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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Opamp buffer @ active crossover input?
Opamp buffer @ active crossover input?
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Old 17th December 2016, 11:11 AM   #11
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
The current draw of an opamp is the datasheet figure for quiescent plus whatever you send to the output.
If you have very light loading and no capacitance to charge/discharge, then the output currents can be very small, leaving the quiescent current as the only significant load for the regulators.

But if you have some capacitance as a load and have lower load impedances, then these can become the dominant load that is passed back to the regulators.
A 10k load driven to 2Vac is only 0.3mVpk from alternate supply rails. Add on the same again for small parasitic capacitance and you have only added 0.6mApk to the quiescent load. Small beer.
But if you had a 2k load driven to 4Vac and significant capacitance, then you can easily have 3 to 4mApk to add to your quiescent values for each opamp.
If there is limited supply rail decoupling at each opamp, then much of those peak currents have to come from the low output impedance of the regulator.
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Last edited by AndrewT; 17th December 2016 at 11:13 AM.
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