[sdiy] Odd OTA behavior

[Tim Stinchcombe]

> >  I took the remaining 13700 and the 082 I was using and tried them
> > on another board and found that the 13700 wouldn't keep a steady  
> > ~-13-14V at the Icon terminal - placing a resistor between +15 and  
> > the terminal (trying with 520kOhm) would rise the voltage 
> at Icon to  
> > ~1.4V.
> 
> I thought the voltage at a control pin of an OTA typically 
> hung out a  
> diode drop or two above the negative rail. What could he have 
> done to  
> make it measure at 1.4?

1.4V sounds about right to me: both the equivalent schematic (page 3 of the
datasheet) show two diode drops (Q2 + D1) and the SPICE model has two diodes
too.

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim102 at tstinchcombe.freeserve.co.uk