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Class D Switching Power Amplifiers and Power D/A conversion

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Old 26th October 2006, 05:37 PM   #21
djQUAN is offline djQUAN  Philippines
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the load that I'm planning on using this amp will be indeed 2 ohms.

the original recommended inductor value (in the daasheet) is 11uH but then jan said to wind the toroids with 26 turns so I did and measured 10.04uH. I thought "hey, it would be a shame to waste the litz wire and 1uH might not make much difference" so I stayed with it. but I still have enough to redo if necessary.

edit: do I still keep the zobel circuit and not have to change anything on that?

also, it's 2am and I need to wake up at 6am. so that means I need to get some sleep. be back tomorrow.
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Old 27th October 2006, 12:05 AM   #22
BWRX is offline BWRX  United States
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10uH instead of 11uH isn't a big deal.

You don't have to change the 22ohm resistor or 0.22uF cap.
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Old 27th October 2006, 07:53 AM   #23
djQUAN is offline djQUAN  Philippines
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ah. will try the 0.47uF cap when I get back at it.
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Old 28th October 2006, 09:55 AM   #24
djQUAN is offline djQUAN  Philippines
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tried the 0.47uF caps.........

with it, the output sine wave drops from 5V peak to 2V peak.

BUT! the caps heat up a bit, just warm to the touch and idle current of the amp goes way up. with the caps on both channels, my current limited supply can't provide enough current. might have to live with the higher sine wave output.
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Old 28th October 2006, 10:36 AM   #25
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That looks like a taken apart commersial amp

PERFECT boards!!!!
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Old 28th October 2006, 10:40 AM   #26
djQUAN is offline djQUAN  Philippines
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Quote:
Originally posted by Tekko
That looks like a taken apart commersial amp

PERFECT boards!!!!

one is a kit from 41hz so that would explain the green PCB but the other two are made by myself. looks perfect only in the pictures.

but thanks anyway!
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Old 28th October 2006, 09:51 PM   #27
BWRX is offline BWRX  United States
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Quote:
Originally posted by djQUAN
tried the 0.47uF caps.........

with it, the output sine wave drops from 5V peak to 2V peak.

BUT! the caps heat up a bit, just warm to the touch and idle current of the amp goes way up. with the caps on both channels, my current limited supply can't provide enough current. might have to live with the higher sine wave output.
Can you draw up a schematic of the output of your amp and how everything is connected?

If the ESR of the caps you used was pretty high then the large ripple current flowing through them will cause them to heat up some. They were film caps, right?
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Old 29th October 2006, 06:03 AM   #28
djQUAN is offline djQUAN  Philippines
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yes, they are film caps. 200V 0.47uF which look like yellow rolled ones but oval shaped.

the slight heatsing is not much of a hassle. it's the much higher idle current that bugs me.

I don't have any drawing, just the schematic of the chipset in PDF file.

the PDF file is too big to attach so here is the output filter portion of the schem from the PDF.

I basically wired the 0.47uF caps across C10 in the schem on both channels.
Attached Images
File Type: jpg output_stage.jpg (20.1 KB, 1323 views)
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Old 10th November 2006, 12:40 PM   #29
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Hey djQUAN

Which toroidal cores are you using for your monster power supply ?

I'm getting an amp going but with the overwhelming number of cores available and the useless sales support from electronics companies in ZA, i'd be keen to know which ones you are using.

Secondly, dont you find the diodes heat up quite a bit with the 1.9V forward drop when delivering the current ?

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Old 10th November 2006, 01:08 PM   #30
djQUAN is offline djQUAN  Philippines
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I have no idea what my cores are since I got them from a flea market.

but I measured their AL value to be about 5+mH/T^2 which is about on the high side and the outer dia to be around 2"


I used 6+6T for the pri and 24T for the sec.

I haven't tested the amp at full power yet since I still have to chassis to be built. I will be using the bottom plate (1/8" thick aluminum) as the SMPS heatsink.
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