DC offset problem

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
M

mravlcax

Member
Joined 2007
AndrewT said:
Hi,
I wonder if the input cap is passing DC (excessive leakage current) to the amp input?
Is the Pot before the blocking cap?
The NFB cap is too low compared to the value you have use at the input. Change the 47uF to 220uF.

The 1k0 is a separate issue related to the missing RF filter.
You should add the 1k0 between the cap and the 22k and also add a cap in parallel to the 22k. A value between 330pF and 1.5nF is suitable . Try 680pF as a starter.
Click to expand...

I put the 1k0 resistor as you said, then I changed the input cap to the 2,2uF instead of 4,7uF and this 2.2uF are from the shop so they are brand new ones. Now I don't have any DC problems everything works fine and I have a few mV at the output, usually 1-3mV.

Greatings
 
A

AndrewT

R.I.P.
Joined 2004
mravlcax said:


I put the 1k0 resistor as you said, then I changed the input cap to the 2,2uF instead of 4,7uF and this 2.2uF are from the shop so they are brand new ones. Now I don't have any DC problems everything works fine and I have a few mV at the output, usually 1-3mV.
Click to expand...
Hi,
It looks like your source has a DC offset AND that the DC blocking cap was passing excessive leakage.

Now that you have changed the input high pass filter to 48mS (22k & 2u2F) you need to change the NFB to >= 68mS. Try 100uF instead of 47uF.

Have you fitted the RF filter yet?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom