little solid state combos and speaker impedance

Greg M

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I have a little Behringer GM108 amp with a 4 ohm speaker and a Marshall Valvestate MG15CD amp with an 8 ohm speaker. I don't know if the impedance is as big a deal with these as it is with tube amps, so I thought I would ask you guys if it would be okay to hook both speakers to the Behringer at once without damaging the amp. The Marshall amp is junk so I figured I could get a bit more volume using two cabs. Thanks for any advice.
 

Ed Storer

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I would recommend against doing that. Solid state amps are fine with more impedance, but tend to fry power transistors if the impedance is below minimum.

I don't think the 8 Ohm speaker would give you any more volume since the 4 Ohm speaker would dtaw 2/3 of the current.
 

PhredE

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A couple of random (hopefully related) suggestions and points I can throw out..

1. Of course, it IS possible, but is such thing advisable and/or without potential problems or side effects?? (answer: yes -- it could be problematic, depending).

2. a. Wiring an 8ohm and 4 ohm speaker in series yields: 12ohm load to amp
b. Wiring an 8ohm and 4ohm speaker in parallel yields: 2.7ohm load to amp
Almost no audio amps --guitar or otherwise-- are designed to support loads that small (4 is the usual practical minimum)

3. A greater load to amp will reduce power output, so a 12ohm load will lower the amp's output power with the greater load (compared to the stock 4ohm speaker). So, you may gain in having a second driver putting out the signal, but will give some that gain back by 'taxing' the amp's output somewhat. "It's a mixed bag", and not easy to predict actual output quantity/quality.

4. Perhaps even a greater consideration beyond the electronics-related stuff, is are you ok with connecting (soldering, adding a jack, etc) the speaker via serial or parallel connection?
It's possible to trash your amp by getting the basic wiring 'wrong' -- so it's fairly important to get the wiring stuff correct in order to make it all work.

5. I went on a cursory search for specs on that 8" Bugera speaker and couldn't come up with very much. A simple speaker swap may give more output if you can find a decent sounding but more efficient replacement. Without knowing the sensitivity rating of the existing speaker it's hard to know if a replacement will give much of a output boost.


Speaker:
Bugera 8" 20W, 4ohm.
 

Greg M

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Thanks for the responses guys. It sounds like it's not really worth attempting. I may be asking more from this little amp than it's fair to expect.
 

rdjones

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Does the amp have an extension speaker output jack ?
Is there anything marked on the rear panel or written in the owner's manual that might provide specific information ?
 




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