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Old 8th December 2009, 02:28 AM   #511
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After a 3 week wait my Lepai finally showed up at the post office. Thing worked great right out of the box but...

I was fooling around seeing how low I could set my mp3 player and still get an 'as loud as a normal human being can stand' level out the speakers. Dreaded silence and the 'light ticking' sound hit me after about 3 minutes of this.

Oh well, already found an eBay supplier that sells chips two for $12 including postage.

Alastair,

From the data sheet
"Diodes D1, D2, D3 and D4 are only required for applications where VDD>13.5V"

The other 4 are there. I checked the 'cheap' smps that came with the amp and it was 13.9V before the on board 'make sure you didn't plug it in backwards' diode. Couldn't check it under a load but it seems close. My speakers are 4R nominal and 3.9R measured with a DVM.

When I get parts and repair it I will try using a lower supply voltage. Things do seem to be just a little odd: No clipping or distortion then just silence with 1Hz ticking.

Rick
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Old 8th December 2009, 10:18 AM   #512
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Default Overshoot protection..

Aye, Thats the 'mode-of-failure' as I recall years ago when I was developing with these chips.

There was somewhere on the Tripath website a single leaf concerning the overshoot issue. --Bearing in mind this was some years ago, I recall that the diodes should be included where 'unusual loads' were expected or when you use the outputs parralelled together (with the appropriate DC Offset correction/servo etc.) to drive 2 ohm loads.

I successfully drove a 2 ohm load with a single channel, ie- four 4 ohm speakers in two pairs driven by one chip and at 14-14.5V for many hours with no apparent damages--Sounded pretty good too, An old pentium heatsink with no fan was added as a precaution as driving a 2 ohm load did make it heat somewhat! ...

As the diodes have no other function and dont affect the sound, it maybe an idea to add 'em anyway--I did in all the schems I used these chips in....
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Old 8th December 2009, 05:22 PM   #513
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Quote:
Originally Posted by ricortes View Post
When I get parts and repair it I will try using a lower supply voltage. Things do seem to be just a little odd: No clipping or distortion then just silence with 1Hz ticking.

Rick
Hi, remove the zener which is connected to the fault pin, the amp will not kill TA2020 IC's then, read the TA2020 datasheet to see why.
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Old 9th December 2009, 01:19 AM   #514
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Originally Posted by MikeHunt79 View Post
Hi, remove the zener which is connected to the fault pin, the amp will not kill TA2020 IC's then, read the TA2020 datasheet to see why.
Looking at mine it is silk screened as a 4148 which is a small signal switching diode. Did they actually use a zener there?

I haven't looked closely but it appears they included it as part of their left handed, cross eyed scheme for a power switch. Normally it is OK to use blocking diodes for combinational logic i.e. [if the on off switch or the fault pin go high then mute system] but there is only one diode here so it has me a bit wary.

Data sheet shows mute pulled up internally on the chip so it should be should be pull down to turn on, float or high to turn off. Mind fart but it looks like the diode is backwards in that case. i.e. if fault is high, mute is already high from pull up. If fault is low, diode blocks it from pulling mute low. IOW it doesn't do anything.

http://img23.imageshack.us/img23/1586/scan10006k.jpg

The only zener I can see is in the overvoltage circuit which combines with the fault pin to mute.

Rick
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Old 10th December 2009, 07:17 PM   #515
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I changed the circuit just a bit. Moved diode in power supply circuit, reversed diode in protection/fault circuit, and added diode in over voltage protection circuit so fault and over voltage function as NOR<?>.
Click the image to open in full size.

This should keep the inductor from burning out if the amp gets reversed voltage and let the fault and over voltage protection work. I'm open for comments or corrections but IMHO I would like to keep this particular focus on circuit corrections and safety rather then improvements like changing out the op amp.

For example: I added the protection diodes as per Alistair's suggestion.

Just as a for instance, the over voltage protection seems unnecessarily complicated. I'm trying to think back to single transistor designs I made with a PNP transistor vs. two NPNs to KISS.

I haven't put the changes in yet as my replacement TPA2020 isn't here yet. I have the schematic up on my personal web space which earthlink sees fit to limit to 10 megs so I don't know how long I will keep it up.

Rick
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Old 10th December 2009, 11:04 PM   #516
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Quote:
Originally Posted by ricortes View Post
Looking at mine it is silk screened as a 4148 which is a small signal switching diode. Did they actually use a zener there?
I'lll have to check my unit, but I have a feeling they did. I seem to remember it was between the mute pin and the fault pin, but I need to open my unit to be sure.

I wanted to wire up a fault LED on my unit, so I removed whatever was connected to the fault pin (i'm 99% sure it was a zener) and instead wired an LED in series with a 2k resistor. It works and I quite like having a fault LED.

To make matters worse, there are 2 different versions of this amp, and we could have differing versions...

Nice work with the schematics btw.
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Old 22nd December 2009, 02:04 PM   #517
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I have updated the tone control on my amp, but now it is acting up. When I plug it in it works fine for a few seconds then the LED starts to flicker and the sound "hacks" but the music is still audible and sounds fine.

Hi res photos of my board.
http://upload.landslide.nu/upl/Tornado/_DSC3941.jpg
http://upload.landslide.nu/upl/Tornado/_DSC3942.jpg
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Old 23rd December 2009, 01:13 PM   #518
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Default Changing the Pots

New to the forum but have recently gone down the modified Lepai T-Amp route coupled with pair of home-made Cyburg Needle TQWT speakers (still under construction) to complement my new 46" Panasonic Plasma TV.

Progress so far:
a) have changed 3.3uF input Caps to 2.2uF MKT types
b) swapped 2200uF for 4700uF Panasonic FC
c) changed all other 3.3uF electrolytics for 2.2uF Panasonic FCs
d) changed 330uF for 470uF Panasonic FC
e) swapped op-amp for NE5532P
7f) added d.c. trimmers etc. (as per #465 on Pg 47)

Still to do...
g) change tone circuit capacitors and resistors (#484, Pg49)
h) change out Pots for better ones
and possibly...
i) add remaining 4 shottky diodes
j) replace 10uH inductors

my question is: do the control knobs come off in one piece or are they fixed to the pot spindles?

Given previous reference to risk of breakage, I have tentatively attempted to prise them off but unsuccessfully. Ideally I would like to re-use the existing control knobs.

Cheers

Last edited by dlpublic; 23rd December 2009 at 01:27 PM.
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Old 23rd December 2009, 02:52 PM   #519
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Welcome to the forum! The Lepai is a fun amp.
On mine, the knobs pulled right off. But I have the older version.
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Old 24th December 2009, 09:47 AM   #520
ias is offline ias  Japan
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Hello everyone

I installed the relay amplifier
Get lost in the noise when turning
Turn off the power when the noise occurs Unfortunately

(Sorry for the automatic translation)


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