[sdiy] Spice model for CA3080 OTA

[Pete Hartman]

Part of the issue I'm having is while I think I theoretically
understand what's going on (OTA -> capacitor -> buffer x 2) I don't
have a lot of practical experience with FETs and feedback paths yet to
be certain what I *should* be seeing.  So I want to simulate it and at
least get a better idea.  The caution about SPICE is a good one
though, I'll keep that in mind.

As for schematic the main differences between this and the original
ARP 4023 schematic are a trimmer between the rails with a 475K
resistor on the wiper tied to the control voltage input, and using
OPA134's instead of LM301's.  The original doesn't show a value for
the balance trim, but this is using a 50K.  The output has a DC
blocking capacitor and a 1K resistor, and there is additional
circuitry for attenuating/summing audio and control inputs, but none
of that is surprising and all of it appears to work fine.  I'm
hesitant to share the actual schematic, but I'll check with the PCB
manufacturer.

I appreciate everyone's input and the models, I have what I wanted,
now I just have to find time to apply it (hopefully before the
weekend).

Thanks

Pete




On Wed, Oct 16, 2013 at 7:02 AM, Neil Johnson <neil.johnson71 at gmail.com> wrote:
> Hi,
>
> Pete Hartman wrote:
>> I'm looking for a CA3080/LM3080 Spice model
>
> Don Sauer has probably more detail on CA3080/LM13600/LM13700 SPICE
> models than you need:
>
> http://www.idea2ic.com/LM13600/SpiceSubcircuit/LM13700_SpiceModel.html
>
> But to be honest I wouldn't use SPICE to debug this circuit.  Sit down
> with a scope, schematic, and some quiet time to think through what it
> actually happening, and why that is different from what should be
> happening (you won't know if SPICE is lying to you).
>
> Can you share the schematic?
>
> Neil
> --
> http://www.njohnson.co.uk