[sdiy] Bipolar Rail to Rail Opamp recommendation

Tom Farrand mbedtom at gmail.com
Mon Mar 2 05:45:29 CET 2020

The LT1013 is not rail-to-rail.  The "+" output CANNOT reach the positive
power rail during a maximum "+" output.  However, the "-" output CAN swing
to the negative rail voltage.

The main properties of the LT1013 are guaranteed low offset voltage,
guaranteed low drift, low offset current et al.  This makes the LT1013 an
excellent choice for CV mixing, but the +5V supply voltage limit of your
circuit will not get you to a +5V output.  The output you would get on the
"+" side would be heavily dependent on the load resistance, but you might
get pretty close to +5V.  I would guess that +4.8V would be possible if the
load resistance was high (in the neighborhood of 100K).

You seem to be looking for a hard limit of +5V, and -5V for the summed
voltage output ... true?  The LT1013 meets your needs on the "-" output but
falls a bit short on the "+" rail.  How close to the power rails do you
need to be?  If your power supply for the rails are not high precision, you
may not get there anyway.  How precise are the power supply rails for
whatever opamp you use?

Tom Farrand

On Sun, Mar 1, 2020 at 8:05 PM Jason Proctor <jason at redfish.net> wrote:

> fwiw, I think Synth Tech's standard CV mixing opamp is/was the Maxim
> MXL1013 (or Analog Devices LT1013), and I would trust Paul to pick
> that part properly :-)
> On Sun, Mar 1, 2020 at 7:15 AM Schwarz Raphael <raphschwarz at gmail.com>
> wrote:
> >
> > Hey List,
> >
> > What would you recommend as good not too expensive bipolar rail to rail
> op amp
> >
> > I have several cv inputs mixed and I need to keep the sum between -5/+5v.
> > It needs to go as close as possible to the supply rails (-5/+5v) and
> have reasonable offset .
> >
> > I initially used diodes but 0.8v is too much.
> >
> > I’m kind of lost there are so many references .
> >
> > Best,
> > Raphael
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