Hi Shaun,
I believe the circuit you're referring to is likely the audio bandpass
filter. It allows you to "peak" the audio on a particular tone for CW
clarity, in addition to the optional IF filters.
I did the OPA2134 mod to mine, and did not quite see the same results. I
suspect the improvement they saw was from removing that section from the
audio path. I still say that the radio is "quieter" even if I can't
prove it with test equipment. I chose to keep the audio bandpass
functionality.
Overall, with the audio mods and the complete alignment I did, plus
adding a 250 Hz INRAD filter, this radio is a dream to operate on CW.
Too bad I got an Orion at the same time.. it will be a very choice to
decide which one stays, because I don't really have the room for both.
On 3/25/2022 9:01 AM, Shawn Upton via TenTec wrote:
Sorry, my new-to-me radio didn't come with a manual. I'm glad that TenTec was
nice enough to post pdf's but the copy isn't that great.
>From what I can tell, audio on the IF/AF board goes first to the notch
filter. The AGC is then tapped off this, and the audio then goes to what I don't
understand just yet.
Looks like audio goes to the bandpass filter made of U3 and U4, and goes to connector 6. But the
audio after the notch filter also goes to here. It almost looks like a fader control here?
As in, you could turn the pot full one way and get one audio path; or full other, and get the
other. Or mix (sum) the two in some way. That would make sense but then I have R64 which
looks like a sneak path around.
[I did see the online mod for hiss reduction; I've ordered the OPA2134 boards to try that
out. Working on seeing if I can make as quiet as my Omni C. :) Am toying
with getting the 1.8kHz filter for some large noise reduction but waiting on that as it's not
cheap!]
Shawn kb1ckt
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