Studio Preamp into a CB Radio

[357]

I picked uo a ART MPA Gold preamp for $5 and it looks like new.
It has tubes in it and so I ran my turner +3 into it and then into my Courier.
It seems to work ok but it puts out alot of audio and I have to turn it down so low the VU meter barely moves which kinda sucks cause I'd like to see the "swing".

Anyone got experience with these?

 

[357]

The xlr plugs have ground, red and white.
I ran the red to the audio wire and grounded the whites.
Seems to be ok.....not sure if its studio broadcast though.

 

[2RT307]

I don't have any experience with the unit, but looking it up on the internet shows you got a really good deal. Do you have a studio type dynamic mic (or one that requires 48v phantom power, which your unit can supply) laying around that you could try on it?

I would think the Plus 3 would have too much gain going into this unit, as it has a preamplifier and compression built in. You're running a preamp mic into a preamp...

73,
Brett

 

[Captain Kilowatt]

Brett is right. You have far, far too much gain. The +3 should drive the snot out of the radio on it's own. I own two Turner +3B's and have yet to see a radio they would not drive with room to spare. The second issue is that the output of the ART is far too high to drive any microphone input regardless of what mic you use. You could make an external attenuator but why boost levels so high and then knock them back down again? There are reasons for doing that regarding signal/noise ratio bit that is not the case here. You have more than enough gain with the mic alone.

 

[357]

lol it is pretty overkill.
I ran a stock mic on it and it sounded like a d104....If I had a old 254C it would probably rock.

Just trying to get some input on the connections.
The XLR has 2 audio lines so it really doesn't perform 100% when its mickey-jigged into a CB.

 

[fourstringburn]

The main reason to use a pre-amps ( for use in communication radio's) is for condenser mics since they have low output by design and require 48 volt phantom power to operate and boost the mic level. Dynamic mics generally don't use phantom power that I'm aware of.

These preamps like yours are usually used in studio recordings and the output level as other have said is too high for a radio input from CB type radios. Most of these preamps have internal level attenuation that is switchable from a pro audio level +4dBu down to a consumer level at -10dv. both are still to high for your radio's mic input gain stage.

If you had a modern HF rig, you could use this patched into the ACC jack using a condenser mic then this will bypass the radio's mic gain stage. It will still be a high output level and wouldn't move the needles much but far less then going direct into the mic input. Other than that, the preamp is a nice one and if it works well, I would sell it for a nice profit since you paid so little for it if you don't see a use for it in the future.. You could easily sell it for a $100 or more.

 

[Captain Kilowatt]

lol it is pretty overkill.
I ran a stock mic on it and it sounded like a d104....If I had a old 254C it would probably rock.

Just trying to get some input on the connections.
The XLR has 2 audio lines so it really doesn't perform 100% when its mickey-jigged into a CB.

The XLR is a balanced audio connector with a shield. Balanced audio lines are used in most pro audio gear as it provides a measure of noise reduction. Any hum induced on the line is in equal and opposite phase and effectively cancels out. The best thing to do is use an audio transformer with the proper impedance windings on each end. usually the gear has an output impedance of either 600 ohms or something compatible with high impedance circuits like 10K or 20K ohms. Some gear, if it has transformers on the outputs, can have pin 3 of the XLR connector connected to ground to make an unbalanced audio circuit which is what you would need to feed a radio.

 

[1502gulfcoastMS]

I picked uo a ART MPA Gold preamp for $5 and it looks like new.
It has tubes in it and so I ran my turner +3 into it and then into my Courier.
It seems to work ok but it puts out alot of audio and I have to turn it down so low the VU meter barely moves which kinda sucks cause I'd like to see the "swing".

Anyone got experience with these?

View attachment 17955

Keep playing with it and asking questions. You'll get it. If not call me anytime to double your money. It really needs to be on an injected radio

Try an unamplified d104 or shure 58

 

[2RT307]

For no more money than you have in it, you could certainly do a project to make it work properly. I say keep playing and have some fun with it. That's why I was asking if you had a "studio" mic to play with. And no, dynamics don't require phantom power, but condensers do. There is an inexpensive condenser mic made by MXL under the name MCA, and it is the SP-1. You used to be able to hot-rod them pretty easily, but the circuit board has changed since then. You can still pick these mics up for 50 bucks brand new, and the frequency response for where our voices work is surprisingly flat. And that's a good thing. Radio Shack makes some decent Shure SM-58 clones that you can find used for about 30 bucks.

Or just keep using your Turner Plus 3, which will sound pretty darned great, and sell the ART preamp.

73,
Brett

 

[357]

I've been trying a art 310 and it seems to clean up the +3 a bit.

the mpa gold, sold

 

[357]

I'm gonna get one of these:

 

[fourstringburn]

Don't mess around with a toy, get one of these...

 

[Robb]

IIRC, that ART Gold uses 'cold plate emulation' since it doesn't have a ~200V xformer in it to drive the tubes as true studio-grade tube preamps work. Doesn't mean you can't make it work for you, as I use almost the same thing ('cold plate emulation') myself.

As already said, using either a dynamic (magnetic) mic, a condenser mic, or even a ribbon mic (lol) would be better suited to reach the best end result with this unit. Otherwise, it will be as CaptainK said; you will just end up driving the output signal into total distorting far too easily with the +3B.

A matching xformer would also be best to use to hook it up to your radio so there will be less freq loss due to impedance mismatching.

And no; you really don't need a mixing board for all of this. Mic, preamp, and matching transformer should do the job well enough.

 

[Beetle]

Probably 30 years ago, my next-door neighbor knocked on the door and asked if I could ease up on my transmit power because I was really messing up his TV reception. I showed him my station - cold, dark and with the rig opened up so I could make a couple minor repairs. I hadn't been on the air in a couple of weeks.

He got this puzzled look and I suggested I turn MY TV on. Sure enough, there was a large amount of video and audio interference, and it wasn't coming from me. "Bill" (that's what everybody called him 'cuz his name was Bill) asked me to come over to his place, which I did. His TV was practically jumping up and down - and then we both noticed a voice from down the hall. In his son's room. Bill went to check and there was his high-school age son with some POS CB radio, trying to feed the output of a 100-watt stereo amplifier directly into the mike connector. Bill grabbed the mike, squeezed it tightly, and it broke into pieces. The kid realized that it MIGHT have been his neck and he started disassembling stuff. As soon as he turned the CB off, the TV returned to its old self. Bill thanked me for my assistance (which wasn't all that much).

 

[Captain Kilowatt]

IIRC, that ART Gold uses 'cold plate emulation' since it doesn't have a ~200V xformer in it to drive the tubes as true studio-grade tube preamps work. Doesn't mean you can't make it work for you, as I use almost the same thing ('cold plate emulation') myself.

As already said, using either a dynamic (magnetic) mic, a condenser mic, or even a ribbon mic (lol) would be better suited to reach the best end result with this unit. Otherwise, it will be as CaptainK said; you will just end up driving the output signal into total distorting far too easily with the +3B.

A matching xformer would also be best to use to hook it up to your radio so there will be less freq loss due to impedance mismatching.

And no; you really don't need a mixing board for all of this. Mic, preamp, and matching transformer should do the job well enough.

That is something most people have no idea about. It is the reason a microphone will sound good on one radio and crappy on another. The frequency response goes all to hell when the impedances are way off. Match impedances first and THEN worry about freq. response.