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Author Topic: Class D amps & Inverters  (Read 4425 times)

Ben Vogel

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Class D amps & Inverters
« on: July 10, 2014, 07:06:28 pm »

Hey everyone! Recently I tried running one of my Peavey IPR 3000 DSP's off of a modified sine wave inverter that I have. The inverter is the type that you connect to a car battery and it provides two household outlets. The inverter displays it's warning sign as soon as I plug the amp in. The standby LED won't even light up. According to the manual this means that there is a short present somewhere. I then tried running a Crown XLS 402D, which is class A/B, off the inverter and it worked fine, although there was a slight hum. Does anyone have an idea why the Peavey won't work on the inverter? My guess is it has something to do with the switch mode power supply.
Thanks!
« Last Edit: July 10, 2014, 07:08:51 pm by Ben Vogel »
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John Roberts {JR}

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Re: Class D amps & Inverters
« Reply #1 on: July 10, 2014, 08:01:44 pm »

Just a guess but the IPR inrush current may be too much for your inverter... Did you try asking Peavey?

JR
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Kevin Graf

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Re: Class D amps & Inverters
« Reply #2 on: July 10, 2014, 08:10:05 pm »

Some newer equipment with SMPS's won't operate off an inverter. Heck, my Sears drill battery charger has a warning:
"Caution"
Do not use any DC to AC power inverters.
Charger will be Damaged!
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Ben Vogel

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Re: Class D amps & Inverters
« Reply #3 on: July 11, 2014, 01:00:04 am »

Just a guess but the IPR inrush current may be too much for your inverter... Did you try asking Peavey?

JR

That's what I initially thought. But it won't even light the standby LED which I find strange.
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John Roberts {JR}

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Re: Class D amps & Inverters
« Reply #4 on: July 11, 2014, 09:27:53 am »

That's what I initially thought. But it won't even light the standby LED which I find strange.

Peavey service should know if it is a common problem.

JR
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John Lackner

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Re: Class D amps & Inverters
« Reply #5 on: July 17, 2014, 03:44:41 pm »

Try using a true - or pure - sine wave inverter. Electronic gear is designed to operate with grid power, which is a pure sine wave. Modified sine wave inverters actually produce a modified SQUARE wave, most likely the source of your buzz.  Also, those cheapo modified sine wave inverters cant handle much inrush current. Try using an Exceltech true sine wave inverter, which is designed to handle large inrush currents. A less expensive alternative may be a Samlex, but the inrush current specs aren't quite the same.
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Steve M Smith

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Re: Class D amps & Inverters
« Reply #6 on: July 17, 2014, 04:01:37 pm »

Try using a true - or pure - sine wave inverter. Electronic gear is designed to operate with grid power, which is a pure sine wave.

True... but a switch mode power supply shouldn't be too bothered by the waveform  - especially if the first thing it does is rectify the incoming ac voltage.


Steve.
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Ben Vogel

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Re: Class D amps & Inverters
« Reply #7 on: July 20, 2014, 12:39:07 pm »

So I emailed Peavey and they replied saying that the problem is probably caused by the modified sine wave inverter as opposed to a true since wave inverter. I was just wondering if anyone had a technical explanation as to why, not just that it won't work!

Cheers
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John Roberts {JR}

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Re: Class D amps & Inverters
« Reply #8 on: July 20, 2014, 01:17:54 pm »

So I emailed Peavey and they replied saying that the problem is probably caused by the modified sine wave inverter as opposed to a true since wave inverter. I was just wondering if anyone had a technical explanation as to why, not just that it won't work!

Cheers

I can only speculate but first the problem us not because it is a class D amp which describes the audio amplifier. All else equal class D uses less energy to make the same power as other classes of amplifier.  Your problem is no doubt related to the switching power supply that could expose the inverter to an unusual start up load (perhaps a diode and caps), that it can't handle.

Your inverter apparently is seeing the low impedance load and thinks it's a short circuit. Perhaps you need a stronger inverter. A true sine wave inverter may be a little friendlier if it partially charges up the power supply, before reaching peak voltage. The cheap inverter just makes a square wave or multi step square wave and ASSumes the load will integrate the power over the entire waveform. In general I would think the peak current is more important than shape of the power waveform.

JR


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Re: Class D amps & Inverters
« Reply #8 on: July 20, 2014, 01:17:54 pm »


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