Help With High End Audio...

[T23]

OK, well I am working on the audio portion of my station now, I have purchased an MXL R144 ribbon mic with a small desk boom stand and shock cage, also an ART Tube MP pre-amp, ok heres my problem I have wired my XLR cable to my 8-pin modular plug for my radio, with the mic directly conected to the XLR adapter it works fine but with the pre-amp inline it gives me a line level buzzing with no audio, I have my output gain on the pre-amp just barely cracked and my mic gain on the pre-amp at little more than half. Even with my output gain at nothing it still gives me the buzzing. The keying circut works fine. Any ideas?

T23

 

[Radio75]

Sounds like an open in the audio line to me.
Are you sure the pre amp is good?

 

[Sonwatcher]

I had the same thing . I bought an ART Zdirect box. Similar to an Ibox. I had to push the button for "ground lift" . It took care of it. Make SURE you do not turn Phantom power on with that mic ! Great mic. That is what I am using.

 

[Captain Kilowatt]

Sounds like a balance issue. You are using an XLR connector which is balanced audio (two wires carrying signal plus a ground) and the input to the radio is unbalanced audio (one signal wire and a ground). On the output of the preamp, tie pin 3 of the XLR connector to pin one which is ground and see what happens. You can unbalance audio leads to feed unbalanced systems by tying one side to ground but you should ALWAYS make sure it is pin 3 that that gets tied to ground. Make sure you have all your grounds connected as well.

 

[Captain Kilowatt]

I had the same thing . I bought an ART Zdirect box. Similar to an Ibox. I had to push the button for "ground lift" . It took care of it. Make SURE you do not turn Phantom power on with that mic ! Great mic. That is what I am using.

Ron, that sounds like it may have been a ground loop issue. I used to deal with balanced and unbalanced audio all the time in broadcasting as all pro gear is balanced audio. In some stubborn cases I would use an audio transformer inline and have to play with/without grounds etc. Basically that box you bought was in effect an audio isolation transformer with a switch in the ground lead.

 

[Sonwatcher]

10-4 !

 

[T23]

I have tried tying the common ground and audio ground on the XLR already my amp does not have the "ground lift" button on it. Could it be a polarity issue or a grounding problem? It seems to be something going on with the amp, it gets great audio in a set of headphones..


I have tried everything, I have even tried taking the grounds completely off the XLR and modular plugs the problem still persists. The only thing I haven't tried is swapping the positive and negative audio leads. It sounds like a polarity issue to me but how can that be I have reviewed all the pinouts?

I am using a Kenwood TM241A 2 Meter. So the wiring is a standard Kenwood 8-pin modular plug.

T23

 

[GnG8d]

You want to run balanced all the way to the radio, and take the audio (-) to ground at the 8 pin plug.

 

[T23]

That was the first thing I tried when wiring it up the first time, then later I tried the ground jumper like stated above, same issue...


T23

 

[ONAWHIM]

60 cycle hum sounds like a ground issue as mentioned.
Just for grins...

If the pre amp has a separate power supply try plugging it and the radio into the same receptacle using a power strip.

If I understand, the mic cable plugs into the pre amp XLR and the output of the pre amp is also XLR. I would check continuity on each wire for shorts with others or opens.

2's Hot, 3 is not, and 1 is ground

Both your mic and pre map are nice products.
Good luck

 

[T23]

Ok, I have done some more testing and it seems when I have my head phones connected to the preamp and it is not connected to the radio when I key up it gives a similar buzzing noise...strange...

I have also seen my preamp seems to act oddly when I key my hand held 2 meter radio near it with the same but more faint buzzing noise..


RF feedback?

T23

 

[T23]

Ok, I figured it out, I still have the problem though... I can hear audio now aparently I didn't have the pre-amp output set high enough, I know its RF feedback now, but what do I do about it? The noise is less on low wattage and louder on higher wattage.



T23

 

[Sonwatcher]

You may need something like an Ibox.