Advice & Questions:On upgrading Power Supplies for a Rotel RCD-855

[dtm1962]

I have a Rotel RCD-855 that I have begun modifying to improve sound quality.

I have replaced all the electrolytic caps on the board, made it NOS and I want to begin upgrading the power supplies especially the+5VDC digital.

I want to have a separate supplies for the SAA7210 (+5VDC), SAA7220 (+5VDC), TDA1541A (+/-5VDC) and as well the analog output stages (+/-15VDC). The existing 7805 will handle the TDA8088/9 & microProcess and other miscellaneous chips.

Questions:

1) Should I use a separate dual secondary/CT transformer for these power supplies or should I tap off the existing xformer that has ~14VAC CT & ~25VAC CT (common CT among both supplies?!?!?)

2) If I do use the existing secondaries is there a problem with sharing a common CT for each of these secondaries?

3) Do I convert (to the new dedicated +5VDC) ALL the +5V feeds including some indirect feeds (ie say +5V feeding a transistor/diode/resistor that feeds another pin on the say.. SAA7210 or JUST the VDD (+5VDC) of each 7210/7220/1541 (-5VDC on 1541 as well)

4) Is there any concerns with say my new +5VDC being slightly different (in regards to say +4.9VDC versus the existing 7805's being 4.7VDC in regards to the proper operation of the circuits. Is there any potential foor upseting the proper operation

5) Do I just lift/desolder the upside (line side) of the resistor/inductor and solder my new PS feeds to this lead which is in series with the +5VDC pin (Pin 28 on 1541A; Pin 24 on the 7220P/B & Pin 40 on the 7210). I'm assuming this is better than cutting the tracing as there are other +5VDC feeds downstreams of these chips and I have to be careful not to cut off its +5V.

Any advise would be helpful on this.

I will be adding a new 11.2896 clock as well as feeing the clock direct to the 710 & 1541 (11.XX Mhz & /2 clocks for 1541) versus being fed from the 7220.

Thanks in advance,

[dtm1962]

I forgot to mention.... these specific power supplies for the 7210/7220/1541 to be built on separate boards using 317/337 regulators with 2200uF feeding 317/337 with 1000uF on the outputs.

I will have a +/-5VDC for the 1541; +5VDC for the 7210; a separate +5VDC for the 7220 & +/-15VDC for the outputs so I will have 4 small power supply boards mounted in the huge space available in the metal cased enlosure. I will also mount a new digital clock board adjacent to the 7220. I will probably bypass the 7220 & feed the clock signal directly to the 7210, 7220 & 1541 versus letting the 7210 feed the other 2 chips. I am referring to procedure as described by ECDesigns titled "Advanced re-clocking for TDA1541-based cd players"