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Old 4th July 2009, 12:00 AM   #441
col is offline col  Australia
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I don't think 7812 will handle the current. you need LM338T or equivalent.

Mine is adjustable and I have it set at 13.2v. I'm currently using a 18v 4.9A Compaq laptop supply to feed the reg but you could put anything from about 14v and up before it.

http://pix.minirig.org.au/main.php?g2_itemId=1054

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Old 4th July 2009, 12:55 AM   #442
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Quote:
Originally posted by col
I don't think 7812 will handle the current. you need LM338T or equivalent.

Mine is adjustable and I have it set at 13.2v. I'm currently using a 18v 4.9A Compaq laptop supply to feed the reg but you could put anything from about 14v and up before it.

http://pix.minirig.org.au/main.php?g2_itemId=1054

col.
Nice, that is a little more elegant than just soldering a 7812 in there!

I was annoyed that mine was cutting out today, and a 7812 was all I had to hand. It was a LM340/LM7812 which has current limiting also, according to the datasheet, which isn't very good when the volume is turned up, but at least the amp isn't cutting out now, plus I've got the LM340 IC heatsinked.

I may try a LM338T, as I'd like to run this amp at 13v if I can, but I think the dropout voltage maybe a little high to achieve this when running 14.4v into the LM338T.

Another crude option I was thinking of is to simply have 2 x MBR745 diodes in seried with the power from the car. Each one is good for 7.5A and drops around 0.5v, so 2 in series should give me 13.4V in theory.

I was going to try bolting them to the case of the Lepai, as I thought it would make a nice heatsink... Electronically isolated tho. Any downsides to doing this?
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Old 4th July 2009, 04:06 AM   #443
col is offline col  Australia
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Are those MBR745 in a TO-220 package? If so screwing them to the case and isolating them with mica washers should be fine. Iv'e never tried running diodes in series but yeah in theory it should work. If you have them at hand i guess give it a shot.

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Old 4th July 2009, 10:21 AM   #444
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Quote:
Originally posted by col
Are those MBR745 in a TO-220 package? If so screwing them to the case and isolating them with mica washers should be fine. Iv'e never tried running diodes in series but yeah in theory it should work. If you have them at hand i guess give it a shot.

col.
Yep they're TO-220, and I also have them to hand so if I get time this weekend I'll give it a go.
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Old 6th July 2009, 05:56 PM   #445
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The quality of these amps has been well debated, but i was wondering if anyone has tested how loud they go, and if they do the rated power of (apparently) 2x20watts?
I am looking into using one of these to power and a level project where i am going to build a couple of speaker enclosures into a TV stand type piece of furniture.
Cheers,
Mike
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Old 8th July 2009, 03:21 PM   #446
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Hi, I'm new on this forum, I've readed (with interest) all the topic, so i decided to buy a Lepai...
It's arrived! Good, it work well!
First of all I drawn the schematic:
http://img23.imageshack.us/img23/1586/scan10006k.jpg
(sorry if it's hand written, but I've no time to put in on CAD)
I hope that it's correct, the component value are of those installed.
On the input section I drawn only one channel, the second is the same.

Some annotation:
  • The transistor circuit on the mute signal serves to mute the amplifier when the voltage exceed about 15V, is a protection? on the mute? dunno...

    Some capacitor are missing on the right side of TA2020 (compared with datasheet), they are important enough (supply decoupling for H-bridge), so i planned to replace the 100u with a good 470u Panasonic and to put other 100n on the solder side.

    The tone control is a Baxandall circuit, I'm curious so I simulated the frequency response:
    http://img4.imageshack.us/img4/1995/lepaibaxandall.jpg
    when I have a little bit of time to make some math I will find the right component value to make it more symmetric.

One thing that is very annoying to me is the pop noise on power-on, so i made a simple pop suppressor:
http://img188.imageshack.us/img188/2...suppressor.jpg
The circuit keep the amplifier sleeping for about 2 seconds after power on.
I made the circuit on a small piece of veroboard. To connect it you have to isolate the SLEEP pin (is connected to ground) milling around the pin with something like a dreamel

Some photos:
http://img196.imageshack.us/img196/3552/dsc00586fcu.jpg
http://img189.imageshack.us/img189/373/dsc00587k.jpg

Now I have to wait the components to make other mods
See you to the next mod episode

Simone
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Old 8th July 2009, 11:22 PM   #447
magixz is offline magixz  Singapore
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Very nice!!!!!!!!!!!!!!!!!!
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Old 9th July 2009, 01:43 AM   #448
col is offline col  Australia
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djnemesi, nice work!

Quote:
The tone control is a Baxandall circuit, I'm curious so I simulated the frequency response: http://img4.imageshack.us/img4/1995/lepaibaxandall.jpg when I have a little bit of time to make some math I will find the right component value to make it more symmetric.
your simulated frequency response, was it made with the component values of the actual components used or the component values that are silk screened on the PCB? I have changed my tone control component values to the ones mentioned on the board and it made a big difference. If these values are wrong I would like to change them to the correct values. So yes, please report back once you have done the math.


Quote:
Some capacitor are missing on the right side of TA2020 (compared with datasheet), they are important enough (supply decoupling for H-bridge), so i planned to replace the 100u with a good 470u Panasonic and to put other 100n on the solder side.
Do you mean the capacitors across the pins 19-22 and 25-28 of the TA2020 data sheet? I noticed that the Lepai designer has made a short cut here and has connected the two pairs of pins together and supply's the pins via one 100uF cap. I have changed this to a 470uF. What pins do the other 100n decoupling caps go on?


Quote:
One thing that is very annoying to me is the pop noise on power-on, so i made a simple pop suppressor: http://img188.imageshack.us/img188/...psuppressor.jpg The circuit keep the amplifier sleeping for about 2 seconds after power on. I made the circuit on a small piece of veroboard. To connect it you have to isolate the SLEEP pin (is connected to ground) milling around the pin with something like a dreamel

I will study this mod and see if I can implement it on my Lepai. Also, will have a good look at your schematic. Do you know what the "not implemented" part is for, is it worth implementing?

Once again excellent work!

cheers,
col.
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Old 9th July 2009, 11:57 AM   #449
col is offline col  Australia
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djnemesi, looking at your circuit diagram and comparing it with others on the net the Baxandall appears to be a "James" variation. There is some software available to simulate the values:

http://www.duncanamps.com/tsc/

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Old 9th July 2009, 08:11 PM   #450
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Quote:
Originally posted by col
djnemesi, nice work!
thanks!

Quote:
your simulated frequency response, was it made with the component values of the actual components used or the component values that are silk screened on the PCB? I have changed my tone control component values to the ones mentioned on the board and it made a big difference.
the simulated frequency response is made with values of actual component, I have also tried with the silk screened value but the result are similar. Probably you changed the poor quality ceramic capacitor on the filter with better ones

Quote:
Do you mean the capacitors across the pins 19-22 and 25-28 of the TA2020 data sheet? I noticed that the Lepai designer has made a short cut here and has connected the two pairs of pins together and supply's the pins via one 100uF cap. I have changed this to a 470uF. What pins do the other 100n decoupling caps go on?
Yes, exactly. I'm waiting for a 470u to arrive too. 100n capacitor are to be placed near pin 27,25,22


Quote:
Do you know what the "not implemented" part is for, is it worth implementing?
It seems a sort of DC offset adjust common to all output, I don't know if it works...



Quote:
djnemesi, looking at your circuit diagram and comparing it with others on the net the Baxandall appears to be a "James" variation. There is some software available to simulate the values:

http://www.duncanamps.com/tsc/
Yes, it can be a variation of variation, because we have an additional resistor (on the treble sliding contact). I've also tried that software, but the results are a bit different, I prefer to use Spice (LTspice) that is more reliable.
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