Just Wondering...

[Sound Phanatic]

I just found this forum on the internet, and I hope you guys can answer my sound question!

 

Okay, I have an amp that is rated @ 1200 watts/channel or so @ 4 ohms stereo and my speakers are rated @ 1200 watts at 4 ohms program. I have never clipped the amp, but I have no idea how loud I can crank it before those red lights flash and kill my speakers. I want to figure out with some music where the clipping point on my amps is with my knobs, buttons, EQs, etc. all set the same. My question is: can I run an amp with sound going through it but no speakers attached to the outputs and find out where the amp clips, or will this damage the amp?

 

I don't want to damage my amp, but I don't want to continue worrying that I cannot crank the music cuz I'll risk blowing my speakers, which from reading some posts on this forum I can almost guarantee I will do!

 

Can you guys help me out?

 

What do you think and what should I do?

[Mogwix]

You can clip a 1400w amp driving a 1200w speaker without blowing the speaker, though it's not advised.

 

The clip lights fire long before the amp actually clips. You can try running the system until the clip lights fire, but don't do it for too long.

 

Definitely do not run an amp without speakers connected though, you'll fry your amp for sure. There's some sort of load box you can buy, I think, that you can hook the amp up to that takes the power and provides a load for it to run into.

[prosigna]

I use a multimeter to measure the voltage being produced between + and - on the amps output while the speakers are being driven. When the voltage reaches what I want I know that is all they should take. I do this while setting a limiter so the input voltage never exceeds a level that will produce too much output voltage. This keeps the amp from clipping. THIS DOES NOT PROTECT THE SPEAKERS FROM A CLIPPING SIGNAL PRODUCED BEFORE THE LIMITER.

 

Also, playing music does not reproduce the dynamic range of a live performance. Get a limiter and learn how to set it. There are too many variables.

 

That said: Listen to the speakers. If the output is distorted turn them down.

[6Imzadi]

 

You can clip a 1400w amp driving a 1200w speaker without blowing the speaker, though it's not advised. The clip lights fire long before the amp actually clips. You can try running the system until the clip lights fire, but don't do it for too long. Definitely do not run an amp without speakers connected though, you'll fry your amp for sure. There's some sort of load box you can buy, I think, that you can hook the amp up to that takes the power and provides a load for it to run into.

 

 

I don;t know if that's a great idea letting the amp clip at all in this case. Too many unknowns to recommend otherwise.

 

I would assume that some amps clip lights come on before clipping, but then some others come on closer to actual clipping.

 

A "load" box would be a 4 ohm resistor with the capacity to dissipate at least 1,400Watts. Not something you can get at Radio Shack.

 

Really, the best way to find out where your limits are is this:

1) Set your input gains, channel levels, master levels, and outboard gear (gain structure) correctly.

2) Bring up your amp attenuator up until there is enough volume for the room.

3) IF you get past the 70-80% mark on the amp and you don't have enough volume, you will need another set of speakers and amps.

 

This way you don't get to the point of clipping. 1,400 watts is a lot of power and can be very loud.

[Sound Phanatic]

Okay... the amp only gives out 1200 watts/channel not 1400, my mistake. And here is how my system goes:

 

2 CD Players/Ipods/Computers, etc. --> Mackie 1202 VLZ-Pro Mixer --> Amplifier

 

The sources are connected to the Mackie Mixer via 2 dual RCA-1/4" cables, and the Mixer is connected to the power amp via a dual 1/4" cable.

 

The mixer is set so that it never clips out and the peaks flash at +10dbu on the meter.

 

The inputs come into stereo channel 5-6 and 7-8 on the mixer. The gains for those channels are set around 1-2 o'clock, and the master knob rests at the detent (12 o'clock).

 

I have never really cranked the system, but then again I haven't ever really had a "big gig" where I needed all that power. I do have a few larger gigs coming up in the future where I may need to utilize that extra "horsepower".

 

Is my system set up correctly? Is there anything I should change first?

 

But you guys speculate that as long as I don't go crazy with the volume and never pass about 3 o'clock on the amp dials then I should be good, right?

 

Or do I need one of those limiters you guys were talking about?

 

What does one of those do? And what would be a good one for me to buy? Could you guys recommend some? (I am on a budget so I can't spend too much on one right now).

 

Thanks guys!

[6Imzadi]

This is what I do for a CD or mp3 player.

 

I set the level with the gain to have a zero on my PFL meter.

I set the master at the zero, or unity.

I set the channel to a level where it is loud enough.

My amp attenuator is set to about 8 at all times.

 

This is how I do it, YMMV.

[agedhorse]

You can clip a 1400w amp driving a 1200w speaker without blowing the speaker, though it's not advised. The clip lights fire long before the amp actually clips. You can try running the system until the clip lights fire, but don't do it for too long. Definitely do not run an amp without speakers connected though, you'll fry your amp for sure. There's some sort of load box you can buy, I think, that you can hook the amp up to that takes the power and provides a load for it to run into.

 

HUH???

 

Almost all amp clip lights flash within 1dB of clip. Long before? never.

 

Solid state amplifiers can be run without load indefinately, even at the clip point. I mean all day long, 24/7. I don't know where you are getting your information but I suggest you change your current source.

[twostone]

How big is the venue and how many people is gonna be there? That might help you out with the more experienced folks here. I know my system is about a 12000w total but that aint {censored} trying to cover a crowd of 200-400 in a medium size venue. Most my system can handle is a small venue with a small crowd of 100 or 150 tops and that's with occasional blinking lights.

[Unalaska]

Oh dear, this is going to be interesting again....

 

What you have given us is not enough to answer your question, try answering these quick ones: What model amplifier? what model speaker? Balanced cables being used between mixer/EQ/crossover/amp? Is there an EQ/Crossover involved? Is the channel EQ pretty much flat or boosted 12dB in any way? Lotta variables here...

 

FWIW: Some power amps will flash the clip light 3db BEFORE the onset of clipping. Some will do this 1db below. Some have what's call IOC or Input Output comparitor with looks at the input signal and compares it to the output and if there is a difference will flash the LED thingy.

Some have proprietary protection that limits the INPUT signal by a fixed amount (not the OUTPUT though)

Some will shut down one channel or the whole amp if driven to thermal conditions (clipping may or may not have occured).

 

So in a properly sized and gain structured system the not knowing what's going on rule of thumb is clip lights that blink occasionally are OK, solid red NOT OK.

 

With CD/MP3 and highly compressed music you'll find the acoustic output so high that you may not want to hear trying to clip the amp. You can indeed not plug your speakers in and that can give you an idea on what it takes to clip the INPUT side. Though under low impeadances and highly reactive loads it may take less. But that depends on what "clip" means.

hope that helps

pete

[dboomer]

As far as how much before clipping the leds come on ...

 

"Clipping" is not a single definite thing. Is it 1% distortion, 5%, 10% 50% 100%? Different manufacturers see it differently so so many dB before means what?

 

To the OP's question ...

 

http://www.peavey.com/support/technotes/concepts/THE_LOUDSPEAKER_SPEC_SHEET_GAME_2005.pdf

 

http://www.peavey.com/support/technotes/poweramps/HOW_MUCH_POWER.pdf

[agedhorse]

3 dB before clipping... never seen one anywhere near that far off.... that's 1/2 power!!!

[Sound Phanatic]

Solid state amplifiers can be run without load indefinately, even at the clip point. I mean all day long, 24/7. I don't know where you are getting your information but I suggest you change your current source.

 

So I can run my amp without speakers connected to see where "the red lights flash" and then mark it for further use? And this won't cause any damage to my amp, right?

 

And as far as what equipment I have goes, my amp is a QSC PLX-3402 which gives out 1100 watts/side @ 4 ohms with .05% THD and 1200 watts/side @ 4 ohms with 1% THD I think, not 100% sure on those numbers tho. And my speakers are Yamaha S215-IV Dual 15" Speakers.

 

Does that help?

[Keyrick]

 

So I can run my amp without speakers connected to see where "the red lights flash" and then mark it for further use? And this won't cause any damage to my amp, right?

 

 

 

Sound Phanatic,

 

The best you can achieve is possible operational range with the method that you are describing. There is no correct answer for every instance.

 

A power amplifier creates gain by taking power from the AC power source (the recepticle where you plug in the amp) and processes that power in a way that closely resembles your input signal to a level that will drive your speakers. The AC power source is loaded depending on how much work the amplifier is doing. If no speakers are connected, then the amp isn't doing much work, and there is no load on your AC source. When the speakers are connected, the amp will be doing some work, and you will load the AC source.

 

Your input reference signal in a live situation is not static. If you use compressed media like a CD, for example, as your input source for your measurement, you will not take into account the dynamic range that you will have to reenforce in a live performance situation. Nobody drops a mic or hits a kick drum to hard on a CD.

 

If you are in a touring situation, you cannot be sure of the power available from venue to venue. If you do your test in your practice room for instance, you may have 125 volts AC with plenty of current available with no risk of voltage drop. But the first venue that you play at may only have 115 volts AC available to you with limitations on the amount of current that you can draw before tripping a breaker. Unless you can wire into a distro and know that the power feed will provide you what you need with sureity, you can't make assumptions.

 

So all you can do is get an approximate operating range using the method described. There are too many variables to provide you with a solution that will always work.

 

Good luck.

 

Rick

[Sound Phanatic]

Okay thanks for the help!

[Craig Vecchione]

 

So I can run my amp without speakers connected to see where "the red lights flash" and then mark it for further use? And this won't cause any damage to my amp, right? And as far as what equipment I have goes, my amp is a QSC PLX-3402 which gives out 1100 watts/side @ 4 ohms with .05% THD and 1200 watts/side @ 4 ohms with 1% THD I think, not 100% sure on those numbers tho. And my speakers are Yamaha S215-IV Dual 15" Speakers. Does that help?

 

 

 

The PLX-3402 is rated as you state. You can indeed run this amp into an open circuit (no speakers attached) til the cows come home. The admonition to not run an amp into an open circuit applies to transformer-coupled outputs, which are typically only found on tube amps....your basic Fender or Marshall or Mesa valve guitar amp, for example.