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DIY implemented replacement DAC for Cambridge D500SE
DIY implemented replacement DAC for Cambridge D500SE
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Old 4th July 2020, 08:36 PM   #1
joydivision is offline joydivision  Portugal
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Join Date: Feb 2007
Location: Algarve
Default DIY implemented replacement DAC for Cambridge D500SE

So, after having found out that the original Crystal DAC is "toast" (I opened another thread about this initially), I decided to build my own replacement DAC board which will be "piggy-packed" onto the original board and connected to all the relevant digital input and analog output lines as well as power rails. I'll also improve the over all power supply section of the player and make a full recap. I decided to go with CS4398, which represents an improvement over the original DAC chip and also because it was available already soldered on a tiny board which adapts to DIP28 (so I don't have to solder SMD). I've already received it, looks nice. Now I finally got the time to finish the schematic and PCB layout on the computer, I'll make a decent home made PCB for this, but before getting "hands on", I wanted to share these, as maybe some improvements can be made and certainly there are some more knowledgeable people on here and also more experienced than me, especially with this (quite popular) DAC.

I logically based my implementation quite directly on the datasheet but also consulted a lot of existing DAC schematics with this chip, which can be found on the internet. I also had a look at the evaluation board schematic from Crystal. I noticed a strange inconsistency between datasheet and evaluation board: the decoupling caps are 100nF in dastasheet (and most commercially available implementations and also CD players I had a look at the service manual), but in the evaluation board and a couple of schematics which can be found on the net, they are 10nF. Maybe a mistake?

I opted for 100nF, makes more sense and is commonly used.

I did my best regarding ground planes and proximity of decoupling caps, I can't use more advanced techniques, as the PCB will be home made and I use quite basic technique, so some severe limitations here, but I still think it can come to good result.

Comments, ideas and criticism is most welcome.

Please remember this will be "inserted" in the existing circuit, that's why no receiver chip and no clock circuit is shown.

Ah, I hope the reset circuitry is alright, as I based it on the original circuitry which is not exactly the same chip, as already said and I couldn't find a comparable implementation for the CS4398.

Also, please remember that after the simple output filter stage (and conversion to unbalanced) which is shown, there follows another filter stage from the original board, for which I'll upgrade the opamps and change a couple of components for the better.
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File Type: png board.png (25.1 KB, 42 views)
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