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Class D Switching Power Amplifiers and Power D/A conversion

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Old 28th August 2010, 03:14 PM   #1781
zdr is offline zdr  Belgium
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I changed input caps with Vishay MKT1813 2,2uF, removed input resistors/caps, and changed output coils to Vishay toroidals 4,7uH.

Caps:
Vishay - MKT 1813 - Metallized Polyester Film Capacitor MKT Axial Type
Coils:
Vishay - Inductors - TJ3-HT - Toroid, High Current, High Temperature, Radial Leaded

I can't say I hear any difference from before, might be a bit better sounding overall.
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Old 28th August 2010, 03:38 PM   #1782
sendler is offline sendler  United States
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Default 20uH

Were your original coils 20uH or 10uH?
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Quote:
Originally Posted by zdr View Post
I changed input caps with Vishay MKT1813 2,2uF, removed input resistors/caps, and changed output coils to Vishay toroidals 4,7uH.

Caps:
Vishay - MKT 1813 - Metallized Polyester Film Capacitor MKT Axial Type
Coils:
Vishay - Inductors - TJ3-HT - Toroid, High Current, High Temperature, Radial Leaded

I can't say I hear any difference from before, might be a bit better sounding overall.
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Old 28th August 2010, 04:04 PM   #1783
zdr is offline zdr  Belgium
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Quote:
Originally Posted by sendler View Post
Were your original coils 20uH or 10uH?
.
Looks like they were 22uH. And yes, I removed the supressors too.
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Old 5th September 2010, 12:30 PM   #1784
zdr is offline zdr  Belgium
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I tried to run without a fan, but the heatsink gets too hot. I don't think making it 30% bigger would decrease temp enough to run passive, especially if placed in a box. Anyone tried to take out EMI with filtering?

I see there is an improved board with different heatsink and fan. Anyone tried it? What is the improvement?
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Old 8th September 2010, 12:51 AM   #1785
sendler is offline sendler  United States
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Default Tuning the filter

Copied from another thread where the poster finds the sound too bright with 10mH coils (even though I am using 3.5mH).
.
That is the problem with the Class D amps that have the filter outside the feedback loop. The frequency response is very load dependent at the top. I would try a 12mH coils and if it it still too bright keep increasing until the sound is just on the edge to maintain as much ripple and loss (good for the sound even if it is inefficient) as possible. You can then add a Zobel to tame the last of the edginess. (R and C in series, the whole in parallel between the speaker terminals). Start with .47uf and 10 pieces of 70 ohm 1/4 watt resistors twisted together in parallel to make 7 ohms. Measure and listen as you cut one resistor at a time to raise the value until you get just enough peak remaining to bring out the detail but not so much that it still sounds too bright. Probably around 10-15 ohms. Once you get an idea of the value, you can replace the parallel resistor mess with something nicer in a 5 or 10 watt resistor. It is a hassle to do this and the results are only good for one particular speaker but it is worth it in order to get the best resolution from the Tripath chips. I am sure you will find that a text book filter with no peak will sound veiled so measure AND listen as you go.
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Originally Posted by MusicSeeker View Post
Hi Scott

in fact my speakers are 4 ohms nominal, 2 ways.
But the impedance of the tweeter is above 20 Ohms at 20 Khz from its specification
I hesitate between two options

- add an RC compensation network (R and C in serie, the whole in parallel to the load)
- tune the L and C value to find flat response

any thoughts ?

GaŽl
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Last edited by sendler; 8th September 2010 at 12:57 AM.
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Old 8th September 2010, 02:28 AM   #1786
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Quote:
Originally Posted by zdr View Post
I tried to run without a fan, but the heatsink gets too hot. I don't think making it 30% bigger would decrease temp enough to run passive, especially if placed in a box. Anyone tried to take out EMI with filtering?

I see there is an improved board with different heatsink and fan. Anyone tried it? What is the improvement?
I found that the purple Zalman passive heatsink got too hot without a fan also.

I ended up putting a 120mm fan running at around 400rpm over the heatsink, it's quiet and it seems to keep the heatsink cool enough.
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Old 8th September 2010, 08:26 AM   #1787
Baka is offline Baka  Montenegro
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Default Tuning the filter

Hi Sendler,

Do better quality capacitors and resistor prove beneficial in the filter, according to your experience?

I would also like to know, since I am using the MeanWell SMPS, is it absolutely necessary to connect its ground to earth?

Thanks, Baki
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Old 8th September 2010, 09:04 AM   #1788
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SMPS that have a third Safety Earth/PE pin should always be connected to PE ! Since they are equipped with a net filter to avoid emission of RFI they need to get rid of this via the PE pin. Of course the primary goal is safety when live AC wiring touches the metal case of the SMPS. When PE is not connected half of the net voltage will be at the case of the SMPS because of the used net filter !! Not safe, not good. So please connect the PE pin to PE for correct functioning of the SMPS and you and your families safety.

On the subject of connecting signal GND to PE (which is a popular subject the last days it seems): I would never connect signal GND to PE directly as pollution from PE will creep into the audiocircuits which has no benefits. On the contrary. It is better to connect signal GND with 10 to 100 Ohm to the metal chassis case (which must be connected to PE). I only recently learnt that Mr. Pass uses a CL60 thermistor or NTC ( 10 Ohm at 25 degrees celsius) for this which seems a simple and elegant solution for this. Look at page 2 and 3 how to connect it.

http://passdiy.com/pdf/balzenpre.pdf

Problem with directly connecting signal GND to PE is that "ground loops" are unavoidable. Just think of the coax antenna cabling of the FM tuner of which the braid is connected to PE => loop !
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Last edited by jean-paul; 8th September 2010 at 09:08 AM.
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Old 8th September 2010, 09:32 AM   #1789
Baka is offline Baka  Montenegro
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Many thanks jean-paul.

Regards,

Baki
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Old 8th September 2010, 09:37 AM   #1790
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Just saw this in another thread :

Audio Component Grounding and Interconnection

It had this comment which I have seen in amps from the seventies/eighties (I think in Onkyo Amps):

Quote:
isolating the chassis from the earth with a 600V 35A bridge wiring up the diodes in both ways would solve many of the problems without compromise of safety and without the inherent problems of a loopbreaker
There are more ways to Rome. It is important to build things safe and at the same time "RF/audio clean".
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Last edited by jean-paul; 8th September 2010 at 09:41 AM.
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