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Old 4th January 2008, 03:02 AM   #1
fumac is offline fumac  China
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Default How to do measurement on Class-D amplifier

hello everyone
i have been here for 2years
most of diyer don't know how to test a class-d amp
and class-d amp is quite different with class-A or AB
so i like to talk about my Experience at this.
also we can talk about how to use a simple equment to test class-d amp on diy.

many people on this forum have very good Experience.
so i also like to hear about other designers share their Experience of testing at class-d.
like eva, ChocoHolic, john.w, panomaniac, etc..

i will post many pictures of test method of measurement.
most of my time is spend on my job for living ,
so perhaps will be not post at a fast speed.

happy new year

fumac
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Old 4th January 2008, 03:23 AM   #2
fumac is offline fumac  China
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most of diyer have no very good test equipments for their project
perhaps just have an osc scope ,a multimeter and a signal generator .
in fact this is ok for test most of class-d amp.

Minimum set of testing equipment:
1.an osc scope: at least 100MHz, better is 300MHz.
2.a signal generator: 0~2MHz, can output Triangular wave, square wave, sine wave.
3. loads 2x4ohm >50W
4. multimeter

A better set of testing equipment(add on ):
5. another signal generator (30hz ,100hz, 400hz,1k, 2k,7k, 10k, 15k , sine wave), must can output a very low thd signal.

6. spectrum analyzer. at least 0~20khz, better is 0~300khz, or 0~10mhz.

all above are cheap price , and very easy to find it at 2nd hand market.
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Old 7th January 2008, 02:58 PM   #3
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Hi, Fumac,

Nice topic. I hope it will be usefull for all of us.

No.6, is it cheap ? How much did you pay for your HP spectrum analyzer?
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Old 7th January 2008, 03:06 PM   #4
BWRX is offline BWRX  United States
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Quote:
Originally posted by lumanauw
No.6, is it cheap ? How much did you pay for your HP spectrum analyzer?
Spectrum analyzers are a really nice tool to have at your disposal. Unfortunately, good spectrum analyzers (especially high bandwidth ones) are often more expensive than good scopes
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Old 8th January 2008, 02:44 AM   #5
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I found a filter for carrier wave, in IR AN1071 page 10
Attached Images
File Type: jpg dlpf.jpg (15.9 KB, 541 views)
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Old 8th January 2008, 06:20 AM   #6
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There used to be an app note on www.audioprecision.com about measurements on class D equipment. May be worthwhile to check it out.

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Old 8th January 2008, 06:39 AM   #7
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tooo busy at end of year (chinese new year)
so perhaps will delay

fumac
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Old 8th January 2008, 06:59 AM   #8
MOER is offline MOER  United States
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Default Class D

Fumac,

If you are too busy then why start this thread!

Most DIY'ers simply do not have the $$ to purchase test equipment.

A decent audio signal generator and a 10MHz scope will suffice for 95% of the guys. I do not count load resistors as test gear. The Mousers and DigiKeys of this world keep 50w load resistors and these can be used to make up virtually any load value required.

Spectrum analyzers are expensive but one can find good deals on Ebay.

Audio Precision is simply out of reach of most DIY'ers so this is not worth discussing. The measurement capability of the APs is probably not required by the guys on this forum.

In case you are wondering we do use APs and spectrum analyzers to test our amplifiers and switchmode supplies.

Steve Mantz
Zed Audio Corp.
CA
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Old 8th January 2008, 07:03 AM   #9
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Default Re: Class D

Quote:
Originally posted by MOER
Fumac,

If you are too busy then why start this thread!

Most DIY'ers simply do not have the $$ to purchase test equipment.

A decent audio signal generator and a 10MHz scope will suffice for 95% of the guys. I do not count load resistors as test gear. The Mousers and DigiKeys of this world keep 50w load resistors and these can be used to make up virtually any load value required.

Spectrum analyzers are expensive but one can find good deals on Ebay.

Audio Precision is simply out of reach of most DIY'ers so this is not worth discussing. The measurement capability of the APs is probably not required by the guys on this forum.

In case you are wondering we do use APs and spectrum analyzers to test our amplifiers and switchmode supplies.

Steve Mantz
Zed Audio Corp.
CA
Hi Steve,

The reason I mentioned the AP website is that they had an app note on the issues of measuring class D. I surely was not suggesting we all rush out to buy AP's! But I would think that knowing the issues would help in selecting what you want for test gear, what filters to use etc.

Jan Didden
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Old 8th January 2008, 07:20 AM   #10
fumac is offline fumac  China
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Default Re: Class D

Quote:
Originally posted by MOER
Fumac,

If you are too busy then why start this thread!

Most DIY'ers simply do not have the $$ to purchase test equipment.

A decent audio signal generator and a 10MHz scope will suffice for 95% of the guys. I do not count load resistors as test gear. The Mousers and DigiKeys of this world keep 50w load resistors and these can be used to make up virtually any load value required.

Spectrum analyzers are expensive but one can find good deals on Ebay.

Audio Precision is simply out of reach of most DIY'ers so this is not worth discussing. The measurement capability of the APs is probably not required by the guys on this forum.

In case you are wondering we do use APs and spectrum analyzers to test our amplifiers and switchmode supplies.

Steve Mantz
Zed Audio Corp.
CA

this topic will tell others how to test most of the class-d just use some cheap tools
but need time to do it

fumac
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