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Author Topic: AMP clipping  (Read 1841 times)

Nathan Lehouillier

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Re: AMP clipping
« Reply #10 on: February 04, 2014, 09:53:46 pm »

1) PFL/Solo each channel set gain to a level so there is enough head room to not clip.
2) Set all channels to 0 then start bring up the main when you have a good level to start
mixing stop.
3) Start building your mix.
If you are worried about where your main fader is your not mixing with your ears.
If your amps are clipping your just out of amplifier power it has nothing to do with
gain staging. At this point you need more "RIG FOR THE GIG" I think that was Geri O.?
A CTS 600 is a very small amp but I don't know what your really doing so its hard to help.

Nate
KDS&L
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Glenn James

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Re: AMP clipping
« Reply #11 on: February 04, 2014, 10:01:54 pm »

If your amps are clipping first, then you have all you are going to get out of your system. If you clip anything else prior or at the same time as your amps, you have lost too much headroom in your signal chain.
Set it up so your amps clip before full output of any channel or output on your desk or processors.
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Jean-Pierre Coetzee

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Re: AMP clipping
« Reply #12 on: February 05, 2014, 06:49:55 am »

What did you use to create your clipping point while doing gain staging? Noise, if so which noise? Music?(Lord help you), or something else? Also are you saying that your amps clip before the rest of the system and this is what you want to solve or is the entire system clipping at the same time?

Another point is what Tim was asking and that is why did you have to redo the gain staging? Was it for sh*ts and giggles or was there an inherent problem...

For your Aviom problem I am pretty sure Aviom uses a digital A-Net link which is immune to noise(well it will drop out if there was excessive noise not introduce that noise to the output signal), the problem is from your Direct outs(which I believe you would be using, are you using the A-Net card in the LS-9, does it have an A-Net option?) and what have you got after your controllers on stage(A-16ii i will assume). If you have IEMs like it seems you do the interferance is likely being introduced right there since as far as I know the A-Net signal come off digital straight from the LS-9 and therefore the noise cannot be anywhere else...

Is the buzz on the mains as well?
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Patrick Tracy

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Re: AMP clipping
« Reply #13 on: February 05, 2014, 01:59:04 pm »

1) PFL/Solo each channel set gain to a level so there is enough head room to not clip.
2) Set all channels to 0 then start bring up the main when you have a good level to start
mixing stop.
3) Start building your mix.
If you are worried about where your main fader is your not mixing with your ears.
If your amps are clipping your just out of amplifier power it has nothing to do with
gain staging. At this point you need more "RIG FOR THE GIG" I think that was Geri O.?
A CTS 600 is a very small amp but I don't know what your really doing so its hard to help.

Nate
KDS&L

Here's one way I do it.

1. Amps off
2. Set input gains per manual
3. Set lead vocal fader to 0
4. Set master fader to 0
5. Set DSP input (or other gain stage between mixer and amps, or amp inputs*) to -∞
6. Turn amps on
7. Bring up DSP input (or...) until lead vocal sits on top of stage volume
8. Mix other inputs to that

*Using amp inputs or the output side of the DSP to trim the system may make DSP limiter thresholds incorrect.

Brad Weber

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Re: AMP clipping
« Reply #14 on: February 06, 2014, 04:23:30 pm »

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.
What are you adjusting when you adjust the DR260 output levels, is it the digital signals pre A/D or the analog signals post A/D?  Are the maximum analog input and output levels of the DR260 the factory default +22dBu or may they have been set for +14dBu or +30dBu via the internal jumpers?
 
If you are actually adjusting the analog output of the DSP then you can adjust the output levels of the DSP to match the input sensitivity of the amps and whether you adjust the levels at the DSP output or at the amp inputs provides basically the same effect.  However, if you are instead adjusting the digital signal level of the DSP, which I think you are, then you may want to use the amp input attenuators for account for how the maximum DSP analog output relates to the amp input sensitivity. 
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Jean-Pierre Coetzee

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Re: AMP clipping
« Reply #15 on: February 07, 2014, 05:57:19 am »

Well here is my take on decent gain structure after the console.

Find out the maximum(clipping) input and output voltage/level in dBu/dBv/dBm(you have old gear 0_o) of all your equipment, let's go with what I have in one of our rooms.

Yamaha MG32fx: +24dBu output
DBX 223xs +22dBu input: +21dBu output
QSC RMX2450 input +4dBu

Now to start off with we can see that the input sensitivity of the MG32fx and the DBX223xs is very similar and to adjust the input attenuators  of the DBX unit down 2 db is really a pointless exercise IMHO but can be done. The biggest thing here is the output of the 223 is 21dBu but the input sensitivity of the RMX2450 is +4dBu, this will cause the clip point of the amp to sit way below that of the rest of the system, the easiest way to fix this would be to turn down the output of the 223 by 17 dB or to turn the input attenuators on the RMX2450 down by 17dB... I would honestly do this at the 223 instead of the amp but as far as I know it shouldn't make a hell of a lot of difference...

You would if you had limiters in place set the limiter to not allow the amp to receive enough input voltage to allow the speakers to exceed their peak power rating but that is a whole other story, you should also not be slamming into your limiter that whole time, it is there to protect your speakers from sudden spikes like a dropped mic, not there to control your fingers.

If there is any mistakes in this please call me out and I will edit it.
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Robert Weston

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Re: AMP clipping
« Reply #16 on: February 07, 2014, 10:45:44 am »

Chris Broadway -

where are you located?  Perhaps someone on the forum is near you and can stop by to help you with the system.

There's a lot of variables involved with setting levels (input -> output).  Simple setup procedures (as outlined in the DBX manual) are only starting points.  Consider this... when setting gain levels for a band (all things being equal), would you set the same peak-level on a vocal as you would for a kick drum?  Setting the gain levels thoughout the signal chain starts with the input.
 
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Patrick Tracy

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Re: AMP clipping
« Reply #17 on: February 07, 2014, 01:45:34 pm »

The biggest thing here is the output of the 223 is 21dBu but the input sensitivity of the RMX2450 is +4dBu, this will cause the clip point of the amp to sit way below that of the rest of the system, the easiest way to fix this would be to turn down the output of the 223 by 17 dB or to turn the input attenuators on the RMX2450 down by 17dB...

You're comparing a peak output level with a nominal input level. I'd be willing to bet that the 2450's output will clip before the input does.

Ivan Beaver

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Re: AMP clipping
« Reply #18 on: February 07, 2014, 03:21:58 pm »

You're comparing a peak output level with a nominal input level. I'd be willing to bet that the 2450's output will clip before the input does.
Maybe not.  It is entirely possible (and I have measure this on a couple of power amps) that by turning down the input gain enough-that the actual front end (before the level control) can clip or exceed the voltage rails of input stage.

I don't know about the 2450-but if the rails are low (say +-15V) and the sending device has higher rails, then the input can clip before the output does.

That's the reason a physical pad is the best way to attenuate the signal.
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Patrick Tracy

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Re: AMP clipping
« Reply #19 on: February 07, 2014, 03:50:41 pm »

Maybe not.  It is entirely possible (and I have measure this on a couple of power amps) that by turning down the input gain enough-that the actual front end (before the level control) can clip or exceed the voltage rails of input stage.

I don't know about the 2450-but if the rails are low (say +-15V) and the sending device has higher rails, then the input can clip before the output does.

That's the reason a physical pad is the best way to attenuate the signal.

Yeah, if you turned down the amp level controls enough and they follow the first active stage you could clip that first stage before clipping the output. But wouldn't that be when the drive signal is abnormally high and the target volume is abnormally low?

In my experience (with one PLX, a CE series, a Stewart and some Peaveys, plus various installed systems) with normal average drive levels around +4dBu that doesn't happen. Rather than "making everything clip at the same level" I aim for +4dBu average levels through the system. If I do that I seem to have adequate headroom in spite of different peak capabilities of the gear.
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