Yep Jeff, that appears to be true. Here is the link to the datasheet. http://cache.national.com/ds/LM/LM4911.pdf
73's Jim, W4ATK [EMAIL PROTECTED] http://web.mac.com/jimrogers_w4atk -----Original Message----- From: Jeff Anderson [mailto:[EMAIL PROTECTED] Sent: Friday, November 16, 2007 6:55 AM To: Jim, W4ATK; Flex-Radio Reflector Subject: RE: [Flexradio] Flex 5000 Front Panel Headphone Jack (Follow Up) What National chip is used? I'd like to check out its datasheet. And how is it wired to the headphone jack? It sounds as though the Flex design connects the headphone shield to a pin on this IC, rather than to chassis ground, correct? Thanks! - Jeff, K6JCA -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Jim, W4ATK Sent: Friday, November 16, 2007 4:38 AM To: Flex-Radio Reflector Subject: Re: [Flexradio] Flex 5000 Front Panel Headphone Jack (Follow Up) Thanks to Bill Winkis for supplying the datasheet information on the audio amp chip used in the Flex 5000. The mystery is, I believe, cleared up as to why some headphones will work while others will not. The Sony headphones have a DC resistance of 10 ohms or so, low DC resistance. The Heil ProSet phones have a DC resistance of 206 ohms. Some will conclude this should not be a problem, but it apparently is. The National chip used in the 5000 has two modes of operation, Capacitor coupled and OCL capacitor less). OCL mode supplies a voltage to the sleeve (common) connection (notice the isolated from ground headphone jack). The amplifier chip monitors the current through this connection and if it exceeds 500 mA, will shut down. The current thru the old 10ohm stereo phones is sufficient to drive them to DC block producing a loud "pop" and may be sufficient to shut the amp down, while the higher DC resistance of the Heil ProSet satisfies the requirement of the device and work perfectly. This may be covered in the specifications or somewhere but being anxious to get the new baby on the air, all this senior citizen saw was TRS stereo headphones and went for it. Anyway this is my story and I am sticking to it until the guys at Flex tell me I am all wet..... 73's Jim, W4ATK [EMAIL PROTECTED] http://web.mac.com/jimrogers_w4atk _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/ _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
