Orion II Audio Output Circuit

(posted to Ten-Tec reflector 4 Sep 2007 by K7HP)

The OII has an entirely separate headphone amplifier IC from the speaker amplifier IC. The master AF gain affects both speaker and headphones - but the basic levels are settable in firmware . Both IC's are basically 3 or so ohms output impedance but the headphone path is stereo - the speaker is mono. A later mod of the headphone output from TT added a RF filter on the headphone output which adds about 24 ohms in each side of the headphone output.

The speaker IC is a TDA1013B - the headphone output amp is a LM4811 - the LM4811 is driven from a PT2258 and out5 and out6 of the PT2258 are tied in parallel to feed the input of the TDA1013B - theTDA1013 has a a 100K resistor to ground fed from two 560 ohm isolation resistors from out5 and out6 of PT2258. That 100K could be lowered to lower speaker path gain- or perhaps raising both 560 will also but that is more involved.

All this is on the Orion II schematics on the web site . A15 566 Audio.