2016-10-31, 22:18
Hi,
New LTC1569 arrived today and fitted, problem with the E-field is fixed.
I have however, discovered another problem, if the input voltage drops a bit, which it does with the extra load of the filter ICs the E-field channel rings at about 1.5kHz. The other channels seem fine.
A measured input of 4.8V or higher (as shown on the status page) seems okay, but below this (4.6V) I see the ringing. My iPad PSU sits at 4.8V, I found another USB psu, which is about as quiet, which gives 5.2V indicated. I also have a linear psu I made about 35 years ago with a fixed 5V output and variable 7 - 15V. Unfortunately the fixed 5V only gives 4.7V under load and suspect the 7V will be too high. Pity because the size of the smoothing cap on this PSU will make it ultra quiet. Perhaps I will pull it apart and modify it.
With all three channels filtered at 17kHz, the only noise I see is a spike at 45kHz which could be switching noise from the psu?
Robin
New LTC1569 arrived today and fitted, problem with the E-field is fixed.
I have however, discovered another problem, if the input voltage drops a bit, which it does with the extra load of the filter ICs the E-field channel rings at about 1.5kHz. The other channels seem fine.
A measured input of 4.8V or higher (as shown on the status page) seems okay, but below this (4.6V) I see the ringing. My iPad PSU sits at 4.8V, I found another USB psu, which is about as quiet, which gives 5.2V indicated. I also have a linear psu I made about 35 years ago with a fixed 5V output and variable 7 - 15V. Unfortunately the fixed 5V only gives 4.7V under load and suspect the 7V will be too high. Pity because the size of the smoothing cap on this PSU will make it ultra quiet. Perhaps I will pull it apart and modify it.
With all three channels filtered at 17kHz, the only noise I see is a spike at 45kHz which could be switching noise from the psu?
Robin