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Old 12th January 2020
Lives for gear
JohnRoberts's Avatar

Originally Posted by Brian M. Boykin View Post
So in the world of swapping modern op amps into older designs I always add a .1uF cap from the +vcc and -vcc to ground and in recent years started adding a 33pf cap across the feedback resistor to further help with stabilization.

1) Is there an instance when I should not add a feedback cap?
When using a decompensated op amp (like NE5534) that is not unity gain stable. The popular 5534 IIRC is only stable down to a gain of 10dB (3x).

2) Knowing this cap can limit bandwidth, what kind of trouble can I get myself into from lowering a 100pf cap to 47pf or 33pf in an existing design to open up the bandwidth a little more?
generally no harm, but little benefit...

[edit] I am not a fan of second guessing design engineers but recall that capacitors cost money to purchase and then pay labor to insert, if design was better without them why waste money? [/edit]

As always,

Thanks in advance