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Author Topic: AMP clipping  (Read 12653 times)

Ivan Beaver

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Re: AMP clipping
« Reply #20 on: February 07, 2014, 06:06:03 PM »

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.
The problem is that manufacturers of "up stream" devices (mixers-processors etc) are in a race to have the highest output voltage.  +24 to +30 is not extreme.

Yet many "power amp" will deliver full output with something in the range of +4 to +10 or so.

So the upstream devices can easily overdrive any power amp when they are pushed a little.

Yes you may have some extra "headroom" in those devices-but it is not "usable" since the rest of the system would already be at max output.

The only way to get more "real headroom" is to use larger amplifiers and/or more sensitive loudspeakers.
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Ivan Beaver
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Patrick Tracy

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Re: AMP clipping
« Reply #21 on: February 07, 2014, 09:03:17 PM »

The problem is that manufacturers of "up stream" devices (mixers-processors etc) are in a race to have the highest output voltage.  +24 to +30 is not extreme.

Yet many "power amp" will deliver full output with something in the range of +4 to +10 or so.

So the upstream devices can easily overdrive any power amp when they are pushed a little.

Yes you may have some extra "headroom" in those devices-but it is not "usable" since the rest of the system would already be at max output.

The only way to get more "real headroom" is to use larger amplifiers and/or more sensitive loudspeakers.

I'm not suggesting using all that headroom. I'm suggesting keeping levels right around +4dBu, with peaks maybe 6 or 8dB above that, through the system. And I'm betting the inputs on most amps designed for a +4dBu world won't clip before +12dBu. Then you can trim back the level as needed at the amp.

If the OP is clipping amp inputs his gain structure is wrong. If he's clipping the outputs it's a not-enough-rig situation. He could be doing both. Solving the input side of things will reveal if there's a problem on the output side.

Jean-Pierre Coetzee

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Re: AMP clipping
« Reply #22 on: February 08, 2014, 07:55:09 AM »

I will be opening up the 2450 to clean it out in the next few days then I will let you know where in the chain the input attenuators are sitting, in one of the other amps I opened recently they were directly after the input jacks so in that case it would make no difference where it is attenuated.
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Ivan Beaver

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Re: AMP clipping
« Reply #23 on: February 08, 2014, 08:46:52 AM »

I will be opening up the 2450 to clean it out in the next few days then I will let you know where in the chain the input attenuators are sitting, in one of the other amps I opened recently they were directly after the input jacks so in that case it would make no difference where it is attenuated.
I have never seen an amp (at least not an amp with balanced inputs) that had the attenuator right after the input jack.

The signal FIRST has to go through the balanced to unbalanced circuit (where the distortion can occur due to the limited voltage rails) THEN to the actual physical level control.

Would you care to name the model numbers of the amps in which the level/attenuator controls were right after the input jack?

I just find it hard to believe-and am curious.
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Ivan Beaver
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Brad Weber

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Re: AMP clipping
« Reply #24 on: February 08, 2014, 09:47:50 AM »

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.
The input sensitivity for an amplifier is the input signal level that results in full rated output.  If the input sensitivity of an amplifier is +4dBu then that is the input signal level that would result in the full rated output of the amplifier.
 
That is different than the rated maximum input level for the amplifier and most amps will accept signal levels well above that needed to create full output.  Addresssing those differences in level, the typically higher maximum input signal level to the lower level needed for full amp output, is one reason why you often use the amplifier's input attenuators.  If you have a +22dBu peak input signal and the amp's input sensitivity is +4dBu, then having 18dB of attenuation at the amp input would seem to match the peak input level to the full amplifier output.
 
The alternative is to provide that same attenuation via a fixed pad located between the amp and prvisuos device or to reduce/limit the peak output of the device before the amplifier (provided you are affecting the actual analog output).
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Jean-Pierre Coetzee

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Re: AMP clipping
« Reply #25 on: February 08, 2014, 09:54:33 AM »

I have never seen an amp (at least not an amp with balanced inputs) that had the attenuator right after the input jack.

The signal FIRST has to go through the balanced to unbalanced circuit (where the distortion can occur due to the limited voltage rails) THEN to the actual physical level control.

Would you care to name the model numbers of the amps in which the level/attenuator controls were right after the input jack?

I just find it hard to believe-and am curious.
I completely agree with you Ivan was just using this particular amp as an example and it has unbalanced inputs... I adopted it when I got this position and have removed it from service but have opened it up for shits and giggles. Its pretty much a no-name amp which is about as far from linear as you can get...

PS: The new 2450a's input clip point happens to be 22dBu which correlates to that of the rest of the system, not that it matters since I use the 223 to attenuate.
« Last Edit: February 08, 2014, 09:58:20 AM by Jean-Pierre Coetzee »
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Patrick Tracy

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Re: AMP clipping
« Reply #26 on: February 08, 2014, 12:17:56 PM »

I have never seen an amp (at least not an amp with balanced inputs) that had the attenuator right after the input jack.

The signal FIRST has to go through the balanced to unbalanced circuit (where the distortion can occur due to the limited voltage rails) THEN to the actual physical level control.

That agrees with the last couple of block diagrams I looked at.

ProSoundWeb Community

Re: AMP clipping
« Reply #26 on: February 08, 2014, 12:17:56 PM »


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