Thanks to some prompting from a Willamette builder who inquired about some performance issues with his rig, I was able to identify an error in the bill of materials which causes a significant degradation in receiver sensitivity.
Fortunately the fix for this problem is very simple. Audio preamplifier collector resistor R49 was incorrectly called out as 10 k, when it should have been listed as 4.7 k. If you have a 4.7 k resistor in your junkbox, just swap it in at the R49 position. A 5.6 k resistor will also work fine here. Alternately, you could just parallel another 10 k resistor across the existing one. I will be happy to supply the correct resistor to any builders who purchased a kit from me and need one.
I’ve determined that this wasn’t a design flaw, but a transcription error. My original hand-written notes have the correct value and my prototype does work correctly (I’m sure NA5N would have caught this problem in the prototype he evaluated). Somewhere in the process of creating the schematics in my schematic capture program, I entered the wrong value. I did build a beta rig with all of the same schematics/BOM that everyone else did, but I didn’t catch the error at the time. I will update the schematics and BOM posted on my website in short order to prevent any further problems.
Please accept a most humble apology from me for not realizing this significant error for a very long time. I do believe that you’ll be pleased with the difference in sensitivity once you install the correct resistor. The receiver should sound like you would expect a proper direct conversion receiver to sound. After the modification, you should be able to run the AF gain at ~75% or less during most operating conditions.
I’d like to thank W0EP, N1RX, WB8ICN, and WB9VTB for their assistance in resolving this matter!