Looking for 8 ohm equivalents for Fane Axiom 10" and speaker matching questions

Rich210

Hi Everyone, 

I've got a pair of 16ohm Fane axiom AX10's currently in my musicman 210 sixtyfive. These were speakers which were in when I bought it, all 18 years ago. Normally these amps come with a pair of 8ohm 10" running at 4ohms. The extension speaker is in series (which is a musicman quirk). I want to be able to run the my 210RH cab which is a 4ohm with the amp - it should be able to do this with a safe mismatch anyway, but I'd prefer not to have the mismatch. Also, I'd like to run both cabs into my (newly acquired, still quite excited about this) Blue Angel using a Palmer cabmerger dongle. 

I might be wrong, and I'd love someone to chime in with some better knowledge. But the way I understand it is I have a 4 ohm and an 8ohm  speaker in series then the 4ohm speaker will be getting more amp umph than the 8 ohm. It might not be an issue, but this is partly my reasoning for doing the swap. 

With that being said, all musicman cabs with two speakers were rated at 4ohm, and the single speaker options in cabs and combos were 8. So these amps were designed to run them both. So is there an issue with this?

Best

Richard

ICBM

It's the other way round for series - the 8-ohm cab will get twice the power of the 4-ohm. The total impedance is 12 ohms, which is safe with the amp set to either 8 or 16 ohms - although I would avoid running the Blue Angel at 16 into 12 in 6V6-only mode since it's already mismatched on the low side - it would be fine in Simul and safe enough in EL84.

I probably wouldn't change anything, in fact - combined with the Palmer, the two different impedances give you more options to control the sound balance than if they're the same.

In parallel, 4 and 8 ohms gives 2.66 ohms, which is safe with the amp set to 4 (though again, avoid the Blue Angel at 4 in 6V6-only) and 2/3 of the power going to the 8.

The Blue Angel ideally needs to run into double the marked impedance in 6V6-only mode (this is in the handbook), but is safe at the marked impedance. I'm pretty sure this was done deliberately because a low mismatch is a characteristic of the overdriven sound of a Fender Deluxe Reverb, which seems to have been made like that by accident... either way, it means you’re probably better keeping an 8-ohm cab.

Rich210

@ICBM ; That's fantastic. There are a lot of speaker outputs on the back of the Blue Angel - so if I was to run it through the EL84's would I run the speakers in parallel and have the 4ohm speaker on a 4 ohm tap and the 8 ohm speaker on the 8 ohm tap, or both speakers on the 4 ohm taps?

Just to clarify, when I'm on the 6v6's I'll be using the 4ohm tap into the 8ohm cab?

And the EL84 would be happy with using the 4ohm into the 8ohm as well as the 8ohm tap into the 8ohm cab?

ICBM

It's even more complicated than that when you're running two cabs together... if you connect *both* the 4-ohm cab to the 4-ohm output and the 8-ohm cab to the 8-ohm output, you also have a low mismatch. That would be a lot of stress on the 6V6s, although OK for the EL84s and possibly best in Simul.

Ideally you would connect the 8-ohm cab to the 4-ohm output and the 4-ohm cab to a 2-ohm output, but the amp doesn't have one, so I would connect both to the 4-ohm outputs, and just probably avoid cranking it too hard in 6V6-only mode. As a general rule of thumb if you can't match the combined impedance exactly it's best at one lower than the cabs for 6V6s, either direction for the EL84s, and one higher than the cab for Simul.

Rich210

Thank god you're around @ICBM. Just to add another query into the mix. Say for example I have the cabs wired up in series with a Palmer CABM, would I still be able to route them through an 8ohm attenuator? 

ICBM

Rich210 said:

Thank god you're around @ICBM. Just to add another query into the mix. Say for example I have the cabs wired up in series with a Palmer CABM, would I still be able to route them through an 8ohm attenuator? 

Yes. 12 ohms is easily close enough to 8 to make no practical difference. The amp sees the attenuator as the load, not the cabs, so still set the amp to 8.

Impedance matching isn't quite as critical as it's often made out to be - up to a 2:1 mismatch in either direction is almost always safe, and definitely if you're not overdriving the power stage. At lower volumes even further out than that is fine, if you're not pushing the power stage hard then even 4:1 is safe.

There are only two really big things to make sure you don't do: never run a valve amp with no load, and never run a solid-state amp below its minimum impedance.