Finally Eryk S got Facebooked > Eryk S Concept on FB
interested in boosting top sound from SONY CDP 101, 501, 701 heavy duty machines!
I would like to share my knowledge, concerning super-vast sound updating issue in 1st gen Sony CDPs. By saying "vast" I mean leveling this already nice sound to fulfill high expectations.
As one of those feeling that hi quality in material, robust build, engineering has inevitably gone in 1990 I had focused on the equipment built mostly during 70-80ties.Sony's concepts during those years should be judged as pure hi-endish and cutting edge ones. As for their first CDPs: 101 and 501/701 released on the market in 1983-84, there was no such company using so advanced technology. For example in Yamaha CD-1 top unit you can spot all DAC boards taken from Sony.Of course on the other side appeared Philips, but in my very subjective opinion the look and touch'n'feel aspect of their equipment did not match Sony's at all.
Again back to the point - First gen CDPs are using almost the same DAC topology: superb CX980 mono pro-dac or later double dac CX20017 DAC > I/V converter > amp stage > analog LPF > 2V output amp stage again. These dacs represent also one pleasant approach from diy perspective - they need external descrete parts to stay complementary. This enables you to feed them with top modern parts now.
Second, sample hold / buffer stage used there is made of good quality HF/LF357 double op-amp - good, but today we can go much further with it!
Third, passive Low Pass Filter (in those CDPs silver cans - see photo below) also consists of op-amps and RC on smd boards -six in quantity - horror! Last stage is also op-amp made with advanced feedback loops.
So even on this very short digital to analog part we see much engineering and complexity. We have 7 op-amps in total for one channel! This might give good measurements, but sonically you get rather mimicked sound from the original one...Quite a bit of a drama...
Tube outputs are becoming more common day by day in our cd players, but I myself do not approve tearing the guts of a good old cd just to push rarely optimal parts in it. I often prefer simple and max effective path, so such thinking went here - do not ruin this good old fellow, just let him finally open his hidden capabilities!
As you can see from the factory drawing I just simply skipped two last stages: LPF and buffer and changed the first buffer/sample holder to top notch AD797 amp, which here works exactly as I/V converter and voltage amp. It's output is directly connected via decoupling cap already used in those CDs before chinch outlets - it is totally enough to extra bypass it with some good mini 50V polypropylene or bipolar 10-22uF capacitor.
And that's all folks!
Few people asked about the sonic artifacts, which could appear due to the lack of low pass filter, but I have not heard to many of them. This Eryk S direct mod I've applied in few such CDPs, playing them with more then few amplifiers and always with great sonic results.
Pls feel free to try it and report your findings :)