The QDOA is an adaptation of a classic American op amp used in southern California large format consoles. It can be used as a microphone preamplifier, line amplifier, a summing amplifier, a balanced differential amplifier, or in an equalizer or compressor.
 
This is a ten transistor design based on the original schematic updated for current production transistors and fit into the popular 2520/990 footprint.
 
It works with a large power supply range (±14 to ±28V) allowing for some high voltage mojo and headroom.