Confused with 0TA3080

[Tony Hardie-Bick]

On 20/01/13 19:36, Marc Nostromo [M-.-n] wrote:
> Any idea how the variable current is processed by the invertor it's
> fed to ? I was under the impression this last one was working with
> voltage difference, not current.

yeah - i'm pretty sure i'm wrong that it doesn't have a voltage you can 
measure,
and you should be able to see this at the invertor output, even if the ota
itself may be a bit sensitive to the impedance you're measuring with.

> Where does it get back to voltage change going forward in the circuit ?

there should definitely be a voltage at the output of the inverters that
follow the otas.

either the ota is fried (unlikely), or there's some error in the way the
bias voltages at the inputs are set up.

*check your resistor values*

if you remove R7, the voltage at pins 2 and 3 of the first ota whould be
half the supply voltage. if you put R7 beck in circuit, the dc level
shouldn't change much.

also check the voltage on the junction of R11.R16, and that this is varying
somewhere in the range 1V..4V, according to the cutoff.

also check that, when you do this, the voltage across R11 is the same or
very similar to that across R16, and that these vary in unison as you
sweep the pot.

Tony (HB)