Cab Ohm to amp Ohm question.

darrenw5094 wrote: »

Is it ok to connect a Blackstar 2x12 120w 16ohm cab to a Mesa Boogie 2:90 power amp?

The rear of the Mesa amp has 2 outputs for 8 ohms and 4 outputs for 4 ohms.
I am not sure what the input jacks are in the Blackstar 2x12. It has Celestion Vintage 30's. I don't know if the speakers are serial or paralell either. Blackstar website is not very helpfull with their info.

Can the amp get damaged if the ohm does not match? Although i read somewhere, that Mesa amps can take the mismatch.

If it's a 16 ohm 2 X 12 then it has to be two 8 ohms wired in series.
I don't think Celestion manufacture a 32 ohm V30. The V30s will have the ohmage printed on the sticker on the magnet if you open the back of the cab. I'll bet my JMP 50 they're 8 ohms though.

Mesa amps are quite comfortable with a 100% mis-match and in fact Mesa themselves often recommend trying it as the tone veries slightly and you may prefer it. Do not go beyond that though ie. 16 ohm cab into 4 ohm head input.

There's a lot of internet guff on impedance mis match and most of it is horse sh*te. Speaker impedance is measured @ 1kHz. A it's resonant frequency (usually around 70 Hz) the impedance jumps to 30 ohms and beyond 1 kHz is rises too. These rises are not uniform across speaker types. Point being decent output transformers are disigned with a large margin for "error" and can take 100% mismatch without breaking a sweat. The only side effect will be that the frequency resonce will be slightly skewed, which you may like.
Valves also take this into account and EL34s are rated for transient peaks of 2kVolts!!
Lesser, cheap sh*t OTs aren't so well design and can fail, Marshall DSLs and TSL have pretty bad OTs for example and fail even @ 100% mis match, but Mesa use the good stuff so you'll be fine.

This advise is not free, clips are required!!

darrenw5094 wrote: »

Thanks for that. I haven't got the Blackstar cab yet, so i can't check the ohm on the back of the 2 speakers. Yeh, i think the Mesa will be ok.

You have just bet your JMP 50 that the Blackstar cab has 8 Ohm speakers.

Info from guitarcenter.com

Blackstar Artisan A212 120W 2x12 Guitar Extension Cabinet Specifications:

* Switchable: Mono / stereo
* Power Rating (RMS): 120 Watts
* Impedance: Stereo – 2 x 16 Ohms. Mono – 8 Ohms. Selectable by input jack.
* Speakers: 2 x Celestion Vintage 30s
* Weight (lbs.): 48.28
* Dimensions (inches): 28.15 x 22.39 x 10.35

Dude that cab 8 ohms, not 16 ohms.
It has two 16 ohm speakers wired in parallel, for a total of 8 ohms.
The JMP is safe for now!!