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LM4766 kit from China
LM4766 kit from China
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Old 31st March 2020, 06:04 PM   #11
chermann is offline chermann  Austria
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ok blackICE...no problem...
hmmmm. ...different input voltage and different "gain"......no idea why this happend


chris
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Old 17th November 2020, 11:27 PM   #12
DaveFred is online now DaveFred  Canada
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LM4766 kit from China
Funny, I was just looking at this exact same amp board on Taobao,

Taobao GC Board

What is your overall impression?

I was going to buy the blank board and fill it with components from Digikey or Mouser.

Thank you,

David.
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Old 18th November 2020, 09:16 AM   #13
chermann is offline chermann  Austria
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Hi


As Turbo wrote. ......useless.....
if you dont need the power of a LM3886 then the 4766 is fine. relay and other things are not needed if you use original parts...


in post 5 i found a mono bridge board.
LM4766 BTL bridge 120W mono power amplifier board|Amplifier| - AliExpress
chris
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Old 21st November 2020, 01:29 PM   #14
TasKitas is offline TasKitas
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Quote:
Originally Posted by Turbowatch2 View Post
There seems to be a simple test for fake LMxxxx chips. Power the amp up an short the speaker out.
Any real LMxxxx will take that and play on when the short is removed. Many fakes just die.
I have assembled LM3886 and it does make pop sounds when turning off. When measured the power it was as it should be and thought this chip should be alright.

Is there a risk it is fake if it pops? In that case the test you mentioned should help.

Last edited by TasKitas; 21st November 2020 at 01:38 PM.
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Old 21st November 2020, 01:48 PM   #15
chermann is offline chermann  Austria
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Hi Taskitas


every chip LM1875,LM3886 should have a short protection mode if its an original chip!
So if you use a chip with unknown source it may be a fake chip without this protection and you short the output during a signal -then the fake chip will die...smoke.burn...what ever.
the lm3886 has a mute circuit . check with datasheet if you components on your board are as recommended.

if I used at the LM1875 the fake chip i get strange sounding pops a max power.



chris

Last edited by chermann; 21st November 2020 at 01:51 PM.
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Old 21st November 2020, 02:08 PM   #16
TasKitas is offline TasKitas
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I have assembled following these instructions:

A Complete Guide to Design and Build a Hi-Fi LM3886 Amplifier - Circuit Basics

Although I'm running it on 24-0-24V toroidal, but did calculations accordingly as mentioned in the guide.

I'm wondering about details of the test, do you play something specific, like 1khz and high volume, or it doesn't have any difference?
And do you just touch the wires or hold for a few seconds?

Last edited by TasKitas; 21st November 2020 at 02:11 PM.
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Old 21st November 2020, 05:48 PM   #17
chermann is offline chermann  Austria
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Hi


if its an original chip you can keep the short some seconds ! please use a current limiter or a bulb limiter at the mains to avoid damage your amplifier. put the amp board out from your housing and use a lab supply.
please read the datasheet and other documents.


As seen in Section 5, a short to ground with an input pulse applied to the amplifier will be current limited by the conventional current limiting circuitry for a few hundred microseconds. When the junctiontemperature reaches its limit, SPiKe protection takes over, limiting the output current further, as the junction temperature tries to rise above 250C.

chris
Attached Files
File Type: pdf LM3886 SPiKe Protection.pdf (1.67 MB, 7 views)

Last edited by chermann; 21st November 2020 at 05:51 PM.
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Old 21st November 2020, 10:07 PM   #18
TasKitas is offline TasKitas
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The lab power supply or to limit the current - I don't have that, everything else, I can do.

Last edited by TasKitas; 21st November 2020 at 10:24 PM.
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Old 22nd November 2020, 08:24 AM   #19
chermann is offline chermann  Austria
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use a fuse with about 3-4 amps in each rail.
you should have that implemented to protect your amp pcb.
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Old 23rd November 2020, 05:24 PM   #20
tomchr is online now tomchr  Canada
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Quote:
Originally Posted by BlackICE View Post
I don't know how this would get 120Wat 4 ohms. The LM4766 is current limited to about 4 amps. So at best I2R = 4x4x4=64 watts for 4 ohms, 4x4x8=128 watts into 8 ohms.
Actually, 4 A is the peak output current for a typical IC (i.e. the mean of the statistical distribution of a large sample size). 4 A, peak would give you P = 4*4*4/2 = 32 W into 4 Ω. The power into 8 Ω would be limited by the supply rails to the IC.
However, note that the LM4766 is only guaranteed to be able to provide 3 A peak, which lowers the output power in 4 Ω to: P = 3*3*4/2 = 18 W.

If you run the chip at the max recommended voltage of 30 V, you get a peak output swing of 30-4 = 26 V, peak. The '4' is the drop-out voltage, which is guaranteed to be no larger than 4 V according to the data sheet. 26 V peak gives you 26*26/(2*8) = 42 W into 8 Ω.
With the 3 A peak output current limit, you're looking at P = 3*3*8/2 = 36 W into 8 Ω.

I would expect a typical IC to be able to deliver about 40 W into 8 Ω and 30 W into 4 Ω, assuming that it can actually run at 30 V and deliver a clean signal to a 4 Ω load.

Quote:
Originally Posted by BlackICE View Post
So they should say 120W into 8 ohms not 4.
Or they just made it up. Or they grabbed the wrong number from the data sheet. Or any combination of the two. It's enough to raise some concerns about the competency level of the designer, that's for sure. That's not to say you can't use the board. It could be a fun platform for experimentation.

Quote:
Originally Posted by BlackICE View Post
Everyone seem to loves the LM3886, but not much is said about the LM4766. In reviewing the specs it seem that the LM4766 if not driven to high output levels has a reasonable low distortion level on par with the LM3886 for my old ears that can even hear 12KHz. Seem like a good chip for 2 channels if driven to less than 20 to 30 watts depending on the PS voltage.
The LM4766 looks like a very capable chip. It looks like a dual LM3886 with their output stages scaled back (and it might indeed be exactly that). I bet the reason "everybody loves" the LM3886 is that it provides higher power. "Want" often wins over "need".

Tom
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Last edited by tomchr; 23rd November 2020 at 05:27 PM.
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