Hi Jesper,
Yes, I do use a lot of Rubycon MU. Reason why is that IME they work better for this type of circuitry than ceramic. You mention impedance and inductance as though they are all that really matters. How about measuring linearity and piezoelectric transduction too? What if they also matter for this application?
The reason for using a lot of the MU caps is that like other bypass caps it helps to pepper the board with distributed caps all of the same value.
Regarding inductance and impedance in particular, part of that is compensated for by layout. There is very little inductance/impedance in the bypass current loop because of layout. As I have written about before the current loops are on low-ish inductance surface fill.
Regarding phase noise measurements, after thinking about it for a long time I decided that phase noise measurements are helpful, but not really what we would like to know. What really matters clock frequency deviation as a function of time. With instruments like TimePod we have no way to display that in graph form similar to the way a scope displays a waveform in terms of voltage versus time. Even when we do measure phase noise, we can only approximately turn that into RMS jitter. Getting to peak to peak jitter from the RMS number is impossible just like it is when measuring voltage if we don't know the time-domain waveform. We might be able to get that time-domain frequency deviation waveform for clock oscillators, but we would have to FM demodulate the sine wave output. It can be done but IIUC its even more expensive than a TimePod for phase noise. Another possible issue is that spurs in phase noise measurements are often filtered out or ignored. Maybe spurs could be relevant for dac clocking? Don't think we really know.
Anyway, mostly what I have to go by is a collection of experiments over time. It started with my first AK4499EQ dac when I designed a clock and PCM->DSD256 conversion board (which used two AK4137 chips). I did experiments using more or less MU bypass caps just for the clocks and or the buffers, putting clocks and buffers on separate or shared voltage regulators, etc. It was work done over a long period of time.
For the present clock board, so far its sounding very good indeed. I will know more when I can use it with the Andrea Mori and or AckoLabs sine wave oscillator clocks. I can then compare Marcel's dac to my Andrea dac. I can also use this clock board to drive the Andrea DSD dac using my best clocks as input sources. I should be able to tease out if this board is doing any harm, or else if it is effectively performing as well as dac equipment that has already been measured for phase noise.
So far its only the stuff external to the clock board, such as the reclocker ferrites, that has been found to be problematic.
Cheers,
Mark
Yes, I do use a lot of Rubycon MU. Reason why is that IME they work better for this type of circuitry than ceramic. You mention impedance and inductance as though they are all that really matters. How about measuring linearity and piezoelectric transduction too? What if they also matter for this application?
The reason for using a lot of the MU caps is that like other bypass caps it helps to pepper the board with distributed caps all of the same value.
Regarding inductance and impedance in particular, part of that is compensated for by layout. There is very little inductance/impedance in the bypass current loop because of layout. As I have written about before the current loops are on low-ish inductance surface fill.
Regarding phase noise measurements, after thinking about it for a long time I decided that phase noise measurements are helpful, but not really what we would like to know. What really matters clock frequency deviation as a function of time. With instruments like TimePod we have no way to display that in graph form similar to the way a scope displays a waveform in terms of voltage versus time. Even when we do measure phase noise, we can only approximately turn that into RMS jitter. Getting to peak to peak jitter from the RMS number is impossible just like it is when measuring voltage if we don't know the time-domain waveform. We might be able to get that time-domain frequency deviation waveform for clock oscillators, but we would have to FM demodulate the sine wave output. It can be done but IIUC its even more expensive than a TimePod for phase noise. Another possible issue is that spurs in phase noise measurements are often filtered out or ignored. Maybe spurs could be relevant for dac clocking? Don't think we really know.
Anyway, mostly what I have to go by is a collection of experiments over time. It started with my first AK4499EQ dac when I designed a clock and PCM->DSD256 conversion board (which used two AK4137 chips). I did experiments using more or less MU bypass caps just for the clocks and or the buffers, putting clocks and buffers on separate or shared voltage regulators, etc. It was work done over a long period of time.
For the present clock board, so far its sounding very good indeed. I will know more when I can use it with the Andrea Mori and or AckoLabs sine wave oscillator clocks. I can then compare Marcel's dac to my Andrea dac. I can also use this clock board to drive the Andrea DSD dac using my best clocks as input sources. I should be able to tease out if this board is doing any harm, or else if it is effectively performing as well as dac equipment that has already been measured for phase noise.
So far its only the stuff external to the clock board, such as the reclocker ferrites, that has been found to be problematic.
Cheers,
Mark