Technics CD Player - locating I2S signals for DAC upgrade?

Dear all,

my father has an ancient, fully functioning Technics SL-PG100 CD Player.
Technics SL-PG100 CD Players

We would like to upgrade the thing a bit, trying some other DACs, because the sound of the player is horrible (despite good reviews on the internet we simply don't like the sound). We listened to the same CDs on the same chain with my Mitsubishi M-C5100 (2x Burr Brown PCM56P) and the difference was like :eek::eek::eek:

But my father insists on keeping his Technics due to functions, emotions, don't know the real reasons, except that he'd like to upgrade the DAC part now.

I told him about I2S and I think we could use tons of great DACs if we could feed them with the player's I2S signals coming from the transport.

I found a basic DAC-related schematics of the Technics, here it is: MN66271 Datasheet(PDF) - Panasonic Semiconductor

From that it's not sure for me where I can locate the I2S input signals going into the DAC. Or maybe I should look elsewhere within the player and try to steal the I2S signals from there ?

The first we would try is this one for example: AKM AK4495EQ DAC Module Board I2S 32bit 384khz 2x L7805CV Regulators

Would you be so kind helping me figuring out what to connect with which corresponding side, if possible electrically at all ? (Without conversion).

Based on the linked datasheet above for the Technics, I see following:

AKM DAC left, TECHNICS (PANA MN66271) right
MCLK <- ?
FSCLK <- ?
BCLK <- Pin1 BCLK (SRDATA bit clock output)
DATA <- Pin3 SRDATA (Serial data output)

The missing parts I need to figure out still + the 2 other findings to be validated ..
What do you think, can it work somehow to get "standard" I2S out of the player and feed this DAC board with that ? :confused:
there is a high chance of wrong data format ... it seems that an EIAJ format is used in this player ... maybe you will end up with an additional converter from EIAJ to I2S (not opposite) :D

someone tried? idk if successful:
HIFIDIY??-EIAJ???I2S?? - Powered by Discuz!


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there is a high chance of wrong data format ... it seems that an EIAJ format is used in this player ... maybe you will end up with an additional converter from EIAJ to I2S (not opposite) :D

someone tried? idk if successful:
HIFIDIY??-EIAJ???I2S?? - Powered by Discuz!

Yes this is what I recalled many Jap cdp's seems to be using EIAJ protocol wonder why. Think those using I2S were the ones with Philips TDA dac.
I've managed to insert TwistedPear COD dac with IVY III I/V convertor, including new clock from Tentlabs (16.9344 MHz). In this way I have balanced outputs also... And yes these MN chips outputs EIAJ format which COD dac (PCM1794A) supports directly, no need for conversion. But recently I've had some transport problem, ie skipping problem of reading CDs from half to the end...
Thanks, @kevinkr

I want a CD changer in the format of a vinyl turntable. I had one ~1991-92 and enjoyed using it. It was not a high-end model, let's call it a low-end model, made by or for Sherwood. I bought it used. It died. Life moves on. Except for that CD changer. Because it died.
s-l1600 (1).jpg

Anyway, 30 years later, I now have a setup that is nearly all digital. Doing my homework on the internet, I can see Technics made several models in this form factor late 1980s to 1991. SL-PC10,14,15,20,25,505,705. None of them have a digital output. Nor do their Panasonic equivalents. All of them use a budget internal DACs from the 80s. So, I want the 80s form factor, AND I want to use my modern DACs. I want to have my cake and eat it.

It is possible that I missed a model that DOES have a digital out, and if you point me in that direction, it may circumvent the rest of this ask.

Looking at the thread above inspired me to dig deeper.
I can see repair manuals for the SL-PC14,20,25 models. SL-PCxxx manuals
The SL-PC25 has an MN6625 DSP, with pins 4,5,6,12 showing SRDATA, SRCK, LRCK, XCK. Great!
Pin 33 tells me there is a 5v supply available.
SL-PC ICs.png

eBay had an SL-PC25 in great cosmetic condition and listed as working for $32+$27 shipping. It's now on its way to my house.
It's cheap. If I destroy it, I don't care. It's a hobby, right? I can reuse the clean chassis for a future purchase that might be tatty.

eBay has several I2S to optical/coax/AES converter cards in the $12-$90 range. Some have one of the outputs missing that I do want. Some have USB, HDMI, and bluetooth, none of which I need.
I'm looking at this one for $25 delivered eBay I2S converter
It wants a 5v power supply, which I assume I can vampirically steal from the Technics.

Seems to me I can connect up pins 4 5 6 12 33 and GND, and it'll work.

I will need to drill/cut some holes in the Technics chassis.

Am I on the right path to creating an 80s top loading changer with digital out, or am I being too naïve?
eBay vendor cancelled the SL-PC25 order and listed the reason to eBay as buyer cancelling the order. Which I didn't. Why do people make up lies like that?
The player purchased is the one pictured above. Appears unmarked and looked nice.

Plenty more to buy, but I won't have one to play with this weekend.

Grr. Again.
This time I chose an SL-PC705. My selection criteria are to choose the one in visibly best condition, and that is listed as working.
ETA Monday 31 July. Actual purchase shown.

The first purchase SL-PC25 was released 1990 at 9lb.
The second purchase SL-PC705 was released 1991 at 10.4lb.
So it must be better. Because that's how it works, right? Not to mention the model number is bigger!

I do not (yet) see a repair manual. I'm optimistic that I'll be able to open the unit, read the numbers of the DSP and DAC, and on the internet find the pinouts of either IC in solus or in another Technics/Panasonic manual.

The physical format is different - on the SL-PC25 the transport is in the left of the unit. In the SL-PC705 the transport is at the back of the unit where I was going to put the I2S converter. Hmm. Didn't realise that until I wrote this update. Oh well. The convertor will either go there, or it'll go in the side. Or I'll remove the existing RCAs. Or I'll make it external.

s-l1600 (2).jpg

The SL-PC705 arrived today. Some minor scratches on the lid that I buffed out with a mechanical polisher and compound. Otherwise unmarked.

Everything appears to work mechanically.

And the BEST BIT... it doesn't sound very good. Excellent! It justifies being modified.

The sound defect sounds like simple clipping. I do not know if the clipping is the DAC in the CD player (seems unlikely); the ADC in my preamp; both; or a mismatch between line-out level and max input level. Possibly I could address this by attenuating the line-out.
Anyway, doesn't matter as the plan is to create a digital-out from the CD player.

Have ordered the I2S to optical parts. They won't arrive for a couple or three weeks :(

Sometime between now and then I need to open the CD player to identify the DSP or DAC to determine the pin-outs. At the same time I will make a plan for where to physically locate the additional electronics, and where to drill holes for sockets for external connectors.
I like this generation of Technics cd player, I had almost all the ones with Philips mechanics and I still have 4 or 5 and suddenly I ask myself the following question, why not simply copy the output? digital P series with the 6625?
knowing that there is a good chance that the main PCB of your changer comes from a single cd model and that said PCB has the original location (unpopulated) of the digital output stage.
These are just guesses but I've seen enough of them to know the similarities between the models.
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I have the SL-PC705.
The only unpopulated section is for the wired remote of the SL-PC505, suggesting the board is only for the 505/705.

We obtain the I2S signal locations from the DSP, MN6626 link (same as the SL-PG100 at the top of this thread)

For what it's worth, the DAC is MN6475A link

Despite the huge size and ample free space, it's not obvious where to put the toslink card when it arrives (the small card at the end of post #11).

From these images, there appears to be space near the existing RCAs, or near the power supply.
That space is not there - it is occupied by housing for the hinges.

Hmm. When the toslink card arrives, I'll see how easy it may be to desolder the optical and coax sockets, and mount those on the back panel while the majority of the card goes in that large space front-left.

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