Bootstrapped Op Amp Articles

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mediatechnology
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Re: Bootstrapped Op Amp Articles

Post by mediatechnology » Wed Jan 10, 2018 7:55 am

I moved discussion of the following "Voltage-bootstrapped current-boosted NE5534 swinging op amp for audio line driver providing +27 dBu into 600Ω" circuit to here: https://www.proaudiodesignforum.com/for ... ?f=6&t=927

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Voltage-bootstrapped current-boosted NE5534 swinging op amp for audio line driver providing +27 dBu into 600Ω
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Re: Bootstrapped Op Amp Articles

Post by mediatechnology » Thu Apr 19, 2018 5:12 pm

I happened to be looking at the dBx 160 output stage today and happened to notice that its op amp supply rails appear to be voltage-bootstrapped by a tap on the output stage bias divider string.

I saved this schematic years ago as an example of a ground-compensating output.

Never noticed the mild bootstrapping until today. It looks like at 0V output the LM301 is seeing about +/-19V.

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dBx 160 Ground-compensating voltage-bootstrapped line driver output with turn-on mute.
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Re: Bootstrapped Op Amp Articles

Post by KMN » Tue Jun 04, 2019 11:20 pm

I think I may have an excuse for trying a bootstrapped opamp circuit. In my case to minimize distortion.

I was looking for an audio grade op amp for doing filters at +/-36V rails, where the non inverting configured inputs may see up to full rail voltage. Power output is very low but precision at large and small signal swings is a must.

LT and Analog have some higher voltage rail capable FET input and chopper opamps. Nothing specifically for audio. The highest Vrail high quality audio grade op amps I've found were the opa604's with +/-25 v rails absolute max. Edit: I should add TI does have a bunch of power amps for audio. I was looking for something in an SO8 package or so, not the giant packages in the TI power amps which are way overkill in my circuit. The LTC6090 is a bit of a compromise. SOIC-8 with power pad is workable, I guess. It definitely wont be getting hot with the amount of light loading in my circuit./edit

In ltspice none of those "high voltage" AD or LT parts seem to do very do well in the upper audio band. They all start distorting pretty heavily, even lightly loaded.

Lets just say that if my simulations are to be believed, the LTC6090 bootstrapped about 18V away from the output up to +/-36V rail...wow that thing is clean now per my sims.

I ended up using something like recommended in this article to get the sims looking real sweet. I started with a circuit similar to the one in the EDN article but ended up at something similar to this. Toward the bottom of the page in the link. Sorry idf this one was already linked and I missed it. https://www.embedded.com/print/4217177:

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Re: Bootstrapped Op Amp Articles

Post by mediatechnology » Wed Jun 05, 2019 5:12 am

Self did a lot of work (also published in Small Signal Design) with bootstrapping to reduce distortion.

Take a look at Dimitri Danyuk's work here: viewtopic.php?f=12&t=928
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