[sdiy] dual prec. op amp options?

[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
>
>