PA help.

MichaelMackie · 17th May 2009

I just got a little Realistic MPA-35A PA amp.
I know the PA frontier is pretty pointless in most recording environments, but I need help with this, and I'm sure someone here must know the answer to this.

So it's speaker out options confuse me. I really have no idea what I'm supposed to plug into the back of this unit to make noise come out.
Wires, types of speaker really.
I got it for free, so I didn't worry about it until I played with a few things and realized my failure.

I'm attaching a picture. Hopefully someone can help me outski.
Thanks.

mprewett · 17th May 2009

I can't give you the full low-down, but I think I can get you headed in the right direction.

You have two mic inputs that are probably high impedance, so you'll need either an old high impedance mic or an impedance matching transformer that will change your balanced xlr low impedance input into an unbalanced 1/4" tip-sleeve high impedance output.

The output from the amp to the speakers is mono. You can choose various different impedances. I'm not sure what the specs on the Com. and 70V outputs are, but the 4ohm, 8 ohm, and 16ohm outputs are typical impedance values for speakers. Check what the impedance value is on your speakers and match them up. They are a standard bare wire crimp connector (I'm not sure what their technical name is). You simply press down on the crimper to open it up, insert the bare wire, and release the crimper so the wire stays connected. Most traditional PA speakers don't use bare wire crimps, so you're going to be needing a "modded" speaker cable with the appropriate speaker connector on one side and the bar wire on the other. Heavy guage wire is usually recommended, but in this case, I'm not sure the bare wire crimps are large enough to accept the usual 10-18 gauge wire sizes. You'll probably end up using 20 gauge or above.

MichaelMackie · 17th May 2009

Thanks alot.
And I think I get the gist of what you're saying.

Basically, that I should either spend money, and mod some speakers...
Or sell it and use the money towards a modern amp.
Haha.

John Eppstein · 17th May 2009

It's really a pretty crappy amp. Old tube versions of that kind of amp are sometimes good for harp amps, but the transistor ones aren't good for much of anything except maybe high school announcements.....

Barish · 17th May 2009

70V output is for line driving. If you are sound-reinforcing a stadium, for example, you don't try to connect an 8 Ohm speaker on the roof to an amplifier's 8 Ohm output lying in a cupboard 8 million cable miles away. You use a higher voltage line feed like that one with a higher impedance, and use a transformer at the end of the line to match the required impedance right on the spot. It doesn't make things sound any better, but makes life so much easier. There are also 100V versions of those systems.

For conventional operations, if your speaker is 8 ohms, then use com(mon) and 8ohm terminals. If it is 16, then use com and 16 ohms and off you go. Same goes for 4 ohms. com and 4 ohm terminals.

B.

17th May 2009	#1
MichaelMackie Gear Head Joined: Dec 2008 Location: Bremerton WA Posts: 62 Thread Starter	PA help. I just got a little Realistic MPA-35A PA amp. I know the PA frontier is pretty pointless in most recording environments, but I need help with this, and I'm sure someone here must know the answer to this. So it's speaker out options confuse me. I really have no idea what I'm supposed to plug into the back of this unit to make noise come out. Wires, types of speaker really. I got it for free, so I didn't worry about it until I played with a few things and realized my failure. I'm attaching a picture. Hopefully someone can help me outski. Thanks. Attached Thumbnails __________________ Naked Women.

17th May 2009	#2
mprewett Gear maniac Joined: Dec 2008 Location: Kent, OH Posts: 194	I can't give you the full low-down, but I think I can get you headed in the right direction. You have two mic inputs that are probably high impedance, so you'll need either an old high impedance mic or an impedance matching transformer that will change your balanced xlr low impedance input into an unbalanced 1/4" tip-sleeve high impedance output. The output from the amp to the speakers is mono. You can choose various different impedances. I'm not sure what the specs on the Com. and 70V outputs are, but the 4ohm, 8 ohm, and 16ohm outputs are typical impedance values for speakers. Check what the impedance value is on your speakers and match them up. They are a standard bare wire crimp connector (I'm not sure what their technical name is). You simply press down on the crimper to open it up, insert the bare wire, and release the crimper so the wire stays connected. Most traditional PA speakers don't use bare wire crimps, so you're going to be needing a "modded" speaker cable with the appropriate speaker connector on one side and the bar wire on the other. Heavy guage wire is usually recommended, but in this case, I'm not sure the bare wire crimps are large enough to accept the usual 10-18 gauge wire sizes. You'll probably end up using 20 gauge or above. __________________ Full Disclosure: I'm just a hobbyist.

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17th May 2009	#4
John Eppstein Gear Guru Joined: May 2009 Location: San Francisco, CA. Posts: 10,191 51 Reviews written	It's really a pretty crappy amp. Old tube versions of that kind of amp are sometimes good for harp amps, but the transistor ones aren't good for much of anything except maybe high school announcements.....

17th May 2009	#5
Barish Lives for gear Joined: Sep 2004 Location: Istanbul, Turkey Posts: 1,803	70V output is for line driving. If you are sound-reinforcing a stadium, for example, you don't try to connect an 8 Ohm speaker on the roof to an amplifier's 8 Ohm output lying in a cupboard 8 million cable miles away. You use a higher voltage line feed like that one with a higher impedance, and use a transformer at the end of the line to match the required impedance right on the spot. It doesn't make things sound any better, but makes life so much easier. There are also 100V versions of those systems. For conventional operations, if your speaker is 8 ohms, then use com(mon) and 8ohm terminals. If it is 16, then use com and 16 ohms and off you go. Same goes for 4 ohms. com and 4 ohm terminals. B.