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Class D Switching Power Amplifiers and Power D/A conversion

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Old 1st November 2012, 11:40 PM   #11
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Quote:
Originally Posted by Tekko View Post
I've now ran this amp for a bit more, this time on a 8 ohm load rather than 4 ohm, after about a hour, the amp started making ticking noises, like if some protection circuit was starting to kick in, then i noticed the output industors were smelling like a overheated transformer, yes they are blistering hot.

This amplifier is clearly not properly made, even one of the blue LEDs on the board is shifting color like its beeing overdriven.

I've came to the conclusion that this amplifier was a complete waste of money.
You could try a t106-2 core with 20 turns on it.
I had trouble with power inductors cooking at 120 degrees before trying the right t106-2 core.

The tick noise sounds like the chip resetting for some reason.
The inductor over heating might cause this as the inductor inductance will change with excess heat. In an SMPS they used gapped cores to get around this.
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Old 1st November 2012, 11:56 PM   #12
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Well, you could try reading the manual, it's not rated for four ohm loads. The heating is mostly down to the voltage regulator, not the actual amplifier. However you're obviously not happy, so why not send it back for replacement or a refund?
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Old 2nd November 2012, 03:23 AM   #13
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Originally Posted by Tekko View Post
I've came to the conclusion that this amplifier was a complete waste of money.
How about try something for a little more money but likely much higher quality like this

Connexelectronic
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Old 2nd November 2012, 02:42 PM   #14
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pinkmouse, the manual states 3.5-4 ohms, and i ran it into 8 ohms.

Also i did not run it at more than a few watts output, nowhere near enuf to cause enough current through the inductors to heat them up to the point of burning.

Sending it back to china is not an option, would cost me more in shipping alone than i paid for the thing.

Yes shipping from sweden is obnoxously expensive, just one of those little LM3886 kits costed me over 50 us dollars to send to the US.
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Old 2nd November 2012, 03:32 PM   #15
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The output filter inductors have been replaced and now the heating of the inductors seem to have lessened, i think the amp is even sounding alittle bit better.

The inductors i used are two free samples i got off of CoilCraft.com some time ago.

I'll report back once the amp have been running for a bit.
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Old 2nd November 2012, 04:10 PM   #16
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Ok heatsink still gets hot so perhaps that is the gate drive vregs after all, however on the output one channel inductor is luke warm while the other is hot, an indication there might be a big difference in switching frequency between the two channels.

Theres no mention about the trimmer pots but i assume they are for adjusting the gain, if they are indeed for trimming the switching frequency, i may see if i can trim the switching frequency to be somewhat similar on both channels.
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Old 2nd November 2012, 08:14 PM   #17
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I think your best bet at the moment is to download the IR app note, the circuit is exactly the same, only using some SMT components, even down to the numbering. I think the frequency is set using fixed resistors, but can't check easily as mine are all cased up. Keep us updated.
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Old 2nd November 2012, 09:33 PM   #18
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The pots are indeed for adjusting the switching frequency looking at the iraudamp7s pdf.

I'll have a look and see if there is a major difference in switching freq between the channels as that is the only thing that can cause one inductor to run hot while the other is just warm.
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Old 2nd November 2012, 10:09 PM   #19
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Turns out one channel was almost 100kHz higher in switching frequency than the other.

I've adjusted the higher channel down to as close as i can get to the other, with the scope set to 2µS/div, i set both channels so one half period spans ~1,5 divisions.

Someday im gonna replace these crappy trimmers withj proper multiturn pots as these have literally no friction to them.
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Old 2nd November 2012, 10:51 PM   #20
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Quote:
Originally Posted by noah katz View Post
How about try something for a little more money but likely much higher quality like this

Connexelectronic
Hey! Thank you for posting that link. I never saw this company before. I have been reading about class D / T amps for quite some time. I got a knock-off of the Sonic Impact T-Amp and I also built AMP3 and AMP6 from 41Hz.com. I'd have to say I like all of them very much.

Recently I got one of those 8W / ch. amps from Sure. It was just a bit over $10 shipped. I got it because I wanted to get an example of Sure's stuff. It's OK, I guess. It hisses like crasy. That might be because I'm using a cheapo line lump switching 12V supply.

Anyway... amps on the connexelectronic look really nice. Does anyone have any real experience with them?

James.
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