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.

If you have hum problems, I suggest you look at installing line bypass capacitors across the AC line and neutral conductors, and also from line to ground and neutral to ground, on your transmitter power supply. I had a hum problem on some, but not all, receivers when listening to my transmitter. It appears that a lot of RF gets pumped back into the power line from the transmitter, and some receivers can deal with it better than others. After I installed the bypass caps, the problem disappeared. Bypass cap value of 0.01µF is fairly standard. Best to use X-Y rated caps if possible.

Ok. The hum only occurred when I had my cellphone connected to the charger and also plugged into the mixer I use and only when the ground connection of the diode load terminal of my R-390 was isolated from the mixer ground with a transformer. I connected the ground terminal of the R-390 and mixer ground by connecting together the two transformer terminals the grounds went to and the hum went away completely.

I still use the transformer as it isolates the diode load terminal from the mixer input should the coupling cap I connected to the diode load terminal ever decide to short and also protects the mixer from the initial charging current of that capacitor. I feed the receiver into the mixer as it allows me to feed the signal into my computer for recording purposes if so desired.

Ok I just tried my RCA K-80 console and the bass distortion is still there somewhat. I must say my K-80 sounds very nice receiving the transmitter which is playing WRDV. It's nice that Winamp works with Live 365.

Maybe I am just trying to run at too high of a modulation percentage? Would that cause the bass distortion I am hearing? I have the VU meter set to read into the red at the onset of audible distortion which IIRC was set looking at the AM waveform. What I need to do is feed an audio waveform through the transmitter and see how the audio waveform looks coming from a receiver. That way I will be able to see what is going on.

While playing around with a length of wire for an antenna without the pi net connected while checking reception on my R-390 I was still receiving the transmitter signal on many different bands. Could that be because the trimmer capacitor is not connected in the circuit since it is mounted on the pi net?

I also just had an idea. I have an LM-7 frequency meter I am restoring. Can it be used in place of the xtal oscillator to allow the transmitter frequency to be adjustable? If so I could adjust for a quieter spot on the AM band and also see how the pi net I built reacts to s shift in frequency above and below 1 MHz.

I am ordering the inductor and transformer today.

Inductor

Inductance 0.5H
Max. Current 250mA
DC Resistance 12 Ohms
Frequency 120 Hz.


Power transformer

Primary (input) Voltage 120Vrms, 60Hz
Secondary (output) Voltage 350V CT @60mA & 6.3V CT @2A

With a full wave power supply using diodes and choke input what B+ can I expect to see? If need be I can use the 6.3 Vac winding to buck the primary in order to reduce B+ if it is over 200 Vdc.

Not including shipping the transformer and inductor come to a grand total of $36.72

The power transformer and choke I ordered are on their way.

Edcor may take awhile to fill and ship an order given the transformer or choke is usually made to order, but is well worth the wait.