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Old 20th November 2010, 04:18 PM   #661
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Join Date: Oct 2010
hi just received my lepai 2020..and have some issues with it..
there is a distinct hiss when i connect it through the jack-mp3 in.
is there a trick to get rid of this...
i power the amp through a 10 x AA batterypack
also the thump/click start-up sound annoys me ,so any help on that is welcome.

what easy improvements can i do to make the sound even better,got lost in the 65 previous pages so any advice on what to replace is very welcome
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Old 21st November 2010, 06:33 PM   #662
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Smile No Smoke

Hello,
I bought 4 of these Lepai TA2020 amplifiers to play with buy-amping some OB speakers. The FAQ wiki is gone and I have read many of the posts and I am not clear. Some users have had their amplifiers destruct in operation. Do these things self destruct out of the box or is it caused by some modification or tweak like over voltage?
Any guidelines or recommendations for out of the box application?
I would rather limit the focus of this activity to the open baffle speakers and active crossovers.
DT
All Just for fun!
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Old 23rd November 2010, 07:05 AM   #663
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Quote:
Originally Posted by ccl View Post
Just got mine a few days ago and now I'm ready to do some mods.

Before I started, I drew a schematic of the version I have (lp2020sch.png) to help me understand the circuit better. The values for some of the components are a bit different from what djnemesi posted on page 45.

From what's been posted so far, I've come up with the following list of mods I'd like to implement:

Safety
1.1. Remove diode between pin 18 and 11 (It's D2 in lp2020sch.png)
1.2. Add overshoot protection diodes (D2, D7, D9 and D10 in lp2020mods.png)

Input
2.1. Replace input decoupling caps with 2.2uF polypropylenes (C4 & C5)
2.2. Ground the volume pot casing (humming)
2.3. Replace volume pot with log 100K pot (original pot is a bit scratchy on mine)
2.4. Replace power filter cap (C32) with 4700uF 16/25V
2.5. Flip the "MP3" input channels

Opamp
3.1. Replace JRC4558 with NE5532
3.2. Replace R2, R3, R6, R7, R8 and R9 with 1% resistors (balance that weird left-right dc offset maybe?)
3.3. Add 0.1uF filter cap between pin 1 and 8 (C37 in lp2020mods.png)

Tone control
4.1. Replace C29 and C34 with 1nF MKT
4.2. Replace C28 and C33 with 10nF MKT
4.3. Replace C26 and C30 with 5.6nF MKT
4.4. Replace C27 and C31 with 56nF MKT
4.5. Replace R18 and R21 with wire
4.6. Replace R17 and R22 with 10K 1%
4.7. Replace R15 and R19 with 20K 1%
4.8. Replace R16 and R20 with 2.2K 1%
4.9. Replace pots with log 100K pots

Fix dc offset
5.1. Add the trimming circuit to pin 10 and 13 (see lp2020mods.png)

Output
6.1. Replace output inductors with 10uH 3A toroids

Extras
7.1. Add LED and resistor to fault pin 18
7.2. Add the pop suppressor circuit (see lp2020mods.png)
7.3. Replace the rest of the decoupling caps (C2, C3, C9, and C10) with 2.2uF MKT

If you don't feel like tracing where some of these parts are located physically, I've labeled them on lp2020-top.jpg.

A couple of other things I notice that might be of help:

There seems to be a confusion of what part needs to be removed to prevent the ticking death of these amps. There are two parts that looks similar on the board. One is a 14v zener and the other is a 1n4148 switching diode. It's the diode that needs to be removed not the zener. The zener is part of the over voltage protection circuit, you shouldn't remove that.

The unpopulated part of the circuit appears to be their attempt at dc offset trimming right at the speaker output pins (see origdcoffset.png). Given that I've got dc offset of 80mV on the left and 100mV on the right, I opted for the two trimmers on the input side rather than to use this part of the board. The other part of this circuit I don't like is the fact that it uses the supply voltage before the power switch so it will always be on even when the amp is off. If I can get the offset to match up with item #3.2, I might try populating this circuit and reroute the supply line to the switched side.

Did I miss any other mods? It's hard to go through 60 pages and not miss anything.
Because C8 and C7 (16V 47uf) there must be replaced with better quality? They are not important?

Thank you
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Old 1st December 2010, 08:10 PM   #664
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To DualTriode:

Its only gues .. there is warning and recommendation to remove some switching diode - at schema you will find the connection between two pins of TA2020, mute pin and fail pin ... datasheet says that FAIL pin can signal about five possible errors (such as overheating, over-currents, short-connected output etc etc)... and some of them will set internal block to prevent any damage ... this state/block can be reset by turning power down and up again OR by MUTE signal.

And thats it! I think the hard wired connection between FAIL and MUTE forces the amplifier to reset itself again and again .... until death! Only in case of some sort of failure state of course. I cant explain source of fail state ... but i think i can explain why internal protections will fail!
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Old 2nd December 2010, 12:22 AM   #665
ccl is offline ccl  United States
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Quote:
Originally Posted by antony28 View Post
Because C8 and C7 (16V 47uf) there must be replaced with better quality? They are not important?

Thank you
I don't think it would help too much to replace them. If I had better quality caps in my parts bin, I would replace them just because. Definitely wouldn't go out my way to buy replacements though.

Speaking of caps, I noticed that C13 (1uF) and C1 (100uF) in my amp are incorrectly installed. Based on the datasheet, I think they should be swapped. It doesn't seem to cause any issue but has anyone else come across this?
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Old 16th December 2010, 10:33 PM   #666
GJG21 is offline GJG21  United States
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Default Does anyone have any experience with new model with protection relay?

Quote:
Originally Posted by Travis Travelater View Post
I received one of these Lepai's last Friday and had a similar problem.

First, the blue LED didn't even come on, but I traced that problem quickly to a flaky "free" 2 amp SMPS. I had a good one that I quickly subsituted.

Then the LED came on when I turned the switch on, but no sound! I checked connections and nothing seemed wrong, and then sit down to look at what I needed to do to return the Lepai.

While I was checking on the return policy, all of the sudden the music started playing!

For whatever reason, it takes a few minutes from powering on till the amplifier actually produces an output. The time seems to vary. There's no thump though. Maybe Lepai has made a change to eliminate the thump but in doing so has produced a situation of turn it on Monday and listen to it Tuesday.
I was looking to buy a Lepia TA2020 on Ebay and noticed they are offering a new model
. It is billed to have Turn-on & Turn-off pop suppression,Over current protection and over temperature protection. IT has a relay mounted on the board. I was wondering if you have one of the new units and the relay is malfunctioning or needs a tweak on the time delay when it is controlling the pops.
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File Type: jpg nlepai2020.jpg (172.9 KB, 643 views)
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Old 17th December 2010, 02:39 AM   #667
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Location: Illinois
Quote:
Originally Posted by GJG21 View Post
I was looking to buy a Lepia TA2020 on Ebay and noticed they are offering a new model
. It is billed to have Turn-on & Turn-off pop suppression,Over current protection and over temperature protection. IT has a relay mounted on the board. I was wondering if you have one of the new units and the relay is malfunctioning or needs a tweak on the time delay when it is controlling the pops.
Thanks for the information! I suspected that there might be something new added, and that mine just isn't quite right. However, I normally have it continuously powered up along with the computer it is hooked into, so the delay is more of a nuisance than an issue. It comes on somewhere between 5 and 20 minutes, and if I switch it off and then immediately back on it comes on almost immediately.

At less than 20 bucks, I won't send it back for another one because everything else about it is fine. I prefer the devil I know to one that hums or doesn't work at all. And if it does quit working, I figure it would be a good project to get it going again and maybe make some of the improvements being touted.

Perhaps it's not a bug but a feature! The speakers don't pop when it does turn on. LOL
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Old 17th December 2010, 03:30 AM   #668
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Default Maybe the old tweaks won't work....

It certainly appears that the circuit board has changed in this newest version of the Lepai Amp. I wonder if the previously published tweaks need a revision? I'm certain mine is the newest version but I am not opening it to see, at least at this time.

Based on the claims made for the new version, I would presume the "ticking death" problem is no more.

What is different coming from this 2011 version Lepai TA2020 Class T Amplifier?
It has high speed relay fully protect to power IC and speakers, auto cut off when the DC Volts high than13.8V; so it will work safe with long life.


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Old 17th December 2010, 08:43 AM   #669
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It seems that you draw the schematics in Eagle, if so are you willing to pm to me. Thanks
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Old 22nd December 2010, 05:04 PM   #670
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Default What's the buzz...?

I'm trying to use my Lepai amp in a somewhat odd situation. It's tucked away in a suspended ceiling of an office meeting room and will be used for PC presentations. The problem is the very loud buzz I get when no device is plugged into the end of the 25' input cable. As soon as a laptop or MP3 player is plugged in it is dead quiet, and with a 6' foot cable the buzz is much quieter, but still very annoying. Most of the time nothing will be plugged in. Seeing as it's in the ceiling turning it on & off or adjusting the volume is not an option.

At the end of the day I have two questions. 1) Do all Lepai 2020's act like this with no device plugged in, or did I just get lucky? 2) Is there any relatively simple fix? (a new soldering rework station is under the tree 4 me :-).

Seasons Greetings!
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