Members madball24 Posted December 17, 2009 Members Share Posted December 17, 2009 Does how loud you crank the. amp have anything to do with the Watts? Say I am running a xti 4000 into 2 mrx 525 @4 ohms its supposed to be 1200 Watts if the gains on the amp is at 2 oclock am I still getting 1200 watts Link to comment Share on other sites More sharing options...
Members Mogwix Posted December 17, 2009 Members Share Posted December 17, 2009 The amp's gain is constant. The knobs on the front aren't "gain" knobs, they're attenuators. It's generally advisable to leave the knobs at 0dB (all the way on) and control volume with the mixer/crossover. Link to comment Share on other sites More sharing options...
Members NUSound Posted December 17, 2009 Members Share Posted December 17, 2009 I just answered this in your other thread. An amps rating is an RMS value, when it clips it can be delivering in excess of 2x its rating. That little knob on the front does not limit the amps maximum output. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted December 17, 2009 CMS Author Share Posted December 17, 2009 Does how loud you crank the. amp have anything to do with the Watts? Say I am running a xti 4000 into 2 mrx 525 @4 ohms its supposed to be 1200 Watts if the gains on the amp is at 2 oclock am I still getting 1200 watts The output of an amp is determined by the input signal strength less the attenuation you've dialed in with what you're calling the "gains". No matter how much you attenuate the signal, you can still fully drive the amp by increasing the input signal strength. Obviously at some point your source driver (mixer, etc.) will run out of gain or clip. Link to comment Share on other sites More sharing options...
Members dboomer Posted December 17, 2009 Members Share Posted December 17, 2009 It's generally advisable to leave the knobs at 0dB (all the way on) and control volume with the mixer/crossover. We disagree on this. Most mixers are capably of overdriving power amps by 15 - 25 dB. This is a lot like revving up your engine's RPM instead of simply changing gears to the appropriate one for the speed you want to go in that it is a big waste of signal to noise ratio. There is usually a much better compromise, namely turning down the input sensitivity controls by 10 dB (or more). Link to comment Share on other sites More sharing options...
Members Mogwix Posted December 17, 2009 Members Share Posted December 17, 2009 We disagree on this. I feel this sets up an awkward gain level, unless the amps are overspec'd and properly limited. For a situation like the OP, wherein he's using an amp too powerful for the speakers, I agree. I hadn't read his other thread when I posted that. Turn down the gains for better SNR and make sure the limiters are set! Link to comment Share on other sites More sharing options...
Members SteinbergerHack Posted December 17, 2009 Members Share Posted December 17, 2009 If you really want to set the gains "right", you should run each line-level connection as close as possible to it's maximum level without clipping (on either end). This will allow both input and output gain stages to operate in their quitest, most accurate range. Then use the amps' attenuators to adjust the final gain level. Of course, this takes quite a bit of effort, but if you were setting up a permanent installation it would be the right way to configure the system to maximize S/N and minimize distortion in each of the gain stages. Link to comment Share on other sites More sharing options...
Members madball24 Posted December 17, 2009 Author Members Share Posted December 17, 2009 So having it at 2 oclock with the main mixer faders at 0 and my limiter at 0 is that okay Link to comment Share on other sites More sharing options...
Members dboomer Posted December 17, 2009 Members Share Posted December 17, 2009 Let me answer this way. Your amp has a maximum output in volts which you cannot exceed. Watts relates to the impedance of the speakers you hang across that output voltage. Your amp has a fixed gain factor. I'll use a Peavey amp as an example (because the math is easy). All Peavey amps have a gain of 40X. Imagine that the max of the amp was 200W/8 ohms. That means if you put 1 volt to the input you will get 40 volts at the output (and if you hung an 8 ohm speaker that would be 200 Watts. Now if you turn down the input control by 6 dB it will take 2 volts at the input to produce the same 40V/200W. Turn it down by 12 dB and it will take 4 volts at the input to get you to full output. You could probably turn down this amp to -25dB and still have enough clean output from a mixer to drive the power amp to full output. Link to comment Share on other sites More sharing options...
Members dboomer Posted December 17, 2009 Members Share Posted December 17, 2009 I feel this sets up an awkward gain level What does that mean? Link to comment Share on other sites More sharing options...
Members Mogwix Posted December 17, 2009 Members Share Posted December 17, 2009 What does that mean? That on a rig like mine, "max" power sits right at 0dB on the mixer's output meters. I can dial down the gains and boost the mixer's output but I'd rather not do that, I like to keep that cushion in case something crazy happens and my mixer can stay out of clip. Link to comment Share on other sites More sharing options...
Members Rezrover Posted December 17, 2009 Members Share Posted December 17, 2009 Link to comment Share on other sites More sharing options...
Members dboomer Posted December 17, 2009 Members Share Posted December 17, 2009 I like to keep that cushion I understand ... but how much cushion do you need? With the setup you describe you've probably got better that a 20 dB cushion (that's a 100 times overload to cause a problem). I would think you could very safely cut that in half and have more than enough cushion. What exact mixer and power amps are we talking about? Link to comment Share on other sites More sharing options...
Members The Chinese Posted December 17, 2009 Members Share Posted December 17, 2009 There's good cases for both arguments here. I htink for most users it's a lot easier to understand by turning down the amps... but for professionals who understand & know limiting, and have speakers that are correctly matched with their Amps, then leaving it wide open can be key. Nothing is worse than runnign out of headroom on your Mixer. That being said, one must also understand the clip point of the input stage on the amp, whcih most pro mixers can hit with ease. The best thing is to truly understand why you pick a method. T Link to comment Share on other sites More sharing options...
Members dboomer Posted December 17, 2009 Members Share Posted December 17, 2009 Professionals do NOT leave their amps wide open! Link to comment Share on other sites More sharing options...
Members The Chinese Posted December 17, 2009 Members Share Posted December 17, 2009 Does how loud you crank the. amp have anything to do with the Watts? Say I am running a xti 4000 into 2 mrx 525 @4 ohms its supposed to be 1200 Watts if the gains on the amp is at 2 oclock am I still getting 1200 watts You are getting 1200 watts if the input to the Amp matches it's sensitivity rating. The XTI400 has an input sensitivity of 1.4V. That means when a signal is 1.4V, then the amp is delivering full output. dBu= 20*log(v/.775), so in your case 20*log(1.4/.775)=5.13dBu So when you are sending 5.13 dBu to the Amp it's at full power. Now, you are turning the Input Sensitvity down by an certain amount, so Therefore you are increasing the amount of voltage needed to drive the amp to full power (you are NOT turning the Amp "down"); I do not know what "2 O'Clock" relates to, but if you can hit the clips lights on the amp, then I'd say you're getting Full power. Bottom line is that since you don't quite have the Full grasp of this, stay away from the XTI6000, most likely you will just end up with toasted speakers. T Link to comment Share on other sites More sharing options...
Members The Chinese Posted December 17, 2009 Members Share Posted December 17, 2009 Professionals do NOT leave their amps wide open! Why I have limiters T EDIT: I learned a lot of this stuff on Bryston & Hafler amps- Both of which didn't have input sensivity knobs. You just had to know how to control things... That stuff is Pro, isn't it? Link to comment Share on other sites More sharing options...
Members srp72ee Posted December 17, 2009 Members Share Posted December 17, 2009 Why I have limiters Even with limiters, reduce the input sensitivity to still allow adequate headroom and improve the signal to noise ratio. Link to comment Share on other sites More sharing options...
Members The Chinese Posted December 17, 2009 Members Share Posted December 17, 2009 I Don't disagree, my point is to understand the why, especially with regard to the OP. Link to comment Share on other sites More sharing options...
Members dboomer Posted December 17, 2009 Members Share Posted December 17, 2009 Even with limiters, reduce the input sensitivity to still allow adequate headroom and improve the signal to noise ratio. Yep ... now you are not only gonna hit the noise floor of the mixer, but the noise floor on the limiter IN ADDITION (is there a crossover in here somewhere ... that in addition too! ... EQ too??) Link to comment Share on other sites More sharing options...
Members The Chinese Posted December 17, 2009 Members Share Posted December 17, 2009 All true. But what's a little White noise between friends? Link to comment Share on other sites More sharing options...
Members madball24 Posted December 17, 2009 Author Members Share Posted December 17, 2009 So if I do what I said about having my amp at 2 oclock is it okay that I move the main cadets past 0 Link to comment Share on other sites More sharing options...
Members The Chinese Posted December 17, 2009 Members Share Posted December 17, 2009 Link to comment Share on other sites More sharing options...
Members dboomer Posted December 17, 2009 Members Share Posted December 17, 2009 Is what OK? Link to comment Share on other sites More sharing options...
Members madball24 Posted December 17, 2009 Author Members Share Posted December 17, 2009 If I move the main faders past 0 Link to comment Share on other sites More sharing options...
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