[DaKi][er]

I got a mint amp here, with your standard component values, ad8620, 2*9v batteries, 470uf 16v pana fc's, 1uf blocking caps, etc.

It all works perfectly fine, 0 offset on both channels except for one little annoying thing... with the Panasonic pot between 2&3 o'clock positions and only at this position, the dc offset spikes to 430-470mV

I’m just completely puzzled to why it would be doing this, I can’t find or think of a single reason it could be doing this, how can dc get in from the pot when there are caps right after it that will block it?

I’m going to remove the pot and measure it, but their a pain the bum to remove and get another in there (tangent- maybe on your next run of boards, you should increase the hole size up a notch)

 

[peranders]

How much mV do have have between the inverting and non-inverting inputs?

When you have a pot connected, do you have any DC paths for the input. Can input bias _DC_ currents flow freely? Do you have any resistor connected from the non-inverting input down to ground?

 

[DaKi][er]

Quote:

Originally Posted by peranders How much mV do have have between the inverting and non-inverting inputs? When you have a pot connected, do you have any DC paths for the input. Can input bias _DC_ currents flow freely? Do you have any resistor connected from the non-inverting input down to ground?

its your standard mint amp here, http://www.tangentsoft.net/audio/min.../schematic.pdf

well i somehow managed to fix it but i dont know exactly what i did

, its nice to know what caused it if i come across it later but i'll settle with the fact its going now (1 down, 9 to go)