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LM4766 kit from China
LM4766 kit from China
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Old 23rd March 2020, 08:29 AM   #1
BlackICE is offline BlackICE
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Join Date: Feb 2020
Default LM4766 kit from China

Has anyone brought one of these. I should get one in the next day or two to assemble. It took a long time to get delivered because the 1st one shipped got bounced back to the seller.

I was looking for a low power reasonable performing 2 channel amp to run my tweeters in tri-amp speaker. The specs aren't the best, but seem ok if you don't push the limits of its power. I doubt if I would use more than 10w peak. The reason for this choice it is seems to have speaker protection that I hope works during power on and power off cycles. Going to use a 100VA 36vct transformer with it. After I bench test it if it works well I have to find a case and heatsink for it.


2018 GC version LM4766 dual channel HIFI power amplifier board diy kit | eBay

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Old 23rd March 2020, 09:27 AM   #2
Turbowatch2 is offline Turbowatch2  Germany
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Hi,
at first sight, this amp looks OK and no major components are missing. The real LM4766 is an amp just sounding perfect. You can discuss the speaker protection, as the real LM4766 chip has an anti pop and fade in fade out function. So why add one at extra cost?
I write "real" because you can trust no Chinese seller to use the expensive ($3) TI chip. There are millions of fake LM3886 (comparable chip, just in Mono) around. Some even work, most not as expected. What the chip fakers are unable to copy, are the advanced safety features and refined sound of the original. So the corresponding pins are connected to similar working, cheap circuits, that is all you get. Most blow, sooner or later.
Anyway, if you have such an amp and the circuit is close to the reverence design, throwing away the LMxxxx is easy and Mouser or RS will sell you a real one, making you a happy camper.
Please, before you connect an expensive tweeter, get the data sheet and compare the values of the parts used, no one in China cares about 1.000 or 10.000 Ohm. They care only for money.
A real DIYS amp...
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Old 23rd March 2020, 10:39 AM   #3
BlackICE is offline BlackICE
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Any way to tell if it is a fake? So a real LM4766 wouldn't need a speaker protection relay as those function at internal to the chip. I saw some assembled LM3886 amp that had speaker protection relays and other didn't. When I looked that the data sheet for the LM3886 I also thought why do you need a relay of the chip does it for you.

I have some old Hafler DH220 that don't have speaker relays and they have an bad spike on power up and a less severe noise on power down. I'm making a power cycle speaker relay for them. If I connected the Haflers directly to a tweeter they would likely be damaged during one on cycle!

To be on the safe side I'm planning to use an 1st order cap as a high pass filter between the amp and tweeters.
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Old 24th March 2020, 04:18 AM   #4
Turbowatch2 is offline Turbowatch2  Germany
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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.
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Old 24th March 2020, 08:30 AM   #5
chermann is offline chermann  Austria
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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.

yep and according to FF experience the UTC 2050 are survive this test too!


a little bit off topic because this amp is BTL but you need a tweeter amp but....:
LM4766 BTL bridge 120W mono power amplifier board|Amplifier| | - AliExpress


chris
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Old 24th March 2020, 10:55 AM   #6
BlackICE is offline BlackICE
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Join Date: Feb 2020
Quote:
Originally Posted by chermann View Post
yep and according to FF experience the UTC 2050 are survive this test too!


a little bit off topic because this amp is BTL but you need a tweeter amp but....:
LM4766 BTL bridge 120W mono power amplifier board|Amplifier| | - AliExpress


chris
The marketing errors

Product specifications:
● Output power: 120W (maximum undistorted power, 4 ohm load)
● Working voltage: 18V+0+18V (AC communication)
●Magnification 22 times
● Product size: 68mm X 70mm
●The power amplifier board is mono
● Power amplifier board weight: 100g


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. So they should say 120W into 8 ohms not 4. It wouldn't fit my needs as I need 2 channels and to have no use for more than probably 10 watts per channel.

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.

I got the thing assembled. No instructions no schematics. Just a PCB and bag of parts. The silk screen has most of the parts labeled except for a few polarized caps. I had to look up the datasheets for the C1237HA and LM4766 to figure out what caps went where.

Last edited by BlackICE; 24th March 2020 at 11:07 AM.
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Old 24th March 2020, 11:46 AM   #7
chermann is offline chermann  Austria
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Join Date: Jan 2017
Location: Vienna
Hi Blackice


Yes as i read the last month - the LM4766 is not so popular as the LM3886. The smaller chips - less power -are mostly LM1875 , LM1876 or the TDA7xxx.
chris
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Old 31st March 2020, 10:35 AM   #8
BlackICE is offline BlackICE
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I assembled it and tested with a bode plot at 3 different input levels. The frequency response seems OK at each given input level, I see a slight phase shift, but of concern I see about a 4 db loss of gain as the input level is increased. I don't have a large enough resistor to test at higher levels, only went to about 8 watts. Should be able to go to 30+ watts in which case the gain loss would probably be even worst.

Amp[1] = input PPV
Amp[2] = output PPV
RMS[2] = output RMS V
Attached Images
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Old 31st March 2020, 02:11 PM   #9
chermann is offline chermann  Austria
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Hi Blackice


i am not sure if i understand your plots correctly. the last - pic 3 is about 8Watt (7,5W) into 8R load. ok fine - you requested about 10WAtts-right?
you transformer is a 36CT - is 18-0-18VAC is after rectifier about 26VDC per rail.
so about the power - you have 7,73rms --> Vout peak is 10,9V --> so out pp 21,8V sin wave so you have some head room to go higher until clipping . i guess that 26VDC rail drop down to something like 23V or so- so with a bigger load resistor you should can go up.


pic 1 - 2 what do you mean with PPV-



purple pic 3

that means the purple line shows the frequency response and i canīt see 3dB loss? - at the low frequency you have a "loss" just about 1db 29,85 down to 28,85dB - this is not bad!
the amp input is 712mV rms and output is 21,8Vrms that give a gain about 30,6 and its about 29,6dB. i would change the gain setting down for less hiss. Rf in the datasheet (pin3-7 and pin1-12) is 20k ohms - i guess you have about 30k there...



chris
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Old 31st March 2020, 04:54 PM   #10
BlackICE is offline BlackICE
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Sorry my brain was working backwards I meant VPP not ppv or volts Peak to Peak. What I meant was at low input voltage in the first picture of the gain is approximately 34 db where 3rd photos the gain at a higher input voltage is about 30 Db. Test resistor was a 10-ohm 10 watt resistor. Another interesting fact about this kit the input impedance is only 1 K ohm.
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