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Old 16th September 2004, 04:57 PM   #1
OliverD is offline OliverD  Germany
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Default Building a CD player from scratch

There have been many threads about CD player modding. While most of these efforts are no doubt very successful providing decent sound for little money, some areas are very hard to improve on. This includes (among other issues) the grounding scheme, design of servo and HF amplification circuitry and the routing of important signals.

Browsing this and other DIY forums, I have seen people virtually re-build their cheap stock players and often wondered why nobody takes the effort to adress some last (but very serious) issues. This would of course include ditching the original PCBs. Which in turn brings up the question, what will be left from the original player anyway (except the drive mechanism)?

Using a drive kit from Daisy laser (you can do worse than that) is too expensive for me - I like to keep this project on a tight budget. I had a look at the Shanling players. They designed their players around the CD7 chipset and luckily failed to repeat some of the most common mistakes. However, there still remains a lot to be desired - like a better clock and DAC part.

So this thread is about building a CD player from scratch, starting with only the drive mechanism - trying to avoid the common mistakes while staying on a low budget.

I have already made some design choices. I will use the SAA7378 as servo/decoder, and the VAM1201/VAM1202/CD12.1 drive mechanism. Both are out of production, but will remain available as spare parts for a long time. You can also find them in many of the players that are considered a good starting point for mods (like Marantz CD 4000 and Philips CD723).

The drive mechanism can be bought online in single quantities for less than $20. It is flimsy, especially the spindle part, but mechanical modifications are easy. What about building a top-loader platter mechanism with the pickup reading the disc upside down?

I will design a "motherboard" around these two parts, including servo drivers, HF amplification, servo/decoder section, system CPU and separate power supplys for each section.

Inputs/Outputs of the board will be
  • Transformer secondaries (lots of them)
  • Front panel key matrix
  • Some status LEDs
  • Infrared remote control sensor
  • LCD Display (HD44780 compatible)
  • CDM 12.1 drive connector
  • I2S audio data output at 1 x fs
  • S/PDIF output (TTL-level)
  • Clock input

Both decoder and system controller will be clocked from the DAC to ensure lowest possible jitter. You can use whatever DAC you like and it can be integrated into the drive or be separate. The system controller will learn your favourite remote's RC5 codes. Software updates will be possible through a parallel port adaptor.

Don't expect this project to be finished tomorrow (probably not even christmas), but I'll keep you updated on progress.

Any comments are welcome, of course.
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Old 10th January 2005, 10:44 PM   #2
Mikelo is offline Mikelo  Antarctica
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I've been thinkng about building a CD player
from scratch, but I need to follow directions,
e.g. as in a kit or following someone else's
footsteps. Maybe this is an appropriate project?


Michael
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Old 10th January 2005, 11:58 PM   #3
sam9 is offline sam9  United States
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What are the possabilities of using a CD-ROM unit? They are cheap to begin with and cheaper still when pulled out to be repaced with a CD-R or DVD-RW. The required data rate is higher than required for CD-audio while there allowable error rate is lower -- at least this is what I've been told. I would like to hear of someone who has done this. Or why it is much harder than it seems at first thought.
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Old 11th January 2005, 01:54 AM   #4
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Quote:
Originally posted by sam9
What are the possabilities of using a CD-ROM unit? They are cheap to begin with and cheaper still when pulled out to be repaced with a CD-R or DVD-RW. The required data rate is higher than required for CD-audio while there allowable error rate is lower -- at least this is what I've been told. I would like to hear of someone who has done this. Or why it is much harder than it seems at first thought.
See here post 223.

http://www.diyaudio.com/forums/showt...ht=#post223462
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Old 11th January 2005, 02:12 AM   #5
jleaman is offline jleaman  Belgium
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This is what i use. AND i love it.. sounds GOOD.
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Old 11th January 2005, 02:19 AM   #6
Mikelo is offline Mikelo  Antarctica
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Quote:
Originally posted by rfbrw


See here post 223.

http://www.diyaudio.com/forums/showt...ht=#post223462
Post 223 is critical of using CD-Rom drives. Meridian 588 and later
uses CD-rom drives with tremendous results. HOwver, they don't rely on the drive but a huge buffer.
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Old 11th January 2005, 02:35 AM   #7
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Quote:
Originally posted by Mikelo


Post 223 is critical of using CD-Rom drives. Meridian 588 and later
uses CD-rom drives with tremendous results. HOwver, they don't rely on the drive but a huge buffer.

The post is not critical of using CDROM drives per se, just the practice of using the drive in CD-DA mode and using the SPDIF output. It also points out the difficulties involved when treating an audio Cd as a data CD.
Having only ever heard the Meridian in passing , I'm in no position to comment on the results of Meridians choices but I would doubt that they are using the drive in CD-DA mode or filling their huge buffer via the SPDIF port at a speed of 1x.
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