Diode across an op-amp???

Zero Cool · 11th February 2010, 01:30 PM

Why in the world would they put a diode across an op-amp like this??

sawreyrw · 11th February 2010, 01:49 PM

The diode protects the input to the op amp, in the event that fast negative going input is applied. You should not need the diode for all amps, just some that are susceptible.

Zero Cool · 11th February 2010, 01:54 PM

this is in a PA amplifier. wouldn't half the waveform always be shorted anytime the signal level gets above .7V?? as this is the first stage of the amp, I would think the signal level to be above .7v but I am not sure?

Juergen Knoop · 11th February 2010, 02:19 PM

there is no voltage difference between input and output of that unity gain buffer, hence the diode doesn't conduct under normal operating conditions.
regards

Zero Cool · 02:23 PM

OH YEA! yea yea I wasn't thinking of it that way. ok i get it now. I am so used to seeing diodes across op-amps in guitar distortion boxes that I wasn't thinking about it.

11th February 2010, 02:21 PM	#5
Zero Cool Audio Junkie diyAudio Member Join Date: Sep 2004 Location: MN	OH YEA! yea yea I wasn't thinking of it that way. ok i get it now. I am so used to seeing diodes across op-amps in guitar distortion boxes that I wasn't thinking about it. Last edited by Zero Cool; 11th February 2010 at 02:23 PM.

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11th February 2010, 01:49 PM	#2
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	The diode protects the input to the op amp, in the event that fast negative going input is applied. You should not need the diode for all amps, just some that are susceptible.

11th February 2010, 01:54 PM	#3
Zero Cool Audio Junkie diyAudio Member Join Date: Sep 2004 Location: MN	this is in a PA amplifier. wouldn't half the waveform always be shorted anytime the signal level gets above .7V?? as this is the first stage of the amp, I would think the signal level to be above .7v but I am not sure?

11th February 2010, 02:19 PM	#4
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	there is no voltage difference between input and output of that unity gain buffer, hence the diode doesn't conduct under normal operating conditions. regards