John Hardy 990

Hi ,

I am wondering what the purpose of the parallel Resistor-Inductor at the output as well as below the differential amplifier on the left side of the schematic.

Thanks in advance

Calvin

P.s. Sorry I can't attach the schematic, will only allow me to post 200kb
Here is the link http://www.johnhardyco.com/pdf/990-2007.pdf

Does this belong in another place?

The inductor in the output is to provide a low source impedance at low (audio) frequencies while being able to isolate capacitive loads (like shielded cable) at high frequency that could destabilize the amplifier.

The inductors in the LTP roll off the open loop gain at very high frequencies, again for stability, while being a low impedance at audio frequencies for low input stage noise.

JR

The Hardy amp is based on the Jensen JE-990 opamp, and Deane wrote it up in great detail. Must Read! Go to this page and request a copy by paper-mail:
http://www.jensen-transformers.com/apps_wp.html