New project: Sequencer

[<<marjan>>]

> PS.: One last thing that has impressed me in the ARP sequencer: How they
> built
>         FET opamps from standard opamps plus a 4007 CMOS chip. Sure, they


It's trick from National app. note AN-4 (well,with matched fets but
noted that CMR is not good because of them and resistors as current
sources).



> have
>         done this because thy didn't have these cheap LF356 or similar
> chips (?),


Back then it was problem in technology to produce quality FETs and 
matched p and n channel MOSFETs on the same chip layer with opamp.
Before early '70ies it was even problem to make such things as 4007
as remaining Na in layers caused treshold/pinch voltage of n and p 
mosfets to move in oposite directions which was bad for using in 
logic gates.Sometimes it became depletion instead enhacement mode 
mosfet during diffusion.


>         but one thing is still impressive today: The common mode range of
> these
>         "4007-opamps" goes up to the positive supply voltage, which is a
> great plus
>         if you build a saw vco and discharge the cap to the positive rail.
> No auxiliary
>         voltage required ...




marjan