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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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In Reply to: anyone got experience of after market clocks in Philips TDA1541 based players? posted by chris.redmond2@bushinternet.com on October 15, 2006 at 04:21:04:
Proper clocking of a TDA1541 can give stunning results...The quote is correct on the face of it, but let me explain: the SAA7220 is the 4x oversampling digital filter, and when used as designed, also generates the bitclock (an 11.288Mhz crystal and its loading caps installed between pins 10, 11 and ground). The clock input required for the TDA1541 chip is *half* this, 5.56Mhz - which is created as a divide-by-two function in the SAA7220. Unusual, and that's the crux of the comment as received - one can't just bolt-on a clock directly to the DAC chip , because the TDA1541 will not accept an input over 6Mhz.
There are many ways round this, though; the simplest is feeding a new precision 'aftermarket' clock into the SAA7220 pin 11, and this will work just fine (NB feed the 7220 the cleanest 5v, 200mA supply you can manage - a super-reg is recommended). The theoretically better way is to follow the new clock with a D-Flipflop set up to divide by 2, and feed the output into the 1541 yet use the clock's direct output into the 7220 pin11, and cut the bitclock link between the 7220 and TDA1541. This does the same job, but removes the potential for interaction (jitter) arising from multiple things going on inside the 7220 chip (which is one noisy beasty)
I'm not going into the 'remove the 7220 and go non-oversampled' discussion here at all (it still gives you the same problem, but different sonics) Suffice to say, there's a mass of info on using and abusing the TDA1541 over on DIYAudio and elsewhere. Good luck!
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Follow Ups
- Re: anyone got experience of after market clocks in Philips TDA1541 based players? - martin clark 11:23:18 10/15/06 (1)
- My brain now hurts after reading the TDA 1541 debates on DIY/Tweaks. :0( [nt] - chris.redmond2@bushinternet.com 11:47:03 10/17/06 (0)
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