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Author Topic: AMP clipping  (Read 12648 times)

chris broadway

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AMP clipping
« on: February 04, 2014, 09:16:18 AM »

I am continually in a quest to slowly optimize an existing system I am now supporting.  The full system is the Yamaha LS9, Driverack DBX-260, and crown 600 amps.  In the beginning, there was not a proper gain structure performed, amps were turned all the way up, and the LS9 console master fader set to about -20.  I wanted to do a gain structure to set the clipping level on all three devices.  I performed the gain structure to the best of my ability as the DBX 260 outlined. After I did this, I marked clipping with tape on all three devices and then lowered the master fader level and the amps.   A couple weeks ago I wanted to fix the master fader and individual channel fader level.  The master fader was -20, the individual channels were between -20 and -30, and the individual channel gain was very high.  I thought it would be better to increase the master fader to -5, the individual channel fader to around 0, and lower the channel gain significantly.  Doing this gives me more playing room when making channel fader adjustments.  Here is the problem.  Ever since I did this, I have periodic clipping at the amp and need to lower the level.  The first day I adjusted the console I had to decrease the mid/high amp by half, the next week was fine, then I had to lower it again this week.  The overall volume in the room is still fine and decreasing the amp is not creating an issue.  My question is, does anyone know why this is happening.  To fix it do I need a professional to come in a do a gain structure?  Is a gain structure at this point even needed?  If so, What would I gain?
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RYAN LOUDMUSIC JENKINS

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Re: AMP clipping
« Reply #1 on: February 04, 2014, 09:26:32 AM »

Who cares where the master fader is if the volume is correct.  Use your ears, not your eyes.  FYI, I really don't like the Driverack's way of setting gain.  I would rather have the gain on all if my amps set for either 26 or 32 dB gain and have all the amp pots turned up all the way.  Make the adjustments in the DR260.  By doing this you can set the level where you want it without adjusting the amps from that point on.
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Tim McCulloch

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Re: AMP clipping
« Reply #2 on: February 04, 2014, 09:58:59 AM »

Because your mixer clips at +22dBu.  In the analog world, the meter pointer would be slammed against the stop at +4dBu.  The analog mixer probably clips at about the same level, but the mechanical meter can't show that level.

Which "Crown 600" amps?  There are several models with the number 600 in the name.  That asked, I'd submit that your amps were probably shipped with input sensitivity of 1.4v.  That means that 1.4 volts of input level will drive your amp to FULL TILT BOOGIE and probably represents 32dB of voltage gain.  Note that my figures are speculative since we don't know exactly what amps you use... but mostly even that can be irrelevant WRT system noise floor.

Is this a mostly academic exercise or do you have a system noise problem?
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Paul G. OBrien

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Re: AMP clipping
« Reply #3 on: February 04, 2014, 10:28:00 AM »

Sounds like you completely missed the most important part of setting gain structure, it's the signal level at each gain stage that matters not the control positions. You set gain structure starting at the input gains and working your way through the console to the outboard gear and then the amplifiers with the goal of having the signal level hot but not clipping at all stages. In general you don't want any stage ahead of the amplifier to ever reach clipping and especially not any stage in a digtal processor like the DR260 so be sure to stay well below 0dB full scale in that device. So instead of using clipping as the reference I suggest you use 0dB or +3db on the meters as your target for all stages right through to the amplifiers, and set their gain controls wide open and use the output level controls in the Driverack to dial back the levels enough to prevent clipping. With that done you should have a reasonable amount of travel in the main fader to use as a volume control.
« Last Edit: February 04, 2014, 10:49:09 AM by Paul G. OBrien »
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TJ (Tom) Cornish

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Re: AMP clipping
« Reply #4 on: February 04, 2014, 10:31:13 AM »

I am continually in a quest to slowly optimize an existing system I am now supporting.  The full system is the Yamaha LS9, Driverack DBX-260, and crown 600 amps.  In the beginning, there was not a proper gain structure performed, amps were turned all the way up, and the LS9 console master fader set to about -20.  I wanted to do a gain structure to set the clipping level on all three devices.  I performed the gain structure to the best of my ability as the DBX 260 outlined. After I did this, I marked clipping with tape on all three devices and then lowered the master fader level and the amps.   A couple weeks ago I wanted to fix the master fader and individual channel fader level.  The master fader was -20, the individual channels were between -20 and -30, and the individual channel gain was very high.  I thought it would be better to increase the master fader to -5, the individual channel fader to around 0, and lower the channel gain significantly.  Doing this gives me more playing room when making channel fader adjustments.  Here is the problem.  Ever since I did this, I have periodic clipping at the amp and need to lower the level.  The first day I adjusted the console I had to decrease the mid/high amp by half, the next week was fine, then I had to lower it again this week.  The overall volume in the room is still fine and decreasing the amp is not creating an issue.  My question is, does anyone know why this is happening.  To fix it do I need a professional to come in a do a gain structure?  Is a gain structure at this point even needed?  If so, What would I gain?
Clipping at the amp (assuming you mean output clipping, not input clipping which can sometimes happen depending on the amp) means that you are asking more of your system than it can give.  Gain structure won't fix this, you need to turn it down.
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chris broadway

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Re: AMP clipping
« Reply #5 on: February 04, 2014, 11:05:11 AM »

Sounds like you completely missed the most important part of setting gain structure, it's the signal level at each gain stage that matters not the control positions. You set gain structure starting at the input gains and working your way through the console to the outboard gear and then the amplifiers with the goal of having the signal level hot but not clipping at all stages. In general you don't want any stage ahead of the amplifier to ever reach clipping and especially not any stage in a digtal processor like the DR260 so be sure to stay well below 0dB full scale in that device. So instead of using clipping as the reference I suggest you use 0dB or +3db on the meters as your target for all stages right through to the amplifiers, and set their gain controls wide open and use the output level controls in the Driverack to dial back the levels enough to prevent clipping. With that done you should have a reasonable amount of travel in the main fader to use as a volume control.


I performed the gain structure per the instructions in the DBX 260 manual.  I just didn't push knobs to "0" and call it a day.
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Tim McCulloch

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Re: AMP clipping
« Reply #6 on: February 04, 2014, 11:07:20 AM »


I performed the gain structure per the instructions in the DBX 260 manual.  I just didn't push knobs to "0" and call it a day.

Again, I will ask:  Is this an academic exercise or are you trying to solve an audible problem?
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"If you're passing on your way, from Palm Springs to L.A., Give a wave to good ol' Dave, Say hello to progress and goodbye to the Moonlight Motor Inn." - Steve Spurgin, Moonlight Motor Inn

Jordan Wolf

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Re: AMP clipping
« Reply #7 on: February 04, 2014, 11:14:42 AM »

Chris,

What are you trying to achieve by resetting the gain structure of this system?

Also, here's a good read on the topic.  There are a few different trains of thought, and each one is a compromise.

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Jordan Wolf
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Paul G. OBrien

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Re: AMP clipping
« Reply #8 on: February 04, 2014, 01:51:21 PM »

I performed the gain structure per the instructions in the DBX 260 manual.  I just didn't push knobs to "0" and call it a day.
Yet your original posts talks almost exclusively about control positions and never once mentioned signal level except when you said the amp was clipping, nothing about that suggests to me that you did anything correctly.
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chris broadway

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Re: AMP clipping
« Reply #9 on: February 04, 2014, 04:19:02 PM »

Chris,

What are you trying to achieve by resetting the gain structure of this system?

Also, here's a good read on the topic.  There are a few different trains of thought, and each one is a compromise.

when I did the gain structure the original goal was to have clip on the console = clip on the driverack= clip on the amps.  This way everything was level set to some point.  I marked on all three devices where my clip level was.  then I turned the Crown CTS 600 amps down to get a good blend in the room.  Since I turned the amps down after the gain structure to get the correct output of the speakers for my room, I thought I would never have clipping.  After that, the goal I was trying to achieve with the faders was to be able "ride the faders" when needed.  Since the channel faders where so low (-30 to -20) it was hard to make small increment adjustments.  I wanted to lower the channel gain to lift the channel fader to be able to operate between -10 and +5.  Also my in ears avioms get their level from the channel gain and I think there is flood light interference causing a buzz in the avioms.  I wanted to increase the master fader to allow even further lowering of the channel gain.  It sounded good in theory....
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ProSoundWeb Community

Re: AMP clipping
« Reply #9 on: February 04, 2014, 04:19:02 PM »


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