pushing 8 ohm monitor with 4 ohm amp?

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pushing 8 ohm monitor with 4 ohm amp?

Postby bcresci » Mon Jul 02, 2012 6:03 am

Ran into a situation at the last gig where the venue's sound man asked me to play into the room through the cab only (not miced). Due to the size of the stage area, volume of the mains / monitors, my proximity to my cabinet (pointed at my knees), I was not able to hear myself well, sometimes not at all. So I was considering using one of our spare monitors as a personal guitar monitor. If it works out I might actually build a small 1x12 for this.

I'm using the Mosvale - 4 ohm amp - Channel A only. It's currently pushing my 2x12 which is also 4 ohms.

My question is, can I use the other output of Channel A to also power an 8 ohm monitor? So there will be one 4 ohm load, and one 8 ohm load on Channel A. Will this cause issues? Overheating of the power amp? Blown speakers? Any other bad stuff.

Any other advice out there is welcome.
Last edited by bcresci on Fri Jul 27, 2012 10:09 am, edited 1 time in total.
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Re: pushing 8 ohm monitor with 4 ohm amp?

Postby JonnyBoy » Mon Jul 02, 2012 4:27 pm

there is no issue with that, but you will have a slight drop in volume through 8 ohms than 4 ohms. It won't hurt your SS amp.
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Re: pushing 8 ohm monitor with 4 ohm amp?

Postby zambiland » Tue Jul 10, 2012 1:11 am

bcresci wrote:Ran into a situation at the last gig where the venue's sound man asked me to play into the room through the cab only (not miced). Due to the size of the stage area, volume of the mains / monitors, my proximity to my cabinet (pointed at my knees), I was not able to hear myself well, sometimes not at all. So I was considering using one of our spare monitors as a personal guitar monitor. If it works out I might actually build a small 1x12 for this.

I'm using the Mosvale - 4 ohm amp - Channel A only. It's currently pushing my 2x12 which when is also 4 ohms.

My question is, can I use the other output of Channel A to also power an 8 ohm monitor? So there will be one 4 ohm load, and one 8 ohm load on Channel A. Will this cause issues? Overheating of the power amp? Blown speakers? Any other bad stuff.

Any other advice out there is welcome.


Yes it will cause bad stuff. By using a 4 ohm load and 8 ohm load on the same channel you will be ending up with a 2.667 ohm load, which is well below the minimum impedance of 4 ohms for that amplifier. It will be especially problematic at loud volumes. Why not use Channel B for the other cabinet? You could also just run 2 1x12 cabs. Even better is putting the cabinet so it points at your head. We don't have ears in our knees, after all! 8)
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Re: pushing 8 ohm monitor with 4 ohm amp?

Postby JonnyBoy » Tue Jul 10, 2012 2:43 am

Totally misread that. Your title, yes you can run 8 ohms in a 4 ohm tap. your actual situation, no you shouldn't run 2 ohms on a 4 ohm tap that's abusing it. If it is a stereo tap, channel A and Channel B both being 4 ohms, use 4 ohms or higher for each channel. 4 ohms is the least it can run.
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Re: pushing 8 ohm monitor with 4 ohm amp?

Postby bcresci » Wed Jul 11, 2012 6:14 pm

Thanks, guys.

I think I will do what you mention - I'm probably going to build a small 1x12 monitor and run that from the B channel. That will also give me a separate volume control for the monitor.

Will search the cab forum to see if anyone has posted any simple designs.
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Re: pushing 8 ohm monitor with 4 ohm amp?

Postby strumminsix » Wed Jul 11, 2012 9:09 pm

bcresci wrote:Thanks, guys.

I think I will do what you mention - I'm probably going to build a small 1x12 monitor and run that from the B channel. That will also give me a separate volume control for the monitor.

Will search the cab forum to see if anyone has posted any simple designs.

Use a closed back 1x12 and some Fender tilt back legs
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1x12 cab

Postby bcresci » Thu Jul 26, 2012 12:53 pm

Thanks for the suggestions. Here's the work in progress. Just need to get some blocks put in for strength and then put in the jack plate.

Regarding a close back - what's the reason for that? More bass response, less volume coming out the back at the audience?

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Re: pushing 8 ohm monitor with 4 ohm amp?

Postby tcsned » Thu Jul 26, 2012 4:05 pm

Yeah, in general I'd say you're right. The classic Marsall stack sound was all closed back. That cabinet looks great!
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Re: pushing 8 ohm monitor with 4 ohm amp?

Postby mijknahs » Thu Jul 26, 2012 5:04 pm

Your speaker should be hitting you in the waist to chest area (not your feet and not your head). Raise it up off the ground if it's at your feet or tilt it back so it aims at your chest. You should be able to hear it pretty good then.
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Re: pushing 8 ohm monitor with 4 ohm amp?

Postby gr8fullfred » Fri Jul 27, 2012 9:52 am

Actually it is best to have the guitarist's speaker cabinet pointed directly at the guitarist's head (ears).
Just doing this will usually lower the stage volume. Guitarists, as well as most other humans, and other species as well, do not have ears in their ankles, or knees for that matter. This is especially effective for overly loud obnoxious guitar players. Point that cab at their heads!
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Re: pushing 8 ohm monitor with 4 ohm amp?

Postby bcresci » Fri Jul 27, 2012 10:13 am

I'm hoping to have the best of both worlds with this one. Behind me when I have access to a stage monitor with a good mix, in front of me (and miced) when I don't have a good stage monitor. Pointed at my belly so as not to damage my ears or my knees.
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