4ohm vs. 8ohm speaker jacks

[Bill Assumpcao]

Howdy folks,
The more that I read this excerpt from my Mark II manual, the more confused I get :?

Three speaker jacks are provided: one 8 ohm and two 4 ohm. With 60 watts models, plug the single 8 ohm speaker into the 8 ohm jack for the
most power and clarity. If two 8 ohm, speakers are used, plug each one into a 4 ohm jack for proper balance. But you may also try other combinations if you want one speaker slightly louder or happen to prefer the tone caused by a slight mismatch; it will do no harm to the amplifier. With 100/60 watt models we recommend that when you run a single 8 ohm speaker you use the 60 watt position and plug into a 4 ohm jack. This will give the strongest possible output without damaging the speaker. You may get more clean power by switching to 100 watts, and still more by also plugging into the 8 ohm jack but remember to avoid lead tone distortion as it increases power dramatically (though not so much the apparent loudness) and may cause speaker damage. With two 8 ohm speakers, one in each 4 ohm jack, the 100 RMS can be safely used.

Question 1: If I had a 60watt model, I'm supposed to plug my 8ohm speaker into the 8ohm jack. But, because I've got a 60/100 model I'm supposed to plug into the 4ohm jack when using 60 watts? Why?
Question 2:

You may get more clean power by switching to 100 watts, and still more by also plugging into the 8 ohm jack...

If I remember correctly (or am I having an old-timers moment?) 8ohms is more resistance than 4ohms. Therefore, the amp should have to work harder, hence clip sooner, and not give me a cleaner signal.
Would anybody care to set me straight on this? I can't seem to wrap my brain around this :roll:
Dee, Dee, Deeeee,
BillA

 

[Russ]

It appears that what they are trying to explain is a situation where there is less load on the amp itself by mismatching the output and therefore creating more output (wattage or perceived power) for a less wattage setting but still not damaging the speaker? Maybe through their testing they found an oddity in how their transformers handle power that actually sounds better to them and are just relaying the information so that you are privy to it and are not scared to configure your setup in that way. I would give it a shot just to see what the hell that they are talking about. In the case of running in 100 watt mode in a correct output matched setup it would be more than likely that you would have more headroom. That is common sense. It would be to Mesa's advantage to have more headroom that way so that their amp sounds better longer as your turn up the volume provided that you are not searching for as much power tube distortion. If you are searching for more power tube distortion then just swap to a different color code that will allow for earlier breakup or have one of your tube vendors assemble a custom set of tubes that will suit your needs.

Yes, 8 ohms is more resistance than 4. The amp will work harder, true. But, the speaker is 8 ohms. They comparing the 60 watt mismatch to the 100 watt mismatch and finally a correct matching of output. Obviously 100 watts will give you more headroom. Then, a correct output matching of output jack to speaker will give you your final step towards headroom. The circuit design may have something to do with it too and how it actually steps the wattage down. Think of this scenario. When you use a 100 watt tube amp you can pull out a pair of tubes but you have to reduce your ohm setting by 1/2. So if you are plugging in a 16 ohm cabinet then you would plug it into an 8 ohm output if you had two tubes pulled. The same goes for an 8 ohm speaker load to the 4 ohm output jack if you are running with 2 tubes removed. There really isn't much wrong with running an amp with a mismatched output with all your tubes in provided you do not push the amp too hard and that you watch the heat of your transformer, tubes, and speakers. If the circuit steps its power down by cutting two of the tubes out of the circuit then it would make sense that you would want to use the reduced load setting. It is all relative. As far as the mention of power increasing dramatically (though not so much the apparent loudness) and may cause speaker damage, I can only assume that they are considering the use of something like a C90 whereas the EVM would take it smiling. A 100 watt tube amp can produce upwards of 200-300 watts if pushed even though rated at 100 watts RMS. This is why some combos destroy speakers. If you do not prepare the combo for punishment by ensuring that its speakers can handle the abuse then it is not a good idea to push it. Also, it is easy to double an amps power by reducing its load but your transformer must be able to handle it or your amp and yourself could catch fire in a worst case scenario.

I hope that this helped. I feel as though I have gone a little bit astray here. But at least, I did address the post and shed some light.

Amps love a heavier load. They do not blow up from having too much load. They do have problems when there is not enough load presented to them. You will remain cleaner with a higher load on your speakers than a lesser load. Clipping is caused by too much power for the load or speaker handling capability (in the case of speaker distortion) or from trying to get too much power out of your amp (going beyond your clean headroom- too much volume or gain). Cleaner signal (clearer sound) is accomplished by your amp staying under its headroom ceiling and having speakers power handling capabilities above and beyond what your amp is capable of producing. There is also clipping that occurs from not enough power going to your speakers. Thus it is important to ensure that your speakers can handle that too. Most guitar speakers can handle that though. You will find this problem mostly with subwoofers than any other speaker.

A bit of advice, stop reading into the manual. Get some ideas on shaping your tone from it and basic operating instructions and just play.... It is less confusing that way.

 

[Bill Assumpcao]

How do Russ,
Thanks for the response.
Wow! I'll have to read that a coupla' more times to try and grasp everything.

A bit of advice, stop reading into the manual. Get some ideas on shaping your tone from it and basic operating instructions and just play.... It is less confusing that way.

But...but...but...okay. Yer right. Good advice
Thanks again,
BillA