Bootstrapped Op Amp Articles

[mediatechnology]

Attached some basic examples of how Pacific Recorders, Auditronics and dbx bootstrapped their opamps for outputs through the 70s into the 90s.

Thanks for posting these examples and joining us here!

It looks like all but the dBx are current-boosted outputs using +/- 15 to 18V supplies.
The dbx has voltage bootstrapping using C13 and C14 to extend output swing.
(I show this in a hand-drawn dbx 160 schematic which may be when they first started using it.)

Voltage bootstrapping to increase swing is the crux of the original post but a voltage-bootstrapped 553X doesn't have enough current drive for 600Ω to near +27 dBu so, in the circuit here, I also used current-boosting to drive the load: https://proaudiodesignforum.com/forum/p ... 918#p10918
The current-boosted outputs you show are certainly needed with voltage-bootstrapped op amps if they're going to drive a peak load current that's more than maybe 20-35 mA.

Thanks again for sharing.

[z11111]

No problem! The dbx one is surely reliable as I use 900 series units daily and rarely have any issues interfacing them with other equipment or running their outputs through long~ish lines.

I think if I were to rework any of these circuits, I’d use the scheme you’ve drawn out. Thanks for that.

[mediatechnology]

No problem! The dbx one is surely reliable as I use 900 series units daily and rarely have any issues interfacing them with other equipment or running their outputs through long~ish lines.

I think if I were to rework any of these circuits, I’d use the scheme you’ve drawn out. Thanks for that.

You're welcome.
You might want to consider the ZTX851/951 for replacement use.
They're super rugged and have high gain.