Amp advice for a newbie

[WeeShiv]

i'm looking for a bit of advice on power amps.

I've found myself the proud owner of my first PA - a Peavey Maxsys system, it's quite old in today's market but still packs a mighty punch and i'm more than happy with the sound quality. The thing is i'm about to purchase a new Allan and Heath mixwizard desk and will need some nice new amps to complete the set up. The spec for the PA is:

2 x 215 black widow subs - 700w rms cont, 1400w rms prog at 4 ohms
2 x 15 black widow tops - 350w rms cont, 750w rms prog at 8 ohms

(still trying to figure out exactly what the difference is with cont and prog)

what kind of amps would be advisable to get the best sound out of this kind of rig?

Any advice on this would be appreciated guys

 

[chuck norriss]

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[WeeShiv]

thanks for the link chuck but i'm in UK and i havn't ever seen those here before

 

[BrianVengeance]

Powering a PA system is a lot like powering a bass rig - headroom is king. You're basically going to want to make sure you can throw enough juice through the cabinets to have them fully express their dynamic range without sizzling the voice coils, so a good rule of thumb is to aim for matching your power amp output to the upper bound of the peak power (or slightly under). I also usually don't suggest driving an amp below 4 ohms if it can be avoided... even if the amp is rated for it (heat, amp life, etc).

With all that being said, you're going to need a ton of juice to make this baby sing.

I've always had good luck with QSC RMX amps for cheap + clean power, but they are backbreakers at about 45lbs each (4050 and 5050 are actually 87lbs each). If this is a mobile application, I'd consider looking at the PLX series... they're much lighter at 21lbs and are FAR easier to haul around.

Assuming you want a stereo top / mono sub setup (probably most common), I'd suggest the following... QSC RMX used for reference, but comparable power ratings in a Crown, Crest, Carvin, Peavey or other will do just fine:

Bass Dumps:
- 1x RMX 4050 stereo @ 4 ohms a side for your subs (1 amp, 2 cabinets) -OR-
- 2x RMX 1850 bridge mono @ 4 ohms per sub (2 amps, 2 cabinets)

High Packs:
- 1x RMX 2450 stereo @ 8 ohms per side

You're also going to want to look at 2way crossovers to split the signal between the highs and lows. A DBX 223 will do nicely, or if you've got some cash to splurge and eventually plan on picking up an EQ / limiter / other dynamics, I'd say go ahead with a DriveRack. Another thing to consider is that you're going to need some beefy circuits to run all this on... the 1850 a full draw will pull 15 amps.

That will easily be enough to get you up and running with enough volume to decimate medium sized clubs and survive outdoor gigs.


Oh, and the easiest way to think about RMS vs peak power output is like this... treat RMS as the amount of wattage that can be continuously sustained without damage, and the peak being the maximum "spike" you can have in your dynamics without damage.

Best of luck!

 

[Jimbob Jones]

Yamaha do some nice stuff for cheap, so do Peavey!

Where are you based in the UK? My church actually has a couple of amps for sale currently! (am I allowed to say that on here?)

Just a note; AFAIK you will need a crossover for the subs, otherwise they will try and put out all the treble as well!

 

[WeeShiv]

Thanks Brian that's given me loads to think about.

I should have said that i have a DOD SR830QXLR Graphic Equalizer and a HZ sound systems crossover already so that side of things are taken care of.

I have researched online and was looking at Peavey and QSC amps so glad to hear them being mentioned in there, do you know anything about the QSC GX range?

Jimbob i'm in Glasgow, Scotland...anywhere near you?

thanks again that's been hugely helpful

 

[BrianVengeance]

No worries at all, Wee... you're quite welcome. There really isn't any sort of crazy voodoo to PA systems, just a lot more of stuff you already know about. Good to know that you've got the cross and graph taken care of, you're one step closer! The A&H mixwizard is a great console, which one are you getting?

Unfortunately, I don't have any direct experience with the GX series so I can't really speak to their build or sound quality, so take whatever I say about them with as much salt as needed.

Overall, they look like it is a cost-conscious, market research / needs driven design where some compromises were made to fit a specific application. Not a bad thing, but the lack of a bridge mono mode and the lower power ratings lead me to think that they may be usable, but not a perfect match, for your application. Bottom line is that power is power, and they will drive speakers... but they do seem to be geared more towards the band that already has a mixer and a pair of high packs and will never need anything but a 2 speaker stereo setup.

In all honesty, the GX7 looks like it would be a pretty good match for your tops, and it may even scale out just enough if you wanted to chain out a second 8 ohm cabinet on each side or swap your 8 ohm 1x15s with a pair of 4 ohm 2x15s. You'd be nearing slightly underpowered, but it would probably be survivable.

It is really the lack of bridge mono that is throwing me... out of the box your subs will be underpowered by 400 watts with a single GX7, and getting a pair of them and running them "single channel driven" (still not exactly sure what that means aside from being less power than a mono bridge) would leave you wanting for 200 watts per sub. It makes me think that for the money / number of amps, you may be able to get a better bang for your buck and a better match elsewhere.

Again, the bottom line is that they will power the speakers and being based off of the PLs may even sound better than the RMX amps, which are clean workhorses, but not hifi by any stretch.

Style of music can also factor in as well (we play melodic thrash metal). I run a QSC RMX2450 on a pair of Turbosound TXD-151s reenforcing vocals only, and it can have a hard time keeping up with 2 half stacks attached to guitarists who believe "turn down" means "turn up more, but just do it less", my SVT4 + PR410HLF, and a thunderous drummer. Other styles are far less abusive of power ratings.

Again, headroom is king... you can always turn a loud amp down and the overdriven amp sound is great for instruments, but it just makes a PA system sound cheap.

Another consideration... does your crossover have a stereo low out, or is it mono only?

 

[Stumbo]

Most important to your setup is sub-placement: Sub stage placement w plots/graphs According to these plots, subs need to be setup together (stacked). You may be able to get away with just one sub. Putting subs on opposite sides of a stage is the least optimal setup, according to the graphs.

Here are a few more links that I've collected that may be useful to you:

~Gigs-stage management
1 Moving equipment
2
3
Coiling cables
Taping down cables

In-ear monitors
Going wireless
Getting your sound "live"

Music stands on stage?
Designing/Managing your sets
Managing sound on stage
Controlling your stage volume
Directing the band on stage-hand signals
[Invalid or Expired Link Removed]
2
Being asked to turn down the VOLUME
To noodle/not to noodle?

~PA/Lighting
First P.A.
1 What size?
2
Configuring
Placing Subs
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1 Upgrading
2

1What mixer is your band runnin'?
2
QSC K series PA discussion
Microphones

Low cost lighting

~FOH
Sound Guy or not To Sound Guy?
Working with the "sound guy"
Cheap vs. Expensive DI
Working a DI
1 Learn live sound mixing
[Invalid or Expired Link Removed]
Link Removed
Frequency ranges of band instruments
Link Removed
FOH vs. on-stage sound
Solving odd feed back situations
Isolating Head/Cabs from stage/each other

Best wireless?
Recording rehearsals/practice/gigs

~Mixing/Recording rehearsals/gigs
Recording/Mixing
Recording software recommendations
Cheap but good studio mics
Home Recording
Sub stage placement w plots/graphs