Hello, I'm trying to design an output stage through an opamp as voltage follower. Since I tried some simulation with LTspice too, I wondered which of these was better. The first one seems rather atypical (though it works), while the second is the classical single PSU for an opamp, with the half Vcc superimposed to AC signal.
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The first one would only 'work' if the opamp input can handle signals below its Vee, here ground.
Depending on what you used in the sim, it may or may not appear to 'work'.
What do you mean by 'work'?
Jan
Depending on what you used in the sim, it may or may not appear to 'work'.
What do you mean by 'work'?
Jan
The opamp is the RC4558. I mean that output AC audio signal swings correctly (from -3V to +3V), as expected
Yes, from LTspice sometimes you can expect fancy thing.
Anyway, the question raised because I got ideas from this h.a. schematic. The opamp figures as not for a single supply operation, in some way is directly biased from the VAC of the tube, but I can't say if this schematic is a simplistic form.
Anyway, the question raised because I got ideas from this h.a. schematic. The opamp figures as not for a single supply operation, in some way is directly biased from the VAC of the tube, but I can't say if this schematic is a simplistic form.
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Well the opamp is biased at 15V with 24V supply, so what would be the problem then? That should work OK.
Jan
Jan
Why would that be necessary? As long a the signal stays within a few volts of either supply, it'll work fine.
Thought experiment: If the need was for exact in the middle, would it stop working when it was 1mV off ;-)
Jan
Actually in that last circuit the opamp has a bipolar supply, not single supply. But we'll keep that for the next step I guess ;-)
Jan
Jan
Keeps more than a few volts from either rail surely.
The RC4558 input stage is not the common "pnp works down to negative rail"
Common-mode input voltage range for this part is given as +/-14 V typ, +/-12 V min on a +/-15 V supply, so usually keeping 1 V, worst-case 3 V away from either side should do the job. About a volt also is what I'd have estimated from the circuit.
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