>
>>Four optos and a dual opamp, and I had a reasonable hybrid.
>..
>ditto the above.  I've been using this same dual-opto arrangement for
>many years in analogue circuits. Originally I used the TIL113
>optocoupler, but later found that 4N25s were much better matched for
>characteristics.


Amazing how many problems go away when you think in terms of current, isn't
it :)