Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 7th March 2011, 08:09 PM   #741
JoeDJ is offline JoeDJ  United States
diyAudio Member
 
Join Date: Mar 2011
Location: NY State
Interesting thread that I will be following.
I just odered one a few days ago from Parts Express and it wiil be intertesting to hear how it sounds.

I'm just going to start off usiing a a pair of Tang Band "W3-881SJ" 3" drivers.
It's only for TV sound.
I will also try connecting a "Sony XDRF1DHD" radio tuner to it.
  Reply With Quote
Old 13th March 2011, 06:53 PM   #742
DrLex is offline DrLex  Belgium
diyAudio Member
 
Join Date: Aug 2009
Lightbulb Bass is back and pops are gone!

Has anyone analyzed the circuit on the newer models, especially the one with the two op-amps? I don't have one, but my guess is that the second op-amp sits between the output of the tone stack and the TA2020's inputs. There is a very good reason why they did this, and in fact you should either add this second op-amp if you still have a Lepai with one op-amp, or bypass the tone controls. I'll explain why.

The 'James' tone stack used in the Lepai only works well if it is connected to a load of fairly high impedance. But it seems that the input impedance of the Tripath chip is pretty low. I can't find any values in the datasheet but some sources say it's about 10kΩ. This is plausible, some other class D chips also have similar impedances when set to a high gain.

Attached are some images that show how the tone curves differ between a high load impedance (1MΩ) and low (10kΩ), both for the original James component values that were installed on my Lepai and the ones I replaced them with while I still thought the TA2020 had a high input impedance. As you can see, especially in the latter case there is considerable loss of bass and overall signal strength.

It may be possible to find component values for the resistors and caps in the tone circuit that produce good curves even with the low input impedance. But the capacitor values will probably be impractically high and even then the curves would still change with variations of the TDA2020's impedance. The only correct solution is to buffer the tone stack's output, and this is also what I did. If you look at the photo, you'll see a little ugly dangling board which is a simple op-amp buffer. The result is impressive: I forgot how much bass I missed in certain songs . And that's not all: the power-on pop is almost completely gone, even when starting the amp non-muted.

The bottom line is: if you still have a Lepai with only one op-amp and don't care about the tone controls, then by all means bypass them. If you want them, adding a buffer amplifier is a must, as is replacing the components.
Attached Images
File Type: png OriginalComponents.png (11.5 KB, 796 views)
File Type: png TweakedComponents.png (11.7 KB, 773 views)
File Type: jpg P1000607.JPG (99.6 KB, 786 views)
  Reply With Quote
Old 14th March 2011, 04:34 PM   #743
JoeDJ is offline JoeDJ  United States
diyAudio Member
 
Join Date: Mar 2011
Location: NY State
I just got my LP-2020A+ a few days ago.
My first impressions from a purely listening standpoint are........

1) It is ony 20wc or about 12wc @8oms so, yeah, you can't expect too much volume out of it before different forms of distortion get too high.
2) The tone controls, are about worthless but, I guess they're better than nothing
I'm going to run it with the tone bypassed and the input run through a vintage Technics stereo 7 band EQ that I had on hand..... recently purchased on e-bay for $10.

I'm also going to run it through the high-pass of a powered sub to power the L/R mains.

So, I discovered so far that a bit of proper freq EQ can work wonders (of course) and the amp sounded fairly decent (with my test speakers) for what it is: a small, inexpensive, low powered amp.
I assume that adding the sub will only improve the sound by taking the low freq load off it.

For me, it's just a fun, inexpensive little amp, although it does look a bit lost sitting on top of the large, vintage EQ.

Last edited by JoeDJ; 14th March 2011 at 04:51 PM.
  Reply With Quote
Old 19th March 2011, 03:46 AM   #744
diyAudio Member
 
Join Date: Nov 2009
candoumi:

The op-amps are the cheapo 4558s. Boo Hiss! I'm in the process of putting in LM4562s. Fortunately I have a technician friend who can do surface mount soldering. That's the one drawback of having a much better board.

I've taken a quick look at the PCB and I don't think the tone defeat bypasses the op-amps.

My two cents,
Ed Perkins
  Reply With Quote
Old 20th March 2011, 04:51 AM   #745
diyAudio Member
 
Join Date: Mar 2011
I got the Lepai a few days ago to connect some bookshelves to my PC. There's a buzz if I turn up the volume past the 11-o'clock position. I can turn the volume higher if I use my iPod touch, but that depends where I put the touch. I'm new to home audio, so I'm guessing this is a grounding problem. What's the cheapest way to fix this without interfering with audio quality?
  Reply With Quote
Old 20th March 2011, 06:33 PM   #746
tvih is offline tvih  Finland
diyAudio Member
 
Join Date: Jan 2011
A bit over a week ago I received a Topping TP30 amp to replace this dissappointing Lepai one - I was meant to get the Topping to begin with, but skimped in the end... bad move! Sure the Topping costs 3,5 times as much, but it's "infinitely" better as well and still cheap! I honestly can't say why the Lepai seems reasonably liked, when to me it just sounds crappy. And I'm by no means overly demanding! This TP30 for example is simply awesome, I've zero bad things to say about it whether I'm driving my 250€ or my 5900€ speakers (not that I paid more than half price for the latter, nor do I normally drive those with the TP30). But the Lepai... thin, more or less harsh sound with any speakers (didn't try with the best ones, would be pointless), and of course the finish is what it is - but it wouldn't matter especially given the price if only the sound was acceptable, which it's not.
  Reply With Quote
Old 20th March 2011, 08:25 PM   #747
diyAudio Member
 
Join Date: Mar 2011
Smile Voltage regulator

I got a Lepai a few weeks ago, it seems to be somewhere between the 2011 version and the old one - it has the output relay, but the rest of the board is the same as the older ones...

I run mine off a 12V lead acid charged by solar panel. I use a LT1764a regulator to keep the voltage at 12.2V (says 12V, 2A on the Lepai jack) and I've had no problems so far - sounds very good and I'm pleased with it. I'm thinking of ordering another one to play with...

If anyones interested in the regulator, its an adjustable low drop out type, 3A output & very simple circuit: it would easily fit inside the Lepai box, although I opted for an external box. See http://cds.linear.com/docs/Datasheet/1764afb.pdf for the datasheet & circuit diagrams.
  Reply With Quote
Old 24th March 2011, 04:11 PM   #748
JoeDJ is offline JoeDJ  United States
diyAudio Member
 
Join Date: Mar 2011
Location: NY State
BTW, is there an easy way to add any sort of line level channel balance control to a sys using a 2020 amp?
  Reply With Quote
Old 24th March 2011, 06:54 PM   #749
Excile is offline Excile  Denmark
diyAudio Member
 
Join Date: Nov 2010
I just recieved my 2011 version Lepai TA2020.

I'd like to turn off the LED, is that possible for an amateur like me? Should i do anything else before taking it to use?
  Reply With Quote
Old 25th March 2011, 06:11 AM   #750
diyAudio Member
 
Join Date: Jan 2011
Location: Seoul
Quote:
Originally Posted by ernperkins View Post
candoumi:

The op-amps are the cheapo 4558s. Boo Hiss! I'm in the process of putting in LM4562s. Fortunately I have a technician friend who can do surface mount soldering. That's the one drawback of having a much better board.

I've taken a quick look at the PCB and I don't think the tone defeat bypasses the op-amps.

My two cents,
Ed Perkins
Ed Perkins, thank you. I'll buy one to test it.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
New ta2020 pcb'S ArjenShenzhen Vendor's Bazaar 98 14th November 2012 11:39 AM
Ta2020 Bengali Class D 0 29th September 2007 05:28 AM
Eb-ta2020 opentop Class D 16 30th May 2005 07:42 AM


New To Site? Need Help?

All times are GMT. The time now is 03:56 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2