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Class D Switching Power Amplifiers and Power D/A conversion

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Old 2nd July 2011, 09:42 AM   #11
ljm_ljm is offline ljm_ljm  China
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From the above test can see, iron silicon aluminium inductance performance is very good. Almost no problem, to know the switch of D will have a little bit of burr process. The same circuit different components of the PCB and get the line can have a big impact, of course, the smaller the better is....... To see now that I used digital amplifier special inductor




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Last edited by ljm_ljm; 2nd July 2011 at 09:55 AM.
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Old 2nd July 2011, 09:43 AM   #12
ljm_ljm is offline ljm_ljm  China
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In the test I use DC + 75 V.

In these conditions shows environment is harsh.

If the voltage reduced to +-60 V. Then the bad phenomena will not be so obvious.




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Last edited by ljm_ljm; 2nd July 2011 at 09:55 AM.
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Old 2nd July 2011, 10:33 AM   #13
ljm_ljm is offline ljm_ljm  China
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Red inductance fever to about 40 degrees Celsius, some small.

Iron silicon aluminium induction and digital amplifier inductance about 50 degrees Celsius. Special


Now the weather is hot, my family the inside temperature is 37 degrees Celsius... 's summer ah
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Old 20th July 2011, 05:03 AM   #14
trevmar is offline trevmar  United States
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Thanks for posting this info, LJM. I am building a modified Linkwitz Pluto with a Peerless Tymphany 890983 'tweeter' as I don't like the resonance in the Aura 'tweeter'.

I have bought a miniDSP board instead of the Linkwitz analog filters, it works well. I am looking for some amplifiers to use to drive the Seas L16RN. They are rated at 80W sinewave and 250 Watts peak IEC longterm noise. I had chosen to use the (bridged) TDA8920BTH boards from Yuanjing, but they oscillate at 50KHz rather badly, and I can't dampen it by changing the output inductors. Must be a grounding problem. So it would seem that I should invest in a higher voltage transformer and a pair of L20 boards I am happy with the TDA7293 boards I bought for the tweeters. Power for the 890983 is somewhere between 7W and 60W, depending on which Peerless data sheet revision you are reading (v1 or v2) so the TDA7293 has plenty of power and looks really nice and clean on my oscilloscope, just what I need for a tweeter, I think

So congratulations on getting the L20 stable, I will order a pair and let you know what I think.

Happy Summer -- I was in Dalian in April and May, and Shanghai in June, but I do remember the heat when I spent August in Chengdu during 2009 -- it is very hot indeed. Much more pleasant here in California, I think We don't even need air-conditioning (just heating for winter). Thanks again for the help...
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Old 22nd July 2011, 05:37 AM   #15
trevmar is offline trevmar  United States
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Ljm_ljm, I notice that International Rectifier do not suggest using the iraudamp7s containing the IRFI4020 with a 4-ohm load. But the IRFI4020 seems to have a higher current rating than the 4ohm-recommended IRFI4019. I am assuming that if I drop the supply voltage to nearer +-50V that the L20D will drive 4 and 6 ohm loads OK? Am I correct?

Thanks.
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Old 5th August 2011, 04:58 AM   #16
trevmar is offline trevmar  United States
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ljm_ljm,
FYI - the L20D from this Ebay source has 63V bypass capacitors on the supply rails. The board is labelled as handling 60V to 80V

2pcs L20D IRS2092 200-250W X 2 Class D amplifier sc | eBay

When testing amplifiers, the first thing I look at is the bypassing. At least the L20D had ceramic bypasses on the supply rails (100V rating) (so many don't), But the main capacitors measured 0.12 ohms ESR and so were headed to the junkheap as soon as they crossed my doorstep, as I draw the line at about 0.05 ohms right now But you might be more interested in their low voltage rating

Incidentally, my two boards only needed about 45 volts to start operating properly, and I haven't taken them above 55V yet. They are running beautifully there, giving my 100W 4/6/8 dummy-load a run for its money at that voltage
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Old 15th August 2011, 01:18 PM   #17
Bernie7 is offline Bernie7  Singapore
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Hi ljm_ljm what is the power rating of the amp at 70VDC for 8ohms and 4ohms? Is its frequency response flat across 4-16ohms (load invariant) or can you show a Load-Frequency graph?

trevmar, since you have the T2 as well, how do both amps compare on listening?
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Old 15th August 2011, 01:29 PM   #18
trevmar is offline trevmar  United States
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Bernie7, I just posted performance curves for my L20D on this forum:

Distortion Tests - HifimeDIY T2 / LJM L20D / SURE TDA7498

If you look at the distortion curves, IMO the L20D is amazing. Power is amazing too, with 150W being easy to reach at low distortion. I am waiting for my higher-power supply to arrive so I can test it above 150W You will need to be careful choosing the correct supply rails if you want to use 4 ohm loads, and if you use rails above 63V you may need to check that the power supply bypass capacitors on the low-cost Hong-Kong boards can handle it. My capacitors were rated at 63V, and I changed them to low-ESR 100V units.

At 4 ohms, you will need to lower the supply rails from 70V. I found that my L20D went into (safe) shutdown when the supply voltage fell below 40-0-40V, due to starvation of the 5V supply rails on the board. Three resistors will fix this.
.
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Old 15th August 2011, 02:23 PM   #19
trevmar is offline trevmar  United States
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ljm_ljm,
I was just looking at your Chinese language forum, and there is discussion there about piracy of your boards and design. Are the Ebay boards (from Hong Kong) pirated? Is there any way we can buy boards so that you get the benefit? All I could find were Taobao stores, which are hard to arrange payment and shipping for somebody who is not in China.

Also, on 1 July 2011 you posted the following comment on your Chinese language board "This is not the maximum power. Goal is to IRAUDAMP9 1200-1700W power." Have you had any further thoughts about a super big amplifier?

Thanks for all you have done for the DIY community.
.
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Old 16th August 2011, 02:57 AM   #20
Bernie7 is offline Bernie7  Singapore
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Quote:
Originally Posted by trevmar View Post
Bernie7, I just posted performance curves for my L20D on this forum:

Distortion Tests - HifimeDIY T2 / LJM L20D / SURE TDA7498

If you look at the distortion curves, IMO the L20D is amazing. Power is amazing too, with 150W being easy to reach at low distortion. I am waiting for my higher-power supply to arrive so I can test it above 150W You will need to be careful choosing the correct supply rails if you want to use 4 ohm loads, and if you use rails above 63V you may need to check that the power supply bypass capacitors on the low-cost Hong-Kong boards can handle it. My capacitors were rated at 63V, and I changed them to low-ESR 100V units.

At 4 ohms, you will need to lower the supply rails from 70V. I found that my L20D went into (safe) shutdown when the supply voltage fell below 40-0-40V, due to starvation of the 5V supply rails on the board. Three resistors will fix this.
.
Hi trevmar

Good catch on the supply caps. Explosive dynamics may not be an accolade here

Yes, I saw your data and it piqued my interest in this amp. I have an UCD amp with linear +-68VDC ps and it would be great if I can swap the ljm amp in. My speakers are 4ohms. Why wouldn't 70VDC rails be suitable for 4ohm speakers for this amp?

Btw I have T3 as well, and since it is said to sound similar to T2, was wondering how your T2 and L20D compared in listening tests.
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