Buying used amps

Is this amp OK?
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rec
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Joined: Tue Jan 30, 2007 1:15 pm
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Buying used amps

#1 Post by rec »

Is there a way to accurately test a used amp with out hooking it up to speakers to
make sure you are not getting a piece of junk?
My initials are in the view finder of every camcorder (REC)
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DJPhatman
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Re: Buying used amps

#2 Post by DJPhatman »

An RMS voltmeter and a test tone generator for solid state amps, but not on tube amps. Most tube amps require an output load. Plus, this will not tell you if the amp has any noise in the chain.
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Ron K
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Re: Buying used amps

#3 Post by Ron K »

You can make a dummy load from these.

http://search.digikey.com/scripts/DkSea ... T200-25-ND

http://media.digikey.com/photos/Hunting ... 200-25.JPG

Set two in parrallel and adjust them to equal 13 ohms each and they will give you a 400 watt 6.5 ohm static dummy load for under 50 bucks. I would highly recommend you mount to a heavy wooden base and use no paint. Mounting to any type of metal would require some sort of heavy duty high heat insulators like ceramic standoffs etc.

With a high current dummy load you can use SMAART or another RTA type program that has the coherency capabilities. You simply compare the noise signal sent through the amp to the original noise signal generated by SMAART.(of course it will be necessary to pad the amps output reading with a series resistor or perhaps go through a D box that accepts speaker level signals. Thats what I generally use. My old DOD direct boxes work well for this.

You will immediately see if there's any difference in output between channels or non linearity's that exist when the amp in outputting the signal!
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rec
Posts: 381
Joined: Tue Jan 30, 2007 1:15 pm
Location: Virginia, C'Ville

Re: Buying used amps

#4 Post by rec »

Thanks, that is what I was looking for
R
My initials are in the view finder of every camcorder (REC)
2xOT12(Deltalite 2512 loaded, w/melded arrays)
2xOT12(Deltalite 2512 loaded, w/flat array) "In Process"
4xT30(24", 4012HO loaded)
1xAT

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