The headphone output IC in the OII is a stereo IC LM4811. I measured about
2.75 ohms output impedance at the headphone jack before I installed the RF
filter . The RF filter in later OII's and the board that TenTec supplies has
surface mount ferrite loaded inductors and the total series resistance in
each lead is about 24 ohms.So output Z is about 27 ohms each side.
14060 MHz 50 uv in to RX Antenna.(essentially S9) Spot Tone 400 hz ,
Sidetone
set at 100 (max) . Received signal output level set to comfortable headphone
level.(Approximately half of the audio bar level readout with my phones)
ver 2.037j firmware . I have not measured the latest beta.
OPEN CIRCUIT LEFT MAIN RIGHT MAIN
set for comfortable 55.1 mv 55.5 mv
level (approx 1/2 bar)
SPOT 101.8 mv 102 mv
CW SIdetone 50.7 mv 51.0 mv
NO signal 3.7 mv 3.7 mv
residual noise
So from the above with about 27 ohms source impedance , you can deduce what
the level will be with various phones.
I use Sony MDR V6 phones which are about 70 ohm drivers and not very
sensitive (I cannot remmember the spec right now) and the cw spot tone level
to me is marginal.
With input signal as above S9 , Maximum output level open circuit wide open
1.2 volts RMS , about 3.5 V pk-pk and no visible clipping of clipping. All
measurements on a FLuke 179 true RMS meter.
I know of seceral guys who have done what was suggested and they just use
the speaker output with appropriate attenuation. You of course lose the
ability to listen to the sub rx in one ear and the main rx in the other ear
but you solve a whole lot of other issues.
73 de Hank K7HP
----- Original Message -----
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
To: <tentec@contesting.com>
Sent: Saturday, August 29, 2009 8:57 AM
Subject: Re: [TenTec] Head-Phone volume in Orion2
> On Fri, 2009-08-28 at 18:58 -0500, Stuart Rohre wrote:
>> Use higher impedance headphones, they are more sensitive.
>> Stuart
>> K5KVH
>
> Not at all necessarily. The original post said 97DB/milliwatt, which
> shows high power sensitivity. Higher impedance will just raise the
> required voltage, though if the driver has a large series resistor, a
> higher impedance headset might receive more power and be louder. There
> are too many schematics in the Orion2 set to casually trace out the
> hardware and see what that output resistance might be.
>
> It might be that raising the voltage to the headset would work for a
> particular headset with a step up transformer. That will work best if
> the headset connection is driven by a solid state audio amp that has
> lots of feedback to give it a low output impedance with no headset
> protecting series resistor.
>
> A sure cure is in the firmware. Maybe in some custom settings, which
> ought to be customizable for the varying voltage sensitivity of
> different headsets.
>
> Another sure cure is adding a series resistor, speaker pot, or L-pad to
> the room speaker line and dropping its level to match the headphones but
> requires turning up the master volume control which made drive the
> speaker amplifier into clipping.
>
> 73, Jerry, K0CQ
>
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> TenTec@contesting.com
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>
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