[sdiy] dual prec. op amp options?

[sdiy]

If you put an square wave through an 741 with 0,5uS Slewrate say with 5 to 
10kHz you can hear by ear and see at the scope that the square is not longer 
a square. You can clearly see the ramps. Higher harmonics disapear.

f=1/T    1/20E-6 = 50E03  thats 50kHz not 50MHz.

Well that is not relevant for volume control. So about 3V/uS Slew rate and low 
offset temp drift is enough for the CV secton of an VCA.

Harald


 Donnerstag, 21. Dezember 2006 16:17 schrieb Seb Francis:
> Do you really need such precision and speed for a VCA?
>
> A slew rate of 0.5V/us will only take about 20us for a 10V swing -
> that's a single wavelength at 50MHz.  Do you really need faster than
> this?  And will the SSM2164 actually be this fast anyway?
>
> And are you going to notice the input offset at all?  For something like
> the MXL1013/LT1013 this isn't going to change much over time, so it will
> just be adjusted out when you set the initial gain.  And even if there's
> no adjustment, 300uV (max) out of a FSR of 10V won't be noticeable (for
> pitch, yes, but not for volume).
>
> Just my £0.02 worth.
>
> Seb
>
> Fernando de Izuzquiza wrote:
> > Hi all,
> >
> > Searching for dual precision op amps for the control section of
> > (M.Irwin) SSM2164 based VCAs.
> > I'm looking for a modest/decent slew rate too, not just low offset.
> >
> > As single op amp I found the OP27GP, at around $2 with a slew rate of
> > 2.8 V/us and max input offset voltage of 100 uV (typical 30 uV)
> >
> > I'd like to find a similar specs op amp but dual (you may suggest
> > alternatives to the single OP27 too...)
> >
> > The OP270GP is very near (sr 2.4 V/us, max ov 250 uV), but at $6 is a
> > bit too much...
> > So, there is a cheaper alt. with similar specs?
> >
> > I see that in single format there many specs/price options, but I only
> > know the OP270 for a dual with still decent slew rate...
> >
> > single        -max- iov (uV)        slew rate (V/us)    notes
> > OP177G        60                0,3                slow
> > OP27G        100 (typ. 30)        2,8 (min. 1,7)        OK
> > LTC1150CN    10                3                great but too expensive
> > AD797A        80                20                too expensive
> >
> > dual
> > LT1013CN    300                0,4                slow
> > OP270G        250 (typ. 50)        2,4 (min. 1,7)        expensive
> >
> > ...
> >
> >
> > Fernando