#1
I have an 8 ohm cab being connected to a 4 ohm head. Is this a setup that will go horribly wrong? the wattage is ok, the head peaks at 800 and the cab only goes to about 400.

I was told that a 4 ohm head could safely run an 8 ohm cab, but I'm thinking that the person who told me this is wrong. Their explanation was this

"Think of a 4 ohm as a wide straw and the 8 ohm as a smaller straw. The 4 ohm will flow more power into the 8 ohm cab and give it the power necesary."

they also told me that this would allow me to make the full stack setup that I want. the other cab is most likely going to be 8 ohms as well. Did I get the wrong information? I'm very worried that I did and I will hurt my cab or, god forbid, my head.
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#3
400 is its peak. What will happen, what should I do?
Quote by Shattuck
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#4
Looks like they gave you decent advice. Remember: You can ALWAYS connect a cab with a higher ohm rating than the the head. For example, if the cab is rated for 16 ohms, you can safely plug it into the 4 ohm jack of the amp. Remember: It's not always safe to connect a lower rated cab into a higher rated amp, or head. For example, connecting a 4 ohm cab into the 16 ohm jack of the amp is generally a bad idea. Some amps, like the Mesa Dual Rectifier are tolerant of this mismatch, others are not and you'll damage the amp. On the Mesa, doing this will cause the power tubes to wear out faster. Hope this helps.

Connecting 2 8-ohm cabs in parallel to the 4-ohm jack of an amp gives you 4 ohms. Connecting 2 8-ohm cabs in series gives you 16 ohms. So, you'd want to connect to the 16, 8 or 4 ohm jack of the amp.
#5
Connecting a 400 watt cab into an amp rated for 800 watts peak could cause trouble if you run the head more than 400 watts peak. You'll overheat the voice coil(s) in the speaker(s) and burn them out. The first signs of this is a popping noise from the speaker(s). This is caused by the speakers bottoming out or travelling to the limits of their excursion.
#6
^^ ok thank you.

I dont move my knob past two, its quiet but we need it that way when we practice. I'll be careful whenever I gig though.
Quote by Shattuck
I need some music that makes you envision a dark room illuminated by only candles and perhaps a creepy middle aged man in a bathrobe.


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Rape: Is it in you?
Last edited by metalisbest at Jan 20, 2009,
#7
Quote by BeerChurch
A cab needs to be rated AT LEAST the same as your amp. If you go less you'll blow the transformer.


No. You'll blow the speaker, which if not quickly addressed by turning off the amp, will result in a blown transformer. However, that's only the case if you have a tube head. If you have a semiconductor head, it doesn't use a transformer in the output stage.

Besides, how would the amp know the cab is rated for less than it can provide? It's not like they talk or anything. Trust me on this one. I'm an electronics tech.
#8
Wait... where the hell did you get an 800 watt head?

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#9
woah an 800 watt head, thats ridiculous


EDIT: sorry for being no help
Gear:

MIA Fender Stratocaster
Jackson Kelly KE3
Ibanez Universe
Marshall JCM 800
Orange Jim Root Terror
Mesa 2x12
Ovation Custom Balladeer
pedals and such in profile
#10
May I please ask WHERE THE **** DID YOU GET AN 800W head? And where can I get one?
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#11
Ohhh wait a second... it's a bass amp, isn't it.

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Electronic Audio Experiments
#12
His profile lists a Ibanez SR706, which is a 6 string bass, so I am guessing that his head is 800w, which is not too terribly uncommon in bass heads.

On topic; yes. IIRC, using two 8ohm cabs together will equal 4ohms.
#13
yeah really, who hasn't heard of a bass amp head?
Gibson SG Standard + 18volt EMG-81 & 85
Mesa/Boogie Mark IV + Recto 2x12
Keeley Modded BD-2
Vox V847a
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#14
*self-*
Quote by Cathbard
If all you had to go on was the forum you'd think a Decimator could cure noise caused by dodgey stage lighting and restock the ocean's population of sperm whales
#15
ah of course, being the typical guitar player that I am, the realm of bass amps didn't even cross my mind
Gear:

MIA Fender Stratocaster
Jackson Kelly KE3
Ibanez Universe
Marshall JCM 800
Orange Jim Root Terror
Mesa 2x12
Ovation Custom Balladeer
pedals and such in profile
#16
Quote by imicius
His profile lists a Ibanez SR706, which is a 6 string bass, so I am guessing that his head is 800w, which is not too terribly uncommon in bass heads.

On topic; yes. IIRC, using two 8ohm cabs together will equal 4ohms.


if i knew that right away......i'm so slow thinking of other things while doing analytical homework...
Last edited by Skierinanutshel at Jan 20, 2009,
#17
Quote by shadow__666
May I please ask WHERE THE **** DID YOU GET AN 800W head? And where can I get one?


Its old, from the 70's... I found it in the back of a crapo guitar store for $150. haha, my luck. Its a sweet head.
Quote by Shattuck
I need some music that makes you envision a dark room illuminated by only candles and perhaps a creepy middle aged man in a bathrobe.


Quote by Skullbolt
Rape: Is it in you?
#18
You will just get less volume running the 8 ohm cab versus 4 ohms. Its probably SS they are much more tolerant of miss matching of ohms. You see it all the time with car stereo amps it can be run several ways at different ohms for different amounts of output. SS stuff tends to use 4 ohm loads as it takes less amp to run 400 watts at 4 ohms. They would need to make the amp section bigger for 8 ohm or 16 ohm loads to equal the rated watts of the 4 ohm amp.