The 5000a uses an LM4911 in an OCL configuration. See the device data
sheet.
The barrel of the headphone jack IS NOT GROUNDED.
Rather it is biased to half the 4911's supply voltage,
as are the left and right headphone outputs. The barrel
and the stereo headphone outputs all show 2.41 volts
on my Chinese DMM.
The results are undefined if you short any part of the headphone
connector to ground.
I listened very carefully with my headphones while plugging them in to
my 5000a and heard NO clicks or pops.
If you measure a DC voltage between the headphone wires, something is wrong.
On 11/23/2014 07:52 PM, Mike Sonn wrote:
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?
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Developer of Industrial ZMODEM(Tm) for Embedded Applications
Omen Technology Inc "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430
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