[TenTec] Corsair II Audio Question

Shawn Upton kb1ckt at yahoo.com
Fri Mar 25 12:02:48 EDT 2022

I did order the OPA2134 op-amps but I'm not sure if I should have now; I'm guessing the lower cost 5532's might be fine, and really, maybe even not that much--it's not that noisy, after all.
Ah I see how the fader works, couldn't see that this morning.  Not sure if I really want to spend the time to redraw this schematic (but I know I will now!)  Thanks for reviewing with me.
Now if I could just get the sidetone cleaned up: I thought I'd try out G3TXQ's (SK) mod, with an L/C across the oscillator, but something is amiss, I killed the audio without cleaning it up. On a scope I see a clean sinewave, but with modulation, and I think I hear that modulation.  [Couldn't find the torroid I wanted, so I put 120 turns onto an FT37-43, and... I'm not happy with how it came out.]

    On Friday, March 25, 2022, 11:45:37 AM EDT, Barry N1EU <barry.n1eu at gmail.com> wrote:  
 Welcome to the hodge podge of the barely readable 561's IF-AF board
schematic.  I haven't looked at it in ten years but I
meticulously dissected it back then and modified the hell out of it.  The
piece you might be missing is the bottom left of the schematic:  U3A/B and
U4A/B comprise the 750Hz bandpass filter and yes, there's a fader that
mixes unfiltered audio with bandpass filtered audio at connector 6.

Barry N1EU

On Fri, Mar 25, 2022 at 6:00 AM Shawn Upton via TenTec <
tentec at contesting.com> 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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