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Author Topic: power amp signal meter question  (Read 1106 times)

mexicanyella

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power amp signal meter question
« on: February 01, 2017, 12:20:49 AM »
Hi all...

I've been using a Peavey M-3000 power amp as part of a makeshift band-practice bass rig lately, and I have a question about whether I can translate the levels I'm seeing on the LED signal meter into approximate output levels in watts. The meter has 10 LEDs labeled in -dB increments, from -27 dB to -0dB, in 3 dB steps.

Peavey says the amp can deliver 130W into an 8 ohm load, which is what I'm driving. Does a 3 dB drop in output power equate to a halving of the output watts? Like, if I am running settings throughout my signal path that result in all but the last light lighting up on the peaks, does that mean that those peaks are roughly half of 130W, or 65W? Or is that 3 dB thing only applicable to acoustic output, and with electrical signals it's some other relationship?

I'd like to know, roughly, what that meter means in terms of electrical output, in case I ever have to plug into a speaker with a lower power handling capability than what the amp can deliver.

Thanks in advance!

Mexicanyella

g1

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Re: power amp signal meter question
« Reply #1 on: February 01, 2017, 01:40:19 PM »
Not sure how fast the response is, it probably shows peaks rather than average, but I'm not sure.
The meter is calibrated for full power at 2 ohm load, so I doubt it would translate to 8 ohms in a purely linear manner.
"The M-3000 features a 10-segment LED indicator that registers output power at 2 ohms in 3dB increments from -27dB to +0dB."

Vitrolin

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Re: power amp signal meter question
« Reply #2 on: February 01, 2017, 04:43:12 PM »
The meter is driven by a LM3915, and its a voltage dB meter, so indicates how far the output voltage is from railvoltage.
or as manual states headroom left.


Loudthud

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Re: power amp signal meter question
« Reply #3 on: February 01, 2017, 05:12:01 PM »
Chances are that if 0dB is 300W at 2 Ohms, it's 150W at 4 Ohms and only 75W at 8 Ohms. The power supplies sag quite a bit on these amps with a 2 Ohms load.

Vitrolin

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Re: power amp signal meter question
« Reply #4 on: February 02, 2017, 03:19:15 PM »
manual states 130W in 8ohm 1%THD
at clipping

https://assets.peavey.com/literature/manuals/80300574.pdf

J M Fahey

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Re: power amp signal meter question
« Reply #5 on: February 02, 2017, 08:23:28 PM »
In general VU Meters are not precision or even measuring instruments by far, specially Led Strip ones, they are more of visual candy than anything else.
Besides, they jump too fast to be *that*  useful on normal program material.

Meaning : donĀ“t get too anxious about what they show.

Original ones  were better, those in AM broadcast radios to avoid overmodulation and splattering signal all over the spectrum and on recording equipment (vinyl and tape) to avoid distortion but in any case too slow to catch peaks, could only adequately cope with average (relatively slow)  signals.

The good one was the British/BBC version, the famous PPM, holding peaks long enough to be seen, with Logarithmic scale and calibrated in DB.
« Last Edit: February 02, 2017, 08:26:04 PM by J M Fahey »

Loudthud

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Re: power amp signal meter question
« Reply #6 on: February 02, 2017, 08:56:05 PM »
manual states 130W in 8ohm 1%THD
at clipping

The chip has no way of knowing what the load is. It just reads Voltage at the output. The amp can put out more Voltage into 8 Ohms without clipping, but the chip just knows that it is more than the calibrated 0dB Voltage.

mexicanyella

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Re: power amp signal meter question
« Reply #7 on: February 03, 2017, 12:40:59 AM »
Thanks all, for the info. I will use the LED signal meter to inform my bandmates, visually, that I am playing something important enough to warrant an LED signal meter, and I will use my ears, not the LEDs, to detect driving the speaker(s) too hard.

 

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