caallday

I just bought a 1959HW Plexi and a 1960AHW cab. Ive read so many vehemently contradictory statements online on ohm matching and am trying to get to the bottom of it with my limited knowledge of electronics.

My question is: As long as you mismatch up you are easing the load on the head, right?

i.e.
head: 4ohm into cab:16ohm
head: 8ohm into cab:16ohm
head: 16ohm into cab:16ohm
head: 4ohm into cab:16ohm, cab:16ohm
head: 8ohm into cab:16ohm, cab:16ohm

I know when you plug a signal into outboard gear (preamp, compressor, etc...) the consensus with most engineers is to flip the outboard ohms (input stage) as high as they will go. same concept?

sorry if im way off but there seems to be so much speculation on something which obviously has 1 correct scientific answer.

Marshall Amps

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indeedido

I can't answer that, but why don't you just match the cab to that head 16ohm isn't it?

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indeedido

And post some pix or it's a Crate

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Marshall Mann

Hey Callday,

Your right, there is lot's of ramble about this.

What I can tell you in basic terms without adding confusion - Marshall recommends that you always run a matched load on your amp.

In a one cab scenario, the impedance (measured in ohms) is one to one.

Example -16 ohm cab, set your head to 16 ohms as well.

In a two cab scenario - on a parallel tap (like your Marshall) you divide the load to find the total.

Example - Two 16 ohm cabs equals an 8 ohm total load on your amp. Set the amp to 8 ohms. Two 8 ohm cabs would equal a 4 ohm total load.

Solid state gear (especially things such as pre-amps and mics that you mentioned) are a totally different animal.


I hope this helps.

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Adwex

Forget about "easing the load". Tube power amps need to have their impedance matched between the output transformer and the speakers. Set the amp to match the cab, it's that simple.

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caallday

i really want asking about my rig (the cab only runs at 16). just trying to better understand whats going on here electrically. nobody knows if you can safely mismatch and what happens if you do?

Marshall Mann

Mismatching impedance is not recommended on a Marshall.

Sorry caalday, I hope I dont sound short here, but this is electronics 101. If want to understand Ohms law, it would be best to get a basic electronics book or read up on line. To over simplify, if you think of electricity as water flowing through a garden hose, think of impedance (measured in ohms) as the walls of the hose and anything else that pushes back on the flow of water (aka resistance).

From what I understand of your initial post, there would be no benefit for you to mismatch your impedance. And as stated, it's never a good idea with a Marshall. So set it and forget it.

Is there a reason you want to run a mismatched load?

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bulldozer1984

The designer of the JVM series has said you can mis match by one step either way and will be safe. That's just talking about JVM though

Mesa Boogie say the same thing with there amps. But apart from the JVM I don't know of any other Marshall where this is safe.

Bottom line. Every manufacturer is different. So just always match your impedence. It says that in the Amplifiers Manual so so in case of warranty you would be stupid not to.

Australian

Yes In the user handbook ,Smith of Mesa Boogie says its ok for that one step mismatch also. For example : 8 ohms amp into a 16 ohms speaker cab.

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Ghostman

I think the confusion comes in when a Solid State enters the picture. Solid State amps, as stated above, are completely different animals.

When using a Solid State, you need a load that is either equal to or above the rated ohms of the amp. For example, if the Solid State amp is rated at 4ohms, then you need a cab, or load, with an impedance of 4 ohms or higher, e.g. 8 or 16ohms.

When the impedance of the load is increased however, the power output of the Solid State amplifier is reduced. Generally the power reduction is for every doubling of the load impedance, the power output is reduced by half. 4ohm output at 100watts, would be approximately 50watts at 8ohms,and 25watts at 16ohms, etc. This is a general rule of thumb with Solid States.

With a tube amp, the electronic circuitry works a lot differently so the impedances have to match up. 4ohm tube amp output = 4ohm speaker load. etc.

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DragonSarc

and just would like to add make sure that the amp is always lower than the cab if 1 step mismatching ie 8ohm amp to a 16ohm cab not the other way around

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Ken

For a SS amp this is instant death.

On a tube amp this may seem to make sense on the surface, as a shorted output will not kill a OT right away so too low on the load might seem to be harmless, but in reality this is not the case. Unless your OT is spec'ed above its normal operating parameters (as the JVM and Mesa amps seem to be), you should never mismatch in ANY DIRECTION.

Marshall amps, especially older models, are a bit like vintage Ferraris: they work well within their designs but have a low tolerance when you nexceed them.

Ken

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Adwex

I think you have it backwards.

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Quasar-Kid

What is this "Solid State" you speak of..?
My people know nothing of this thing

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GIBSON67

Marshalls are not like othe amps! They sound better for one, hee hee, and they don't like mismatches!

RussBert

Yes, you are way off.


Set your head to MATCH your speaker cab. Simple as it gets!