RFI Audio Problem...

[RatsoW8]

Yes it is a 2 meter radio, I know it sounds overkill for 2 meters, but I just wanted to take advantage of the FM audio quality, apparently the mic is loud enough without the pre-amp after I did some more testing, my monitor radio is a Icom IC-2A series handheld and I used some headphones with it to test the direct mic only audio and it sounds great. As for the pre-amp I keep the output gain very low so as to not damage the radio.

Hey Ratso could you elaborate on the impedance mismatch, just trying to look at this problem from all angles...

Give Robb's artical on high quality audio for your export radio a read, thats what I have based most of my audio setup on.


T23

Understood. You still,however are going to need an interface like I mentioned. I'm betting the inedance mismach is the root of the hum.

I'm not affiliated with w2ihy but the link below will be a start for you.

W2IHY iBox

 

[T23]

Well I just looked the output impedance of my pre-amp and its 600 ohms, so that doesn't sound like it could be an impedance mismatch.


T23

 

[RatsoW8]

Well I just looked the output impedance of my pre-amp and its 600 ohms, so that doesn't sound like it could be an impedance mismatch.


T23

What's the mic input impedence of your 2m rig?

 

[T23]

The specs say " 500 to 600 OHMS"


T23

 

[Captain Kilowatt]

I just realised this is a 2m radio you are using. Get rid of the preamp and forget about "that tube sound". There is NO advantage to using it on FM. The microphone you use will have more affect than a tube preamp. The fact you have to keep the preamp turned way down "to protect the radio" says it is not needed at all and eliminating it will solve your problems.

 

[KE3W]

I still think he is getting AC hummmmmm from a bad transformer on his wall circuit.

 

[T23]

Ok, I guess your right Captain KW, May I ask for a more elaborate answer as to why it would have no effect on FM?


T23

 

[T23]

Ok, it was the pre-amp, I have connected a "VoiceOne" effects box to my radio and there is no buzzing, but when I put the pre-amp back inline before the Voice One box because it needs a mic pre-amp the buzzing returns, so it looks like I just need to find a new pre-amp, most likely solid state.

T23

 

[Captain Kilowatt]

Ok, I guess your right Captain KW, May I ask for a more elaborate answer as to why it would have no effect on FM?


T23

Actually the fact it is FM is really inconsequential. It could be any mode and I only said on FM because I was only thinking along the lines fuller sounding audio due to the wider bandwidth of an FM signal. You are limited by the weakest link in a chain and the weakest link in this case is the microphone amplifier and modulator in the radio. Most of the time when "that warm tube sound" is obtained it is a case of tubes being used all the way or at the very least in the last stage of a modulator circuit. In this case and "warmth" created by the tube preamp will be negated by following it up with the stock circuitry in the radio.