You haven't seen it used because it doesn't work very well. It appeared in
a few pieces of Heathkit equipment but I don't think HP or Tek used it at
all. Any AC component of base to collector voltage has a small but definite
effect on Vbe which transfers voltage in the reverse direction from
collector to emitter even though the base is held at AC ground. A three
terminal regulator does a better job of suppressing ripple from a power
supply.
Regulators use a zener diode as the reference and there are circuits in
which a zener is used as a noise source. What does that tell you? The
quietest power supply is an analog regulator followed by one or more RC
filter sections. The inductor in an LC filter is likely to pick up more hum
and noise than it filters out. My presumption is that a low noise power
supply is likely to be providing a small amount of power to the load and
load regulation is probably not a problem.
Regards.
Max. K 4 O DS.
Email: m...@maxsmusicplace.com
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----- Original Message -----
From: "Joe Leikhim" <jleik...@leikhim.com>
To: <time-nuts@febo.com>
Sent: Thursday, January 31, 2013 2:39 PM
Subject: [time-nuts] Low noise power supplies?
Back when I was in product engineering there was a VCO design that used a
"superfilter" circuit. It consisted of a pass transistor and a filter cap
from base to ground. The gain of the transistor multiplied the effective
capacitance. I have not seen this configuration since.
--
Joe Leikhim
Leikhim and Associates
Communications Consultants
Oviedo, Florida
jleik...@leikhim.com
407-982-0446
WWW.LEIKHIM.COM
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