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Amp clipping confusion

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Fracture_clinic View Drop Down
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    Posted: 20 December 2018 at 4:37pm
This is a basic question so it's going in here.
As much as I've read there's one thing I'd just like clearing up.

Am I right or wrong in thinking that if I drive my amp from say a mixer that's got a hotter signal over a 3.5mm jack output, for example, the amp will output more at the same gain structure with a mixer and clip sooner because of this.

Two cases I observe:

Case 1:

So let's say its rated at 1400w 8r bridge gains at -3dB so putting out 700w in theory.

Driven by a laptop 3.5mm jack output (into crossover all filters assumed correct)

No clipping.


Case 2:

Same set up 1400w 8r bridge, same crossover and settings, same -3dB gain.

This time driven from a mixer.

Clipping observed with same gain structure.

What I'd like to know is, at the -3dB gain on the amp but driven by a mixer is the amp putting out more power than when driven by the 3.5mm jack or the same?

Note: The input signal lights in both cases are not clipping.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote spongebob Quote  Post ReplyReply Direct Link To This Post Posted: 20 December 2018 at 5:04pm
Think about if you installed the same tap in two seperate houses - one house has high water pressure, one has low water pressure. You could turn the tap to exactly the same amount of "on" in both houses, and a vastly different amount of water will come out depending on which house you're in. In this example, the water pressure is how much voltage (signal) you're sending to the amp and the tap is the "volume" (attenuation) knob on the front of the amp

Be it a phone or a mixer, any clip indicator (indeed use caution with clip indicators, they're often wildy inaccurate) is simply a rough indication if the device had reached (or exceeded) it's maximum possible output potential. The output potential of each device varies wildy, for example a phone or laptop 3.5mm output is designed to power extremely sensative drivers in a set of earbuds, where the outputs of a mixing desk are designed to cater for a large range of both sensative and unsensative devices

Almost everything in audio can be related to gain, and it's something you need to understand. Maybe have a read of https://www.minidsp.com/applications/dsp-basics/gain-structure-101

I'm sure someone will be along shortly to tell everyone my above examples are crap and not 150% correct but hopefully they help you understand abit more.


Edited by spongebob - 20 December 2018 at 5:05pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 20 December 2018 at 5:40pm
Another way of looking at is to consider the power amplifier as a voltage multiplier say input volts x 32, so 1 volt into the amp will give 32 volts out. The volume control on the power amplifier is an attenautor so reduces the input voltage to the power amp, the amp will still multiply it by 32.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 20 December 2018 at 9:56pm
Originally posted by Fracture_clinic Fracture_clinic wrote:

Am I right or wrong in thinking that if I drive my amp from say a mixer that's got a hotter signal over a 3.5mm jack output, for example, the amp will output more at the same gain structure with a mixer and clip sooner because of this.
  If the mixer output is on balanced XLR or TRS then yes, with everything else the same a balanced output is 6dB hotter than an unbalanced output from the same device.

Originally posted by Fracture_clinic Fracture_clinic wrote:

So let's say its rated at 1400w 8r bridge gains at -3dB so putting out 700w in theory.
For the comparison of signals you are trying to do here that is correct, but overall your experiment proves that  turning down the amp gains does not reduce the amps potential output at all, all it take to get full power is a little hotter input signal.

Originally posted by Fracture_clinic Fracture_clinic wrote:

What I'd like to know is, at the -3dB gain on the amp but driven by a mixer is the amp putting out more power than when driven by the 3.5mm jack or the same?
Yes, with the hotter input signal the amp is producing more output power.

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Crashpc View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Crashpc Quote  Post ReplyReply Direct Link To This Post Posted: 26 December 2018 at 5:14pm
Yes. That´s why it´s rather SAFE to turn your amp knob full right, and atenuate elsewhere in the chain - so nobody can come to the amp, and turn it up even more.

The amp knob doesn´t say how much power exactly will come out of it. there is more elements in the equation - input signal level, and amplification (gain) of the amp.

You turn down the amp gain, you turn up the input signal level, and you end up with the same power output.
Of course, every element can clip. If you turn the amp gain too low, and run the input too hot, it will most likely clip also, because you saturated the input stage.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote freddymendez Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2019 at 9:27am
Edit :)

Edited by freddymendez - 10 January 2019 at 11:16am
120-140 bpm, pianos and bass.
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