[sdiy] dare I say - decoupling?

[Oakley Sound]

> Would it be ok in the feedback loop of an op-amp like in some of the
> old Oakley stuff?

This would reduce ground currents, but at the expense of taking it out of
the main supply rails. I tended to keep the maximum LED current to around
5mA which should have only a little affect on the stability of the rail
potentials. But star power distribution [or as close to it as possible]
was always assumed in an Oakley modular.

Note also that when the input voltage to that circuit has small
perturbations around zero volts, the output of the op-amp will rapidly
switch between the two forward voltages of the LED. This will produce
high frequency hash that will then be picked up by other parts of your
circuitry. It is best therefore to slug the output response with a cap
across the op-amp, from inverting input to output.

What I did in one module with a lot of LEDs, the OMS-820, was to use a
constant current sink set to 5mA. The LEDs were then wired in series from
the sink to the 15V rail, each LED would be then turned on or off with a
separate bypass transistor. This had two advantages; one, the current
taken is constant; two, several LEDs can be on and take only 5mA from the
supply.

Tony

www.oakleysound.com