[sdiy] Odd OTA behavior

[Mike I]

If the OTA V(-) supply pin has mistakenly been connected to ground instead
of (-)15V, the Iabc pin will sit at two diode drops above ground (in the
case of LM13700) when current is fed through it from a resistor connected to
V(+).....

Have you checked to make sure the OTA is being powered from +/- 15V and not
+15V/GND ?



----- Original Message -----
From: Tim Stinchcombe <tim102 at tstinchcombe.freeserve.co.uk>
To: 'SDIY' <synth-diy at dropmix.xs4all.nl>
Sent: Friday, April 25, 2008 2:11 PM
Subject: RE: [sdiy] Odd OTA behavior


> > >  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
>
>
>
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy