[Elecraft] Option to bypass audio amp?

[George, W5YR]

Tim,

Sorry if I made it sound confusing  . . .  <:}

Let's look at the PROs first. They bring out transmit audio IN and receive
audio OUT to ACC1 for external connections. I use these for three reasons:

1. they are convenient to get to with cables, etc. and provide/accept
signals at Line levels and impedances.

2. the receive audio line come out before the analog amp chain in the PROs
which, to be kind, is not the world's finest for low noise, wide frequency
range or wide dynamic range. It is adequate but not overly so, in my
opinion. The output is also at Line level and impedance, with the signal
level independent of the AF Gain control,  which makes it convenient to
interface with external equipment.

3. the transmit audio IN goes almost directly into the input audio channel
A/D converter to feed into the DSP section where the actual transmitted
signal waveforms are generated mathematically. Thus the transmit audio
undergoes a minimum of internal analog signal handling as compared with
feeding the Mic connector. The Mic amp section is noted for noise,
distortion and lack of dynamic range and is easily overdriven, etc. , all
relative to the quality of the signal when applied directly to the ACC1
input.

Let's be real clear about one point here: I am not putting down the PROs
internal audio sections for any reason other than to point out their
shortcomings when viewed from a rather critical performance level. They are
more than adequate for routine operation. But if one is attempting to obtain
the best in transmitted and received audio, there is merit in avoiding their
use. Evidently, Icom agrees to some extent with this view or they probably
wouldn't have provided the ACC1 connections . . .

Now, to the K2:

First, it has a headphone jack on the front panel that comes off the
internal audio amplifier output but which has the high frequencies rolled
off with RC filters. The other receive audio output is the Speaker jack on
the rear panel, which is connected directly to the internal audio amp output
but without any high-end rolloff - always use this output for maximum audio
frequency range, as when aligning filters with SpectroGram, etc.

Since the K2 internal audio amp is pretty good and since there is no output
available prior to the amp's output, one has only two choices for getting
receive audio.

In my posting, I was suggesting that you just use the Speaker output to
drive an external audio system (or a speaker system to the extent that the
K2 amp has enough power output) and not worry about trying to bring out an
internal audio tap point ahead of the audio amp. As to the K2 signal already
being amplified and then you amplifying it again in an external system, that
is a non-problem if you remember to keep the K2 AF Gain setting low enough
that you do not overdrive the external system.

To summarize, and this should probably be the entire content of the wordy
posting (!), I use the PRO and PRO2 ACC1 receive audio output because  (1)
it is there and easy to connect to, Line level, etc. and (2) the output
signal is cleaner in the sense of wider frequency response, less noise and
wider dynamic range without clipping/distorting. I use the K2 Speaker output
directly because (1) it is there and easy to connect to and at a signal
level and impedance level that will "work" into a Line input even though the
specs don't exactly match up; and (2) the K2 audio amp is quite clean, quiet
and of adequate dynamic range, so there is no real need to avoid using it;
its gain can be controlled such that its output level does not overdrive
external equipment.

I suspect that once again I have created more questions than I have answered
. . .

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"In the 57th year and it just keeps getting better!"


----- Original Message -----
From: <tlogan7@cox.net>
To: "George, W5YR" <w5yr@att.net>; <Elecraft@mailman.qth.net>
Sent: Wednesday, February 12, 2003 5:42 PM
Subject: Re: Re: [Elecraft] Option to bypass audio amp?


> George -
>   OK, I'm confused here. In the Pro II situation you bypass the internal
audio amp, right? Otherwise you are amplifying an already amplified signal -
which I thought you would want to avoid. If I amplify off the speaker jack
on a K2 the signal still has gone through the internal audio amp, right?
Isn't there an advantage to bypassing the internal amp as is done with the
Pro II type setup?
>   It sounds like in the Icom setup you bypass an internal audio amp but
not in the K2. Why is there a difference in the approach. Again, this is for
fun - not necessarily sensible with a rig like the K2 - but curiousity
prevails. Thanks George :-) 73/Tim