I have decided to add a transformer input to the transmitter. So far it works good and will reduce the possibility of ground loops. Another benefit is one can use a different model of Edcor matching transformer (they have several with different impedances) to better match the source impedance with the transmitter which might serve to get slightly better audio quality and if the transformer is used in step up mode the first audio stage might be able to be eliminated.
Only problem is I do get hum in the audio of my R-390 if I have my cellphone charger plugged in and my cellphone connected to the mixer. Connecting the R390 ground to the shield of the cable going to the mixer solves the problem.
Bass distortion is still there somewhat, but it largely depends on the song. I will have to check on another radio to be sure it is not just something with the R-390.
I do love the audio the Stereo Tool plugin provides. I use the AM Soft Europe as the AM Soft USA seemed to emphasize one midrange frequency a bit too much for my liking. I did modify that preset somewhat to better suit my ears and saved it under a new preset name. I then took that preset and reduced the post amp gain to make the transmitter sound good on my AK-40 radio and saved that as another preset. I have noticed that the 20's TRF radios seem to not like much modulation percentage when they are receiving a very strong signal such as from my two tube broadcaster.
I can also tell which internet radio feeds use processing on their audio as there will usually not be much of an increase in the audio level with the Stereo Tool processing turned on whereas those feeds which do not use processing will show a very noticeable increase in level with the Stereo Tool processing turned on.
I suspect if someone wanted to try the settings I use for Stereo Tool I could email the settings file.
I may try to record a sample of the audio as that might help diagnose the bass distortion problem.
I still need to find a better antenna though for more range. I am wondering if one of those tall CB antennas that were so common in the CB radio heyday will work? I would more than likely need to alter the coil used in the pi network and remove the capacitor on the output of the coil.
Thinking about it maybe I am getting bass distortion due to the pi net and the fact that it is being fed by a regular wire which of course as I have found out causes many harmonics which could be distorting the bass somewhat.
Thank you 35Z5 for turning me on to Winamp and the Stereo Tool plugin. For about the same price as it would have cost for me to build a compressor I got the necessary compressor and so much more. Also with the ability to feed the line input to Winamp I can process anything fed into the computer from my mixer.
Would this choke work for the power supply? http://www.edcorusa.com/products/770-xc ... 250ma.aspx
Once I get the transmitter finalized I will neaten up the internal wiring which might help its operation somewhat.