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Amp Advice Please


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HI Guys

 

i have a old 1200 watt peavey amp which i have used for years, touble is it is one hell of a heavy lump,

my mate has a 600 watt amp for sale and i was thinking of getting it to replace the peavey ( purely because of weight )

i am running a pair of peavey 300 watt pro 15`s with bass boxes.

what will the difference be if i came down to the smaller amp, apart from size, is there any negatives in doing so?

will my speakers sound C:cense:p because of this switch.

will i be able to put out enough sound to sound right in a medium sized hall 150 - 200 guests.

you knowledge on this would be grateful before i take the plunge in buying it off him,

cheers

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No it will be seriously underpowered, Please read original post again.

He would be running 300 watts per channel into a pair of Peavey Pro 15's (300 watt rms) this would be fine 300 watts of amp power per channel into a 300 watt rms speaker (No problem) BUT and a VERY BIG BUT at that he states with bass boxes....................So where is the other power coming from for the bass cabs ?

 

If it is from the same amp then its " No way Jose"

 

Also something to consider is the 600 watt amp is 600 watts into 4 ohm (I would Imagine) now Peavey do the Pro 15's in different models some are 8 ohm some are 4 ohm.

Now if they are the 4 ohm version you will get the full 300 watts per channel into the speakers, however, if they are the 8 ohm version you will only get about 175 watts per channel................Seriously underpowered.

 

 

I would definatley give the 600 watt amp a miss, especially if your running 8 ohm pro 15's ..........This is without even considering bass bins.

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If it is from the same amp then its " No way Jose"................................

 

.........................Seriously underpowered.

 

 

 

Seriously underpowered for what?

 

 

If there is enough power for the type of gigs being done what does it matter?

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I will certainly try for you Spinner :D :D

 

 

The underpowered amp can damage speakers by "clipping".

 

 

When an amplifier is pushed to create a signal with more power than its power supply can produce, it will amplify the signal only up to its maximum capacity, at which point the signal can be amplified no further. As the signal simply "cuts" or "clips" at the maximum capacity of the amplifier, the signal is said to be "clipping". The extra signal which is beyond the capability of the amplifier is simply cut off, resulting in a sine wave becoming a distorted square wave type waveform.

 

Underpowering a speaker is likely to damage the voice coil due to the excess heat created by distortion. This distortion, called clipping, is created when the amp is not able to supply the power demand when the volume is turned up.

 

The signal going to the speakers from the amp is AC (Alternating Current).

(the voltage is alternating too, but they have to call it something ).

This means that to play say a 100Hz tone, the amp will alternate the output voltage (and hence current) between say +12V and -12V (or +1.5A and -1.5A) 100 times a second (the actual voltage/current level depends on the volume you select and the impedance of the speaker, which I've assumed to be 8ohms in the above example).

 

Now, a powerful amp may be able to deliver a maximum of +/-100V across a speaker, or +/-12.5A into it, where a low powered amp can only deliver +/-40V or +/-5A.

What happens if the low powered amp tries to deliver +/-80V or +/-10A?

The tips of the voltage or current wave are simply "cut-off" or "clipped" - for the duration of the "clip", the voltage/current is steady, which means it's DC (Direct Current - ie not alternating). This is very bad for speakers, especially tweeters (you may think the series capacitor in the crossover would protect the tweeter from DC - it won't in this case, as essentially what you have is pulsed DC, which a capacitor will pass).

 

Imagine a sine wave, and simply slice off the tips - you'll have what's beginning to look like a square wave - the flat bits now at the tops and bottoms of the wave are the DC component.

DC can burn the voice coil out (if long enough in duration) - and can cause it (and hence the cone) to move too far, which can cause mechanical damage to the speakers motor assembly.

 

As an amp is turned up closer and closer to its maximum level, the level of distortion increases. So the idea is that if you are using a underpowered amp and have to turn it up near its max to achieve the level of loudness you desire, it is working real hard to reproduce the waveform accurately and may clip. That is why it is better to have an amp with greater power than you will actually need.

 

A little guide on Impedance (for those who may not understand)

 

An amplifier is not expecting to "see" a certain load and they are not built to drive a certain load. They have power values stated at certain standard impedances and have a minimum impedance which they are capable of driving, which is related to the amps ability to dissipate heat. An amplifier will generate more heat the lower the impedance attached to it. A higher impedance will make it run cooler not hotter.

 

Image pushing a big rock along the ground. The size of the rock relates to impedance and the effort required to move it relates to the amps power. When you have a big, heavy rock (8 ohm for example) there is more resistance to movement and you have to push hard and it moves slowly (low power output). If you halve the size of the rock (4 ohm) you don't have to push so hard and you can push it faster (higher power output). Halve it again (2 ohms) and you can run with it! (max power output). The faster you are moving, the more heat you produce. If you get to the point where you are running so fast you cannot keep cool, you will overheat and die.

 

This isn't supposed to sound patronising, its just an easy way to simplify certain principles.

Edited by Bolan-Boogie
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Patronising or not I could have written the same post, if it was relevant to the point in question. I knew all that already.

 

I don't mean to be patronising either but I must assume that you misunderstood my original post.

 

My comments were made on the basis of using the amp properly.

 

I said that so long as the amp isn't overdriven ( or put into clipping) there won't be a problem.

 

Provided the amp is run conservatively and provides a clean signal, there should not be any question of any long term damage.

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Patronising or not I could have written the same post, if it was relevant to the point in question. I knew all that

My comments were made on the basis of using the amp properly.

 

I said that so long as the amp isn't overdriven ( or put into clipping) there won't be a problem.

 

 

 

Hence my reply, If the amp is going to be running tops & bins like the original question states then there will be clipping issues. 300 watts rms per channel into a potential 600 watt speaker rating. in my experience this is always going to clip.

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Depending upon your budget, consider looking at the QSC GX range of amplifiers.

 

Fantastic value for money, and fairly lightweight.

 

I know this post isn't asking for recommendations, but I thought it would be worth mentioning.

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Hence my reply, If the amp is going to be running tops & bins like the original question states then there will be clipping issues. 300 watts rms per channel into a potential 600 watt speaker rating. in my experience this is always going to clip.

 

 

I'm struggling to find the logic in this. How and why?

 

If, for argument's sake, the combination provides enough output for the venues it will be used in why, unless it is misused, will the amp be run into clipping?

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Yes the speakers will be calling for more power than the amp can provide, therefore causing coil damage to the speakers.

 

 

Sorry but that's simply wrong.

 

If that were true it would mean that a a speaker of any given wattage would be damaged if it's designated rating wasn't being fed to it all the time!!!

 

On that basis no-one would dare reduce the signal from their mixer for fear of starving the speakers of power.

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You are correct when saying that having headroom on an amplifier will normally avoid clipping BUT,

 

Spinner is also correct of course when he says that if the amp is run within its parameters then you will get no clipping and not damage the speakers.

 

And what are you talking about when you say that if a speaker has a higher rating than an amplifier it will request more power than the amp can provide thus sending it into clip?

 

Sorry Spinner that post was obviously not directed at you,and I must learn to type faster!!!

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You are correct when saying that having headroom on an amplifier will normally avoid clipping BUT,

 

Spinner is also correct of course when he says that if the amp is run within its parameters then you will get no clipping and not damage the speakers.

 

And what are you talking about when you say that if a speaker has a higher rating than an amplifier it will request more power than the amp can provide thus sending it into clip?

 

Sorry Spinner that post was obviously not directed at you,and I must learn to type faster!!!

 

 

Hi Andy,

If you are not putting enough power into the speaker (obviously not enough working on the theory of 4 speakers at approx 300 watt rms) then you are not moving the speakers enough to keep the speaker coil cool resulting in a gradual burnout of the voice coil.

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Where you get this idea from I'm not quite sure!

 

Using your theory would result in any system having to be run at full chat to avoid you damaging any drivers.

 

The damage to drivers/voice coils comes from overdriving them or sending them a clipped signal,neither of which will you get by running the amp within its correct parameters.

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As a rule, I always aim to have more the RMS output necessary - meaning that if the woofer is rated at 400W RMS, I use an amp that produces at least 600W RMS (Headroom) at the impedance I will be running the speaker at.

 

There are a few reasons to do this. One is that the amp puts out less distortion, less heat, and lives a longer life when working less hard. Think of yourself trying to paint a detailed picture right after you've ran a marathon, or spent an hour power-lifting at the gym. Its pretty tough to do any kind of quality work when you're exhausted from running full-bore. Now if you spent a liesurely day sipping a beverage by the pool before trying to paint, the results would be much different. You'd be alert and able to focus on the job at hand. Same goes for your amplifier. A larger amp working below its full potential is much happier than a small amp being run full-bore at all times.

 

Another reason is that the woofer will take more power than its RMS rating, provided its a clean, unclipped sine wave. This translates to increased volume from your woofer, which you claim you want. You can always adjust the gain to produce the desired output level - just because the amp makes 800W, doesn't mean you need to set the gain so that its making full power.

 

 

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As a rule, I always aim to have more the RMS output necessary - meaning that if the woofer is rated at 400W RMS, I use an amp that produces at least 600W RMS (Headroom) at the impedance I will be running the speaker at.

 

There are a few reasons to do this. One is that the amp puts out less distortion, less heat, and lives a longer life when working less hard. Think of yourself trying to paint a detailed picture right after you've ran a marathon, or spent an hour power-lifting at the gym. Its pretty tough to do any kind of quality work when you're exhausted from running full-bore. Now if you spent a liesurely day sipping a beverage by the pool before trying to paint, the results would be much different. You'd be alert and able to focus on the job at hand. Same goes for your amplifier. A larger amp working below its full potential is much happier than a small amp being run full-bore at all times.

 

Another reason is that the woofer will take more power than its RMS rating, provided its a clean, unclipped sine wave. This translates to increased volume from your woofer, which you claim you want. You can always adjust the gain to produce the desired output level - just because the amp makes 800W, doesn't mean you need to set the gain so that its making full power.

 

 

All of the above is quite correct,but that is not what you WERE saying now is it! :msn-wink:

And it's not just woofers that take more than their advertised rating :dukesy:

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HI Guys

 

is there any negatives in doing so?

will my speakers sound C:cense:p because of this switch.

 

 

Yes that's exactly what I'm saying :D

 

DJH asked if there were any negatives in doing so, I'm trying to point out various negatives even though we are going around the Mullberry bush to get there, even though it's interesting debate :dukesy:

 

To simplify terms and not get all testicle (oops i meant Technical :ads: )

 

I would stay with the theory its better to have too much power than not enough, as long as it's used correctly. :amen:

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HI Guys

 

i have a old 1200 watt peavey amp which i have used for years, touble is it is one hell of a heavy lump,

my mate has a 600 watt amp for sale and i was thinking of getting it to replace the peavey ( purely because of weight )

i am running a pair of peavey 300 watt pro 15`s with bass boxes.

what will the difference be if i came down to the smaller amp, apart from size, is there any negatives in doing so?

will my speakers sound C:cense:p because of this switch.

will i be able to put out enough sound to sound right in a medium sized hall 150 - 200 guests.

you knowledge on this would be grateful before i take the plunge in buying it off him,

cheers

 

You have been given different views on this,but to be honest we would need to know the specifications of your current and potential amps.

 

eg: how many watts/channel RMS they will deliver and into what load. (4 ohms or 8 ohms?)

 

Also what the specifications of the speakers you are using are.

 

eg: 300watts RMS at 8ohms or 4 ohms?

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This is quite a heated debate!

 

the speakers will be calling for more power than the amp can provide, therefore causing coil damage

This of course doesnt happen, speakers can't 'call' for power. Only the DJ's ears can feel the need for more power so he allows his fingers to wander over to the master volume and turn it up to 11.

 

not moving the speakers enough to keep the speaker coil cool

I dont think this is an essential feature of speakers, no doubt some manufacturers cite the principle in their marketing blurb? A bit like the Behringer powered speakers that say the amp is cooled by the bass reflex breeze...but unfortunately also shaken apart by it?

 

 

 

 

So which is better...a 600W amp ticking over or a 300W amp running flat out?

 

There's only one way to find out...

 

http://i174.photobucket.com/albums/w113/jackb2302/HarryHill_fight-1.jpg

Edited by superstardeejay

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This debate is rather interesting and a few rather interesting comment coming out of it...

 

Just thought I would throw my views into the mix.

 

Should DJH run a bigger amp, it will mean that his amp will last alot longer than if he ran a smaller amp flat out, flat out being the operative word...

 

If DJH mainly does venues where he would quite happily run within the parameters of the smaller amp, this amp will be just as reliable. Depending upon what Manufacturer the smaller amplifier is, will determine its reliability. A QSC or a crown, you can get away with hammering it on an odd occasion, and it is quite happy.

 

Basically what I am suggesting is... if DJH is working venues where a 600 watt amplifier is ample (how many of us actually exceed 325w in the majority of local pubs and hotels?)

 

Thats me done :)

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