EMRFD Message Archive 9443
Message Date From Subject 9443 2013-11-28 09:51:56 Glen Leinweber Re: An Incidental NE602 Discovery by bkopski Bob's discovery isn't new. Its more of a noisy regulator problem
than a NE602 problem. Philips' data sheet is fairly clear that
the two outputs on pin 4,5 have 1500 ohm load resistors directly
connected to Vcc supply pin 8 - thus power supply rejection
with respect to ground (pin 3) is zero.
Those circuits that take a single-ended output from either pin 4
or from pin 5 risk amplifying regulator noise coming into pin 8,
especially if the amplifiers are ground-referenced. This would
include most NPN-type ampifiers. A PNP audio preamp that is
supply-referenced (specifically referenced to the same supply as
the NE602 pin 8) is more immune to regulator noise.
Also more immune are amplifying circuits that use both pin 4
and pin 5 outputs to a differential amplifier. A good example is
the "Direct Conversion 7-MHz receiver using two integrated circuits"
(Fig. 1.9 on page 1.8, Chapter 1 of EMRFD). The LM386 has
differential inputs (pin 2,3) connected to NE602 outputs (pin 4,5).
Any regulator noise on Vcc is rejected as a common-mode signal.
Many regulators have output Z less than 0.1 ohm throughout the
audio range, rising slowly at higher frequency. This makes it hard
to use a Vcc bypass capacitor to smooth Vcc noise. The equivalent
series resistance (ESR) of the capacitor may not be low enough to
effectively reject regulator noise. And the NE602 provides NO
internal supply rejection.
FATCA disclaimer:"I am not now, nor have I ever been an American citizen"
9444 2013-11-28 16:36:42 Jim Miller Re: An Incidental NE602 Discovery by bkopski This may be useful:Wenzel has a lot of useful articles on his site.jim ab3cv