Author Topic: impedance help please  (Read 2281 times)

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Offline paco)))

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impedance help please
« on: November 19, 2007, 10:20:03 am »
  Hello, I just bought a beta bass amp with a beta 105 cab. Well the amp has an issue but I'll get to that later. Right now I'd like to run the 105 cab with my 205 cab out of my 190B amp. What's the right configuration for that combination as far as impedance? The 190B just has a single 4ohm & 8ohm output.

  Now the beta bass amp problem is that when you turn the volume up the sound goes down??? It doesn't reach full volume at all when you turn it the opposite way or anything. It does seem to sound good but just not working right. Does that sound like anything anyone's ever experienced before?

Thanks!
Chris

Offline xsolarusx

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Re: impedance help please
« Reply #1 on: November 24, 2007, 02:52:50 am »
The impedance should be listed on the back of the cabinets.  From there, if you described how you were connecting the cabinets, someone might be able to offer a suggestion.

Thanks!
(2) 73 1st Gen Model T
Late 70's Marshall JCM 800 1960B cab

Offline EdBass

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Re: impedance help please
« Reply #2 on: November 24, 2007, 01:31:29 pm »
With old cabinets like that, I wouldn't trust the label even if there is one.
Hook the cab(s) up to a multimeter and see what's going on in there. Also, your 190B should have 4, 8 and 16 ohm taps from the OT. If you need 16 ohms to make your cabs work, you just need to switch the jacks on the chassis around to make the outputs 16 and 8 instead of 8 and 4 ohms.
You might want to check the outputs on the 190B anyway just to be sure the switch hasn't been done already.
You know of course that the outputs are wired in parallel, right? If not, this means if you plug in one cabinet it will use that specific output tap (4, 8 or 16 ohm), and if you use both jacks it will default to the lower or secondary of the two used OT output taps (usually 4 or 8 ohm).

In other words, you can't plug a 4 ohm load into the 4 ohm output and an 8 ohm load into the 8 ohm output simultaneously, you would actually be showing the 4 ohm tap a 2.67 ohm load.

Well you could, it might be fine at least for a while. But you might eventually find yourself looking for a new output transformer, or power tubes and other miscellaneous parts…