Is 4ohm amp + 8ohm cab OK?

15000volts · #1 08-11-2010, 10:24 AM

I never really understood how this works..

The amp is an ashdown little giant 350 and gives 350W @ 4ohms, and the cab I'd like to pair it is a GK 210MBX that works at 8ohms.
Will this damage the rig?
What are the consequences of using that amp with a single 8ohm cab?
and btw, if it were 350W at 8ohm and the cab was 4ohm, how would that turn out?

**cosmicpimp2** · #2 08-11-2010, 10:27 AM

4 ohm head to 8 ohm cab = Fine. you'll loss a little power
8 ohm head to 4 ohm cab = explosion! lol.

you can run two 8 ohm cabs which would = 4 ohm load then ur head is running 4 to 4

PSPookie · #3 08-11-2010, 10:28 AM

Is the amp's power section tube or solid-state?

picklebarrel · #4 08-11-2010, 10:49 AM

I have a newb question. What's the benefit of getting an 8 ohm cab? Is it just that you can run any head through it?

I have a chance to pick up a 8 ohm cab for cheap but a lot of the heads I've been interested in are 4 ohm.

KJung · #5 08-11-2010, 10:50 AM

Quote:

Originally Posted by picklebarrel

I have a newb question. What's the benefit of getting an 8 ohm cab? Is it just that you can run any head through it?

I have a chance to pick up a 8 ohm cab for cheap but a lot of the heads I've been interested in are 4 ohm.

There is a pretty good sticky about all this in the FAQ section.

PSPookie · #6 08-11-2010, 11:30 AM

Quote:

Originally Posted by KJung

You cannot do this with your particular head. Combining an 8ohm cab with a 4ohm cab in the typical parallel connection will result in a total nominal impedance of 2.67 ohms... below the safe 4ohm minimum of almost all small/micro heads. Your head will overheat and shut down when pushed, or worse.

If you did have a head that was safe to 2.67 ohms (or 2 ohms), then the 8ohm cab would get 1/3 the power of the head, and the 4 ohm cab would get 2/3's. This works great with, for example, an 8 ohm 210 and a 4ohm 410 from the same manufacturer. Each driver will get the same amount of power, given you a modular 610.

Actually, Ken, I believe he was asking if it is ok to use a single 8 ohm cab with his amp.

Yeah, you're fine but the cab won't draw the full 350W. Max output from this amp will probably be somewhere around 210-225W with an 8 ohm load.

PSPookie · #7 08-11-2010, 11:31 AM

Quote:

Originally Posted by picklebarrel

I have a newb question. What's the benefit of getting an 8 ohm cab? Is it just that you can run any head through it?

I have a chance to pick up a 8 ohm cab for cheap but a lot of the heads I've been interested in are 4 ohm.

The other benefit is that you can add another 8 ohm cab (to make a total load of 4 ohms) if you find that one cab isn't getting the job done.

KJung · #8 08-11-2010, 11:32 AM

Quote:

Originally Posted by PSPookie

Actually, Ken, I believe he was asking if it is ok to use a single 8 ohm cab with his amp.

Yeah, you're fine but the cab won't draw the full 350W. Max output from this amp will probably be somewhere around 210-225W with an 8 ohm load.

Ooops! Thanks for the clarification, and +1. I deleted my post.

**A Strohman** · #9 08-11-2010, 12:11 PM

Okay, I thought I was understanding ohms after reading the sticky threads but now I'm confused again. Example: I just bought a Line 6 HD750. The amp says to use a 4 ohm single OR an 8 ohm pair. I will most often be using my GK 8x10 cab which is 4 ohms so thats obviously okay. But I also have two separate 8 ohm cabs. Again, it would be fine to run *both* of those 8 ohm cabs but what about if I decided to run just *one* of the 8 ohm cabs? The instructions say "Only use 8 ohm cabs when feeding a pair." Now...not that I have any reason to run a single 8 ohm cab but just for my understanding....if I do so will I destroy (or potentially destroy) the amp or will I just suffer power loss?

KJung · #10 08-11-2010, 12:23 PM

Quote:

Originally Posted by Lucas Ford

Okay, I thought I was understanding ohms after reading the sticky threads but now I'm confused again. Example: I just bought a Line 6 HD750. The amp says to use a 4 ohm single OR an 8 ohm pair. I will most often be using my GK 8x10 cab which is 4 ohms so thats obviously okay. But I also have two separate 8 ohm cabs. Again, it would be fine to run *both* of those 8 ohm cabs but what about if I decided to run just *one* of the 8 ohm cabs? The instructions say "Only use 8 ohm cabs when feeding a pair." Now...not that I have any reason to run a single 8 ohm cab but just for my understanding....if I do so will I destroy (or potentially destroy) the amp or will I just suffer power loss?

It is never a problem to run a solid state amp (tubes amps are different) at a HIGHER than safe impedance as indicated by the manufacturer. The only thing that will happen is the amp will put out a bit less (40% or so) power into the 8ohm cab versus running it at the optimum 4ohm level (in your case).

With two small 8ohm cabs, you can actually look at that as a positive, since the amp 'adjusts' its output to a one cab and two cab situation.. putting less power into the single cab, and then kicking the power up at 4ohms when you use two!

Remember, 'impedance' is based on the word 'impede'. The more of it (i.e., higher number), the more the power from the head is 'impeded' (i.e., reduced).

With tube amps, it is different. Their output transformer design requires matched impedance, and these big tube amps have separate output jacks for different cabinet impedance (or switches to adjust the impedance).

**A Strohman** · #11 08-11-2010, 12:43 PM

Thank you, Kjung! I now understand.

Last question (until I think of another - lol!):

What happens if I run two cabs, one 8 ohm and the other 4 ohm? I ask becasue there was a time I did exactly that (this was before I started to actually educate myself on these things).

Lester4string · #12 08-11-2010, 12:53 PM

To add to the fun. What if you run two different cabs in series. A 4 ohm and an 8 ohm (for a total of 12 ohms)? Will the balance between the two be off?

KJung · #13 08-11-2010, 01:02 PM

Quote:

Originally Posted by Lucas Ford

Thank you, Kjung! I now understand.

Last question (until I think of another - lol!):

What happens if I run two cabs, one 8 ohm and the other 4 ohm? I ask becasue there was a time I did exactly that (this was before I started to actually educate myself on these things).

In the standard, parallel hook-up (i.e., running each cab out of the output jacks on the back of the amp, or daisy chaining the cabs together... same thing) you will end up with a 2.67 total nominal impedance, with the 4ohm cab getting 2/3rds the power and the 8ohm cab getting 1/3rd the power. You would either need an amp that is 'dual mono' (i.e., two power amps like the Genz Shuttle Max 12 or the Eden WT800), or an amp that is safe to operate at 2.67 ohms (or 2 ohms... like the Genz GBE1200, the Eden WT550, the Mesa M6 or M9, etc.).

This combination works particularly well when you have an 8ohm 210 and a 4ohm 410 from the same company (i.e., basically the same design and drivers). That results in each driver getting the same wattage, and gives you a wonderful 210, 410, 610 modular system, with the amp putting out appropriate power (higher or lower)relative to the number of drivers. Whoohooo!

KJung · #14 08-11-2010, 01:05 PM

Quote:

Originally Posted by Lester4string

To add to the fun. What if you run two different cabs in series. A 4 ohm and an 8 ohm (for a total of 12 ohms)? Will the balance between the two be off?

Can't answer that one... someone will. However, you would never want to do that. That is such a high impedance, you would be generating VERY little power from your amp. Very rare to run speakers in series.

Grooveman1961 · #15 08-11-2010, 03:04 PM

Quote:

Originally Posted by Lucas Ford

Okay, I thought I was understanding ohms after reading the sticky threads but now I'm confused again. Example: I just bought a Line 6 HD750. The amp says to use a 4 ohm single OR an 8 ohm pair. I will most often be using my GK 8x10 cab which is 4 ohms so thats obviously okay. But I also have two separate 8 ohm cabs. Again, it would be fine to run *both* of those 8 ohm cabs but what about if I decided to run just *one* of the 8 ohm cabs? The instructions say "Only use 8 ohm cabs when feeding a pair." Now...not that I have any reason to run a single 8 ohm cab but just for my understanding....if I do so will I destroy (or potentially destroy) the amp or will I just suffer power loss?

Two 8 ohm cabs connected together usually gives a total load of 4 ohms.

If the amp munufacturer says never go below four, you gotta do what they say.

You will only suffer power loss with a single 8 ohm.

There is an exception, the mesa simulstate amps actualy reduce their output when going to lower impedances...giving similar output into 4 or 8. I doubt the line 6 is like that. So the 8 won't go a loud as the 4's.

15000volts · #16 08-11-2010, 03:08 PM

thanks for all the replys. this is turning into a very good thread, full of info

Grooveman1961 · #17 08-11-2010, 03:08 PM

Quote:

Originally Posted by Lucas Ford

Thank you, Kjung! I now understand.

Last question (until I think of another - lol!):

What happens if I run two cabs, one 8 ohm and the other 4 ohm? I ask becasue there was a time I did exactly that (this was before I started to actually educate myself on these things).

8 and 4 together give 2.67 ohms. (in paralell)

12 ohms if in series, either way the 4 gets more power.