a75 front end supply

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I am in the process of gathering parts to build my a75, and I was planning to go a different approach on the front end power supply. The standard circuit uses the voltage doubler and discrete op-amp regulator. I was planning on using a seperate transformer for the front end anyway, so I was wondering if it would be better to go with passive inductive/capacitive filtering and get rid of the active filtering. I have read elsewhere that it is preferred over feedback regulators. I need some opinions on how this would affect the sound, and maybe some hints on what inductors/cap values to use.
I'm fond of regulated supplies, myself, but can see the attraction of passive ones. Having an independent power supply for the front end is a wonderful idea, as it sidesteps much of the rail problems you get from the back end.
Bear in mind that there's more than one kind of regulator. Somebody go tap Jam on the shoulder and get him in here to expound on the whole shunt regulator concept. I'd start in on it, but he's better versed on that stuff than I am.
Just keep in mind that there are pros and cons to everything. I'm content with series regulators, but intend to try shunt ones one of these days (they're wasteful, but they are attractive, at least in theory). Passive supplies have a couple of good things in their favor, as well.
Values? Hmmm. You're not going to need a huge amount of current, so ripple won't be that bad. Just tossing numbers in the air, I'd say start with a PI filter with, say, 10,000uF on each side and a couple of mH between. You could use smaller caps, I suppose, possibly even as small as 1000uF, but when I go passive I like a bit of buffer in case the AC line drops a volt or two while I'm listening. Keeps the voltage more stable, in addition to making the rail quieter.


I am not particularly fond of the voltage doubler circuits (with all due respect to Nelson Pass and Norm Thagard). I would use a seperate transformer and bridge rectifier to power the front end of the A-75. You could choose to regulate it or not. A series regulator would be easier to construct. There would be quite some complexity to a shunt regulator, due to the voltages and current involved.
A simple solution would be to use a seperate supply for the front end and regulate it with a pass transistor or mosfet with a zener reference attached to the base or gate depending on the device used, like the Pass balanced preamp supply.


I still like shunts for preamps and such but might be too much of an undertaking for this project. You have to burn as much current through the shunt element as the circuit to get it sounding it's best.
By the way you were right about Geritol.


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