🚀 go-pugleaf

In article <116@deeptht.UUCP> spcecdt@deeptht.santa-cruz.ca.us (John DuBois) writes:
>
>     I'm looking at the sheet for the MC1437 dual op-amp.
>Each op-amp has two connections for "input lag". 
>Does anyone know what they are for?  Thanks...

	The MC1437 is not an internally compensated op amp, so...
a cookbook amplifier made with the MC1437 will oscillate at some
high frequency (instead of amplifying).  One can obviously 
add a filter to the feedback network, but it is simple to tap off
a few places inside the amplifier where the impedance is relatively
high.  The 'input lag' connects to a 25k ohm impedance point in
the amplifier, so a relatively small capacitor (to the 'output lag') 
will suffice to stop oscillation if placed there, and the 
feedback components can be changed WITHOUT changing the 
compensation capacitor.

	The word "lag" refers to the phase-lag of the compensation
scheme; some compensations are possible with 'lead-lag' networks
for special purposes.

	Externally compensated op amps are very useful for making
low-noise preamplifiers (one can add an input stage and correct
the compensation for the extra gain), for high-frequency amps 
(where one can make an exact choice of compensation for the particular
gain), BUT no one would want to use the MC1437; it's not a 
very good design, compared to even the old-fashioned uA748
(aka "MC1748").


	John Whitmore