Sunday, 17 April 2011

Mission PCM2

The Mission PCM2 was the fourth CD player from Mission / Cyrus, having been preceded by the DAD7000 the PCM4000 and the PCM7000.  All four of these players were based on Philips models modified in the following ways:
  • DAD7000: Based on the Philips CD104, this player was the least modified of all four.  This player had a different paint job and a passive filter added at the analog outputs.
  • PCM4000: This model was based on the Philips CD650.  Apart from a new front panel and display, it differed very little from the parent design.
  • PCM7000: This model was also based on the Philips CD650 and shared the PCM4000's display and front panel.  This player also had a Mission designed output stage which added a variable level output.

The PCM2 was based on the Philips CD670.  The CD670 and PCM2 can be found with either CDM-2/29 or CDM-4/11 laser mechanisms, and used the TDA5708 / TDA5709 servo chipset, the SAA7210 decoder, SAA7220 digital filter and the TDA1541A DAC IC.  The Mission PCM2 contained an additional PCB which, like the PCM7000, added a variable level output.  The Mission PCM2 also had an extensively modified case.  As well as a different front panel and display the PCM2 had spacers and a different lid to convert it to a full height player (the Philips CD670 was a low height player).

The additional circuit board is a dubious improvement.  The additional signal stages added degrade the sound quality, especially as each use the lackluster NE5534 opamp.  The variable level output is of little practical use as it defaults to maximum volume each time the player is powered off.  This player cannot be attached directly to a power amplifier because of this, unlike many more modern players with a variable output.

In terms of performance, in stock guise this player is not particularly impressive.  Once modified this player can become reasonably good, but unless extensively modified, to the stage of not being recognizable, it will never be a top shelf player.  I carried out the following modifications to this player:

  • Replace the electrolytic capacitors.  This is a necessary task in almost any electrical appliance of this age.  It will improve both the reliability of the player as well as increase performance.  I used Nippon Chemicon LXZ type capacitors to decouple the decoder, DAC and output stage ICs, a PSA type to decouple the digital filter IC and KMG types for the rest of the player.  The PSA type is a solid polymer capacitor with an extremely low ESR.  The SAA7220 is a power hungry and noisy IC that will really benefit from an ultra low ESR decoupling capacitor.
  • Replace the output stage opamps.  Leaps and bounds have been made in the design and manufacture of opamps since the PCM2 was designed in the mid '80s.  It currently uses two LM833s, these can be replaced with many more modern dual opamps.  I chose a pair of National Semicoductor LME49720 opamps for this player, but many others will do just as well.

Many more modifications could be applied to this player, but the limited space means that the player would have to be seriously altered.  I prefer to keep my own players in a condition where they at least resemble their standard configuration.  Items that you could consider if you weren't concerned with limitations are:
  • Low phase noise clock
  • Replacement power supply
  • Replacement output stage (discrete solid state or vacuum tube), including removal of the existing variable output stage
All in all, I was attracted to this player for its mechanics and looks rather than its sound.  This is why it is not in my main system.  I wouldn't recommend it as a good platform to modify, as it simply has no free space for more extensive modification.  It can be rearranged to overcome this, but you might as well just buy a player without this limitation to begin with.