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Class D Switching Power Amplifiers and Power D/A conversion

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Old 19th January 2013, 03:12 PM   #51
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Join Date: Aug 2008
If you bypass the volume op-amp (post #6 details keeping the volume control without the op-amp), you won't have to worry about C42 and C43

Sorry, I don't have a capacitance meter and it's not written on my boards.
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Old 19th January 2013, 07:29 PM   #52
lwj5 is offline lwj5  Singapore
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My multimeter can only be used on polarised caps I will bypass it for the time being. I also bought a flip switch for bypassing, and also to switch back to use the op amps when I want to.

I love the op amp too. So I am going keep it there for now... I found a schematic of the old lepai board from the 2020 thread and there is a similar capacitor there which is of 33pF.

I am going to try change to that and see what happen, hope for the best.
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Old 20th January 2013, 01:21 AM   #53
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Originally Posted by sofaspud View Post
I'm not sure I understand the question.
I swapped the stock 4558's with a couple SOIC LM833's I had on hand. When the volume was turned way up, where the distortion began getting extremely harsh to the ears, it seemed to improve the sound significantly. I don't have any measurements, and I'm not even certain of the input configuration, for my amp. But any improvement there is worth it IMO so I've no regrets about the mod.
Also IMO... the credit to Chu Moy is that he designed and web-published a great sounding, easy to build, readily modifiable portable DIY headphone amplifier project. Maybe more popular than he ever imagined it would be. So, his credit is well deserved, but I'm not prepared to call every op amp gain block a "CMoy."
Sorry, but you are just amp'n his op amp design through a Tripath. Rebuttal?
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Last edited by tamasic1; 20th January 2013 at 01:28 AM.
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Old 20th January 2013, 06:31 AM   #54
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His was a headphone amp design, not an op amp (circuit) design. I won't say it again.
Parry question: So what if it is "just amp'n his op amp design through a Tripath"?
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
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Old 24th January 2013, 02:41 AM   #55
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hey guys, new here to the forums. i just received my 2020a+ from parts-express. will be using it to push pioneer bs-21 for my pc setup. the supplied power supply that i received is rated 12v 2a. would i be better off using something like this? (Amazon.com: 12v 6a Adapter Power Supply for LCD Monitor with Power Cord: Computers & Accessories) also, what are some of the popular mods that are done to these amps? i'm very much looking forward to modding this amp. thanks guys
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Old 25th January 2013, 03:35 AM   #56
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Yes a 6A power supply would work better for your setup. I don't know if the one you linked has a plug that will fit, or whether it's centre positive or centre negative. Read through this thread, I detailed some of the common mods (replacing capacitors, inductors and removing/bypassing the opamps).
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Old 6th February 2013, 01:48 AM   #57
blossom is offline blossom  New Zealand
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Hi guys, good to see people still playing with these. Anyway I might have damaged mine, not sure, thought I'd just post and see if anybody can help me.

The problem is it does not put any sound out. LOL. But i think i know why, I did a few mods to mine as you can see in the pic. But what happened is, where I bypassed the O.P. amp stage, the 2 wires ended up touching each other just after they come away from the board near the RCA plugs. Anybody know if this could be a course for the TA2020 chip to fail? Or perhaps it can be reset? If anybody in the know could give there opinion i would be greatfull.

P.S. this picture is taken after a rewire.
Click the image to open in full size.
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Old 11th February 2013, 02:13 AM   #58
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Hi, I discovered this forum a while back and have been reading a lot of threads and saw all the discussion about modding the Lepai 2020A. I haven't done any diy amps or mods before. But this one looks like a perfect amp for what I am wanting to build.

I have a raspberry pi that I am wanting to use as a music player for in our bedroom. I already have the raspberry pi set up and running SqueezePlug and it works great. But I want to build a box to hold everything instead of a bunch of individual pieces that look ugly.

I drew up a little plan of what I am wanting to do and was hoping someone could point me in the direction of where to start with this, or if this is even going to work.

A few things I am wanting to accomplish.

1. One case for everything - Amp, RaspberryPi, Power Supply, DAC, USB Hub
2. Get rid of the cheap connectors and knobs on the amp and use good stuff.
3. Have the power supply built into the case so I can have 2 cord going to the wall. The power supply will need the 12V for the amp and 5v for the raspberry pi and usb hub
4. Have an Input Selector Knob to choose between 3.5mm aux, line in, and raspberry pi
5. Have Line Out -if possible

Here is the drawing I made.
Click the image to open in full size.

Hopefully it makes since. I have a power switch in the front, but after thinking about it, I don't want it in the front. Instead I want a main power switch in the back and individual power switches for the raspberry pi and the amp.

I see that many of you have been bypassing the bass and treble controls. I may want to do that as well, but it might come in handy so for now I will plan to just relocate the knobs to the front panel of the box.

I plan to also replace the caps on the amp. I see a lot of people are replacing them differently than others. This is just for our bedroom. I am not needing crazy power out of this thing, but I do want good quality sound and the option to be able to crank it when I feel like it.

Most of this I doesn't seem to complicated to me, but the power supply is where I am totally lost. I don't know if I should be looking at a DIY psu, or what kind of psu I should buy.
The power switches, volume/tone control knobs and input selector are the other big ones.

Any advice/tips on how to go about this or even where to start looking would be great.
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Old 15th February 2013, 03:43 AM   #59
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A good place to start if you want good quality sound: don't use the Raspberry Pi. The "analogue" output is class D just like the LP-2020A+, but it's done with software and is only capable of about 11 bits of resolution. I have one, connected to a pretty good amp, and it sounds like crap.
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Old 15th February 2013, 04:04 AM   #60
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A usb DAC would be used, not the onboard analogue out from the Raspberry Pi.
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