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turning a combo amp into a power amp

Sahe_Bassist

Sahe_Bassist

Jun 27, 2010
392
96
Tampa, Florida, USA
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#1
alright so,

i have an old behringer ultrabass bx600 combo amp. i took the thing apart for fun and now i have a use for it.

i turned the enclosure and 100w speaker into an extra cabinet by wiring the speaker to a jack.

now i want to turn the combo amp into a power amp, so i can run a pre amp (like the lind 6 pod i have) into the frankenstien power amp, into the speaker cabinet. or as a cheap in-home monitor for band practice vocals. i want to completely bypass or remove the EQ section of the amp and just use it to power the signal to a useable rating.

im well aware that this can only produce 60w of power, but its more for the fun of doing something with this amp thats just sitting around my house.

heres a pic
f7729dcc.jpg
what im thinking is that if i wire a jack to the 3blk 1red wires coming from the EQ board that would be the input to the power amp, then i also have to wire a jack to the 1blk 1red wires as an output from the power amp to the speaker cabinet.

does this make sense? i dont know if those wires do what i think they do...or even if this is possible...:help:

what do you all think?
 
#3
yes thats it. i figured i could use the power amp in spot for the input, but then i still need an output. i tried using the other jack (pre-amp out) but the level wasnt right. i also tried the line out jack and thats not right either. im OK with using the power amp in for the input and not doing more work than i have to.

think i could just wire a jack to the 2 poles that were the original speaker connections? they should be pos. and neg. right?
 
#4
Yes, that should work. The only thing I would suggest is to insulate the jack from the chassis since without knowing the power amp circuit, you could have a problem if one side of the output is not referenced to the chassis (ground loop or possibly damaging the amp). Also make sure you pay attention to the minimum load that the amp can drive (i.e. 8 ohms or 4 ohms). Hopefully in the manual.
 
#6
Sahe_Bassist said:
amp is 8 ohm, i know that for sure. the speaker im trying to put it to is 8 ohm also.

how would i insulate the jack from the chassis? basically dont mount the output jack to the chassis itself? i was just going to put it in one of the empty spots.
Click to expand...

If you have access to an ohmmeter or DVM you could check to see if one of the speaker leads already has basically 0 ohms resistance to the chassis. If that's the case you'll probably be OK. You could use insulated shoulder washers or make a mounting plate out of a piece of plastic, but the easiest solution is a combination speakon 1/4 inch jack like this:

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All plastic and it mounts with screws. Have to enlarge the hole but I think it's the best solution. Make sure it's a combo jack or you'll be forced to use a speakon plug. You'll have the option to use either this way.
 
#9
Its fairly simple, just unscrew everything. The two screws that good the handle on the top also hold the amp in place, as well as the screws on either side. Then it should just slide out. But be careful, the wire from the amp to the speaker was pretty short so in order to get to work on the amp you have to disconnect the wire from a board on the amp.
 

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