Pairing Ampeg V4-B (70s model) w/ both 8 ohm and 16 ohm cabinets

[gtabassist]

Hello all,

I have a 70s Ampeg V4-B that I've been running with an 8 ohm Ampeg 410HE cab. My longer-term plan was to run 6x10 speakers when needed, but didn't want to deal with a 610 (the gear lives a floor up at my place, plus just like the modular setup idea of a 410 + 210 based on gig, etc).

That said, I understand that running two matched-impedance cabs means each gets half of the amps power, which isn't ideal when running two cabs of different speaker counts.

My plan was to take an Ampeg MC210E cab I have and replace the speakers with two 8 ohm speakers wired in series, for a 16 ohm load. If I'm understanding things correctly, this will result in a 5.33 ohm load (would run the amp on it's 4 ohm switch), and roughly 2/3 of the power will go to the 410, and 1/3 to the 210, which is ideal (each speaker getting basically the same power).

However, I've noticed Ampeg seems to universally advise to "never use two or more cabinets with different impedance ratings. This will create an unbalanced load." My gut is this is to stop people mixing cabs who aren't doing the math (eg, incorrectly assuming an 8 ohm and 16 ohm cab comes out to 12 ohms total and running them out of the 8 ohm output, etc). That said, I don't want to willingly damage my amp either - I also understand the trade-offs of using speakers in a cabinet (MC210E) that aren't designed for it, etc etc, but my main risk concern in this experiment is that of the effects on the amp, not sound (yet).

Anyone have experience running something similar through a V4-B, or other tube amp, and can speak to the results they found?

TIA!

 

[Wasnex]

It really comes down to two things.
1. How tolerant is the amp to an impedance mismatch. Some amps are tolerant and some are not. AFAIK the degree of mismatch is relative. Many amps tolerate a mismatch of one order high or one order low, I.E. 2:1 or 1:2. If an amp is good with a 2:1 mismatch (16 ohms on 8 ohm output), AFAIK it should be fine with a 3:2 mismatch (12 ohms on 8 ohm output).

2. Is the amp more tolerant when the impedance is higher than expected or lower than expected. In other words, is it preferred to run a 12 ohm loud on the 8 ohm output or the 16 ohm output. One may be fine, and the other may be risky. Or the amp may be fine either way.

Note: 8 and 16 ohms in parallel is 5.33 ohms. So the question would be: Is this combination safer on the 4 or 8 ohm output.

I do not know if a vintage V4B is safe with a mismatch or whether it has a preference for high or low. AFAIK, Ampeg's official position is run the expected load.

 

[6thplanet]

It's posted all the time on TB, you can't just put random speakers in an enclosure and expect it to be fine.

In your case, yeah, you can end up with an impedance that satisfies your goal, but now the cab will probably not perform at it's full potential.

 

[gtabassist]

It really comes down to two things.
1. How tolerant is the amp to an impedance mismatch. Some amps are tolerant and some are not. AFAIK the degree of mismatch is relative. Many amps tolerate a mismatch of one order high or one order low, I.E. 2:1 or 1:2. If an amp is good with a 2:1 mismatch (16 ohms on 8 ohm output), AFAIK it should be fine with a 3:2 mismatch (12 ohms on 8 ohm output).

2. Is the amp more tolerant when the impedance is higher than expected or lower than expected. In other words, is it preferred to run a 12 ohm loud on the 8 ohm output or the 16 ohm output. One may be fine, and the other may be risky. Or the amp may be fine either way.

Note: 8 and 16 ohms in parallel is 5.33 ohms. So the question would be: Is this combination safer on the 4 or 8 ohm output.

I do not know if a vintage V4B is safe with a mismatch or whether it has a preference for high or low. AFAIK, Ampeg's official position is run the expected load.

Thanks for this! I had read about that mismatch threshold as well, from everything I'm reading - it's just kind of an unsure and very likely amp-specific, like you said.

I did end up setting it up tonight, sounds good to my ears but will continue researching this before I play it out anywhere. Thanks again!

 

[gtabassist]

It's posted all the time on TB, you can't just put random speakers in an enclosure and expect it to be fine.

In your case, yeah, you can end up with an impedance that satisfies your goal, but now the cab will probably not perform at it's full potential.

Thanks for your reply - you're right, speakers are chosen for the enclosure / they are designed together, so I don't expect my modified 210 to perform as well as it good (I used Eminence Alpha 10s which are for a sealed enclosure, like mine, so at least a bit of an alignment, ha).

It's a pretty cheap cab to begin with, one of Ampeg's cheapest I think. Sounds pretty good at home - levels seem even across both cabs as per plan. I might have to live with the sound quality trade-off if I want this kind of set-up, but will see how it holds up to louder volumes / after I do some more research on the longer-term effects on the transformer. Thanks!