BC780 Line Out issues
 

Is there a reason that the audio output level coming from the speaker and
from the line out jack don't agree with each other on this thing? I also
wondered why is the line out jack amplified to begin with.

I have to turn this thing up blastingly loud to get any recordable sound
from the line out jack. The only remedy I know of is to record via the
external speaker jack with a Y-connector plugged into it and my recording
device and speaker/headset plugged into the branches. Quite convoluted I
might say.

Jeff Seale
Louisville, KY
BC780, Pro95, Satellit800, YB550PE, ETraveller, DX440

In article cxwYc.338355$%_6.329265@attbi_s01,
Jeff Seale wrote:
I have to turn this thing up blastingly loud to get any recordable sound
from the line out jack. The only remedy I know of is to record via the
external speaker jack with a Y-connector plugged into it and my recording
device and speaker/headset plugged into the branches. Quite convoluted I
might say.

Convoluted but familiar. Something similar's happened to me before now.

Usually the cause is that the output stage is designed with driving a
32 ohm load (the speaker, headphones). Connecting to the line in of
a sound card/tape recorder -- which has a much higher impedance -- results
in no sound, weak sound, or sound that starts ok and fades out. The output
stage is trying to deliver current into a high-resistance, and it can't
do that efficiently. Speaker outputs are about current transfer, line outs
are about voltage transfer, broadly speaking.

Your Y-adaptor bodge works because it is correctly loading the output
stage, and you are tapping the signal present across the load.

Without the speaker as a load, and without the headphones etc, the output
fails to achieve a useful voltage.

You could make a lead up with, for example, a jack connector to plug
into the scanner, a piece of screened cable, and whatever connector you
need at the far end for the recording device, and then fit a resistor
across the signal and earth at one end of the lead. This provides the
load the amplifier is looking for.

Or you could buy a ready made lead (openable, not moulded!) and adapt by
adding a resistor. The resistor would need to be sufficient to provide
a load. Try 100 ohm, 64 ohm, 32 ohm in order until you get some useful
level.

Mike.
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Mike Brown: mjb[at]pootle.demon.co.uk | http://www.pootle.demon.co.uk/