help choosing the right power amp (live)

[viva_zapata74]

hi all,

although this is not exactly home recording related, I hope some1 will be able to help:

I've been using the in-house PAs for live gigs so far, now it's time to buy our own.

I set my eyes on a couple of passive JBL EON 1500 225W @ 8 Ohm. Now I have to choose the right power amp.

Does anyone have any suggestions with regards to the tech specs I'd be looking for in a power amp for those speakers? Any preferred brands?

As usual, thank you all in advance for the attention

 

[cusebassman]

It all depends on what you want to do with them. I run the PA for my acoustic group, as well as use it for DJ'ing, so I need a stereo setup (most modern music mixed in stereo kinda sounds like shit blended to mono). So, I need a much higher-wattage power amp so that the stereo channels will both put out a decent amount of power. If you are just looking to blend L and R together from your board into a mono power amp, and out to a set of speakers, then you only need to find a power amp that will push about 500 watts in mono (bridged) mode. This will be a lot cheaper than finding a power amp that pushes 250 - 300 watts per side, but having this added power means you can push more in bridged mode if you ever decide to go to mono, with more PA cabs.
As for brands, I have never had much budget for power amps (it always ends up going into guitars, amps & recording equipment), so I don't think I've ever spent more than 300 bucks on a power amp. The latest I bought was a Gem on musiciansfriend.com which claimed to push 300 watts per channel at 8 ohms, and I was running each side to a separate 1x15" 500 watt cabinet. This thing could really push some air, but I won't attest to the quality or durability of Gem power amps since they are so cheap. I would look to spend about 500 bucks to get a decent power amp you won't have to worry about capping out in the middle of a show. Mackie makes some decent products, and the FR-2500 looks like it has some good specs for around 500 bucks:

http://www.musiciansfriend.com/product/Mackie-FR2500-2Channel-Stereo-Power-Amplifier?sku=487210

I am by no means an expert on live sound since it is really the latest thing I've gotten into, so I'd search the forums here and see if there are already some threads for power amp suggestions, however, the Mackie looks pretty decent, and check out some other mid-range amps. Cheers

 

[michaelst]

We use all QSC PLX series amps(3402 x 2, 2402 x4) in our 12k system. They are rock solid, clean as a whistle, lighter than most every other amp, and have a good resale value. With the newer series out, there are very good deals on used ones on e-bay. It's definately a pro audio piece of equipment and will last years, but it ain't cheap.

 

[viva_zapata74]

thanks for the replies, guys!

well, the band is a 4 piece ragtime blues band, mainly acoustic and we definitely do not play for huge halls, but rather small to medium sized pubs and clubs. Digital piano, acoustic guitar, drums and the hell of a harmonica player. We need a bit more presence for the upcoming Xmas gigs that's all, and there are situations in which our own amps are not enough

the idea is to get these two 225 W JBL at 8 Ohm and find a decent poweramp, then, which pushes out, as you say, to two stereo channels (I guess I have to make sure that the Ohm spec match between speakers and poweramp)

what would happen if the poweramp pushes out more W than the speakers' wattage? say the JBL are 225 W @ 8 Ohm and I get a poweramp which pushes 300 W @ 8 Ohm per channel? What's the story there? Do those specs need to match exactly?

thanks again, lads

E

 

[xstatic]

I reccomend buying an amp capable of two to three times the amount of power as the speaker needs. In most of my rigs we are using Crest CA series amps and Crown Macrotechs. I am now however adding FACE audio amps to my lineup and probably will not be buying any more Crown for sure, and probably Crest also. The FACE audio stuff comes in priced liked a QSC PLX or Crown Xi etc... but sounds more like a Macrotech or Power Pro as far as output and quality goes. The only drawback I have found on them so far after 6 months of use is that they are very heavy. But then again they also run very cool.

 

[cusebassman]

You don't need to match the wattages from the cabs to the power amp. If you buy a power amp that says it puts out a max of 500 watts per channel (L and R), and run it out to two PA cabs that each can handle 250 watts, you just won't be able to turn the power amp up as high as it will go (well, you can, but you will max out the cab and potentially damage it). If you get a power amp with less wattage than each cab can handle, you just won't be able to use the cabs to their full potential. So, as one of the previous posters said, it is good to get something that can power a lot more than what you have, for expandability reasons, but it also depends again on your budget. Id' say close to 500 bucks is enough to get something that will fit your needs and more, but I don't know how much you have to spend.

 

[dementedchord]

2x's the power is not uncommon and imo is the minimum... and FWIW stereo is not just unnecessary for most clubs... it's a disadvantage...

 

[boingoman]

If you buy a power amp that says it puts out a max of 500 watts per channel (L and R), and run it out to two PA cabs that each can handle 250 watts, you just won't be able to turn the power amp up as high as it will go.

Just to point something out-

You can get a power amp to put out full volume even if the controls aren't fully up just by sending a hotter signal. They are input attenuators, not output power controls.

If an amp puts out full voltage with 1volt input, and you turn the controls down halfway, it may take 1.5volts to reach full output. That's just an example, the actual numbers will vary depending on the amp.

Turning down your amp won't protect your speakers all by itself.

 

[Ford Van]

You don't need to match the wattages from the cabs to the power amp. If you buy a power amp that says it puts out a max of 500 watts per channel (L and R), and run it out to two PA cabs that each can handle 250 watts, you just won't be able to turn the power amp up as high as it will go (well, you can, but you will max out the cab and potentially damage it). If you get a power amp with less wattage than each cab can handle, you just won't be able to use the cabs to their full potential. So, as one of the previous posters said, it is good to get something that can power a lot more than what you have, for expandability reasons, but it also depends again on your budget. Id' say close to 500 bucks is enough to get something that will fit your needs and more, but I don't know how much you have to spend.

I am sorry, but you have absolutely NO idea what you are talking about!

First off, the rated wattage on speakers are ALWAYS VERY CONSERVATIVELY rated! Also, they are usually rated at RMS power (think, average power). They do have a Peak wattage rating too! This peak is at least twice the RMS, and ofter 2.5 more!

You should get an amp that is capable of the Peak wattage of the speaker.

The safe range was suggested earlier, 2 to 3 times the RMS of the speakers. In this case, that would be about a 500 watt per channel amp (rated at the same ohm load as the speaker cabinet). You could go higher, but then you need to be VERY careful.

I do not recommend turning down the amp if you are highly over powered though! I recommend keeping the last stage of the mixers volume lower.

DO NOT under power the speakers! This is FAR more dangerous to them than over powering them! The reason is that if you NEED all the volume the power amp has, and you keep turning up your mixer to get more volume, at some point, you will "clip" the input of the power amp. When a power amp is "clipping", it produces up to 5 times it's rated power!!!

So, to illustrate, if you have a 200 watt per channel amp, and you clipped the input of it, you could potentially drive 1000 watts to your speakers! Those speakers WILL NOT handle that kind of power and you will damage the drivers and possibly components in the crossover in the cabinet!

Hope this helps.

 

[Ford Van]

Just to point something out-

You can get a power amp to put out full volume even if the controls aren't fully up just by sending a hotter signal. They are input attenuators, not output power controls.

If an amp puts out full voltage with 1volt input, and you turn the controls down halfway, it may take 1.5volts to reach full output. That's just an example, the actual numbers will vary depending on the amp.

Turning down your amp won't protect your speakers all by itself.

This is the technical reason why I say turn down your mixer rather than the inputs on a power amp!

It is also a good technical description on why it is much better to over power a speaker cabinet than under power it!

 

[boingoman]

This is the technical reason why I say turn down your mixer rather than the inputs on a power amp!!

Yup, usually better S/N, too.

Also partially explains why I use a crappy limiter on my system.

"Geez, man, that limiter sounds like shit."

"Maybe you shouldn't hit it quite so hard."

 

[Ford Van]

"Geez, man, that limiter sounds like shit."

"Maybe you shouldn't hit it quite so hard."

Hehehehe...I used to do that to rave dj's! Fuck! No matter how fucking much power I give them, they push it to distortion! A few of the good ones at a club I worked at, I would have them stand out front and listen to the music before it hits the limiter, then after it hits it. Imagine their surprise when the music sounded quieter while hitting the limiter!!! They usually got the point then.

 

[cusebassman]

Ahh, makes sense (leaving the power amp on its highest setting, and regulating the final output from wherever your final mixer's output level is). I run my mixer's final output at as close to 0dB as possible so as not to distort any outputs running to recorders, etc., so I try not to use the master faders as a makeshift volume control. I just pay attention and make sure nothing coming into the board is clipping, and if everything going out is around 0dB, I won't have to worry about clipping at the power amp (which is of course caused by pushing out too hot a signal from the board - again, why I don't use the master fader for volume control). I guess we just go about doing things differently. The one thing I definitely didn't mention before was the whole RMS/peak power ratings they attach to PA cabs... whoops. I think I will stay away from just cranking my power amp volume all the way up and using my master section to regulate volume, and I've seen my power amps clip before, never to the detriment of the cabs they were running out to, but again, since I don't push my board up past 0-5 dB, I suppose I don't have to worry. I just feel a little hesitant to do that since my power amps can push a lot more than my speakers can handle, and at 0dB that would blow those cabs away. My two cents, can't wait for more reaming!

 

[boingoman]

I think I will stay away from just cranking my power amp volume all the way up and using my master section to regulate volume, and I've seen my power amps clip before, never to the detriment of the cabs they were running out to, but again, since I don't push my board up past 0-5 dB, I suppose I don't have to worry. I just feel a little hesitant to do that since my power amps can push a lot more than my speakers can handle, and at 0dB that would blow those cabs away. My two cents, can't wait for more reaming!

There is nothing wrong with your approach!! If you need to turn it down, you need to turn it down somewhere. Personally, I have found that amps get noisier than mixers when turned down, and would prefer to run my board or crossover a little lower. YMMV. Just wanted to point out that neither method will save you if some tool decides to ram the faders all the way up!!

 

[cusebassman]

hehe good point. Sorry if I sounded harsh - sometimes I take the defensive on these forums... people can get nasty when there's no face attached! At my price range, if something explodes, it also won't bankrupt me - what amps and cabs are you running?

 

[xstatic]

Like mentioned above, overpower things and leave the amps at full. This is MUCH safer than underpowering, or turning down the amps. Amps very rarely blow speakers. What is MUCH more common is sending a signal to hot for the amps INPUT. This will cause the amp to reproduce a bad signal at a high output. This will quickly damage speakers. This is also often caused by turning down the amp. If you turn it down, it causes a loss in output power. As a result, many people drive the front end harder to regain volume. The next result is a locked up driver, or even blasting the speaker right out of the basket. It is important to remember that this can even be a fire hazard. A locked up driver still tries to move and speakers can actually start on fire partly due to the excessive heat created by the friction.

 

[Ford Van]

Ahh, makes sense (leaving the power amp on its highest setting, and regulating the final output from wherever your final mixer's output level is). I run my mixer's final output at as close to 0dB as possible so as not to distort any outputs running to recorders, etc., so I try not to use the master faders as a makeshift volume control. I just pay attention and make sure nothing coming into the board is clipping, and if everything going out is around 0dB, I won't have to worry about clipping at the power amp (which is of course caused by pushing out too hot a signal from the board - again, why I don't use the master fader for volume control). I guess we just go about doing things differently. The one thing I definitely didn't mention before was the whole RMS/peak power ratings they attach to PA cabs... whoops. I think I will stay away from just cranking my power amp volume all the way up and using my master section to regulate volume, and I've seen my power amps clip before, never to the detriment of the cabs they were running out to, but again, since I don't push my board up past 0-5 dB, I suppose I don't have to worry. I just feel a little hesitant to do that since my power amps can push a lot more than my speakers can handle, and at 0dB that would blow those cabs away. My two cents, can't wait for more reaming!

You are very confused about all of this. But do what you will.

 

[Ford Van]

Like mentioned above, overpower things and leave the amps at full. This is MUCH safer than underpowering, or turning down the amps. Amps very rarely blow speakers. What is MUCH more common is sending a signal to hot for the amps INPUT. This will cause the amp to reproduce a bad signal at a high output. This will quickly damage speakers. This is also often caused by turning down the amp. If you turn it down, it causes a loss in output power. As a result, many people drive the front end harder to regain volume. The next result is a locked up driver, or even blasting the speaker right out of the basket. It is important to remember that this can even be a fire hazard. A locked up driver still tries to move and speakers can actually start on fire partly due to the excessive heat created by the friction.

I couldn't have said it any better.

20 years of running big ass sound systems. I have seen it all happen!

 

[cusebassman]

Well, I certainly don't claim to know much about running PAs - I'm more of a recording nut and musician... I've only had a couple shows where I needed to actuall run the thing. Next time I'll be sure to run the power amp hot and just make sure no one futzes with my mixer, so the main faders don't get pushed to the point of overloading my speakers!

 

[Ford Van]

The fact is, your speakers have a better chance of survival with the power amp on full.