Mark Five head and 4X12 cab switchable 16 ohm or 4 ohm

[Elliot Twist]

I have a Mark Five head and a 4X12 cab (v30's)
I would like to know what you think is the best way to plug this cab into the head.
I currently have been running the cab with the switch to 16 ohm into the 8ohm (combo) socket on the amp head.
I'm going to try changing the switch on the cab to 4 ohms and running it into a 4 ohm socket on the amp head.
What would you do ?
Thanks in advance for telling me to go with what sounds best to me. If that was the case I wouldn't have asked your opinion.

 

[mace]

Well, since what sounds best doesn’t seem to matter, I’d match 4 ohm to 4 ohm. Ohm sweet ohm.

 

[DECEMBER]

Always match impedance with tube amps, unless the manual for a specific amp explicitly states that a certain mismatch is safe for that amp. Solid state amps are fine with a 16 ohm cab in an 8 ohm output, it will just be limited to 50% power. But tube amps work differently. Putting 16 ohms in an 8 ohm outlet makes a bottleneck, where does all the extra power go?
If you're using it at lowish volume, you'll probably get away with any mismatch for quite a while, but it will be slowly damaging something. Not worth the risk on amps that cost as much as our Marks.
Use the 4 ohm output, or get another 16 ohm cab/speaker (or load box) and put that and the 16 ohm cab in the two 8 ohm outputs.

 

[Elliot Twist]

Always match impedance with tube amps, unless the manual for a specific amp explicitly states that a certain mismatch is safe for that amp. Solid state amps are fine with a 16 ohm cab in an 8 ohm output, it will just be limited to 50% power. But tube amps work differently. Putting 16 ohms in an 8 ohm outlet makes a bottleneck, where does all the extra power go?
If you're using it at lowish volume, you'll probably get away with any mismatch for quite a while, but it will be slowly damaging something. Not worth the risk on amps that cost as much as our Marks.
Use the 4 ohm output, or get another 16 ohm cab/speaker (or load box) and put that and the 16 ohm cab in the two 8 ohm outputs.

Thank you ! I'll start using the 4 ohm output and switch the cab to 4 ohms right away.

 

[mace]

Running a 16 ohm cab on the 8 ohm tap, or running an 8 ohm cab on the 4 ohm tap will not harm the amp. Mesa lists these scenarios as ‘safe mismatches’. In fact, in the Mark VII manual they encourage using a 8 ohm cab or speaker with the 4 ohm tap for a variation in the tone.

 

[DECEMBER]

Running a 16 ohm cab on the 8 ohm tap, or running an 8 ohm cab on the 4 ohm tap will not harm the amp. Mesa lists these scenarios as ‘safe mismatches’. In fact, in the Mark VII manual they encourage using a 8 ohm cab or speaker with the 4 ohm tap for a variation in the tone.

But, like I said: only if the manufacturer specifically states it's a safe mismatch in the manual for a specific amp. So always check the manuals.
I've seen a Marshall that said an 8 ohm & 16 ohm is safe if plugged into specific jacks (the 8 in the 4 ohm tap & the 16 in the 8 ohm tap, or something...)

 

[esowden]

16 ohm tap will do a 16 ohm or 8 ohm cab,
8 ohm tap will do a 16 ohm or 4 ohm cab,
4 ohm tap will do an 8 ohm or 4 ohm cab.

I've been following that rule since the 80's and have never had an issue.

 

[DECEMBER]

16 ohm tap will do a 16 ohm or 8 ohm cab,
8 ohm tap will do a 16 ohm or 4 ohm cab,
4 ohm tap will do an 8 ohm or 4 ohm cab.

I've been following that rule since the 80's and have never had an issue.

Never put a 4 ohm cab in an 8 ohm tap. It's never ok to put a cab with lower impedance than the tap.

 

[Eevil]

Never put a 4 ohm cab in an 8 ohm tap. It's never ok to put a cab with lower impedance than the tap.

In Mk V manual it is considered as a safe mismatch

 

[DECEMBER]

View attachment 4493

In Mk V manual it is considered as a safe mismatch

That shows a 8 ohm cab in a 4 ohm tap, not a 4 ohm cab in a 8 ohm tap.
When cab impedance is lower than the tap impedance, that's the most likely way to blow the output transformer.
I have the Mark V 90W and the manual and I just checked it again. It has extensive diagrams for all kinds of cab combinations.
None of the safe mismatches allow a cab of lower impedance than the tap.
It does allow:
8 ohm tap -> 16 ohm cab
4 ohm tap -> 8 ohm cab
And both at the same time.
But:
16 ohm tap -> 8 ohm cab
8 ohm tap -> 4 ohm cab
are NOT safe mismatches.

 

[Eevil]

That shows a 8 ohm cab in a 4 ohm tap, not a 4 ohm cab in a 8 ohm tap.
When cab impedance is lower than the tap impedance, that's the most likely way to blow the output transformer.
I have the Mark V 90W and the manual and I just checked it again. It has extensive diagrams for all kinds of cab combinations.
None of the safe mismatches allow a cab of lower impedance than the tap.
It does allow:
8 ohm tap -> 16 ohm cab
4 ohm tap -> 8 ohm cab
And both at the same time.
But:
16 ohm tap -> 8 ohm cab
8 ohm tap -> 4 ohm cab
are NOT safe mismatches.

Yep you’re right

Shouldn’t open the phone before noon

 

[Elliot Twist]

Never put a 4 ohm cab in an 8 ohm tap. It's never ok to put a cab with lower impedance than the tap.

Yes, you're right LoL ! I was using the 16 OHM cab on the 8 OHM output for a while.
I think I'll just switch the cab to 4 OHMs and use the 4 OHM output.
I was just looking for opinions.

 

[DECEMBER]

Yep you’re right

Shouldn’t open the phone before noon

No problem. Just tryna make sure no one blows up their nice amps.

 

[DECEMBER]

Yes, you're right LoL ! I was using the 16 OHM cab on the 8 OHM output for a while.
I think I'll just switch the cab to 4 OHMs and use the 4 OHM output.
I was just looking for opinions.

The Mk V manual does say 8 ohm tap -> 16 ohm cab is a safe mismatch. But you probably get reduced output power that way. Running 4 ohm -> 4 ohm would let the full power flow.
I've been experimenting with several reactive load boxes lately, and one is switchable 4/8/16 ohms. In direct recordings, there is some difference between using it on 4 vs 8 ohms with the Mk V. So there can be subtle differences in the sound of the same cab at different impedances.

 

[esowden]

Never put a 4 ohm cab in an 8 ohm tap. It's never ok to put a cab with lower impedance than the tap.

I think you're confusing tube with solid state amps. Never safe to connect a ss amp to a 4 ohm load if the amp isn't 4 ohm stable. General consensus (since the '70s for me) is the basis of my post. I've done it many times with many different brands over the years - I've yet to lose a transformer.

 

[DECEMBER]

I think you're confusing tube with solid state amps. Never safe to connect a ss amp to a 4 ohm load if the amp isn't 4 ohm stable. General consensus (since the '70s for me) is the basis of my post. I've done it many times with many different brands over the years - I've yet to lose a transformer.

No confusion here... The cab load should NEVER be a lower impedance than the output tap impedance.
i.e. 8 ohm cab -> 16 ohm tap
4 ohm cab -> 8 ohm tap
should never be connected on any kind of amp. It will pull more power than the tap is meant to provide and burn out the OT. If you're not using high volume, you can probably get away with this kind of mismatch for quite a while, but it will probably be slowly damaging it.
I just read thru the whole Mark V manual again. It has extensive speaker wiring diagrams, showing all kinds of ways to connect combinations of up to 3 cabs. A cab with LOWER impedance than the amp output tap is never a 'safe mismatch'.
The only 'safe mismatches' are:
16 ohm cab -> 8 ohm tap or
8 ohm cab -> 4 ohm tap
or both simultaneously.

You can download all the manuals here:
https://legacy.mesaboogie.com/support/user-manuals.html

 

[esowden]

No confusion here... The cab load should NEVER be a lower impedance than the output tap impedance.
i.e. 8 ohm cab -> 16 ohm tap
4 ohm cab -> 8 ohm tap
should never be connected on any kind of amp. It will pull more power than the tap is meant to provide and burn out the OT. If you're not using high volume, you can probably get away with this kind of mismatch for quite a while, but it will probably be slowly damaging it.
I just read thru the whole Mark V manual again. It has extensive speaker wiring diagrams, showing all kinds of ways to connect combinations of up to 3 cabs. A cab with LOWER impedance than the amp output tap is never a 'safe mismatch'.
The only 'safe mismatches' are:
16 ohm cab -> 8 ohm tap or
8 ohm cab -> 4 ohm tap
or both simultaneously.

You can download all the manuals here:
https://legacy.mesaboogie.com/support/user-manuals.html

I understand you're going by what a single manufacturer prints in their manual about their product.

I'm speaking from experience as a former touring tech and an electronics engineer. What has your experience been?

Did you know most tube amps short their signal to ground (0 ohms) as a precautionary measure should one forget to plug their amp into a load? I wouldn't recommend playing the amp unloaded but the short offers a lot less risk of damage than an open circuit.

 

[DECEMBER]

I understand you're going by what a single manufacturer prints in their manual about their product.

I'm speaking from experience as a former touring tech and an electronics engineer. What has your experience been?

Did you know most tube amps short their signal to ground (0 ohms) as a precautionary measure should one forget to plug their amp into a load? I wouldn't recommend playing the amp unloaded but the short offers a lot less risk of damage than an open circuit.

I'm going by what every manufacturer has stated in every manual I've ever seen. I've had 8 tube amps from 5 manufacturers, and I've read thru several other manuals. I've seen this discussion countless times on every forum. No one has ever told the users that a 4 ohm cab -> 8 ohm tap is a 'safe mismatch'. Cab with lower impedance than the amp output is always the hard no, not a safe mismatch.
You are the first person I've ever seen insist that this is safe. There's always someone asking "can I put my 8 ohm cab into my 16 ohm amp?" and the answer is always a resounding "NO!"
The ONLY "safe mismatches" I've seen listed in any manual are: cab impedance higher than amp tap impedance.

 

[esowden]

I'm going by what every manufacturer has stated in every manual I've ever seen. I've had 8 tube amps from 5 manufacturers, and I've read thru several other manuals. I've seen this discussion countless times on every forum. No one has ever told the users that a 4 ohm cab -> 8 ohm tap is a 'safe mismatch'. Cab with lower impedance than the amp output is always the hard no, not a safe mismatch.
You are the first person I've ever seen insist that this is safe. There's always someone asking "can I put my 8 ohm cab into my 16 ohm amp?" and the answer is always a resounding "NO!"
The ONLY "safe mismatches" I've seen listed in any manual are: cab impedance higher than amp tap impedance.

Again, my experience is different. You keep mentioning what you've read, not what you've experienced. What I've read by most manufacturers is any mismatched combination is not recommended. What I've experienced is most modern tube amps are designed to handle that stress.

Some additional info: Click here, and here.

Not saying the output transformer and/or tubes aren't stressed. Lower impedance results in a higher current draw, higher impedance results in higher flyback voltages. Both situations are capable of causing component failure. Ultimately, it's your decision whether or not the risk is worth it.

 

[bandit2013]

I would probably just run the cab switched to 4 ohm and use the 4 ohm tap on the amp. At least that is a proper impedance match.

Review the manual if you are uncertain. It can be found online from Mesa as well. At least it will be up to date if any changes were made.
Customer service pages also detail how to connect cabinets of different impedances, much the same as in the Mark V manual (the one I have downloaded some time ago) covers that on pages 53 thru 58, much of what others have referenced or stated.