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Class D Switching Power Amplifiers and Power D/A conversion

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Old 10th December 2012, 01:10 AM   #21
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The (lack of) diodes to VDD are the reason the design is capped at 13.5V.
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Old 10th December 2012, 01:35 AM   #22
Fynn is offline Fynn  Germany
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Amplifier:Lepai T Amp - diyAudio

Quote:
Then we need at least a 12v Power Supply Unit and preferably not above 13.5v (because above of that the Lepai zenner diode for protection will reduce it, and will be useless, and some users reported that sound quality decreases). The higher the Voltage supplied, the more power will be able to output the amp, so 13.5V are desirable.
Must be too outdated then.
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Old 10th December 2012, 02:06 AM   #23
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Read the datasheet for the chip, don't listen to the manufacturer in this case.
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Old 11th December 2012, 10:35 AM   #24
Fynn is offline Fynn  Germany
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Well i read that off the lepai-2020 wiki page on the DIYaudio website, that's why i was confused by it.


Today I finally got this power supply: (2.5 weeks shipping)
12V 3.2A Power Supply Transformer for LED Light Bulb (AC 110~240V) - Free Shipping - DealExtreme

Adjustable range between 9.3V - 14.2V. And it does pretty well in holding that voltage.
Set to 14.2V, even at 2.5amps load there is 14.2V at the terminals, my amp gets ~13.8 and the rest is lost on wires. Probably going to double them up or something, as they are relatively short already.

The output inductors are getting warm after a short stress test (just below clipping, 13.8V @ 2.5A - 5Minutes), the added schottkys seem to do their job, as they also heat up somewhat.


For now I think I am finished with modding it.
So far it sounds great and can go really loud without dipping out.
That PSU also is definitely worth the 10$, if you want to drive the TA2020 close to its limits without clipping.
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Old 11th December 2012, 12:41 PM   #25
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Those are good power supplies, we use them at work.
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Old 11th December 2012, 03:54 PM   #26
Bare is offline Bare  Canada
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Toshiba Laptop 12v 5 amp supply works well too :-)
Same ~price and self contained in a black block package
It's the Meanwell brand PS .. that's proven reliable, not nearly so much, the cheap copies of it.
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Old 14th December 2012, 11:41 PM   #27
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Thanks for all the great info!

I just received my Lepai 2020A+ (red board) and will be modding it soon.
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Old 19th December 2012, 01:26 PM   #28
lwj5 is offline lwj5  Singapore
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Hi guys, first time posting here!

I bought the amp last week, and already started modding. There was just problems and problems for me... luckily I managed to find out what happen just today.

Just a note for you guys when taking apart the amp from the case dont put too much pressure on the screw for the RCA inputs! The extremely thin little wire that connects the RCA to ground might just break off, that was what happen to me and I spent days finding the problem and reflowing every little SMD! haha silly me.

For extra support, spam solder on the ground pin for the RCA, it is the one in between the connectors and the board to strengthen it. You can see it from the back.

Thing done... my inspiration came from redshift, so most of it is similar to his.

1) Change all the caps to low ESR Panasonic caps, these are really good and value for money!

- Powercap from 3300uF to 5600uF+0.22uF and soon to 2x(5600uF+0.22uF)
- 2.2uF input caps to polyester Wimas MKS, was deciding between EVOX or Wima! any1 knows the difference? The MKPs are just too huge, smaller the better for me
- 1uF caps to polyester, hard to find low ESR for these so polyester the way to go
- Removed diode D2, I really thought it was a stupid diode.

Already sound pretty good here!

- Both op amp to OPA2132... ugh the decision between AD823, took the burr brown one due to low current req in the end anyone recommend otherwise?
- Add solder and reflow every joint for through pin and SMD components, the joints are of really bad QC

Still to come

- Change all the inductors to cheap(okay value for $$) toriods (I have a budget!), and the power inductor to a shielded, higher ampre >4.2A low inductance ~3.3uH for safety
- Addition of 4 schottky, got some SMD schottky lying at home rated 30V
- Addition of 47uF bypass to V+/V- of both op amp. If I am not wrong, this is where the question comes

Anyone got any idea whether there is already a cap to bypass the op amp? And I am supposed to bypass the V+/V- pins and not the others right?

Decisions and decisions, I wished there was a button to change op amp on the go so I have both AD and OPA on the board! Any other op amps recommended?

No op amp bypass for me! Find the op amps gives the sound more volume and airy feeling and smoother bass

Thanks for reading and happy modding! Pictures after I get my toriods and finish modding the rest!
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Old 19th December 2012, 02:37 PM   #29
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Nice to hear you made some improvements lwj5!

I really like the OPA2132 in everything I've tried it in. I compared once to a LME49710HA, but the circuit was borderline oscillating and it had a lot of sibilance. Being that the 49710 is a much higher speed opamp, that's no surprise.

C26 and C27 are local (0.1uF?) ceramic bypass caps for each opamp, and C28 is the large local bulk capacitor for them both. As the opamps are being run single supply, bypassing V+ to V- is the same as V+ to ground.
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Old 19th December 2012, 04:47 PM   #30
Bare is offline Bare  Canada
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Quote:
Originally Posted by lwj5 View Post
Hi guys, first time posting here!

I bought the amp last week, and already started modding. There was just problems and problems for me... luckily I managed to find out what happen just today.


1) Change all the caps to low ESR Panasonic caps, these are really good and value for money!

- Powercap from 3300uF to 5600uF+0.22uF and soon to 2x(5600uF+0.22uF)
- 2.2uF input caps to polyester Wimas MKS, was deciding between EVOX or Wima! any1 knows the difference? The MKPs are just too huge, smaller the better for me
- 1uF caps to polyester, hard to find low ESR for these so polyester the way to go
- Removed diode D2, I really thought it was a stupid diode.

Already sound pretty good here!

- Both op amp to OPA2132... ugh the decision between AD823, took the burr brown one due to low current req in the end anyone recommend otherwise?
- Add solder and reflow every joint for through pin and SMD components, the joints are of really bad QC

t!
Couple of points; 'genuine' 2.2 uf Wimas are Huge things .. seriously unlikely you could fit them to the board or in the case.
The Lepai tone controls are sad efforts. Compared to a decent manufacturer's tone setup, the Lepai lashup is simply poor.
Total waste of time.. sound quality improvement wise IMO.
But then Fiddling can be fun :-)
OEM inductors can be rewound DIY for almost no cost and minutes of your time..these are 16 turns oem.. Just use a thicker magnet wire with same number of turns.

Last edited by Bare; 19th December 2012 at 04:51 PM.
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