I recently posted in response to some of Ken's comments denying that I had
tinny or poor audio on receive from my PRO.
That is a true statement, but I failed to point out that I take the receive
audio from the ACC1 rear connector where the signal is removed from the
digital data stream approximately by only a DAC and an isolation amplifier.
Audio taken from this point of the system is the cleanest I have ever heard
from an amateur receiver. Using a heterodyne from a BC station in USB, I
can observe a sine wave signal virtually to zero frequency with no
discernible waveform distortion at all. I have looked at the single
frequency distortion products of the PRO and they are down in excess of 50
db. All that says to me that my ears are hearing correctly.
Another point that I may not have mentioned is that the ACC1 receive audio
goes through a snall mixer/EQ unit to a large stereo amp and a large stereo
speaker cabinet system. This system can produce discernible 20 Hz audio in
the shack and at 30 to 40 Hz, I can rattle the walls and furniture.
Listening over that arrangement produces outstanding audio quality for AM
BC stations and for many of the SSB stations whose operators have made an
effort to achieve clean, balanced, well-articulated transmit audio.
So, *my* view of the PRO audio is heavily biased by how I hear it, and I
should have pointed that out before.
I think that maybe what Ken observed is sound produced by the absolutely
and totally crappy output audio amplifier chip used in the PRO and probably
in the original 756 as well. It does indeed produce highly inferior audio
compared to the ACC1 receive audio signal. Even with the standard Sp-21 or
the much better SP-20 Icom speakers, the sound is far removed from what can
be obtained. I understand that most of the receiver output audio circuitry
and devices have been replaced in the PRO II, which probably accounts for
it improved audio.
So, based upon my assumption that Ken merely plugged in his headphones, I
am not surprised that he found the resulting audio tiring and "tinny" after
a while. I find that with my setup, using the Heil ProSet, I can operate
for extended periods of time without suffering any hearing problems.
The plan of attack for most serious PRO owners is to avoid using any of the
analog internal audio circuitry in the radio and use the near-digital
signals available from the rear connector. This results in superior
transmit and receive audio.
I wonder if the Omni VI+ has a similar facility for extracting the receive
audio near the demodulator and inserting transmit audio near the balanced
modulator?
72/73/oo, George W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771
Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437
All outgoing email virus-checked by Norton Anti-Virus 2002
n4lq@iglou.com wrote:
>
> He was really asking about the original 756 not the Pro which is a
> totally different reciever. QST did mention the rough audio in the Pro
> but that it was cleared up in the ProII.
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