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Re: What's next?

Posted by Dave I on July 25, 2000 at 08:56:22

In Reply to: Re: What's next? posted by tenor39 on July 25, 2000 at 04:54:10:

I don't ever recall experiencing a loss of highs or reduced volume due to the PLL filter change. Was it set up so you could easily install and remove the additional cap? Or was it based on memory? My experience is just that the sound becomes more open with better body and depth and bass when the capacitance is increased. I think it would be better to stay with film caps or solid tantalum though and avoid the large aluminum electrolytic cap as you will probably need to implement a time delay for consistent operation from power off and other modes. Some aluminum electrolytics are rather leaky and not very good until they have "formed" to the working voltage which is only a couple volts in this case. Maybe this is what was happening to you. Sometimes subjecting them to a higher voltage first and then discharging improves their leakage performance.

Changing the receiver PLL external filter components does not provide much jitter reduction and certainly not to the level of the old AA dual PLL setup. I have made jitter measurements on the MCLK from the receiver with both the stock filter and high capacitance filter but have not been able to verify the reduction in jitter that the large sound improvement would seem to indicate. There does seem to be a change in the jitter spectrum which may account for it but I don't have the necessary equipment to analyze the entire bandwidth and my measuring setup is optimized for data correlated jitter.

I use a different jitter reduction system now so have not played with the input receiver PLL as you are doing for a couple years. At that time I had a relay with a time delay from the lock signal that either reduced the value of the series resistor or shorted it out after a few seconds. The last one used a 1000uF capacitor I think but I am not sure on the resistor. That was on my own dac. At one point I changed the values on a friend's Parts Connection DAC to 100 ohm and 100 uF tantalum with .1uF in parallel (again, values are from memory) and no relay and it had no problem. I will try to look up the schematic on my design that used the relay later and check the values but I don't think there is much to be gained by increasing it more.

It sounds like you have made some extensive changes. My own designs follow a little different philosophy so I won't comment much except to say that I would experiment with the termination of the digital input if I was you, removing all the components that may be there now and directly connecting to the receiver. Then try it with the series capacitors that are probably there now. And then experiment with the resistor termination value. Sometimes it works better with a higher than 75 ohm termination value and sometimes a small cap helps and sometimes changing the input grounding (if present) helps. I have seen some DACs with a large 60 or 120 Hz jitter component due to the way ground was connected to the digital input cable shield.

Dave

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