In article , Don Pearce
wrote:

Fair enough. Why were you regulating the rails - couldn't get the kind
of CMRR you were after from the preamp?

So far as I recall, it was purely because I started off assuming I might as
well. At the time the 'conventional wisdom' was to use ICs to regulate
rails, and discrete devices for the amp stages.

But I eventually concluded that making a 'smooth' PSU was simpler and
worked nicely. FWIW The stages had decent rejection, and I added per-stage
rail decoupling anyway. So I ended up with some transistors in the PSU
(essentially capacitance multipliers) and ICs for the gain stages. Simply
found it worked nicely.

Jim

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On Sat, 30 Apr 2016 18:01:30 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:

Fair enough. Why were you regulating the rails - couldn't get the kind
of CMRR you were after from the preamp?

So far as I recall, it was purely because I started off assuming I might as
well. At the time the 'conventional wisdom' was to use ICs to regulate
rails, and discrete devices for the amp stages.

But I eventually concluded that making a 'smooth' PSU was simpler and
worked nicely. FWIW The stages had decent rejection, and I added per-stage
rail decoupling anyway. So I ended up with some transistors in the PSU
(essentially capacitance multipliers) and ICs for the gain stages. Simply
found it worked nicely.

Jim

And back then regulators, as I remember, were incredibly noisy at
their outputs. You could kill that with a series resistor plus big
electrolytic, but that kind of destroyed the regulation. As you say,
for the kind of current drawn by a preamp, smoothing the PSU is really
no problem.

d

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