I’ve got an Ampeg V4-B and matching 212AV cab. The 212AV is 4ohms. Looking at a used Ampeg 115 SVT EV cab that’s 8ohms. Can I run both of these cabs at the same time with my V4-B? It does have individual jacks for those ohms plus it does have 2ohm jacks so I know it can go that low.
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8ohm and 4ohm cab with Ampeg V4-B
- Thread starter Mo Boogs
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- 115 svt ev ampeg ampeg 212av v4-b
It is in the owners manual:
"ALWAYS match the amplifier’s speaker output impedance to the impedance of the
speaker that is being used. Use only one type impedance output at a time. If
more than one speaker is connected at the same time, make sure they all have
the same impedance rating. Never use two or more cabinets with different im-
pedance ratings. This will create an unbalanced load. When using multiple speaker
cabinets (with the same impedance rating), match the total load impedance of the
speaker cabinets to the Speaker Output of the amplifier."
I am far from an expert on the subject (one might chime in), but in general I have noticed...
- Tube amps, you want the impedance to match what the output section is. That is why you have separate output jacks for a given load or a switch for a given load.
- Solid state is where you would have flexibility to do mismatched as long as the total impedance of the mismatch is greater than or equal to the amplifier rating. Noting sometimes you see a switch here to enable 2 ohm operation, but it is a different setup than how tube works (believe it typically just runs the cooling fan more often).
Since I am not super knowledgable on it, I cannot tell you why. I just know I have seen it to be true on the amplifiers I have used.
"ALWAYS match the amplifier’s speaker output impedance to the impedance of the
speaker that is being used. Use only one type impedance output at a time. If
more than one speaker is connected at the same time, make sure they all have
the same impedance rating. Never use two or more cabinets with different im-
pedance ratings. This will create an unbalanced load. When using multiple speaker
cabinets (with the same impedance rating), match the total load impedance of the
speaker cabinets to the Speaker Output of the amplifier."
I am far from an expert on the subject (one might chime in), but in general I have noticed...
- Tube amps, you want the impedance to match what the output section is. That is why you have separate output jacks for a given load or a switch for a given load.
- Solid state is where you would have flexibility to do mismatched as long as the total impedance of the mismatch is greater than or equal to the amplifier rating. Noting sometimes you see a switch here to enable 2 ohm operation, but it is a different setup than how tube works (believe it typically just runs the cooling fan more often).
Since I am not super knowledgable on it, I cannot tell you why. I just know I have seen it to be true on the amplifiers I have used.
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Must be a smart Amp to know that 4 X 8 Ohm or 2 X 4 Ohm is OK to run at 2 Ohms, but 2 X 8 + 4 is not?...
I could see why 4 + 8 (or 3 X 8) is not good, as there is no 2.67 setting, but that first example has me scratching my head.
Same thought when I read it. I can see why they would write it that way in their manual though. Plenty of uninformed "can my amp run" questions on this forum. Not knocking those questions as it is better to ask than break stuff, but their existence would make me write the manual the same way Ampeg chose to. Overcomplicating the explanation in the manual is going to create more issues than it fixes.
If it was me, I wouldn't do it. Tube amps prefer matched loads. If I wanted more oomph from a V4-B/212AV rig, I would get a second matching 212AV cab which, combined with your existing 212AV cab, would give you a +3dB increase in volume.
That arrangement would also ensure that each of the four speakers receives the exact same amount of wattage from the amp. And if, by chance, you are thinking that a larger speaker diameter (15") means more lows, please don't think that. The only thing speaker diameter tells you is how big around the speaker is. There are bass cabs with 10" speakers that go WAY lower in frequency response than 12's or 15's or 18's (such as Acme cabs for example). It's all in how the speakers and cabs are designed.
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The individual jacks are intended to be used one at a time.
- If you have one 8 ohm cab use the 8 ohm jack
- If you have one 4 ohm cab, use the 4 ohm jack.
- If you have two 8 ohm cabs, connected them in parallel to the 4 ohm jack.
At the very least an impedance mismatch will reduce how much power the amp can make and increase wear and tear on the tubes and components. At worst the amp could be damaged.
Many tube amps can tolerate a minor impedance mismatch. Some amps are okay with a 2:1 or 1:2 mismatch. Some are safer if the impedance is higher than expected, some are safer if the impedance is lower than expected. Some amps should not be used with an impedance mismatch.
I recommend showing the amp the expected load. I believe the V4B is relatively safe at 2.67 ohms, but I don't know if you should use the 4 ohm tap or the 2 ohm tap. Choosing to run an mismatch means you accept increased risk to the amp...I.E. if the amp blows up it's on you. My advice is determine which tap to use, and only do so if you have an emergency.
@beans-on-toast explains here and recommends using the 4 ohm tap: 2013 Ampeg V-4B 100W Reissue Pt2
Then he recommends the 2 ohm tap here: Ampeg V4B 212AV+210AV (2.67ohms)
Perhaps beans will comment regarding the change in advice.
It's important to keep in mind that the rated impedance of a speaker is (supposed to be) the lowest impedance it will have at any frequency in its specified operating range. Two different types of speaker will have impedance that varies with frequency differently - their lowest impedances might not be at the same frequency so the lowest combined impedance might not be what a simple calculation based on their rated impedances might suggest.
Combining speakers of different types is like opening the spice cabinet, selecting a few things at random and throwing them in the soup pot. You might like the flavor, you might not.
Combining speakers of different types is like opening the spice cabinet, selecting a few things at random and throwing them in the soup pot. You might like the flavor, you might not.
Sorry, but this is not correct.
The rated impedance is a nominal value...sort of an average over the expected operating range.
Here's an example JBL 2206
Nominal Impedance 8 ohms
Minimum Impedance 6.9 ohms
DC resistance 5.3 ohms
Plot of 2206 frequency response and impedance:
Impedance on this curve is measured in free air. AFAIK the way the cab is tuned will impact the impedance curve.
Per IEC standards, min Z should not fall below 80% of nominal Z. However, not all speakers comply.
Either can be used. Try both and see which sounds best. In general, I sonically prefer using the 4 ohm tap with a 2.67 cab combination. The amp will run hotter. An 8 ohm cab on a 4 ohm tap will result in some power loss. An impedance mismatch may benefit from a power tube bias optimization.
Never mix the taps on the amp. Do not connect the 8 ohm cab to the 8 ohm tap and the 4 ohm tap to the 4 ohm cab at the same time.
Edit: oops, I didn't read your post all the way to the bottom - you clearly cite the IEC standard. My bad!
Anyway, I think my main point still applies: the minimum impedances of two different speaker systems may not be at the same frequency, and may not combine in a way that matches a simple computation based on their nominal impedances. By "speaker system" I mean the driver in a cabinet, which will have an impedance curve that differs from that of the raw drivers, sometimes quite significantly.
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This is the real world answer. The output transformer on most tube amps can tolerate a 2:1 mismatch either way. Ampeg says not to do it to cover their butts legally, but the many rental SVT’s I’ve been supplied with an 8 ohm cab despite SVTs taking 4 and 2 ohms officially tell me it’s no problem to plug them into the 4 ohm tap.
And +1 about not mixing taps. That’s a very bad idea.
I once connected a 4ohm and 8ohm cab to an amp that could handle down to 2 ohms. Company lawyers and internet told me not to and it exploded, stole my tractor, and took my dog too. It was a sad day.
