Would an 12v to 240v inverter run an amp?

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fatmarley

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Joined 2003
#1
Quick question for you electronic gurus.
I'd like to take some ground-plane measurements of my speaker and i'd also like to use my Onix oa21 (50w channel) amp because I spent a while calibrating it in Lspcad.

Would one of those cheap eBay inverters, hooked up to the car battery have enough grunt to power my amp? The amp is only used in short bursts of a few seconds to get a measurement.
 
#4
Please note that efficiency when running an amp on an inverter is far less than the inverters maximum efficiency as the average music signal has only about 10% of it's peak output.

Also note that many inverters are not built to handle variable loads like an amplifier but meant to be used with a reasonably stable load.
 
#6
The efficiency only goes down because idle losses start dominating when the power output decreases. For ground plane measurements outside I cannot see you needing any more than 5 watts of clean power, let alone 50, or however more, even a small inverter should be able to power an amp to deliver power like that.

The other option is to buy a small class D amplifier from one of the ebay sellers that are designed to work from single supply rails at low powers and power it directly from the cigarette lighter. The only thing to watch out for there is that the class D output will be bridged and not referenced to ground, so two channel measurements would be out of the question.
 
#8
5th element said:
The efficiency only goes down because idle losses start dominating when the power output decreases. For ground plane measurements outside I cannot see you needing any more than 5 watts of clean power, let alone 50, or however more, even a small inverter should be able to power an amp to deliver power like that.

The other option is to buy a small class D amplifier from one of the ebay sellers that are designed to work from single supply rails at low powers and power it directly from the cigarette lighter. The only thing to watch out for there is that the class D output will be bridged and not referenced to ground, so two channel measurements would be out of the question.
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I tried to use my Muse M20 EX2
 but I couldn't get the SPL high enough to get a measurement. I had the same problem with a 20w channel, Teac micro system.

When taking measurements I have the volume knob of my Onix in the 12 o'clock position, so quite loud really. Don't know how many watts it would be pushing out though.
 
#10
but I couldn't get the SPL high enough to get a measurement.
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I find this amazing, "standard" SPL measurement and speaker curves are made using 1 W RMS !!!😕

Any bridged car type amplifier fed straight 12V will give you up to 8W RMS at 8 ohms, ample measuring power.

Please describe your setup, there must be something wrong.

And, sorry, but you can't just say:
When taking measurements I have the volume knob of my Onix in the 12 o'clock position, so quite loud really. Don't know how many watts it would be pushing out though.
Click to expand...
😱

That is not a "measurement" to begin with.
And any curve under such conditions is meaningless.
 
#11
When taking measurements I have the volume knob of my Onix in the 12 o'clock position said:
I'm reminded of the movie "This is Spinal Tap".....

Musician: "I have a special amplifier for my guitar. It's louder than other amps.....!"

Interviewer: "Why is that?"

Musician: "Because the volume control doesn't stop at 10. Mine goes all the way to 11....!"

(A must see, classic movie!)
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#12
Spinal Tap is a great movie.

I did write a long reply trying to defend myself regarding my measuring technique but can't be bothered to argue (lifes too short). I know i'm getting good, accurate measurements, so that's all that counts.

I'm still unsure if an inverter will run my Onix. Anyone else have have an opinion? I may have to just buy one and see for myself.
 
#14
JMFahey said:
"I couldn't get the SPL high enough to get a measurement"
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In JustMLS (LspCAD) you have to press 'Test levels' to try to get the 'Level meters' high enough for a good measurement (Yellow is perfect, red is too much). I also have to adjust the gain knobs on my M-audio Mobilepre to make sure the signal stays in the green and out of the red. With the Muse/Teac, no amount of adjusting could get the levels high enough for a descent measurement. IIRC I couldn't even get the green bars in JustMLS to light up, let alone the yellow.
I can't see how I could have done anything wrong because there are only three knobs to adjust, but also I have no problem taking measurements with the Onix. If I can take measurements with the Onix, then why can't I with TWO low powered amps?
 
#15
Those cheap "modified" sinewave inverters are usually not very modified from a square wave. The power transformer in the amp is likely to get a little warmer than usual from all the harmonics and who knows what kind of noise will make it into the amplifier output signals... but it should "work".
 
#16
Andrew Eckhardt said:
Those cheap "modified" sinewave inverters are usually not very modified from a square wave. The power transformer in the amp is likely to get a little warmer than usual from all the harmonics and who knows what kind of noise will make it into the amplifier output signals... but it should "work".
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As long as I get a good measurement of the lower end of the frequency response, i'll be happy. It's just to confirm that my near-field to far-field splicing technique is accurate (the join around 500Hz).
 
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