OK, we are going towards summer and room temperature is close to 25~26 Celsius, but I have noticed recently that certain PCDP's do indeed heat-up a bit. I have been using two different players, a Philips D6800 and a Sony D-9, and I have listened them for over an hour each, both powered with an external 9V power supply (a modern switching PSU, not their original). At the end of the respective listening session, both players were warm in the area close to the 9V plug; checking the service manuals, internally they both operate at 6 V and have a step-down DC/DC converter. In the D6800 the heat surely comes from the 6V regulator IC which Philips opted not to attach to any kind of heat sink. In the D-9 I could not identify the heat source but it is very likely the 6V regulator circuitry. My point is: heat is wasted energy and a portable device powered by batteries should not waste energy. The D-9 is actually powered by a 3V battery and the step-down converter is only used with external PS. Maybe the step-up converter does not waste precious energy. The D6800 is indeed powered by 6 AA batteries providing 9 V, but part of that energy is wasted by the 6V regulator; not a very wise idea...
A few things to consider What happens when the cheap Zinc Carbon batteries the user installs drops down to 1.1V a cell ? With an internal 6V regulator there won't be a problem. How do you switch between the internal batteries and the external supply ? A cheap and easy solution is to make the external supply higher than the maximum expected battery voltage. It does seem strange to use a 9V adaptor to drive a 3V supply, but maybe Sony had a warehouse full of 9V adaptors that they wanted to use up. It also saves having to use a special plug to prevent someone plugging their Watchman adaptor into their 3V Discman.
Q409 (at input 9-14V DC to 6.4V) gets seriously hot during operation off external power supply. i also noticed that Discmans sound a bit better off the batteries vs. ac/dc converter. Not very practical for D-90, rechargeable BP-2 lasts for just an hour or two. But for D-7, D-25, Technics SL-XP5 with a snap-in battery pack it makes sense to exchange dead rechargeable cells for the fresh ones. Original transformer-based Sony 9V power supplies usually available for $10-20 off ebay, I think they worth it. Some of the switch-mode ps from my collection are so "dirty" that it is impossible to get a decent "eye pattern" when calibrating Discmans. Switch-mode ps from iFi tests and sounds OK, but I still prefer original 9V Sonys
It makes perfect sense to use a higher voltage for the PSU, as in some case the extra voltage is used for LCD back-light. All first generations Sony CD player are powered by 9V PSU even though some use 4 batteries and others (the slimmer ones) only two or a rechargeable battery pack; they almost all works internally with voltages from 6 to 3 V and it is quite sensible to have regulators to stabilise those voltages. Philips has indeed a less refined power supply section and the input voltage is used AS-IS for the headphone amp: the weaker the batteries, the weaker the output; the digital circuitry is indeed powered by a stabilised 6V but, as I was mentioning in my original message, some power is wasted in the step-down conversion. No surprise a full set of six batteries would last ~2 hours. What i'm mostly surprised is that in both case (Sony and Philips) no heat sink was added for the step-down converter: the heat you feel on the case is mostly radiated and that means the components get pretty hot. Both players have a metal bottom and that could be used as a heat-sink. As for the original Sony/Philips PSU, I have several of them, but their design is very basic: a transformer, a diode and a capacitor. They are half wave rectifier (the output is a train of pulses at 50 Hz) with a smoothing capacitor. But those capacitors are some 30 years old and you are lucky if they still holds 70/50 % of their capacitance. The output "DC" voltage will mostly be a 50 Hz sawtooth whit amplitude modulation proportional to required current. Some PSU can be opened and the components replaced, but I opted for a modern switching PSU rated for guitar pedal effects and so far it has not disappointed.
Agreed, that little $5 ps never gives me any headaches! As with all things audio, probably its all in my head... but every time I use switch-mode ps I hear that short-lived in my system Linn Akurate CD/SACD player: it shat soo much into the rest of my all-Naim stereo that I had to let it go, with serious hit onto my wallet... As with Black Gate caps I install (and sometimes even sell) in my Discmans: its probably all in my head!!! Its a good Q, as soon as I finish my "groundbreaking" research into CD pressing quality (at square-2.com) I shall check different ps. There is a nice educated discussion on rechargeables vs alkalines going on at Boomboxery: Walkman/Discman crazies should check it out!
