Question for John Curl...Please!

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Technical and scientific discussion of amps, cables and other topics.

John,
I have a couple of 72-74 vintage Pioneer pieces. An SX-828 receiver and an SA-8100 integrated amp. I got both pieces recently, and as is my custom, measured the power output and frequency response. I also tried to measure the source impedance. i have done this literally dozzens of times. But with the Pioneers I ran into some odd behavior. The power output and frequency response were fine and about what I expected. I measure source impedance by running the amp up to the nominal rated output voltage under no load (20 volts RMS for a 50 Watt amp) and then apply an 8 ohm non-inductive power resistor. The drop in voltage with the load applied is the ZI drop through the source impedance. However, on the Pioneers, the voltage rises when I apply the load. From 20-22 volts. So I borrowed another SX-828 from a friend and got the same result.
To me this implies negative impedance or some positive feedback. Yet the amp is stable and shows no sign of oscillation on the scope and no clipping during the tests. They all sound good, too.
Do you have some idea of what's going on here? And do you have a suggestion for an alternative method?
Jerry

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Topic - Question for John Curl...Please! - Bold Eagle 15:17:42 09/19/04 (5)

Re: Question for John Curl...Please! - john curl 11:11:14 09/22/04 (4)

Re: Question for John Curl...Please! - Bold Eagle 12:14:04 09/22/04 (3)

Re: Question for John Curl...Please! - Nelson Pass 14:54:11 10/21/04 (1)

Re: Question for John Curl...Please! - Bold Eagle 16:55:30 10/21/04 (0)

Re: Question for John Curl...Please! - john curl 20:28:17 09/23/04 (0)

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