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Class D Switching Power Amplifiers and Power D/A conversion

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Old 11th September 2011, 05:19 PM   #1301
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Quote:
Originally Posted by CPX View Post
It seems i have omitted r8.With r7=82 kohm and r8=10 kohm and C1=1nF much of the signal modulated white noise has disappeared....
How does this affect to input gain ( 10K in serial with input signal)?
Do I need higher singal level for same power and gain?
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Old 11th September 2011, 09:06 PM   #1302
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Originally Posted by Th3 uN1Qu3 View Post
Remove any tape that is over the transformer. Put transformer into water. Boil for an half hour or more. Remove transformer from boiling water. Wrap your hands in kitchen towels or something and pull it apart. Or you can use a sharp knife or cutter where the halves meet, but do it carefully, if the glue isn't totally softened you'll end up cracking the core. Cracked cores can be superglued back together, they will still work fine.
Thanks. You're talking about EI cores, not toroids, right ?
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Old 11th September 2011, 11:08 PM   #1303
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Of course. There would be no need to boil a toroid, you simply unwind the wire off it. Toroids from PC PSUs are next to useless in higher voltage supplies anyway.
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Old 11th September 2011, 11:39 PM   #1304
CPX is offline CPX  Romania
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Quote:
Originally Posted by Dzony988 View Post
How does this affect to input gain ( 10K in serial with input signal)?
Do I need higher singal level for same power and gain?
Yes..you need a higher signal level...

Quote:
Originally Posted by Dzony988 View Post
Ok, most of P3 PC smps has EI 33. I cook it and take apart

One think I dont understand. When I increase a gap to 2mm on example with paper or peace of plastic on central leg of letter E, foreign sides ( 2 legs od letter E) are gaped too. I cant fastened core like before, I use strong glue tape but all the kicking. And when I wind the core, some of winding must go over the gap, I dont know what can i do!?

Can I wind it like on the picture? On example is needed 20 turns, 10 turns up and 10 turns down?

How much turn of wire is needed for inductance of 20 and of 30uH, with this core?
Thanks
You have to cut the center leg of the core.Use a rotational stone cutter..be carefull ferrite is breaking easy.

Last edited by CPX; 11th September 2011 at 11:59 PM.
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Old 11th September 2011, 11:47 PM   #1305
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Originally Posted by CPX View Post
Yes..you need a higher signal level...
Ok, thanks.

Do you know how much is voltage drop, and how much higher signal have to be.

If gain is 28x on Lacis schematic, I need 1.03VAC input signal for maximum power on +-42VDC.

With your change, instead of 1.03VAC, how much i needed?

thanks
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Old 12th September 2011, 12:09 AM   #1306
CPX is offline CPX  Romania
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Originally Posted by Dzony988 View Post
Ok, thanks.

Do you know how much is voltage drop, and how much higher signal have to be.

If gain is 28x on Lacis schematic, I need 1.03VAC input signal for maximum power on +-42VDC.

With your change, instead of 1.03VAC, how much i needed?

thanks
10000/470=~21

So you need ~21 volts..but i used r7=82kohm so i need around 5.72 volts rms..anyway this is testing only..i will search for the lowest stable value for r8 and highest for R7

Last edited by CPX; 12th September 2011 at 12:11 AM.
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Old 12th September 2011, 12:13 AM   #1307
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Ok, CPX.
Post here new value for R8 when you find out. No noise, that is important
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Old 14th September 2011, 09:56 PM   #1308
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I can not stop 50hz hum with gapped core..with ungapped core i was able to reduce it to very low levels..

With gain 10x also white noise is very smal but then it is necesary to add ultra low noise input buffer with gain 3x..

But I have many more problems..amp is not souding good at all...please try to listen with 0.22 ohm load at low volume..it sounds distorted or not?..does output level decrease with added load or not?
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Old 14th September 2011, 11:58 PM   #1309
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With smaller impedance distorsion is bigger. 4ohms load has bigger distorsion of 8ohms load. This is normal for all kind of amlifiers. Ofcourse you have lot of distorsion on 0.22 ohms load.

P.S I dont know why do you have a noise. Probably because you still use test board and bad grounding. Whit PCB and good grounding I don have noise, and I use gaped EE core. Well, I dont know, maybe little when I'm very close to speaker, but many comercial AB and G amps have it. Main problem with noise is in input part, grounding and gain (that was problem with my desing)

Regards

Last edited by Dzony988; 15th September 2011 at 12:02 AM.
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Old 15th September 2011, 12:11 AM   #1310
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In some kind of good PA AB amps, I have seen two GND's. One gnd is power gnd (central wire from transformer and capacitors) and second gnd is input gnd ( from signal source).
This two GND's are not the same wire on PCB. All input stage of amp is input gnd and finaly power GND is conected to input GND accros 10 ohms 2W resistor on PCB.

Try this one, maybe helps.
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