Okay now I understand! Thanks for the terrific explanation Bob!
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On Apr 14, 2020, at 12:37 PM, w9ran <w9ran@...> wrote:
On 4/14/2020 12:06 PM, K0WDO Will Osborn via groups.io wrote:
Are you thinking we’re using the speaker as a dynamic mic of sorts instead of the electret and that’s why we have to crank the gain all the way up and shout?To be clear, the speaker connection from the speaker-mic is not hooked up inside the radio, only the mic terminal is used. It's on the ring closest to the sleeve and seems to be a non-standard wiring scheme. The PTT switch is connected in series inside the mic and PTT is sensed by Q14 and U2 while the mic audio from the electret element is capacitively coupled to another section of U2 where it is amplified and gain-adjusted. If the radio is switching to transmit mode (speaker audio is muted) but there is no TX audio, I'd look in that area.
I guess it was done this way because of the desire to supply a mic as part of the kit, but in my view it would have been preferable to go with a conventional mic preamp and PTT line that would be grounded to transmit so users would be able to easily use any mic of their choice, or an external audio source. The supplied mic sounds OK but lacks the mids and highs that greatly improve speech intelligibility. I use a TRRS extension cable on it since the right-angle plug was always rubbing against the knob and adjusting the mic gain setting for me ;-)
73, Bob W9RAN