Allright, so I opened my CD930, found the schematic of the output stage and I'm ready to work on it 
I'd like to :
- modify the I/V stage. Normally, the I/V conversion is done by the opamps integrated inside the saa7350. The idea would be to bypass those and go for a pair of opa1632 for I/V and some opa134 or so for the output. That'd give that schematic at the bottom of the post. Hopefully, I won't need any coupling capacitor anymore. I've just a doubt... should I ground the outputs of the internal opamps ?
- improve the voltage references for the switched capacitor networks (VDACR, VDACL), as suggested by JohnW in another thread.
- maybe suppress the npc sm5840, as suggested by Sander Sassen here : http://www.diyaudio.com/forums/showthread.php?s=&threadid=74219 . The digital path of the CD930 is the same (except the sm5840 is smd in the cd930).
Any obvious mistake in there ?
I'd like to :- modify the I/V stage. Normally, the I/V conversion is done by the opamps integrated inside the saa7350. The idea would be to bypass those and go for a pair of opa1632 for I/V and some opa134 or so for the output. That'd give that schematic at the bottom of the post. Hopefully, I won't need any coupling capacitor anymore. I've just a doubt... should I ground the outputs of the internal opamps ?
- improve the voltage references for the switched capacitor networks (VDACR, VDACL), as suggested by JohnW in another thread.
- maybe suppress the npc sm5840, as suggested by Sander Sassen here : http://www.diyaudio.com/forums/showthread.php?s=&threadid=74219 . The digital path of the CD930 is the same (except the sm5840 is smd in the cd930).
Any obvious mistake in there ?
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Hi Ben,
I stumbled upon your thread when searching how to disable the sm5840.
I have a CD940, and I believe they are the same from a hardware point of view. I thought they had LM833 opamps on the outputs. Are they just for buffering and IV is still performed internally? Can't say I've looked at that portion of the player much.
I want to use mine as a transport.
Currently, my CD940 has a riser board, that plugs into a DIL socket where the PCF3523 sits, from here I tap off I2S, and convert to RS423, which I send to an external TDA1541A DAC.
It seems to work well.
I hope to fit a clock to the SAA7310, and electronically disable the digital filter and DAC.
Being a CDM9. I think this can be a good transport. Although, somewhere else, I spotted Jean Paul commenting on how poorly some of the grounding and decoupling is laid out - especially around the servo circuit, maybe its worth investigating that.
I have noticed one of the servo chips doesn't have any capacitive decoupling nearby.
I also think, like most CD players (check out the monstrously big CD63/67 mods thread for ideas), there are improvements to be had seperating out power rails, with either inductors or seperate regulation, improved decoupling caps etc.
Cheers,
Phil
I stumbled upon your thread when searching how to disable the sm5840.
I have a CD940, and I believe they are the same from a hardware point of view. I thought they had LM833 opamps on the outputs. Are they just for buffering and IV is still performed internally? Can't say I've looked at that portion of the player much.
I want to use mine as a transport.
Currently, my CD940 has a riser board, that plugs into a DIL socket where the PCF3523 sits, from here I tap off I2S, and convert to RS423, which I send to an external TDA1541A DAC.
It seems to work well.
I hope to fit a clock to the SAA7310, and electronically disable the digital filter and DAC.
Being a CDM9. I think this can be a good transport. Although, somewhere else, I spotted Jean Paul commenting on how poorly some of the grounding and decoupling is laid out - especially around the servo circuit, maybe its worth investigating that.
I have noticed one of the servo chips doesn't have any capacitive decoupling nearby.
I also think, like most CD players (check out the monstrously big CD63/67 mods thread for ideas), there are improvements to be had seperating out power rails, with either inductors or seperate regulation, improved decoupling caps etc.
Cheers,
Phil
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