Sunday, 22 May 2011

Arcam Alpha

The Arcam Alpha was the first CD players in Arcam's lower cost Alpha line.  This player is based on a Philips model, and uses a Philips mainboard, loader and laser mechanism, but uses a Arcam case, power supply and DAC board.  It shared the same style as contemporary Alpha components, namely the Alpha 1, 2 and 3 integrated amplifiers and the Alpha tuner.  It is not to be confused with the much more modern Alpha One, to which it bares no resemblance.

This player uses a familiar range of ICs; the TDA8808 and TDA8809 servo, the SAA7310 decoder, the SAA7210 digital filter and the TDA1541A DAC IC.  Arcam tapped the I2S line from where it would have entered the mainboard's original DAC IC (a TDA1543), and routes it to an Arcam designed and made DAC board.  This board contains the TDA1541A DAC, the two OP27 and two NE5334 single opamps that form the output stage and two LM317Ts and two LM337Ts that regulate the supplies needed for the DAC IC and output stage opamps.  The board also contains a rectifier bridge and filter capacitor bank.

The sound quality of the player in stock standard form is actually quite good.  The better power supply to the DAC and improved output stage put this CD player a step ahead of many others, such as the previously posted Mission PCM2.  However, as always there is room for improvement.

I've owned two examples of this player, one was an Arcam Alpha, one was an Arcam Alpha +.  There are only a few differences between the two models, specifically:

  • The + has Blackgate output capacitors, whereas the regular model uses general purpose types.
  • The + adds a pre-regulator to the DAC board supply.
  • The connector is keyed opposite on the + compare to the regular model, hence the pinout is reversed.

The particular example pictured, a plain Alpha, I bought in poor condition.  It could only read some CDs, and when playing the few it could play it would often skip.  In previous posts I've often said that electrolytic capacitors should be replaced in players over 20 years old for reliability, and for the Alpha this was the case.  Degraded electrolytic capacitors in the servo caused the player to perform so poorly, and all that was needed was their replacement.

I haven't yet extensively modified this player, it is a work in progress.  I have done the following things:

  • Replaced the electrolytic capacitors.  As I said above, this was both to make the player functional and to increase performance.  I used the same combination of Nippon Chemicon KMG, LXZ and PSA series capacitors as I normally do.  For the output coupling (also known as DC blocking) capacitors I used Nichicon ES capacitors.  These are reasonably priced, and are the best coupling capacitor to use where you have limited space.
  • Replaced the output stage opamps.  The OP27s and NE5534s were much better than what was used in the average CD player when the Alpha was made, but the state of the art has moved a long way since then.  I replaced them with LME49710s, but this is by no means the only opamps suitable.  This player uses only single opamps, which gives it better channel separation.
 This is another player that will benefit from a low noise clock.  I plan to install one once my newer, more compact clock design is ready.  I have now received the PCBs for it, but I am still waiting on a cople of components.

All up, this player is not too bad in stock form, but can be quite a good performer when upgraded adequately.  It definitely a good base for modifications and worth buying if you see one for sale in the second hand market.