Running a 2 channel amp with only 1 channel

[teleguido]

I've got a QSC RMX 1450 (http://www.qscaudio.com/products/amps/rmx/rmx.htm), and I'm wondering if it will damage the amp to run it with only one of the two channels connected to a load (Yamaha wedge monitor)? I know I could bridge the channels, but that would be sending waaay to much juice to power the single Yamaha. Couldn't find anything in the manual about this.

I realize this question is a bit goofy, so here's more of the backstory:

Need to run two monitors on a VERY cramped stage. The QSC is being re-purposed for the monitors after being used to run the mains for a long time. We are now running Mackie SRM450s for the mains. Have access to a single Yamaha wedge monitor (passive), and a single powered Samson monitor. If I bridged the channels on the QSC it would greatly exceed the maximum recommended wattage of the Yamaha.

[cooljuk]

Bridge the amp into the one monitor and be realistic about how hard you drive it.

Overpowering a PA monitor is far better than underpowering it, if done responsibly. Just make sure your impedance is within range and the amp is set right.

[loudboy]

Just use one side. If the amp has an input mode switch, set it to "2-channel," keep the volume down on the other side and don't plug anything into the unused input and you'll be fine.

Do NOT bridge it, unless you want to blow up your monitor.

Rule of Thumb:

Approx, 1.5X the speaker's RMS power is the correct RMS wattage for the amp driving it.

[teleguido]

Just use one side. If the amp has an input mode switch, set it to "2-channel," keep the volume down on the other side and don't plug anything into the unused input and you'll be fine.

Cool! That definitely makes it easy.

So does this mean that PA amps are significantly different from guitar amps, in that you won't fry them just by powering on without a load?

[SteveO]

Originally Posted by teleguido

Cool! That definitely makes it easy.

So does this mean that PA amps are significantly different from guitar amps, in that you won't fry them just by powering on without a load?

Actually, it's a solid state v.s. tube thing.

[GCDEF]

Originally Posted by cooljuk

Bridge the amp into the one monitor and be realistic about how hard you drive it.

Overpowering a PA monitor is far better than underpowering it, if done responsibly. Just make sure your impedance is within range and the amp is set right.

This is a really bad answer. Really bad. The correct answer is no, you won't hurt your amp by only using one side of it.

[teleguido]

GCDEF, loudboy, SteveO - you guys rock. This is why I dig the Recording/Live room so much! Seems like there's lots of knowledgeable folks ready and willing to help.

Someday, when I've achieved guru status, I will return the favor.

[cooljuk]

Originally Posted by GCDEF

This is a really bad answer. Really bad. The correct answer is no, you won't hurt your amp by only using one side of it.

Why do you say that my answer is bad? I'm not questioning your view point, I just wanting to understand it. I think that if you are going to shoot down my response flat out like that you ought to at least say why so the OP can make an educated decision.

I worked with live sound for 15 years and I'm quite confident that overpowering damages less speakers than under powering in the PA world. Distortion (from driving an underpowered amp too hard) causes DC to go to the speaker which causes excessive heat and burns coils. That, in my personal experience, is far more common than damaging a speaker by overexertion.

[loudboy]

Originally Posted by cooljuk

Why do you say that my answer is bad? I'm not questioning your view point, I just wanting to understand it. I think that if you are going to shoot down my response flat out like that you ought to at least say why so the OP can make an educated decision.

I worked with live sound for 15 years and I'm quite confident that overpowering damages less speakers than under powering in the PA world. Distortion (from driving an underpowered amp too hard) causes DC to go to the speaker which causes excessive heat and burns coils. That, in my personal experience, is far more common than damaging a speaker by overexertion.

All true, but there are limits - you don't put 800 solid watt RMS into a Yamaha wedge.

[teleguido]

cooljuk - yeah, I definitely agree that in general underpowering is responsible for far more incidents of damage than overpowering. However, in this particular scenario the amp is waaay over the recommended for that Yamaha wedge.

Thanks for chiming in though; I really do appreciate it!

[cooljuk]

Most problems have more than one solution. I'm just glad that you got your rig working and are back to making music!

Cheers!

[GCDEF]

Originally Posted by cooljuk

Why do you say that my answer is bad? I'm not questioning your view point, I just wanting to understand it. I think that if you are going to shoot down my response flat out like that you ought to at least say why so the OP can make an educated decision.

I worked with live sound for 15 years and I'm quite confident that overpowering damages less speakers than under powering in the PA world. Distortion (from driving an underpowered amp too hard) causes DC to go to the speaker which causes excessive heat and burns coils. That, in my personal experience, is far more common than damaging a speaker by overexertion.

We have this discussion all the time and it never goes anywhere. Clipping an amp is not the same as "underpowering". I don't know why the solution to not having enough amp for the job is so often confused with having an amp that produces more power than speakers can safely handle.

You can run a 1 watt amp into 1,000 watt speakers and you won't damage the speakers from underpowering them. Let's say you have a 100 watt amp and you drive it to clipping. Which do you think would have a better chance of survival? 100 watt speakers or 500 watt speakers?

Go over to HC's Live sound forum. Peavey's product development manager hangs out there as does a guy that builds and recones speakers for a living. I'd suggest you get their input too.

You can read this if you want more information.
http://www.peavey.com/support/techno...MUCH_POWER.pdf