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Old 23rd March 2009, 02:03 PM   #1
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Default Bogen Challenger CH8 conversion...newb needs help!

Hey all,

I picked up a bogen Challenger CH8 pa amp, and want to change the "strange" (strange to me) output on it to a 1/4" jack.

The output looks almost like a tube socket... but with different impedence (4ohm, 8ohm, 16ohm) written next to each hole on the socket, and "Com" writen next to another hole on the socket.

Can someone give me a couple hints as to how to disconnect this output, and change it to a 1/4" output?

I tried last night without a schematic (couldn't find one online), and this is what I did (and did it wrong!!)...

There were two wires connected to the 8ohm part of the old speaker jack... and two wires connected to another part of the speaker jack (which I assumed were ground connections). I de-soldered these connections... and connected what I though were the possitive 8ohm connections to the new 1/4 jack, and wired what I assumed were the ground wires to the 1/4 ground connection. I sealed it up, plugged in a 8ohm cabinet, turned it on, and after it warmed up it started to let out a high pitch squeel trough the speaker. I quickly turned it off, and left it for the night.

I know this kinda "seat of the pants" stuff is obviously not the right way to do things, but I was bored, and wanted to tinker.

Why are there 4 wires going to that speaker output? Anyone got any tips for connecting this correctly?

Thanks for any help you can give!
shamus
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Old 23rd March 2009, 06:38 PM   #2
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I do not know any details about your PA amp, but, in general a typical tube amp has the following output taps for the speaker: common (usually grounded to chassis) 4 ohm, 8 ohm, 16 ohm. The speaker negative lead goes to the common, then the other speaker lead is connected to the appropriate 4, 8, 16 ohm tap.

If the amp uses negative feedback (which it probably does), the feedback is usually taken off of the output taps, so that may explain the extra wires.

First, with the amp unplugged, using an ohmmeter, find the common lead, it's (hopefully) connected to chassis ground, or only a few ohms above ground potential. Then locate the 8 ohm tap and install the 1.4" jack observing the correct polarity. Finally, convince yourself that the common is still grounded and any feedback leads are still connected as they were. If the original connector body is not connected to chassis metal (ground), you may also need to mount the new connector isolated from ground.
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Old 23rd March 2009, 07:18 PM   #3
brsanko is offline brsanko  United States
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sounds like an old microphone INPUT!! to me.
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Old 23rd March 2009, 07:25 PM   #4
brsanko is offline brsanko  United States
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sounds like an old microphone INPUT!! to me.
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Old 23rd March 2009, 07:26 PM   #5
brsanko is offline brsanko  United States
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the speaker outputs are the little screws above that.
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Old 23rd March 2009, 08:22 PM   #6
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nope...the mic input is on the front. There's no screw terminals on this PA like my other Bogen... just this strange socket. It litterally looks like a tube socket. I'll take a picture of it tonight and post it up.

thanks for your help though!
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Old 24th March 2009, 06:39 AM   #7
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That "socket" may be a testing point for adjusting bias. Have seen that on other amps. Just a WAG.
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Old 24th March 2009, 03:16 PM   #8
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Hey all,

this is the speaker output I was mentioning before. The 1/4 socket to the right of this output was added by me...but wired up incorrectly. the other hole drilled was my first location for the 1/4 output, but i changed my mind.

anyone seen this type of connection before?

Thanks,
shamus
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Old 25th March 2009, 06:39 PM   #9
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bump..
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Old 29th March 2009, 02:05 AM   #10
seamas is offline seamas  United States
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I have a chb-20y that has 2 of these.It is the speaker plug.My amp came with 2 jensen P12S 12" speakers,and that is how they connect.
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