extension cabinet for beta lead combo??

[tonyr13]

I"ve got a beta lead 2x12 and I"m thinking of picking up a beta 1x15 cabinet to run as an extension. Both the output of the beta lead and the speaker in the beta cabinet are rated at 4ohms...
Will it cause problems for me to use both simultaneously? I love my beta and wouldn't want to wreck it.
All this impendance stuff gets the best of me every time.
Great forum, btw.
tonyr

[JoeArthur]

I wouldn't chance going below 4 ohms.  The existing 4 ohm cabinet with the new cabinet (and I'm assuming it will be 8 ohms with the 1 - 15") will drop the impedance to 2.67 ohms... an easy way to burn out output transistors.

[Don T.]

Hello:
 Actually, both the power board and the transformer will go to 2 ohms. The amps current limiting circuit kicks in at 1 ohm. The only reason it was rated at 4 ohms is because there is insufficient heatsinking. With extended use (like gig or practice) you will put your amp into thermal runaway and indeed the transistors will pop.
Don T.

[tonyr13]

On 2002-08-16 14:06, JoeArthur wrote:

I wouldn't chance going below 4 ohms.  The existing 4 ohm cabinet with the new cabinet (and I'm assuming it will be 8 ohms with the 1 - 15") will drop the impedance to 2.67 ohms... an easy way to burn out output transistors.

Hmm.
Well, the rear panel of the beta 15 cab says 4ohms, 100watts....if the 15 is indeed 4ohms, does that change the situation?

I guess all this is really leading me to ask: Is there a way that I can run an extension cab from my 2x12 combo while still using the amp's internal speakers? It seems that there would be some way to do this since the back panel of the beta has 2 speaker outputs (one of which plugs in to the combo's internal speakers)... what sort of cab should I be looking for? Can this even be done?

thanks for your replies, but I'm still a little confused.
tonyr

[Don T.]

Hello:
 If you run the cabinets in series you will have an 8 ohm load at the amp. This will cut output to 70 watts but you will be running twice the cone area so acoustic output should be close to what you had before.
Don T.

[tonyr13]

On 2002-08-19 12:10, Don T. wrote:
Hello:
 If you run the cabinets in series you will have an 8 ohm load at the amp. This will cut output to 70 watts but you will be running twice the cone area so acoustic output should be close to what you had before.
Don T.

Thanks Don, thats better news but...
what exactly do you mean by 'run the cabinets in series"? Would running the 15 cab out of the 'ext. speaker 2" jack be in series? or is that parallel?

Had I known I would be displaying this much ignorance in public I woulda posted anonymously
- tonyr

[Don T.]

Hello:
 The speaker out jacks are in parallel. Series means that the + from the amp goes to the + of the first set of speakers. The - of the first set of speakers goes to the + of the second set of speakers. The - of the second set then returns to the - of the amp. This means that you add the impedances for the total.
Parallel means the + from the amp goes to the +'s of both speaker sets. The - of both return to the - of the amp. This means the impedance is half.
  You can install a switching jack into one of the speaker outs to accomplish this. So when you plug in an extension speaker it automaticall puts the two in series.
Don T.

[Don T.]

Hello:
 I just happen to think of something. If the extension speaker is 8 ohms then all you have to do is disconnect one of the speakers in the amp (2X12" model) so it too will be 8 ohms. Now when you plug in your extension speaker the amp will see 4 ohms. I don't know how having only one of the angled speakers working will sound. If you have the closed back 4X10" cabinet the jack idea would probably be better.
Don T.

[JoeArthur]

Being "ignorant" is better than blowing up your amp... so that would be highly intelligent.

If both of the cabinets are 4 ohms, then running them in series would give you the sum... 8 ohms.  As Don says, this will reduce the overall power output, but you probably wouldn't notice the difference.

The Beta Lead is rated for a total of 4 ohms, not 4 ohms per output jack.  If you were to plug in two 8 ohm speakers, you would use both of the jacks but still have the total of 4 ohms (two 8 ohm loads in parallel gives 4 ohms).

Your 2x12 is wired in parallel with two 8 ohm speakers... therefore you use one jack and have the 4 ohm total.  Plugging in another 4 ohm speaker would give you 2 ohms.

The switching jack that Don suggests, could be done.  You would have to dedicate one jack to be the "normal" output, and the other as the "series" output.  It would be possible to install two switching jacks, so that both would be "normal" and the other one be the "series" output.  If you are the only one that will ever use this amp, that might be an option.

I would suggest wiring up a special cord... one end would plug into the head, and the other two ends would plug into the speakers... and would put them in series.  That way, you wouldn't be changing the normal wiring of the amp.

You could also swap out your 2-12" speakers for two 16 ohm speakers wired in parallel for 8 ohms, and put an 8 ohm 15" speaker in the other cab.  Then you could plug both in to the existing parallel jacks for a total of 4 ohms.

[tonyr13]

Thanks again Don and Joe.
I've got some more information on the Beta 15 cab...
It turns out the cabinet has 1 input and then 2 outputs--one is parallel the other series. If I've been following this exchange properly, I should be able to run a speaker cable out of the head, into the input on the 15 cab, then out of the series output jack on the back of the 15 cab and into the beta's internal 2x12 jack. I don't know if there are any drawbacks to running the 15 first in the series, but this seems like it would accomplish the same thing as the wiring tricks mentioned above (both of which   threaten to burn out *my* head).
Hopefully this'll be the last time I hound for your guidance.
Thanks again.
tonyr

[Don T.]

Hi
 Yeah, that should work fine. Blaze on!
Don T.