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Class D Switching Power Amplifiers and Power D/A conversion

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Old 4th August 2009, 03:20 PM   #471
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Hello, you guys probably dunno who I am nor care but I plan to buy one of these soon for my new speakers.

Anyway, has anyone tried the LME49720NA with this as I plan to buy this opamp along with 2 LT1057's for my Asus Essence STX?

I know that the LME49720NA is supposedly the same as the LM4562 but of course there's debate about this etc....

Any opinions on the LME49720NA or LT1057 in this speaker amp would be great!

TIA.
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Old 5th August 2009, 03:22 PM   #472
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Default Pop Suppressor

hi to all,

djnemesi , the power switch is on the mute in my lepay, but i use a battery with another power switch on the line and i put on the switch on lepay before that i start the battey.
the lepay go in sleep for five secon, but after this time i have the pop and the ampli works.

sorry for the english.........

thanks
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Old 10th August 2009, 04:45 PM   #473
Dreas89 is offline Dreas89  Sweden
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I'm quite new here, been reading in this thread for maybe a month. I got my Lepai today, now i need a set of speakers to my Lepai.

How big speakers can they handle?

My eyes is right now set on these ones http://www.fynda.se/index.php?prodid=2434

I'm from sweden so if you have a better suggestion, please let the shop be in the Nordic countries.
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Old 20th August 2009, 12:41 PM   #474
DrLex is offline DrLex  Belgium
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Well, I couldn't resist trying the Lepai 2020 so I bought one from the Bay. It's the same one as the right one in this photo by MikeHunt. It works pretty well out-of-the-box but being a seasoned hacker, I have made some modifications in the meantime. Here's a list:
  1. Grounded the volume pot casing: it wasn't grounded due to the plastic ring with the LED separating it from the case, and a hum could be heard when touching the volume knob. I guess they just forgot to solder the grounding wire in my amp.
  2. Added a 'mute' switch (which is connected to the IC's standby pin). I use this to avoid the turn-on pop.
  3. Replaced the opamp with a NE5532AP. Also started to replace some of the tone circuit components, but this is still a work in progress.
  4. Added some more decoupling capacitors and replaced some of the existing bulk capacitors with larger values.
  5. Added DC offset correction with the circuit shown by Lostcause. I trimmed the DC on the speakers from a whopping 120mV and 60mV to near zero. This is a highly recommended mod. There's just enough space on the underside of the board to fit the trimmers if you sand them down a bit.
  6. Dimmed the blue LED by giving it a larger series resistor.
  7. Corrected the swapped L/R channels on the 'MP3' input.
Now, the amp performs very well but I have the impression it lacks slightly in bass output. I have to crank the bass control all the way up to get decent bass on good speakers, so on inferior speakers I can't reach a satisfactory bass level. What would be the most likely cause of this? I guess I'll try replacing the inductors and further cleaning up the tone controls...
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Old 21st August 2009, 03:07 AM   #475
msj965 is offline msj965  United States
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Default drlex

Any pictures on your moded lepai?
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Old 21st August 2009, 03:14 AM   #476
col is offline col  Australia
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drlex, that sounds like an impressive list of mods. I found that changing the inductors made the biggest improvement in bass. Another mod that is totally worthwhile but I seem to be the only person to do it so far, is to replace all the resistors with 1/2 W metal film. This lowers the noise floor considerably.

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Last edited by col; 21st August 2009 at 03:17 AM.
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Old 23rd August 2009, 09:47 PM   #477
DrLex is offline DrLex  Belgium
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Quote:
Originally Posted by col View Post
drlex, that sounds like an impressive list of mods. I found that changing the inductors made the biggest improvement in bass. Another mod that is totally worthwhile but I seem to be the only person to do it so far, is to replace all the resistors with 1/2 W metal film. This lowers the noise floor considerably.

col.
Here are some pictures. The trimmers in the second photo are sanded to about 4mm thickness and glued to the bottom.

The third image shows some frequency responses obtained through an improvised set-up. I fed the amplifier a constant amplitude sweep from 16Hz to 20kHz, and recorded the speaker terminals' output in Audacity with a 6Ω load (didn't have any 4Ω resistors handy). This was done through a transformer, which causes the small bump at the lowest frequencies and the 'wobble' at the highest frequencies.
There seems to be an overall loss of bass indeed: with both treble and bass set to max there's only a +6dB bass boost while there's a +12dB treble boost. With both controls set to min, bass is attenuated much more than treble.

I have followed col's advice and ordered 10H 3A toroids from arjenhelder. I'll repeat this experiment when they arrive. To get the tone controls truly balanced I may need to replace those components too
Attached Images
File Type: jpg lepai2.jpg (56.9 KB, 933 views)
File Type: jpg lepai3.jpg (71.4 KB, 921 views)
File Type: png Lepai-curves.png (57.2 KB, 898 views)
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Old 27th August 2009, 03:03 PM   #478
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Hi

Can I use 10000µF cap in this LEPAI 2020 ?

thx
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Old 27th August 2009, 04:03 PM   #479
jkeny is offline jkeny  Ireland
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I'm expecting a Lepai TA2020 in about a week & was invesitigating mods. Are there further mods in addition to Dr lex's ones? Can anyone give a link to the dc offset correction mod schematic? I have some 10uh toroid inductors which I intend to try - is this the correct value?
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Old 27th August 2009, 04:32 PM   #480
zlab is offline zlab  Hong Kong
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Quote:
Originally Posted by UltimateX86 View Post
Hi

Can I use 10000F cap in this LEPAI 2020 ?

thx
Already done with a Rubycon 25V 10000F which help to boost the base a bit.
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