Does ohm Setting on Amp Affect Sound?

[Mikoo69]

I am interested in acquiring a Marshall JMP 50watt non master volume head from the 70s.

 

I own a 2x12 cabinet that is loaded with 2 8ohm speakers wired to a 4ohm load.

 

I know the JMPs have ohm selector switches between 4, 8 and 16 ohm. Is it preferable to run the head with any particular ohm setting? i could rewire the cab for 16 ohms if that would be a better sound. does ohm choice affect sound?

[sled]

the two speakers in Parallel (4 ohm) versus Series (16 ohm) will have a bigger impact than the amp's ohm setting difference

 

parallel wiring is more of an impedance averaging whereas series is basically additive.

 

try both. the only correct answer is what sounds best to you.

 

I often rewire my cabs. right now I have two 2x12 cabs parallel and one series.

[AndrewGG]

I would be wary about using anything other than matched settings. At best an impedance mis-match will shorten the life of your power tubes. If you, for example, have an 8ohm head you can safely plug it into a 4ohm cab but you'll lose power. Don't try the same thing with a 16ohm cab; the chances are your amp will blow as it tries to produce more power.

[sled]

I don't think the OP is talking about a mismatch.

[Mikoo69]

correct. my main question is that if i have the option to do 16ohm or 4ohm with my speaker wiring, and the head can handle both with an impedence selector switch, which would be the preferable ohm choice?

[teemuk]

There is no correct answer to that.

 

Try both. If you hear any difference, use the one you prefer.

[gh0st]

There shouldn't be a sound difference unless there is an output difference in terms of wattage relative to the load. If your amp puts out 100wrms at 8/16 ohms, I don't see why there would be a difference in sound. Running more than one speaker though is going to share the output though. If you have two speakers, each speaker isn't getting 100wrms.

 

I could be wrong though, just speaking off my car audio experience. It seems like guitar amps are designed to deliver the same power at different ohms which is different from how car audio amplifiers function(sans the JL models).

[xgamer791]

I thought less ohms men't more power?

[teemuk]

 

I thought less ohms men't more power?

 

 

Not when a transformer is used to match impedance.

 

Power (P) = U x I, voltage times current.

 

A 16 ohm tap in an impedance matching transformer feeds correspondingly more voltage across the load than the transformer's tap used for lower impedance settings. Hence the power fed to the load remains equal.

[Krallum]

^ though its theoretically possible that depending on your wiring [mainly in 4x12s] that you could be dispersing the power in some uneven fashion if the speakers have different impedance but the overall impedance is legit for the transformer.

 

 

or in general if the speakers have different power ratings then the way you wire them could affect how loud each speaker is effectively, but from a sonic standpoint the sound is the 'same'

[rlord1974]

It was my understanding that amps with ohm selectors operate as follows (for the example, let's use an amp with a selector switch for 4 ohm, 8 ohm or 16 ohm loads):

 

If set to 4 ohms, you are only using 1/4 of the output transformer

If set to 8 ohms, you are only using 1/2 of the output transformer

If set to 16 ohms, you are using the entire output transformer

 

Out of the above three options, use of the entire output transformer is usually recommended (why only use 1/4 of it?!). That is to say, you should typically try to use the highest ohm rating you can, based on whatever cabinet you are running it through.

 

Please feel free to correct me if I am wrong.....

[grayeyes777]

 

I would be wary about using anything other than matched settings. At best an impedance mis-match will shorten the life of your power tubes. If you, for example, have an 8ohm head you can safely plug it into a 4ohm cab but you'll lose power. Don't try the same thing with a 16ohm cab; the chances are your amp will blow as it tries to produce more power.

 

 

i thought it was the other way around...

 

you can plug an 8 ohm send (from head) into a 16 ohm load but not the other way around.