MY CD63SE has benefited greatly from 1) a Superclock III, 2) Audiocom voltage regulators in place of the IC regs, 3) AD825 OpAmps on Brown Dog adapters, 4) replacement of electrolytics with better quality, 4) by-passing power supply electrolytics, 5) replacing power supply diodes with Schottky 11DQ10, 6) additional by-passing on the DAC outputs under the board, 7) a ferrite collar on the mains input, 8) IES power socket and upgraded power cord (PS Audio with ferrite-jacket and shielding), 9) damping applied to the cabinet.
I'm still experimenting with different electrolytics and by-passing. My output path has four different electrolytic variants on it, I'm going to replace all with Elna Cerafines (on order) and see how it sounds. I've not taken the HDAMs or the muting transistors out of the path, I'm wondering about the wisdom of that. In fact, there is a lot of stuff online about mod'ing the CD63 and I think a lot of it is suspect. I've waded through a lot of it and only done mods that seemed to have a consensus of opinion behind them.
I installed sockets to facilitate switching OpAmps. I tried Burr-Brown OPA2604s in the CD63 and found them to be oily-smooth and laid back in their sound - a little dark and veiled for my liking, though they are easy to listen to; my wife loved them. The 2604s were a huge improvement over the NJM2114 that Marantz uses, but I felt there wasn't enough life to them. I switched in a pair of AD8620s, which to me sounded great, much more dynamic, though the base response was off a bit compared to the 2604s. BUT, my wife could not listen to the 8620s, they were too harsh in the high end. Females hear high frequencies we males don't get. Maybe the 8620s can be tamed a bit with better by-passing, I don't know. So I put the 2604s back in, and found that I couldn't listen to them after hearing the 8620s. So I carefully soldered four AD825s onto Brown Dogs and popped them in. Soldering these itty-bitty surface-mount OpAmps had held me back from trying them, even though I've had them for a year or more. But WOW! Everything I've read about how good these sound is right on the money. Now we can both listen to the player, and it sounds fantastic. I have put LM4562s into another player and liked them a lot, but I like the 825s so much in the CD63, I think my OpAmp experiments are done.
I'm extremely pleased with the CD63SE after all these changes. With my latest changes, I seem to be at a point of diminishing returns; we'll see if the Cerafines help matters any more. But there are other areas that may merit attention. I am considering a separate power supply for the clock, and I plan to look at the non-electrolytic caps and resistors, to see if upgrading some of these will produce further gains. Also, I understand the sockets add capacitance to the output path and can adversely affect the performance of the OpAmps (this is even mentioned in the data sheet for the LM6172, which I haven't tried for this reason), so I may take the sockets out and solder the Brown Dog adapters directly into the PCB. I wonder if any AKers have any experience in this?
