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adjusting quiescent current on 2 channel power amp question?

172.135.152.196

Posted by alley-kat on November 22, 2004 at 19:40:33

hi, if i understand correctly, i have one mjl4281a npn and one mjl4302a pnp per channel. i have a duall .22 ohm emitter resistor for each channel. the left channel trim pot was going bad causing 8 to 10 mv. across both outside legs of dual emitter resistor for that channel with 20 mv. across duall emitter resistor for right channel. i replaced both pots with better 15 turn sealed trim pots. when measuring across one dual resistor being dual .22 ohm from outer leg to outer leg, it should measure .44 ohm correct? i come up with .6 ohms instead, on both duals and extras i have laying around with two different meters. i adjusted for 30 mv. across outer leg to outer leg on each dual one per channel. would this mean 30 mv. divided by .6 ohms would give me 50 ma. quiescent per channel? i notice transformer begins to hum a tad bit more when quiescent is increased can hear only, with ear close to amp in quiet room. is it normal for hum to increase slightly when raising bias level? when amp was new, the measurements were 20 mv. across duall resistors. should i go by actual resistance measurements across dual resistors or, what's printed on them when calculating. it just gets barely warm on heat sink at 50 ma. quiescent. any advice would be appreaciated thanks, alley-kat

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