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Cambridge Audio 640c - RPi swap
Cambridge Audio 640c - RPi swap
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Old 28th January 2018, 11:07 AM   #1
drmabuse71 is online now drmabuse71
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Join Date: Apr 2017
Default Cambridge Audio 640c - RPi swap

Hi community,

I bought a Cambridge Audio 640C V2.0 with defect drive for little money on ebay. The owner said, he tried to exchange the drive, because it was out of order, but didnīt get it to work, everything except the drive should work properly before.
When the player arrived, it seems to be in good condition, only the caddy doesenīt open.
My idea was to swap the cd-drive with a RPi, so that I could use the D/A Board stand alone (Wolfson Chip seems to be quite good).

But it seems much more complicated, that I need help. The service manual shows several connectors, which I dinīt get. Perhaps someone can help me or give me a hint.

CN1: powersupply
ok, because from original ps

CN2: Masterclock
MCLK - because PI has no masterclock I will take BCK signal from Pi?
GND - From Pi


CN3: I2S
DEM
BCK - from PI
DATA - from PI
LRCK - form PI

Donīt know what DEM is, seems to be deemphasis, but what should I do with this signal ? leave it open ?

CN4:Service manual says:"Mute" - from servo PCB
signal
GND


CN9: Service manual says:"Mute" - IR from front panel
signal
GND

Are these two connectors "unmuted" when unconnected or do I have to add voltage to unmute ?

CN10: digital in from servo PCB
GND
Do I have to connect this @ all because Iīm using only I2S signal ??

Seems getting weired .......

But perhaps some of you can help for one of these issues

THX for your help in advance,
kind regards,
Michael

Sorry for my bad english
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Old 30th January 2018, 07:50 AM   #2
JonPike is offline JonPike  United States
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Join Date: Feb 2004
Location: Irvine
Interesting... you're wanting to do what I want to do. I was given an old Resolution Audio player, was well thought of in it's day. Tried to fix the transport, and wasn't successful there. But, I also wanted to patch in a RPI with Moode Player as a wireless source and use the nice DAC, remote volume control, etc...

So far, it sounds like you're mostly on track with connections. In my case, no schematics, and even the Resolution guys don't have copies 18yrs after, so you're a bit ahead of me there. Resolution rolled their own servo board on their transport, so I can't just look up the output of the standard one they based it off of. I kinda set it back on the shelf, months ago.

Things that need to be known, and I've been finding surprisingly hard to find out:

1. Does the CD transport connect to the rest of the filter and DAC by standard I2C signals?

2. Is the data in a standard format that the DAC section would recognize, or will you need to "translate" it from the standard that a RPI puts out?

I hope somebody with more info than I've been able to dig up so far will let us know what's what here... That said, going with what I'm mostly sure of so far:

The Masterclock, not sure, maybe as you think just supplying the I2C clock would be OK. It's the clock for the Transport? Try without it.

The signal names you have suggest that 1 is probably true. 2 probably could be answered by finding data sheets on the chip that is receiving the data for the DAC section, and comparing to what the RPI "speaks". Though I've not been doing too well answering this question for my own set of chips...

The De-emphasis would be a logic level toggle to say "it needs de-emphasis" to the DAC, I think it doesn't matter, in that you're streaming data files, very few CD's ever needed it, and I don't think most players have a decode for that anyway. Leave it disconnected. (or, more specifically, pulled the direction that indicates "no de-emphasis")

I would think the two Servo PCB sigs you don't have to worry about, the mute is probably a mute control so when a disk is removed, stopped, etc, the DAC will be muted, I'd guess the other is digital control from the main PCB to control the transport for track selection, play/stop, eject. No transport, you don't need the signals. (as before, make sure you pull the mute in the direction that doesn't mute the DAC)

But, the other mute signal from the IR control, that you probably want to hook up, it should enable you to mute the DAC from the remote control, which you probably want.

So, try feeding it some I2C music data with the Pi, and let us know what happens! Now I'm motivated again, to try to find these on mine!

Last edited by JonPike; 30th January 2018 at 07:55 AM.
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