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Old 25th August 2012, 05:44 PM   #1
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Default Test Signal for max power test of Class D?

Hello,

If i have a 60W Class D guitar amplifer and i want to do maximum power testing on it...then what frequency of sine wave input signal should i feed to it?

Is it ok to choose anything between 100 and 1000 Hz?
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Old 25th August 2012, 06:31 PM   #2
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You shouldn't test amplifiers with sine waves at all. The only thing you will effectively test feeding an amplifier sine waves is the power supply.
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Old 25th August 2012, 06:49 PM   #3
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Ok Thanks,

Thats actually what i mean to do...to test the power supply which powers the class d amp.

So which frequency of since wave would you choose?
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Old 25th August 2012, 07:49 PM   #4
Pafi is offline Pafi  Hungary
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I use 30 Hz, this way the puffer capacitors and short term overloadability are tested too. But not pure sine, 1:1 burst instead! (Eg. 1 sec signal, 1 sec rest) Input filter may have to be disabled.
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Old 25th August 2012, 08:28 PM   #5
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You need to be careful with sine waves into a class d amp.
Class d half bridge can suffer from bus pumping raising the power supply voltage and possibly damaging the power suppply and amplifier.
It seems to be worst with low frequencies.
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Old 25th August 2012, 08:36 PM   #6
AP2 is offline AP2  Italy
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if you have an oscilloscope, put a probe on the output (on load) and ch2 on rail voltage. (this help you to understand some things)
Use 33-66ms burst 1Khz. if the amplifier is created along with the psu for guitar, is probabbile that has been designed for the frequency range suitable.
33ms (duration of sine 1K) , 66ms pause.
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Old 25th August 2012, 09:07 PM   #7
Pafi is offline Pafi  Hungary
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Quote:
Originally Posted by nigelwright7557 View Post
You need to be careful with sine waves into a class d amp.
Class d half bridge can suffer from bus pumping raising the power supply voltage and possibly damaging the power suppply and amplifier.
It seems to be worst with low frequencies.
This is why it has to be tested. :-) Maybe not with full power immediately.
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Old 26th August 2012, 03:43 PM   #8
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Thanks.........I note that some diy'ers are choosing 30Hz , and some 1KHz, and some want burst operation, and some not.

Is there any concensus of opinion.

Also, why 30Hz....?.....why not 10Hz?

And why 1000 Hz, ...why not 500Hz?

Does any reader know of a graph of input sine wave frequency and power draw from the power supply powering the class d amplifier?

For example, would a 30Hz sine wave into a class d amplifier make the power supply deliver more power than a 1000 Hz sinewave into a class d amplifier?

Also, why sine waves?....we are testing the power supply, not the amplifier.......why not put a square wave signal into the class d amp.......?

...surely that will make the power supply deliver the maximum power, and then we can really see if the power supply is fit to supply the class d amplifier under all worst case conditions?
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Old 26th August 2012, 03:55 PM   #9
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Quote:
Originally Posted by eem2am View Post
Hello,

If i have a 60W Class D guitar amplifer and i want to do maximum power testing on it...then what frequency of sine wave input signal should i feed to it?
you know exactly what you want?
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Old 26th August 2012, 05:40 PM   #10
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Basically i am asking about testing an SMPS which is designed to supply a 60W class D amplifier.

What signal would you put into the class d amplifier to test that the power supply was well capable of doing the job reliably for a long time.?

I would say that the highest power would be drawn from the smps when a square wave signal of any frequency was fed to the class d amplifier....am i correct?
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