I'm dropping this circuit in the analogue source forum, as it would most likely be used on an RIAA preamp. This ciruit is somewhat similar in priciple to the Salas simplistic shunt regulator, but adds a common base stage and Darlington to act as error amplifier/current comparator, and uses a resistor rather than a zener to determine output voltage, along with a jfet reference current sink. It would be interesting to sub a zener diode (like Salas) for the resistor. This may make it possible to eliminate a stage. I'll try that when I get a little mode idle time. At any rate, this is thrown out as food for thought, and may possibly spur more ideas and spin-offs.
Here's the simulation results for a 0.1A current transient with 10us edges. If you do the math, the dynamic impedance is 4.5 milliohms, and the static impedance is ~0.8 milliohms. A lot of this is due to the second Darlington in the schematic. It would be an interesting experience to build this up and check stability, as only lead compensation is used. The lag capacitor has been reduced to a vanishingly small value (less than what stray capacitance would be), and serves merely as a place holder.
I've got a zener-based regulator (detailed in one of my other threads) in the RIAA preamp I have installed in my living room system, and I'm thinking of subbing a series string of (15) yellow-green GaP LEDs to see it there's any audible effect. I have the little board all built up and ready to go.
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