[david henman]

...over the weekend i acquired a power amp for my stage monitors. problem is, it puts out 4 ohms, and my speakers are rated at eight ohms.

will i encounter problems?

thanks,

-dh

 

[david henman]

...thanks, guys. its a solid state stereo (alesis) amp. i'll try running it in bridged (mono) mode. one speaker out will send the signal to my own monitor. the other will go to the bassist's monitor and then "through" (series, i think) to the drummer's monitor. the monitors are all rated at eight ohms.

-dh

 

[david henman]

David, my buddy's band has an Alesis RA300 which they use for practice PA.
It has 4 8-ohm monitors attached to it, 2 per side. This gives 4 ohms load into each channel. If they use only 2 monitors (one per side), then it still works fine but at less power.
You could put two monitors on one side (4 ohm load) and one on the other (8 ohm load) but I wouldn't guarantee that it's not gonna hurt the amp. (Comments from more experienced sound monkeys welcome.)
I definitely wouldn't bridge the amp into 3 (or more) speakers. The specs on this amp seem to indicate that it wants a MINIMUM load of 8 ohms when bridged.
Can you find one more monitor and run 2 monitors per side?

...no. i can't see carrying around an extra monitor just to have a "dummy load".

i find it very difficult to grasp these concepts. for example, you mention "per side". when the amp is bridged, that is in mono mode, does this not eliminate the stereo/per side factor?

also, when you guys say "less power", what do you mean? how much less?

 

[david henman]

...i'm still confused:

1. mono source

2. alesis ra300 power amp

8 ohms - 300 watts rms bridged (mono) mode
8 ohms - 90 watts per channel stereo
4 ohms - 150 watts per channel stereo

3. three eight-ohm monitor speakers

i sent a letter to alesis tech support, and to a friend who is a sound tech.

-dh

 

[david henman]

No need to be confused....
- Monitor Out from your mixing board needs to go into both channels of the amp (hopefully there are 2 Monitor Out jacks on your mixer - if not, a Y cable is required)
( like this) http://www.directproaudio.com/product.cfm?directid=23399
- leave amp set for Stereo
- connect 1 monitor to one channel of the amp
- connect the other 2 monitors together and connect them to the other channel of the amp
- position the monitors where you need them
- adjust the volume controls of the amp as required
- Rock out!

...thanks, bro'!

there's only one monitor out, so i'll have to fashion some sort of "Y" adaptor.

but i'm curious...why wouldn't i run everything mono?

-dh

 

[david henman]

You will be, you just need a way to get your single monitor send input into both sides of the amp. The switch on the back of your amp switches from stereo (dual mono) and bridged mono (2 sides of the amp working as one amp in a push-pull configuration), but does not have a mono input option (according to the manual on the manufacturer's site). You need some way to get the signal into the second channel, and the "Y" cable is the simplest means to accomplish this.

...i read the manual carefully last night. it says clearly that i should NOT send a signal to the second channel when the amp is in bridged mono.

just waiting to get the final word from justin taro at alesis.

the only concern i have now is power: will the 300 hundred watt alesis amp (solid state) have sufficient power for three large vocal monitors, each rated at 250-500 watts program?

-dh

-dh

 

[david henman]

Hi David,
You don't want to bridge the amp mono. You will be running a 3.3Ohm load if you do, and the amp won't take it. You should have 2 monitors on one side of the amp and one on the other and the switch should be set to stereo mode.
It will run your monitors, but you won't have allot of volume or headroom, so try not to be clipping the amp all of the time as it is bad for the speakers and the amp.

...i have been wondering if this amp will have enough clean headroom. i have it on a 30-day trial.

-dh

 

[david henman]

If I wasn't already booked, I'd drop by your show at the Congress this weekend and confuse you further, but alas I have prior commitments. Rock On!

...thanks, bro'.

i haven't heard back from alesis, but the consensus here and among a couple of tech friends seems to indicate that i should run it in stereo.

have to dig into my collection of patch cables for a "Y" adaptor...

-dh

 

[david henman]

Hi David,
300 Watts is not really that much power to be honest with you.

...as i suspected. i'll return the alesis before the 30-day trial period is up.

i am looking at picking up a Mackie Tapco J800 for about $335.

-dh