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CDX reverse engineering


Guest rasteri

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Guest rasteri

Spent the weekend poring over CD specifications and component datasheets and I'm thinking maybe the mp3 board will be the one to replace after all. The servo interface turned out to be more complicated than I thought, what with its subchannel interfaces and linear-feedback shift register scramblers and even-odd byte sequencing and so on.

 

Replacing the mp3 board will also give us more flexibility, like FLAC support etc. I was going to try and emulate the I2S interface this weekend but the chip I was gonna use (STM32) doesn't allow 24bit frame sizes. I really wanna use the STM32 because they're really powerful, so maybe I can hack 24bit i2s by generating the LRCK using an external counter chip synced to the bitclock, or something.

 

EDIT : (note for future Andy) you could use two i2s peripherals, using one for the PCM out and one for the LRCK

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  • 3 weeks later...
Guest rasteri

I managed to get some stuff done this weekend.

 

It seems that the only signals which need to be emulated to fool the DSP into thinking there's a CD present are the I2S signals from the MP3 board (BCK, LRCK, PCMD) and the subcode readout from the servo board (WFCK, SCOR, SBSO). The subchannel protocol confused me for ages because they weren't clocking enough bits on EXCK to read the whole subcode, but it turns out they're using a trick so they only have to read the Q-channel (which is what holds things like the CD's table of contents, etc). I wrote a program to decode the servo's output and sure enough :

 

 

Interestingly there's a huge number of Sub-Q packets with invalid CRC because the CD drive is really knackered in this CDX. There are nasty audible clicks in the audio too.

 

There's a line of STM32 chips that can do I2S output at 24-bit, so I've ordered a dev board :

 

 

Hopefully I can have a proof-of-concept working soon.

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this wank worthy thread may possibly go down in history as a goat or whatever cool people call it.

 

p.s I don't understand the techy stuff, just how amazing it would be to have a working cdx without the shitty cd drive.

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very interesting thread!

 

love what your are doing, and hope ur succesfull at it.

 

I have a pair of sl-1200-dz i want to mod too. There is this platter mod diy kit as a starters and then the idea would be adding a rpi dvs inside. I unsure about that though since the screen has to be outside anyways, keeping the whole dvs sistem boxed in the screen would make it portable and interchangeable with other units.

 

best would be some bare metal programming, but im tottally clueless about that. But the technics should have some neat possibilities because of the way it tracks the relative position and the speed. Its a clear film attatched to the platter and a photosensor reading through it which determines the direction and speed of the playback, this means its basically relativemode timecode, if you can manage to see what sort of algorithm its using. Heck you could probably just connect those 3-4 pins into rpis gpio directly to be used as the "timecode".

 

If that was possible you could actually empty most of the cd inside and run the unit through software, or it could even make a reasonably easy way to mod any turntable with just that film a sensor and pi.

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Modding relatively expensive gear like the Technics is a fools economy, these CDX are pennies on the pound for now because of a shitty $2 cable inside, and the fact that CD is about as popular as herpes.

I would not mod that Technics if you paid me to do so, in ten years when the modded one is worth $10 and an original is worth $1000, you will be kicking yourself.

Some stuff is collectable, some stuff is Rasteri-able hahahahaha

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@ximo

 

It was done in low cost (arduino instead pi and just midi controller) and the code was adapted from Rasteri's project

http://www.midibox.org/dokuwiki/doku.php?id=scratchcontroller

 

So look at other threads I'm posting (and also inside the pt01 modding topic) to see work done. Also we could open a new one about digital encoders even there is a work with ttm1, ir mouse and even audio2schmidtt trigger work inside some of them.

 

I bring some info related to the standalone option due it's the path pursued by Rasteri and support by most of us. CDX was cappable of doing most of the new PiDeck as projects or even faster (texas instruments dsp inside) but until now nobody look deep inside (thanks Rasteri once again). Said that it could be possible to attach the internal digital encoder to rpi as it was done with arduino in the past.

 

For the sldz mod the modder has done a great work and I suppose rpi mod will be in their roadmap as soon he will be aware. Someone know about the guy directly? I remember he is from uk too?

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Modding relatively expensive gear like the Technics is a fools economy, these CDX are pennies on the pound for now because of a shitty $2 cable inside, and the fact that CD is about as popular as herpes.

I would not mod that Technics if you paid me to do so, in ten years when the modded one is worth $10 and an original is worth $1000, you will be kicking yourself.

Some stuff is collectable, some stuff is Rasteri-able hahahahaha

 

i mean the technics cds. they are pretty cheap too second hand, i got my pair for 200€. I actually just wanted to mod one and leave the other as is as i like the modded platter without the shitty screen in the middle.

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@ximo

 

It was done in low cost (arduino instead pi and just midi controller) and the code was adapted from Rasteri's project

http://www.midibox.org/dokuwiki/doku.php?id=scratchcontroller

 

So look at other threads I'm posting (and also inside the pt01 modding topic) to see work done. Also we could open a new one about digital encoders even there is a work with ttm1, ir mouse and even audio2schmidtt trigger work inside some of them.

 

I bring some info related to the standalone option due it's the path pursued by Rasteri and support by most of us. CDX was cappable of doing most of the new PiDeck as projects or even faster (texas instruments dsp inside) but until now nobody look deep inside (thanks Rasteri once again). Said that it could be possible to attach the internal digital encoder to rpi as it was done with arduino in the past.

 

For the sldz mod the modder has done a great work and I suppose rpi mod will be in their roadmap as soon he will be aware. Someone know about the guy directly? I remember he is from uk too?

 

Ill take a look, i like all this this stuff.

 

about the arduino, teensy is enough, its another addition i had in mind for my v2 dvs. get a tinsy in there to get some fake dicers and get cue points in there.

 

stuart you mean, yeah he is uk ive been in touch with him to get the diy mod, dont know him directly though as im in spain :d

Edited by ximo roca
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Modding relatively expensive gear like the Technics is a fools economy, these CDX are pennies on the pound for now because of a shitty $2 cable inside, and the fact that CD is about as popular as herpes.

I would not mod that Technics if you paid me to do so, in ten years when the modded one is worth $10 and an original is worth $1000, you will be kicking yourself.

Some stuff is collectable, some stuff is Rasteri-able hahahahaha

 

i mean the technics cds. they are pretty cheap too second hand, i got my pair for 200€. I actually just wanted to mod one and leave the other as is as i like the modded platter without the shitty screen in the middle.

 

 

Pairs of CDX are regularly around for £50 or less broken, and they are not going up in price yet, because they have a reputation for breaking (Keep in mind here, the only thing that breaks is being entirely removed by this project)

 

Technics will always appreciate in price (Fanboys and all that)

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Modding relatively expensive gear like the Technics is a fools economy, these CDX are pennies on the pound for now because of a shitty $2 cable inside, and the fact that CD is about as popular as herpes.

I would not mod that Technics if you paid me to do so, in ten years when the modded one is worth $10 and an original is worth $1000, you will be kicking yourself.

Some stuff is collectable, some stuff is Rasteri-able hahahahaha

 

i mean the technics cds. they are pretty cheap too second hand, i got my pair for 200€. I actually just wanted to mod one and leave the other as is as i like the modded platter without the shitty screen in the middle.

 

 

Pairs of CDX are regularly around for £50 or less broken, and they are not going up in price yet, because they have a reputation for breaking (Keep in mind here, the only thing that breaks is being entirely removed by this project)

 

Technics will always appreciate in price (Fanboys and all that)

 

 

oh that cheap?... ill look around and inform myself then :d

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I buy mine for 50 includding shipment from Madrid to Barcelona. It had also the motor drive issue but I replace it with old one (spare part from the cdx at vid) and it return to life. It will be interesting fixing the parts pointed in service notes...

 

https://instagram.com/p/BKvlRA6D58q

 

Teensy is great but difficult to buy from Spain (there is an adafruit dealer in Girona but it goes to high with extra shippment). Arduino and Raspi boards are available at local stores.

 

About Stuart... why not drop a mail to him? ;)

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  • 1 month later...
Guest rasteri

I really haven't had time to work on it recently. I think all I have to do is implement SQSO subchannel emulation for the servo, I have I2S and SBSO all sorted. I'll update after xmas when I have more free time.

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Hi there,

I'm a cdx lover user for quite some time now.
With some friends we tried to mod this player for couple of years.

Trying to improve, or get rid of the platter fluctuation..

-easy mechanical fix shown here:

https://www.youtube.com/watch?v=P7Aiet-T-Vs&t=5s

 

I own 5 pairs *(I think) of cdx

and are happy to help with any tests or modifications.

We tried to make the cdx work as a serato dj controller,

making the platter scratch encoder work for mp3 play

to work with serato timecode..

It would cut off the use of display and some functions of the cdx

only left witk working platter, pitch, and play stop buttons

Now seen this thread - this is what we wanted to achieve

but due to less and less free time.. we spent 3 years debating about it

and nothing worth came out of it.

So we would like to contribute.

 

My friends also have some big electronic knowledge,

and have some "laboratory" equipment to use for this project.

Not to say some over the average skills in electronics.

 

Waiting for some good news :) Cheers

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  • 2 months later...

Hi guys,

Finally I'm done... I need space in the basement and I don't expect making more "experiments" or tools related to turntables (maybe even djing as mixing songs neither) so I put a topic in the market section (and fb focus group) for someone interested in pieces or so.

 

http://www.digitalvertigo.co.uk/forum/index.php?showtopic=39894

 

I need to move on and make new things like practice with the talkbox and live looping performances to improve my happiness health factor.

 

-m!

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