Elecraft › [K3]

K3 AF line out to mic attenuation

Classic

List

Threaded

5 messages Options

Chris Meagher-2

K3 AF line out to mic attenuation

Hello,

I want to connect K3 audio line out to a Toshiba laptop which only has a 3.5
mic socket for audio in.
Does anyone have recommendations for attenuation/impedance matching?
I was thinking of a simple votage divider.

Thanks,

Chris VK2LCD

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Don Wilhelm-4

Re: K3 AF line out to mic attenuation

Chris,

A simple voltage divider *may* be required, but I would suggest trying
it without any attenuation first. It all depends on where the soundcard
controls the microphone gain - be on the lookout for overload in the
soundcard, and if present, add an attenuator. A series resistor may
work just fine, or as you suggest, a voltage divider.

Impedance matching is not necessary nor desirable. Audio devices
operate well by using a low impedance source (able to provide more
driving current than is required) and a high impedance sink (which will
limit the current drawn). The characteristics of the sink (in your
case, the microphone input) will determine how much current is drawn
from the source (the K3). An analogy is to consider utility power
wiring - the outlet receptacle provides a very low impedance source, and
the device that you plug into that wall socket will determine how much
current is drawn, therefore the amount of power that is transferred from
the power company to your device. Within limits, an audio source/sink
combination works the same way, but the actual source impedance will not
be as near zero as the power company source, it will have some finite
value such that if the current drawn is too large, distortion products
will be developed in the driver.

When the available source power is near the power to be dissipated (as
in a transceiver/antenna situation), then impedance matching becomes
important for maximum power transfer - because the source power is
limited (or more correctly, not vastly greater than the power required
by the sink).

73,
Don W3FPR

Chris Meagher wrote:

> Hello,
>
> I want to connect K3 audio line out to a Toshiba laptop which only has a 3.5
> mic socket for audio in.
> Does anyone have recommendations for attenuation/impedance matching?
> I was thinking of a simple votage divider.
>
> Thanks,
>
> Chris VK2LCD
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 8.5.287 / Virus Database: 270.12.8/2086 - Release Date: 04/29/09 06:37:00
>
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Steve Ellington

Re: K3 AF line out to mic attenuation

In reply to this post by Chris Meagher-2

Chris
Watch out for the DC phantom voltage on that laptop's mic jack. I doubt if
you want to feed that back to the K3. Otherwise you should be ok to just do
a direct feed. Hopefully you won't have any ground loop problems. An
alternative would be to use a cheap external USB sound card.
Steve Ellington
[hidden email]
----- Original Message -----
From: "Chris Meagher" <[hidden email]>
To: <[hidden email]>
Sent: Wednesday, April 29, 2009 8:53 PM
Subject: [Elecraft] K3 AF line out to mic attenuation

> Hello,
>
> I want to connect K3 audio line out to a Toshiba laptop which only has a
> 3.5
> mic socket for audio in.
> Does anyone have recommendations for attenuation/impedance matching?
> I was thinking of a simple votage divider.
>
> Thanks,
>
> Chris VK2LCD
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Ken Kopp-3

K3 AF line out to mic attenuation

In reply to this post by Chris Meagher-2

Hi Chris,

I connect both LINE OUT and LINE IN directly to
the microphone and headphone jacks of my HP
laptop without anything between. The IN and OUT
gain settings of the laptop handle the levels OK.

73! Ken Kopp - K0PP
[hidden email]
http://tinyurl.com/7lm3m5
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Matt Zilmer

Re: K3 AF line out to mic attenuation

In reply to this post by Chris Meagher-2

Chris,

I think this is one of those "your mileage may vary" things. With
this older HP laptop, I have a bit of overdrive going the other way -
from the computer to the Line In on the K3. Adding an attenuator
allowed the me to get better control (more granularity) over the
laptop's audio out and at the same time lowered the drive level at the
K3.

You can build a Pi or T attenuator for either in or out at the
computer. A fairly good calculator for this can be found at
http://www.daycounter.com/Calculators/PI-T-Pad-Attenuator-Calculator.phtml

FWIW, I designed and built a 5 dB attenuator for 1k line impedance. It
seems to work and allowed volume adjustment to occur in smaller steps,
which in this case is what was necessary to combat too much drive at
lower Line In settings at the K3 (setting 4 was as high as I could use
it, and setting it at 3 was too low).

You can also buy a better sound device like the EMU-0202 from Creative
Labs. This approach has the additional benefit of keeping digital
modes' sound separate from whatever your computer o/s and applications
generate.

73,
matt W6NIA
K3 #24

On Thu, 30 Apr 2009 10:53:38 +1000, you wrote: