In Sornette, J. Phys. I France 2 (1992) 2065, a scenario for self-orga
nized critically (SOC) has been proposed according to which SOC relies
on a non-linear feedback of the order parameter on the control parame
ter(s), the amplitude of this feedback being tuned by the spatial corr
elation length xi. Implementing such a feedback mechanism, it is possi
ble in principle to convert standard << unstable >> critical phase tra
nsitions into self-organized critical dynamics. Here, we analyze this
idea in more detail and suggest to couple a standard experiment on cri
tical phenomena with some probing radiation or some electronic feedbac
k using a microprocessor or analog device which pushed the temperature
or analog control parameter to that value where the susceptibility, t
he correlation length or the inverse of the decay rate is maximal. The
practical realization of the feedback thus corresponds to an optimiza
tion of the response of the system under the action of a probe or a di
sturbance. We discuss liquid-vapor and binary demixion critical points
, and briefly the He4 superfluid transition, magnetic systems, and sup
erfluid transitions.