noob cab ohmage questions

[alagow]

I'm not planning on trying out all of these. I'm just trying to get a better understanding of how heads work with cabs.

What happens if you...

1. plug a 4 ohm cab into an 8 ohm insert?

2. plug an 8 ohm cab into a 4 ohm insert?

3. plug a 4 ohm cab and an 8 ohm cab into the same head but in the correct inserts?

4. fill up all the cab inserts with whatever type of cab each is made for?

5. you don't plug a cab in, and turn the amp on?

I'm guessing some of these are pretty dangerous. I'm just playing through a combo right now, so I'm new to this stuff.

 

[clutch71]

5. you don't plug a cab in, and turn the amp on?

I'll let other guys answer the rest but I can tell number 5 is bad. Might not be dangerous until you actually plug in and play.

If your lucky it will blow the fuse and the power tubes. Worst case afformentioned, tranny, and a whole lot of other whodads inside that motorscooter.

 

[gsda]

The indicated inserts show that it should be plugged into AT LEAST as the indicated one. :lol:
For example :

1.) 8 ohm (amp side) can plug into cab 8ohm(correct match) , and 16ohm(safe mismatch).
2.) 4 ohm (amp side) can plug into cab 4ohm(correct match) , 8ohm(safe mismatch) and 16ohm(safe mismatch).

For safe mismatch will reduce the life of power tubes and the output
transformer will run HOT.
But remember DO NOT turn on the amp without connecting to cab or plug into the cab that impedance is smaller than the insert of amp side.

If there's anything wrong , correct it is appreciated.

 

[domct203]

Number 5 is a definate NO-NO. ALWAYS have a speaker load on the amp, ALWAYS.

Number 1 is almost the same. Never give the amp a smaller load than expected, (ie. 4 ohm cab into 8 or 16 ohm jack) over time that will end up like number 5, and most likely take out the Output Transformer.

Number 2 is fine, and some people do that to change the amp's response and tone. It is generally OK to give the amp a higher load than expected (ie. 16 ohm cabinet into the 8 or 4 ohm jack)

Number 3 and 4 are not short answers. It depends on how the amps speaker jacks are wired. Most (if not all) tube guitar amps will NOT handle a 2-ohm load, with the exception of some bass heads, so most likely the 4 and 8 ohm combo would drop the total impedence too low and end up like number 1.

You can find alot of info on this on the internet. Also, check out some Mesa manuals. My Triple and Roadster manual has Ohm-mismatch charts showing examples of correct and in-correct speaker hookups.

Dom

 

[srf399]

I thought I read somewhere in the MKIV manual how connecting a high load (8 ohm) cabinet to the 4 ohm output changed the sound.... and it described it. I cannot find it now.

Can anyone describe how the sound is changed?

Also, When connecting an external cabinet to a combo... do you keep the combo speaker connected or disconnect it?