Brett- Glad you found a solution. So far, I haven't heard from anyone else experiencing this issue.
I set the audio volume on the Retro-75 up for 'room-filling' levels. The ALC control engages only at high signal levels and keeps the LM386 audio final from clipping. With the 3" speaker I'm using, I can fill the entire house with audio before this happens. It's admittedly not much of an AGC function per se. It wouldn't be too difficult to improve on the receive AGC action, but it would take more complexity. In particular, an additional audio amp stage would provide the levels needed for a lower AGC threshold. The AF gain control would also need to be relocated outside the control loop. Otherwise, the gain control does nothing once the threshold has been reached. I solved this on the old WM-75 with a 100-ohm pot/rheostat right at the audio output. 73- Dave Benson, K1SWL > [Original Message] > From: Brett Gazdzinski <brett.gazdzin...@verizon.net> > To: Discussion of AM Radio in the Amateur Service <amradio@mailman.qth.net> > Date: 4/9/2010 10:41:08 PM > Subject: [AMRadio] retro 75 > > I did some signal tracing tonight, and found the 1 meg resistor off the > detector seems to be the cause of my excessive rx audio distortion. > Not sure if the fet detector (Q3) is bad or not, but with a 100k in place of > the 1 meg, the audio cleans up nicely. I still have plenty of gain. > > I am not sure if anyone else is having distortion on the rx audio or not. > > With the resistor changed, the receiver sounds very good, but the lack of > any agc makes the levels all over the place.... > > Brett > > ______________________________________________________________ > Our Main Website: http://www.amfone.net > AMRadio mailing list > Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ > List Rules (must read!): http://w5ami.net/amradiofaq.html > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Post: AMRadio@mailman.qth.net > To unsubscribe, send an email to amradio-requ...@mailman.qth.net with > the word unsubscribe in the message body. > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
