Disabling the noisy SAA7220 oversampling filter


2002-04-08 6:41 pm
Hi All,

If you're using that most venerable of DACS, the 16 bit TDA1541, it will probably be linked in some way to the SAA7220 4x oversampling filter that precedes it.

Up to now, I had been running my DAC in "zero-oversampling" mode, where the clock, word and data lines are fed directly to the DAC, without going to the SAA7220. This tweak gave DRAMATIC improvements in sound quality.

Having recently seen posts about how noisy the SAA7220 is on the power lines, I managed to switch it off entirely:

1. The SAA7210 (precedes the SAA7220) has on pin 19 a "clock in" and on pin 18, a "clock out".
2. Since I was using a new clock (by Guido Tent), I was able to very simply disconnect the clock in line from the SAA7220 (pin 21 I think) and feed it to pin 19 on the SAA7210.
3. Pin 19 of the SAA7210 was then connected to Pin 18 via a 100 Kohm resistor
4. Power to the SAA7220 was then disconnected and viola, we have no more SA7220 at all in the circuit.
5. Sound improvements appeared fairly subtle in my system ( I'm still listening though), but then I think that the filtering/shielding set-up is fairly comprehensive.

My 2c.