T106-2 core vs.??? core Amplifier problem - Page 2 - diyAudio
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Old 8th January 2008, 09:27 PM   #11
Eva is offline Eva  Spain
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44 turns on T106-2 should give 26uH which is a suitable inductance value. Wire gauge is not critical as long as it can handle speaker current without overheating. With +/-40V rails, 680nF output capacitor, and 300Khz idle operation this should produce a bit over 1Vp-p carrier residual. If it doesn't then there is something wrong with your circuit.

I bet the offset has been always there but at first you just didn't notice. You can try comparing one channel with the old inductor against other with the new (if you are enough scientific minded).
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Old 8th January 2008, 09:30 PM   #12
zox2003 is offline zox2003  United States
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Eva I have 470nF on output currently...I will just add some turns to reach same effect like with 680nF

Just to remind you that I loaded these modules to full power (with old core) and they worked beatifully.So I do not see what would be 'wrong' with circuit.....Maybe....
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Old 8th January 2008, 09:48 PM   #13
zox2003 is offline zox2003  United States
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And as far as offset...I use same PCB and just swapped inductor and that is where I have seen DC offset problem (THAT is my main problem) so it was not there with old inductor....MEASURED 100%...That is a first thing I checked on both versions (old/new inductor)...
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Old 9th January 2008, 03:58 PM   #14
zox2003 is offline zox2003  United States
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OK...

Amplifier is fixed...I used Eva's advice and inserted 100uF capacitor in series with 1K that goes from pin 2 to GND (LM311) + I added variable resistor (5K) to offset adj. pins on LM311 (with this I was able to do precise adjustment).So far so good...I am attaching updated schematic here:

Thanks,Eva
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Old 9th January 2008, 06:01 PM   #15
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zox2003;
I'm really glad that you've your amplifier working right, and that you've learned a new circuit trick.

But I do have a question for you, I also need to learn some circuit tricks myself: why do you have the 5 CD4069 inverters in series? Do you want to create a delay?
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Old 9th January 2008, 08:03 PM   #16
zox2003 is offline zox2003  United States
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Yes, that is why I used 5 of them (inverting + creating delay time).
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Old 18th March 2011, 12:00 AM   #17
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Inductors in class d are a minefield for the uninitiated.
I used power inductors to start with and they got very hot around 120 degrees.

Someone suggested a t106-2 core, I found this with 2 yards of SWG18 worked fine with my class d amplifier. It doesnt even get warm. I also found a little extra inductance didnt load the amplifier quite as much.

You are finding different levels of carrier on the output due to different inductances.
The inductance is basically a voltage divider with the output capacitor.
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Old 18th March 2011, 01:25 PM   #18
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Quote:
Originally Posted by nigelwright7557 View Post
Someone suggested a t106-2 core, I found this with 2 yards of SWG18 worked fine with my class d amplifier. It doesnt even get warm. I also found a little extra inductance didnt load the amplifier quite as much.
You have to take into account that more inductance + less capacitance = higher output impedance, which means higher filter overshoot and higher distortion at low ohm loads.
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Old 18th March 2011, 02:30 PM   #19
luka is offline luka  Slovenia
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yes, lower the inductance, low the THD
That why Tripath and other with HIGH freq. have low THD from output filter
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Old 18th March 2011, 11:03 PM   #20
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Originally Posted by Th3 uN1Qu3 View Post
You have to take into account that more inductance + less capacitance = higher output impedance, which means higher filter overshoot and higher distortion at low ohm loads.
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