Favorite quad op-amps for synth design?

Jim Patchell patchell at teletrac.com
Wed Mar 22 21:26:05 CET 2000



Tim Daugard wrote:

> LM324 - Distortion highly visable as the negative input crosses from greater
> than to less than the plus input reference level. Doesn't mater what the
> supply is the cross over distortion has to be from switching some internal
> trasistors. - This was more evident in a log amp than a straight amp. I
> wanted to use the 324 for natural frequency rolloff but distortion was
> outrageous.
>

    The LM324 has a class B output stage.  Because of the slow slew rate, you
will see the crossover notch even at low frequencies.  By putting a resistor
from the output to the negative rail, you cause the amplifier to be biased
closer to class A, eliminating the cross over notch.  Still, if you are
interested in audio of any sort, LM324's are not the answer.  They are very nice
to use in DC applications where the input bias current is not a problem.  And
the input common mode rage goes from V- to V+ -1.5 volts, which by the way,
matches the range of voltages that the output will go over.  I stand also stand
with those who do not dismiss this part out of hand.  It has it's uses.

> Tim Daugard
> Lurking and trying to make a living at real estate.

    -Jim




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