Anyone want to check my BPA schematic?

[Arx]

Hi,
I need to go back to school and learn to read.
That 205k gives about 12V*1k/205k=58mV of maximum correction at the inverting input.
Does this result in a maximum correctable output of 58*20.5/1=1.2V
That gives plenty leeway for correcting gross errors.

Cs7 &8, are they 68uF or 68nF?

DC servo near or slightly less than 1Hz is usually about right.

The output filter with 100k & 150nF @ 10Hz. Could you simulate that?

Have you seen Gootee's take on filtering the servo?

Cs7 and 8 are 0.68uF Does anyone number capacitors like resistors? would 0u68 make sense? Those decimal points are hard to see, and don't even always show up if it's scaled badly.

I wouldn't really know how to simulate that. I'll have to see if I can find some decent software for linux.

I'll have to search for that thread.

-Nick

 

[AndrewT]

Does anyone number capacitors like resistors? would 0u68 make sense?

Hi,
yes, some components use 0uxxF and even omit the leading 0 and trailing F giving uxx
But even 0u68F =680nF is probably too big. Frequency ~=0.1Hz.
It will take a long time for the servo to settle to it's final value on every step change in DC, it will also take a long time to correct any more gradual error.

I suggest you measure the caps you have and adjust the resistors to give a reasonably quick acting servo that minimises it's effect on the low frequency audio. That is the problem, trying to meet the compromise that results in better/worse sound than the cap you are trying to eliminate.

 

[Arx]

Hi,
yes, some components use 0uxxF and even omit the leading 0 and trailing F giving uxx
But even 0u68F =680nF is probably too big. Frequency ~=0.1Hz.
It will take a long time for the servo to settle to it's final value on every step change in DC, it will also take a long time to correct any more gradual error.

I suggest you measure the caps you have and adjust the resistors to give a reasonably quick acting servo that minimises it's effect on the low frequency audio. That is the problem, trying to meet the compromise that results in better/worse sound than the cap you are trying to eliminate.

I actually removed the capacitor just for space reasons. 30uF of filmcap is pretty large and the board is going to be quite small.

I have a bin of misc caps. I'll either find something of a more reasonable size, or I'll shrink the resistors a little to speed it up (or some combination of the two) The main thing is that the PCB doesn't need to change. I'm doing the layout now.

-Nick

-Nick