Tentlabs XO3 with its own dedicated power supply and SPDIF output, which I will terminate in BNC, to hook up to my external DAC.

Stay tuned....
 
Could you post the specs of the toroidal PT that you are using?

I am not sure if Lampizator still sells individual toroids. I know he had them made by a Polish manufacturer over there.
So I went ahead and purchased a US made Antek transformer. These are the specs:

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The 200V output is ideal and there's an extra 6.3 V winding. I can use that to power a green LED to shine over the CD while it's playing. For some reason my player has the opening for the light to shine through on the front panel but no LED.... Perhaps it was omitted for the Japan domestic market version> mmmmm
 

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Indeed. All the parts should arrive this week. Will begin wiring up the turret board for the main circuit. I decided to go with a simple RC filter network instead of a LC filter for the first filter stage of the power supply. I am using Duncan Amps free power supply modeling software to choose the values. I will be using cutting edge Cree Silicon Carbide Schottky diodes for the bridge which should be a first for this kind of project!

The coupling caps for the output will be Muldorfs. Most of the player's main PCB 'lytics will be upgraded to Oscons.

I may even go for transformer covers for the toroid and main power transformer to dress up things a bit. Copper sheets for the lower chassis and cover are also for consideration!
 
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Looking forward to the next instalment. I'm distracted by rebuilding part of a Heathkit AA-50 tube amp. But, at the moment, I'm using my Panasonic in preference to my Nakamichi. Both still in stock condition.
 
Progress is being made. I got most of the parts in the mail. The gold plated glass epoxy turret boards are really nice quality and the toroidal transformer is huge, larger than I had expected. The original power transformer will need to be relocated to the rear panel. The Murdorf output oil caps look very nice. The F&T power supply electrolytics are nice also, but one of them came unmarked. It is physically identical to the other two, hopefully the supplier didn't mess it up..

I recapped the main motherboard with OSCONs , WImas and Nichicon Muse caps. I also proceeded to bypass and remove all the output stage buffer OP-Amps. The negative signal from the MASH chip goes directly to the original low pass filter network which also applies de-emphasis if needed. The output from this will go to the tube output stage. The headphone amp will be fed from the tube stage. I recapped the headphone amp PCB with bipolar Nichicon Muse caps..
Since the tube circuit inverts polarity, the output will be correctly in phase.

I will start wiring up the turret boards very soon...


IMG_0956.JPG
IMG_0957.JPG
mash PCB.jpg
 
Thanks! I was pleasantly surprised by the quality of the original motherboard. No lifted traces with my Hakko at 800 degrees using standard Kester 44 solder. Every component is clearly marked on both sides of the board, a huge plus compared to my Magnavox/Philips CD100. The Philips board traces were very easy to lift also.
Overall, this thing is a pleasure to recap and work on.
 
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