Lepai T-Amp with TA2020 - Page 50 - diyAudio
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 31st August 2009, 03:30 PM   #491
DrLex is offline DrLex  Belgium
diyAudio Member
 
Join Date: Aug 2009
Quote:
Originally Posted by msj965 View Post
Drlex,
Can we eliminate the pop noise on this amp?
The first thing you should do to reduce the pop is implement the DC bias correction and trim the outputs so they are near 0mV. Otherwise there will always be a pop no matter what you do. Next, there are a few options:
  • Add a 'mute' switch like I did, which toggles pin 17 between the 5V reference (pin 8) and ground. Pin 17 is the 'sleep' pin, alternatively you could use pin 11 which is the 'mute' pin. I don't know which one works best. Set this switch to 5V when powering on the amp, and flip it a few seconds after. It still gives a pop, but it's very acceptable and doesn't make the speaker cones wiggle back and forth. And it allows to mute the amp without touching the volume knob.
  • Automate the above by replacing the manual switch with a timer circuit. Look in this older post for a possible circuit.
  • Add a relay which physically disconnects the speaker terminals until a few seconds after powering on the amp. This will completely eliminate the pop, but may be tricky to solder. You will need to break traces and find space for the relays.
  Reply With Quote
Old 1st September 2009, 08:42 PM   #492
DrLex is offline DrLex  Belgium
diyAudio Member
 
Join Date: Aug 2009
All right, the capacitors for the tone circuit and the toroids arrived yesterday. I first did the tone circuit and repeated my "poor man's frequency response test". The curves look much better now, and approximate the ones from the simulator. And of course it sounds a whole lot better. As you can see, with the controls 'flat' (i.e. both knobs centered), there is already a bass and treble boost. To get the response really flat I need to turn the knobs more to the left. The reason is that the built-in potmeters aren't logarithmic . They appear to have some weird sigmoid-like characteristic.

After this I replaced the ridiculously small inductors with the toroids, and repeated the experiment. But there was no effect on the curves, they look identical. I guess this is because I had to set the volume very low to avoid oversteering the line-in of the recorder. At such low volume the currents are small and the crappy built-in coils probably don't cause much degradation yet. So the only test I could do is hook up some speakers and crank the volume, and it certainly sounds great.

While I was experimenting anyway, I did some tests with bypassing the entire opamp/tone section and only the tone controls. The good news is: the frequency response is perfectly flat in both cases. That is, of course, after all my hacks, so I can't tell what it would have been with the standard components.
Attached Images
File Type: png Lepai-curvesFixed.png (57.2 KB, 1232 views)
File Type: jpg Lepai-newToneAndCoils.jpg (89.5 KB, 1214 views)
  Reply With Quote
Old 7th September 2009, 10:44 PM   #493
msj965 is offline msj965  United States
diyAudio Member
 
Join Date: Feb 2009
Default Need help:)

Hello Masters,
Just wanna ask how to check the dc bias on my lepai. I measure the voltage of both speaker connection but what I get is 3 - 0mv. Is this one?
Thanks,
Ann
  Reply With Quote
Old 8th September 2009, 03:56 AM   #494
diyAudio Member
 
panda360's Avatar
 
Join Date: May 2009
Quote:
Originally Posted by DrLex View Post
All right, the capacitors for the tone circuit and the toroids arrived yesterday. I first did the tone circuit and repeated my "poor man's frequency response test". The curves look much better now, and approximate the ones from the simulator. And of course it sounds a whole lot better. As you can see, with the controls 'flat' (i.e. both knobs centered), there is already a bass and treble boost. To get the response really flat I need to turn the knobs more to the left. The reason is that the built-in potmeters aren't logarithmic . They appear to have some weird sigmoid-like characteristic.

After this I replaced the ridiculously small inductors with the toroids, and repeated the experiment. But there was no effect on the curves, they look identical. I guess this is because I had to set the volume very low to avoid oversteering the line-in of the recorder. At such low volume the currents are small and the crappy built-in coils probably don't cause much degradation yet. So the only test I could do is hook up some speakers and crank the volume, and it certainly sounds great.

While I was experimenting anyway, I did some tests with bypassing the entire opamp/tone section and only the tone controls. The good news is: the frequency response is perfectly flat in both cases. That is, of course, after all my hacks, so I can't tell what it would have been with the standard components.
Hi DrLex,


Would you please change the capacitor as mentioned in the post no#258? The sound quality is much better. Can you test with your equiment? Thank you.
  Reply With Quote
Old 8th September 2009, 01:56 PM   #495
DrLex is offline DrLex  Belgium
diyAudio Member
 
Join Date: Aug 2009
Quote:
Originally Posted by msj965 View Post
Hello Masters,
Just wanna ask how to check the dc bias on my lepai. I measure the voltage of both speaker connection but what I get is 3 - 0mv. Is this one?
Thanks,
Ann
You should switch on the amp, wait a minute until it stabilizes, and connect a voltmeter to the red and black socket of each speaker terminal. It is possible that you're lucky and that your amp has nearly no bias, but mine had more than 120mV on one channel and about 60mV on the other. If you correctly trim the DC bias, you should hear nothing when you connect speakers while the amp is powered on. Otherwise you'll hear crackling sounds.

Quote:
Originally Posted by panda360 View Post
Hi DrLex,


Would you please change the capacitor as mentioned in the post no#258? The sound quality is much better. Can you test with your equiment? Thank you.
I doubt whether this will show any visible difference in the curves, due to the same reason I gave in my previous post. I could try to attenuate the line-in with a potmeter so I can crank the volume, but even then I can only give the amp a 5W load because that's as far as my resistors will go. I may do the test when I have better resistors and the correct capacitor, but that could take a while... I could also hook up some speakers of course, but playing that constant amplitude sweep up to the highest frequencies at maximum volume will probably damage both my ears and speakers and make all the dogs in the neighborhood go crazy
  Reply With Quote
Old 25th October 2009, 02:12 PM   #496
diyAudio Member
 
Join Date: Oct 2009
Default burn it

Hello,

I bought a LEPAI TA2020, but when I connected in to the power supply 12vdc 10A, my Lepai broke.

I opened it and I saw that an inductor burned, please, look at the photo.

I have to replace it, wich inductor or coil (i don't know) i have to put it (specs).

Thanks

Dj_vini
Attached Images
File Type: jpg 25102009019.jpg (113.0 KB, 977 views)
  Reply With Quote
Old 25th October 2009, 11:50 PM   #497
Bone is offline Bone  United Kingdom
diyAudio Member
 
Join Date: Jun 2004
Location: Dorset, UK
Hi dj_vini are you sure that you have your supply the right way round. The diode next to the inductor will short the supply if it is the wrong polarity and cause the inductor to burn. The inductor is probably the same as the others on the board ie 10uH. It needs to be able to carry the full supply current about 4-5 amps.

Tony
  Reply With Quote
Old 26th October 2009, 12:27 AM   #498
jkeny is offline jkeny  Ireland
Banned
 
Join Date: Feb 2007
Location: Dublin
I got my Lepai & bypassed all the input circuitry including the 3.3uF (?) input capacitor by using a transformer input - one end of secondary winding connected to input & the other end connected to pin 14 Biascap. So no capacitors in the signal path - sounds wonderful (I'm feeding it directly from a PCM1793 differential Vout DAC - the primary is handling the 1.4V bias on each differential output leg)

I've changed the Ri & Rf resistors both to 20K metal & changed the output inductors to 10uH toroids that I had around for my SI amp.

I didn't change the 0.47uF output caps (Co in the datasheet) yet - are the stock ones low quality? Does this make much of a difference? I haven't changed the Zobel 0.47uF cap either - same question again. Should this be 0.47 or 0.22uf as in the datasheet? Same for the Cdo differential 0.01uF cap.
  Reply With Quote
Old 26th October 2009, 12:59 AM   #499
jkeny is offline jkeny  Ireland
Banned
 
Join Date: Feb 2007
Location: Dublin
The other mod I must do is add the missing schottky diode on each signal line for safety purposes - is this one difficult to implement?
  Reply With Quote
Old 27th October 2009, 10:23 PM   #500
jkeny is offline jkeny  Ireland
Banned
 
Join Date: Feb 2007
Location: Dublin
No answer on whether the stock output 0.47 caps are worth replacing? With PolyP?
  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 10:21 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