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Because i need a voltage follower and a comparator ; linear op amp used as comparator do not works well as the lm393. For my application the comparator is priority. Obviously i could use 2 devices, but i want use less components as possible .
Regards
Gianni
opamp wired as a comparator is fine, but you can't get a comparator to act like an opamp
you are asking for a voltage-follower as opose to gain which implies you are more interested in Hi-Z input, just use yr signal going into the -ve input thus you don't need a voltage-follower
Because i need a voltage follower and a comparator ; linear op amp used as comparator do not works well as the lm393. For my application the comparator is priority. Obviously i could use 2 devices, but i want use less components as possible .
Regards
Gianni
You also need a compensation capacitor for low gains.
I can't find a slew rate specification for the LM392 so I can't be sure that it's fast enough for audio but it's bound to be better than a comparator that's being used as a linear amplifier.
You also need a compensation capacitor for low gains.
I can't find a slew rate specification for the LM392 so I can't be sure that it's fast enough for audio but it's bound to be better than a comparator that's being used as a linear amplifier.
The LM392 is the opamp from a lousy old LM324 quad or LM358 dual and the comparator from an LM339 quad or LM393 dual.
The opamp is terrible for audio because it has crossover distortion, noise and its full output response (28V p-p) is to only about 1kHz. The datasheet shows response up to only 5kHz at 14V p-p. The response drops and severely distorts above 5kHz because it integrates the signals into triangle-waves.
A modern dual opamp like a TL072 has very low distortion, very low noise and full output response up to 100kHz. It is probably faster than the LM392 comparator.
Tanks.
I found AN74 from National Semiconductor that confirm what Ericgibbs says.
Well i'll use a CA3130 and a LM311. (i have a lot of them)
My purpose is to build the input stage(50KHz low pass filter) for the PIC A/D converter. And use the comparator for trigger level in meantime measure the frequency.
Regards
Gianni
The very old CA3130 opamp was invented by RCA (remember them in the 60's?). It is the very first Cmos opamp and is (was) the noisiest (hissssss). It needs a compensation capacitor which reduces its max frequency.
Yes it is old. (me too!)
There are some good reason to use it.
1) i have it (the most important)
2) it is single supply and the output is rail to rail
3) i use unity gain and suppose that 23uV of noise are little enough for the 20mV resolution(8bit) of A/D converter.
Regards
Gianni
Any opamp can be powered with a single supply voltage if its inputs are biased at half the supply voltage.
A very good audio opamp is inexpensive. A TL071 single opamp is $.53US, a TL072 dual opamp is $.64US and a TL074 quad opamp is $.48US at Digikey today for only one. Surface-mount ones cost less.
The old CA3130 is available for $.93US only if you buy all 2000 of them they still have.
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