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Old 28th October 2003, 04:26 AM   #11
sully is offline sully  United States
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Join Date: Sep 2003
Location: Long Island
Default Hmmmm..interesting procedure..

Originally posted by jcx
an interesting approach to exercising output of single ended amps is to connect a resistive load between the outputs; diving the 2 inputs with relatively phase shifted signals allows simulating any impedance load

in "Output Resistance and Intermodulation Distortion of Feedback Amplifiers" JAES V 30, #4 4/82 pp178-190 Cherry and Cambrell suggest driving the 2 channels with 5:7 frequency ratio sines to sweep out the I-V characteristics of the outputs and test for "Interface Intermodulation Distortion", a sharp rise indicating ouput stage strain

( any sound card should let you test to < 0.1% IMD )

I have been discussing this method as a means of measuring the hf phase (temporal) errors in an output stage as a result of reactive loading.

My concern was the transient chip dissipation and the thermal tracking output bias set inability to follow chip level thermals, as they are 100 uSec to 10 msec in nature, while the bias tracking is tens of seconds.

I was interested in transient response shifts as they pertain to soundstage, that being the 20 microsecond shift range.

Guess I'll look that one up..

Thanks for the reference.

Cheers, John
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