|Marantz CD67mkII-OSE modifications|
This player has been modified twice: first the original PCB was used and adapted. Later the same PCB from a (cheaper) CD57 was used to repeat the job more thorough and to install a number of improvements. The HDAM circuit is not present in the 57. This saves a lot of desoldering when, instead of the opamps, a discrete outputstage is fitted :-)
The first three photo's are of the original CD57 PCB that was used for the second modification-round. Pay special attention to the frightful small electrolytics that are fitted for C803 en 804 originally!
The original analog filter characteristic can be modified to a Bessel slope with a more constant group-delay by lowering C605/606 to 470p and adjusting R605/606 and R611/612 to 12k1. The results for the sound are slight smoother and more relaxed highs. In this plot of the filter simulations the difference can be seen between the original and the modified filter. In this article by Pedja Rogic more information can be found on this subject.