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
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|