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Old 27th April 2008, 04:45 PM   #21
fumac is offline fumac  China
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Quote:
Originally posted by Pabo
lumanauw


You are correct to some degree. Saying that a higher frequency improves the high frequency reproduction needs to be proven, not just taken for a theoretical to practical translation.

Self oscillating amplifiers gets more loop gain the more it attenuates the switching ripple but at some point the propagation delay and switching nonlinearities will take over and cause more distortion. My experience is that going above 600kHz is difficult without generating very high levels of radiated emissions. Of course if one is only building for DIY it would be OK as long as the neighbours pace maker does not stop.

Saying that EMI decreases when the switching frequency is pushed above 1MHz is pure fantasy and based only on the assumption that if the residual decreases in amplitude the EMI decreases. If you switch twice as many times the radiated emissions double and if you want to use this higher frequency for improving the sound the DV/DT need to be shortened easily doubling the radiated noise again.

hello Pabo
good question.
do you heard about the AES17 filter?
most of testing class-d by ap system must insert this filter between ap system and class-d AMP
why? because the EMI, the The residual amplitude will make the input stage of AP system err.

you can take a look at our test. we have not connet the AES17 (same like).

MCD is the only one class-d amp can Measurement same like class-AB AMP
we can test the THD at 80k bandwidth, no other class-d can, because they must insert a 20~20khz bandwidth filter (AES17 same like)

rg

fumac
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Old 27th April 2008, 05:00 PM   #22
fumac is offline fumac  China
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Quote:
Originally posted by Eva
Fumac's claims are not based on scientific criteria.

yes eva, your are right
all my job is base on god,
one day ,two years ago,
when i Pray at a cave, : "God help me please, give me a class-d amp,give me a class-d amp..."
Suddenly, a pcb droped to my head.
then i got MCD,
here is the picture what happened that day

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Old 27th April 2008, 05:08 PM   #23
fumac is offline fumac  China
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Quote:
Originally posted by Eva
Fumac's claims are not based on scientific criteria.
yes you r right, eva,
after one year ago,
i goto there again,
i Pray at a cave, : "God help me please, give me a class-d amp, more power full, more power full..."
Suddenly, a new pcb droped to my head.
then i got MCD-V,



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Old 27th April 2008, 05:20 PM   #24
fumac is offline fumac  China
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Quote:
Originally posted by Eva
Fumac's claims are not based on scientific criteria.

yes you r right, eva,
after one year ago,
i goto there again,
i Pray at a cave, : "God help me please, give me a class-d amp, more and more power , more and more power ..."
not Suddenly agian, a new pcb droped to my head.
then i got mhzpower-4,


Click the image to open in full size.
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Old 27th April 2008, 05:43 PM   #25
Pabo is offline Pabo  Sweden
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fumac

The AES17 filter is not there to filter out EMI. The AES17 filter is a software filter simply there to filter out the harmonic components outside the audible band.

The AUX0025 filter on the other hand is a filter provided by Audio Precision to filter out HF noise from the signal before it is sent into the AP.

The radiated noise I am referring to is at a very high frequency. If you are using fast modern MOSFETs it usually occurs around 100MHz. Have you measured radiated noise according to CISPR22 or EN55022? If so please provide measurement data to convince me.

I am sorry I started filing replies here as you seem to be on a level much too low to listen to critisism with an open mind.
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Old 27th April 2008, 05:48 PM   #26
fumac is offline fumac  China
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Quote:
Originally posted by Pabo
fumac

The AES17 filter is not there to filter out EMI. The AES17 filter is a software filter simply there to filter out the harmonic components outside the audible band.

The AUX0025 filter on the other hand is a filter provided by Audio Precision to filter out HF noise from the signal before it is sent into the AP.

The radiated noise I am referring to is at a very high frequency. If you are using fast modern MOSFETs it usually occurs around 100MHz. Have you measured radiated noise according to CISPR22 or EN55022? If so please provide measurement data to convince me.

I am sorry I started filing replies here as you seem to be on a level much too low to listen to critisism with an open mind.

hi
S-AES17 Low Pass Filter
S-AES17 is a hardware filtering kit for optional installation in System Two, System Two Cascade or Cascade Plus that satisfies

the AES17-1998 specification for a standard low-pass filter for THD+N measurements of digital-to-analog converters (DACs) which exhibit high-level out-of-band noise.

APWIN 2.20 and later versions support the use of this filter. The filter can be set to either of two bandwidth selections: 20kHz or 40kHz. The S-AES17 Low-Pass Filter Option improves upon the capabilities of the earlier S2-AES17LP filter, which is no longer available.

please goto here
http://www.audiotech.com.tw/AES17%20Filter.htm?

aux0025 is a new filter for class-d
http://www.tti.co.uk/products-resale/ap/aux0025-1.htm?

we have no this two filters too, no any filter between class-d and AP system

we are testing our finished AMP to pass CE, and FCC, when it ready , i will post it for you



rg

fumac
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Old 27th April 2008, 05:58 PM   #27
Pabo is offline Pabo  Sweden
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fumac

Yes, I know what the AES17 filter spec says. I just thought you where referring to the one inside the audio precision software.

Anyway, I am not saying that it is impossible to switch at 1MHz or above. I am just saying that if the flanks are very fast and you switch at such a high frequency you will generate much more radiated noise. This noise is of course possible to handle but at a higher price and with more time spent to do it.

I would certainly like to see your emissions between 30MHz and 1GHz. Specify the measurement setup when you post the result so that it is easily comparable.
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Old 27th April 2008, 06:03 PM   #28
fumac is offline fumac  China
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Quote:
Originally posted by Pabo
fumac

Yes, I know what the AES17 filter spec says. I just thought you where referring to the one inside the audio precision software.

Anyway, I am not saying that it is impossible to switch at 1MHz or above. I am just saying that if the flanks are very fast and you switch at such a high frequency you will generate much more radiated noise. This noise is of course possible to handle but at a higher price and with more time spent to do it.

I would certainly like to see your emissions between 30MHz and 1GHz. Specify the measurement setup when you post the result so that it is easily comparable.
this test need a Shielding room to test it, so we send our amp to a Certification company to test it , when it ready, i will post it for you

rg
fumac
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Old 27th April 2008, 06:09 PM   #29
Pabo is offline Pabo  Sweden
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fumac

I see what you where saying about the AES17 filter. I do not know how the Audio Precision modules is made in detail but I was assuming that 60dB attenuation from 20kHz to 24kHz with less than 0,1dB attenuation at 20kHz was mode in the digital domain.

I was wrong there and I will need to study how that is done.
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Old 27th April 2008, 06:19 PM   #30
fumac is offline fumac  China
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Quote:
Originally posted by Pabo
fumac

I see what you where saying about the AES17 filter. I do not know how the Audio Precision modules is made in detail but I was assuming that 60dB attenuation from 20kHz to 24kHz with less than 0,1dB attenuation at 20kHz was mode in the digital domain.

I was wrong there and I will need to study how that is done.

if you do with one well know class-d amp , when you use 2 modules in one case, and when you put the two modules nearby each other,
that will found the noise floor goto very high. sometimes beep.
i have no this class-d amp modules, all this is one of our oem user told us,
they just can place the two module at two side of the case.
but our modules can place nearby each other,
and the noise floor same like stand alone, MCD nevre beep.
perhap this will let you know about the emi of mcd.
after all, i will post the test after ready

nice to meet you, and the post of the god is not for you.
sorry for it

rg
fumac
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