Hank:
Great minds think alike! I wrote almost the exact same response you did at
the same time!!
I hope Ten Tec is reading this...
Ron N6IE
www.N6IE.com
----- Original Message -----
From: "Pfizenmayer" <pfizenmayer@worldnet.att.net>
To: <geraldj@storm.weather.net>; "Discussion of Ten-Tec Equipment"
<tentec@contesting.com>
Sent: Tuesday, September 04, 2007 9:52 PM
Subject: Re: [TenTec] O II and headphones?
> The OII has an entirely separate headphone amplifier IC from the speaker
> amplifier IC. The master AF gain affects both speaker and headphones - but
> the basic levels are settable in firmware . Both IC's are basically 3 or
> so ohms output impedance but the headphone path is stereo - the speaker is
> mono. A later mod of the headphone output from TT added a RF filter on the
> headphone output which adds about 24 ohms in each side of the headphone
> output.
>
> The speaker IC is a TDA1013B - the headphone output amp is a LM4811 - the
> LM4811 is driven from a PT2258 and out5 and out6 of the PT2258 are tied in
> parallel to feed the input of the TDA1013B - theTDA1013 has a a 100K
> resistor to ground fed from two 560 ohm isolation resistors from out5 and
> out6 of PT2258. That 100K could be lowered to lower speaker path gain- or
> perhaps raising both 560 will also but that is more involved.
>
> All this is on the Orion II schematics on the web site . A15 566 Audio.
>
> FWIW -
>
> 73 Hank K7HP
>
>
> ----- Original Message -----
> From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
> To: <tentec@contesting.com>
> Sent: Tuesday, September 04, 2007 9:03 PM
> Subject: Re: [TenTec] O II and headphones?
>
>
>> On Tue, 2007-09-04 at 21:36 -0600, Richard Williams wrote:
>>> Tom,
>>>
>>> Yep, I have the same problem. I didn't notice the problem with my
>>> older
>>> Heil headset with the switchable elements; but it didn't have the noise
>>> canceling feature.
>>>
>>> Maybe it is something Ten-Tec needs to look into!
>>>
>>> Dick K8ZTT
>>
>> OK its solvable. What it means is that the headphone output has a
>> resistor to limit the power applied to the headphones and the headphones
>> are presumed to need a great deal less power than the speaker or the
>> noise canceling headphones. You can use an outboard amplifier with the
>> noise canceling headphones or identify that resistor and shunt it with
>> something having lower resistance to give the headphones more audio
>> power. It could be that resistor is wired on the headphone jack, but its
>> more likely on the audio output board. I don't think its a matter of a
>> coefficient in the DSP because most solid state audio amplifiers have a
>> very low output impedance so different loads shouldn't vary the audio
>> voltage much and the low impedance loads will naturally take more
>> power.
>> --
>> 73, Jerry, K0CQ,
>> All content copyright Dr. Gerald N. Johnson, electrical engineer
>>
>> _______________________________________________
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>>
>
>
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