4PM - HP modes seems to be wrong

Hi there,

After some time of using 4pm filter board I realised that there might be something wrong with HP modes there. When cutoff is on 0 I expect the whole signal to be heard, but there seems to be some low pass filtering also. It works like a little bit wider band pass filter. Is it ok or I made something wrong? I’ve checked the elements and everything seems to be fine. I’ve read the document about the pole mixing and in the table showing filter responses there is column which indicates that LP1 stage should be disabled for HP filters. I’m just wondering if my problem might be due to LP1 stage is not turned off? I tried to spot which IC is responsible for that, but I’m not quite shure which one exactly is. In attachement I’m putting my board, maybe I have not spotted something.

Piotr Figiel

Here is the link to the photo as I was unable to upload image somehow :confused:

Hi , i think you have mixed the resistors wrong . Or there is a bad solder point on one resistor .
Or the 4051 had a bridge somewhere .