Lepai T-Amp with TA2020

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Scootxyz said:
Hi there

(New to the forum...)

The mod that I really want is the noise suppresion one - but is this really something that a total beginner can learn to do?

If I don't do it I'm worried that my speakers are going to pop out one day when turning the thing on...
:bigeyes:

Also - I am rnning the preamp out from my NAD into the input of the lepai. Is this ok?

Thanks in advance for any advice...


Welcome aboard Scootxyz, I hope you realise which road you have just turned down...:D

Things seem pretty complicated at the start but you'll soon pick it up.

For starters I used Nick's NE555 circuit (about 3/4 down the page) to supress any start up pops but I was also supressing the startup sound from my modified PS1 so I liked the adjustable timing.
Alternatively you can do it this way for a manual method that cuts out the complicated bit of the one above. It's also shown in the diagram directly above the NE555, so you have two diagrams of the same simple circuit.
You could use the mute opion on the chip and use a selector switch to do pretty much the same thing... it is mentioned several times in this thread and other TA2020 amp threads so have a search.
There are even more options with DC coupling ... but I wont get into that now.
Option 2 is probably the eassiest to do and just as effective as the 1st so start with that and when you get more adventurous...... well, you'll probably start rebuilding the whole amp like everybody else does;)

Lee
 
thanks to both for these replies. Never ceases to amaze me how many helpful people are out there on t'internet. :D

I quite like the look of option 2 as it looks the simplest for anyone without any soldering experience to do... I guess i just remove the wires from the old switch, replace it physically and then solder in the new one?

Is this switch & resistor (?) something that I can buy as a complete unit or do I have to buy the resistor and wire separately?

I had a quick look at the maplin website and couldn't see it there. Is there a good place to buy this sort of thing?

Sorry for all the questions :ashamed:

I take it that the thump that I get will damage the speaker cones if i continue to use it that way?
 
After around 60 years of playing with valve (I’m not going to call them tubes at this stage in my life) circuits I was rather intrigued by the current crop of class D designs.
Started with a Sure TA2024 4 channel board and was not overly impressed. Too much background noise and hiss definitely not Hi-Fi.
Then decided to try the Lepai 2020 and the first thing I did after switch on was to measure the dc offset.
On my version the readings were 10mv on one channel and 120mv on the other
Being used to valve circuitry to me this was quite unacceptable.
I know the specs state that offset could be up to 150mv but to me having a dc voltage of over 100mv across the speaker terminals displacing the voice coil away from its linear operating position is definitely not a good idea.
On a stereo amp having this level of dc on one channel and around 10 times less on the other must have an effect on performance.
In view of this I decided to try the HLLY TA2020 board. This has multi turn pots to null out dc offset
On switch on with this amp I measured less than 1mv per channel and was able to tune this down to zero. I’ve run this for over a month and have just measured .2mv on one channel and zero on the other.
Nice little amp and absolutely no switch on thump.
I did most of the mods to the Lepai promoted on this thread ,op amp change, tone control bi-pass,
Cap changes etc but I would still like to address the dc offset situation.
Surely correcting this on the Lepai would help the switch on thump situation.
From what I can find it seems that 1 50k multi turn pot 1 resistor and a cap on each channel is all that would be needed.
Has any one tried this.
Being unused to SS circuitry I need some guidance on how to implement this type of mod
Stu
 
Hi Stuart, here's the DC trim circuit shown on one channel.
Very simple and easy to impliment 'in the air'
Hope it helps
 

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Re: djnemesi pop suppressor

Hi to all! I'm a little bit out of work because my ta2020 replacement isn't yet arrived... however

totoelettro said:
Dear djnemesi,

i had make your scheme of pop suppressor, but it doesn't works, i think that i have make a mistake.
The ampli sleep for two-tree second, and after this time the lepai start but with the pop on the speaker.
What do you think that i can try to do?
Thanks

It seems strange, if the ta2020 is correctly powered and the signal on mute pin is correct it should work (have you checked it with a voltmeter?). A thing to check is where the power switch is connected. On some lepay I've seen that it's connected on the mute signal and the pop suppressor can't work; the power switch have to be interrupt the main power.

Anyway a little pop sound is still audible with the pop suppressor but is 1/10 of the original one.

Ciao, Simone!
 
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.
 
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
 
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...
 
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.
 
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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.

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 10µH 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 :)
 

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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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