I think I found my answer and you guys were right... Quote: "The headphone circuitry in the FLEX-5000 uses Output Coupled Load (OCL) amplifier with a 2.5V bias."
Headphone requirements for the Flex 5000 That sucks, love my earbuds, they're so much better due to weight, but don't really want to mess around adding a capacitor. Thanks,Mike KF9AF On Sunday, November 23, 2014 10:31 AM, Bill Guyger <bguy...@yahoo.com> wrote: A couple of separate answers: - Capacitors in series do roll off the lows, but if you pick a cap whose reactance at one octave below the lowest frequency that you wish to be "flat" is equal to the reactance (though you can probably get away with simply using the DC Resistance of the headphones for all practical purposes...) of the phones, the frequency response will be 3 dB down at that frequency but will be back to flat at one octave above the "corner" frequency. So if you assume a lowest desirable frequency of 300 Hz. for communications purpose pick a corner frequency of 150 Hz. - And back in the day (1920's - 1930's) the voice coil of the speaker was used for the filter choke, and if you look at old radio schematics, say in the ARRL Handbook, you will see the headphones in series with the B+ for the amplifier tube. But that went the way of the Dodo when transformers became more readily available. Most high end amplifiers either use a transformer, or in the case of transistor amps have complimentary output devices with B+ and B- supplies so (in theory) there is very little DC at the common point the speaker is connected to. If you do loose one side of the power supply the full tilt boogie voltage of the other supply will be applied to your speaker and you have a good chance of blowing the voice coil. I have literally seen a speaker cabinet catch fire and burn because the amp went into DC. High quality amps have protection circuits to prevent that, but the Certain Vagrant (Cerwin Vega) amp that caused the fire did not because Vega was really cheaply designed. Bill AD5OL ________________________________ From: Rob Keijzer <pa3...@amsat.org> To: Bill Guyger <bguy...@yahoo.com> Cc: flexradio <flexradio@flex-radio.biz>; Mike Sonn <fatfend...@sbcglobal.net> Sent: Sunday, November 23, 2014 7:34 AM Subject: Re: [Flexradio] Flex 5000A w/earbuds There is indeed dc on the 5kA phones output. When I plug in a headphone I hear a loud pop (almost to the level it makes me think it'll be blown). I asked once why on earth this is needed, and got the answer that blocking this DC (by transformers or capacitors) would also block the lowest audio frequencies. I simply don't use the headphones output. BTW: I never heard that high end audio required our equipment to run DC through our voice coils. Rob, PA3CNT 2014-11-23 5:06 GMT+01:00 Bill Guyger via FlexRadio <flexradio@flex-radio.biz>: Forgot to add grab a voltmeter and check for DC > >Bill > >Sent from my iPhone > > >> On Nov 22, 2014, at 10:04 PM, Bill Guyger via FlexRadio >> <flexradio@flex-radio.biz> wrote: >> >> Heating in headphones and speakers is usually caused by D.C. coming out of >> the amp. I underline usually maybe something I'm not considering though..... >> >> Bill AD5OL >> >> Sent from my iPhone >> >>> On Nov 22, 2014, at 8:27 PM, Mike Sonn <fatfend...@sbcglobal.net> wrote: >>> >>> Anyone else use earbuds? I've used a set for years with my Flex 3000. I >>> now have upgraded to a FLEX 5K and when I stuck my earbuds in for the >>> first time, they were very warm. I thought I had them leaning against >>> something warm in the shack, but after sitting on the desk for 10 >>> minutes, they are still warm. My ear canals won't get cold, but >>> clearly, there's something strange going on here. Any ideas? >>> _______________________________________________ >>> FlexRadio Systems Mailing List >>> FlexRadio@flex-radio.biz >>> To opt out of the Reflector: >>> http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz > > > > >> >> _______________________________________________ >> FlexRadio Systems Mailing List >> FlexRadio@flex-radio.biz >> To opt out of the Reflector: >> http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz > >_______________________________________________ >FlexRadio Systems Mailing List >FlexRadio@flex-radio.biz >To opt out of the Reflector: >http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz > -- Rob Keijzer PA3CNT _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz To opt out of the Reflector: http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz
