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Beogram Commander Remote Control: Maybe This is the Final Version!..;-)

This is a follow up to my recent post about the redesigned Beogram Commander remote control board, which now works in both (DC-motor) Beogr...

Friday, September 16, 2011

Beomaster 8000 No-Load Current vs. Time

I guess I was wrong about the voltage drift I observed during the left channel no-load current adjustment. I connected the right channel again to the power supplies and the voltmeter to R236/7 and turned the output stage on. I adjusted the voltage to 14 mV after about 30 sec. Then I observed the voltmeter over time. After about 40 min the voltage reached a constant 18.2 mV. It appears this voltage strongly depends on the temperature of TR211 in the constant current source that feeds current into the trimmer.
I blew some air on TR211 with a straw, and immediately the voltage decreased by several mV. Even air current like from an AC can have significant influence.

I repeated this experiment with the suspect left channel. A similar result. After about 20 min the voltage was at 19 mV and after 1:30 hours at 19.6 mV remaining constant there after. Same sensitivity to air flow across TR211.

I think this experiment shows that both output stages may be running correctly. I guess the rule to adjust the trimmers when the Beomaster is still cold assumes that the final no-load voltage spec is higher than 18 mV after the Beomaster has warmed up.

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