Hello Duncan,
Glad to provide the info. I hope it helps someone revive a problematic D-555. All three of the same type SMD capacitor (100uf 6.3v) had gone bad. Maybe it was a bad production run or these SMD types had not matured enough at the time of manufacture. I would suggest that any D-555 owner skilled enough to replace SMD aluminum electrolytic types to investigate doing so. Especially if the D555 starts to sound thin. Leakage of electrolyte from these caps could ultimately damage the circuit board.
In reading through some of the D-555 posts last night (including your reviews of the classic Sony units -- great work, by the way) you mentioned a difference in sound between the headphone and line out. Maybe the following from the schematic and my restoration will help shed some light:
Line out:
The Burr Brown PCM66P D/A converters are coupled to the line out amplification stage by 2.2uf Tantalum capacitors. The line out utilizes a single NJM2107F opamp per channel. Coupling to the outside world is done via a tantalum 4.7uf capacitor through a 2.2uh inductor (removes ultrasonics but the phase relationships at audio frequencies should be relatively untouched).
Headphone out:
The headphone stage is separate. It taps off the 2.2uf tantalum at the Burr Brown output and then goes to a NJM2107F opamp, just like the line out (total of four NJM2107F in this player). The output of this opamp then goes to the CXA1263W headphone amp coupled by another 2.2uf tantalum. The headphones are coupled by a 100uf 6.3v (the bad types indicated earlier) through a 2.2uh inductor as well.
My previous restoration notes are a bit simpler than what actually happened (didn't want too many side notes). As I understand it, the best coupling for 32ohm headphones requires a 220 uf capacitor or larger. I experimented a bit with very expensive Kemet 470uf 6v polymer SMD tantalum types (low ESR), Panasonic 470uf 6.3v FC (low ESR 105deg) leaded type as well as the Nichicon 220uf 16v UD (low ESR 105deg) SMD type.
Results: Kemet -- the capacitors fit perfectly but the sound was muddy and the highs muffled. Completely unsatisfactory. Too bad, these capacitors cost a lot of money.
Panasonic -- great sound. One problem - the capacitors were too big. Could not seat the printed circuit board properly despite efforts to do so. Ultimately unacceptable because of the size problem.
Nichicon -- great sound, perfect fit. No doubt the quality of these capacitors exceed the originals.
I'm sticking with the Nichicons.
Space is very limited inside these little Discman boxes so the ability to provide audiophile-type enhancement is virtually nil. Still, improvement of the headphone output coupling caps has some limited possibilities.
Best regards,
Paul
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