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-   -   eBay mono LM1875 kit (https://www.diyaudio.com/forums/chip-amps/341675-ebay-mono-lm1875-kit.html)

Bare 18th August 2019 03:45 PM

eBay mono LM1875 kit
 
(Mod note... thread split from here:
Beginner's Gainclone, HiFi LM1875, The Amplifier Board)

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Hmmm Been looking at this as well.
Couple of points;
I located the 'Original'.. and quite good actually..design (haodiy.net) of the currently widely available on ebay, as the 'cloned' 2$ lm1875 'kit'.
PCB layouts..Amp and PS are downloadable at haodiy.net..for DIY PCBs.

Ebay Vultures have shrunken the pcb tho (cheaper to make).. but it's still a good usable layout .. absolutely so for the price ;)
Their Odd low quality parts / value substitutions are definitely for the trash bin though. Just use the pcb.

Daniels' final circuit, seems as oddly complex.. IMO .. with 24 parts.
Certainly seems so as compared to the often described as 'excellent' ESP layout which uses Far fewer parts (15).
Note though that Both the Hao design author And Rod Elliot (esp)both state that the 1875 approaches High end audioweenie sound.. but does not quite achieve it.. all claims aside

Your choice... Suggest trying either the Haodiy OR the ESP circuit as experiment, then comparte Could be interesting and worth reporting back on it?

chermann 18th August 2019 05:15 PM

hi


you mean this board as this thread?:
LM1875 Amp layout


its the board which John audio tech tested...


chris

Bare 18th August 2019 10:53 PM

Yess... But.. John Audio tested it with it's then supplied Recycled genuine 1875 chip ... A rarity indeed.
Still.. it's crippled by the ..significantly different.. ineptly substituted / cost reduced .. cap values.
A departure from the still available Haodiy schematic and pcb design.
Ie; the input caps were designed as 2.2 uf and 22 uf , both 16 v NP types ( or Films.. if the builder could afford it) DIYers en chine often have budgetary constraints.
Should really read the Haodiy.net build article.. It has interesting info and a decent Power Supply design /PCB .
No mention of 'Protection' circuitry tho :D.

rabbitz 19th August 2019 06:45 AM

1 Attachment(s)
That eBay kit caught my interest as the PCB looks quite good so I'll buy a pair. The first thing to do is throw away all the parts and buy them from a reputable supplier such as Digikey etc.

The circuit uses a schematic from the Silicon Chip "Schoolies Amp" but some of the values on the PCB are different. Maybe better to use another schematic such as:

A. TI typical applications schematic
B. ESP P72
C. The one in this thread (I haven't read the full thread so I don't know if the parts count would suit)
D. Gobo LM1875
E. Chipamp.com used to have one but can't see details now
F. Some other circuit

rabbitz 19th August 2019 06:55 AM

Quote:

Originally Posted by Bare (https://www.diyaudio.com/forums/chip-amps/341675-ebay-mono-lm1875-kit-post5888627.html#post5888627)
Y
Should really read the Haodiy.net build article.. It has interesting info and a decent Power Supply design /PCB .

http://www.haodiy.net/a/jishuwenzhan...0617/7340.html

That's a copy from the Silicon Chip article Dec 2004.
Silicon Chip Online - Schoolies Amp

kurtvisti 19th August 2019 07:12 AM

I would like to compare the sound from the one on this thread (already made) with the sound from ESP P72.
Could you please help with the exact placement of components (ESP P72) on the ebay PCB from post #857?

rabbitz 19th August 2019 07:29 AM

Just compare the ESP P72 schematic and the one from Silicon Chip link in post #858 and it falls into place on the PCB.

kurtvisti 19th August 2019 08:20 AM

I have off course compared the 2 schematics.
What about R3 on the P72 and the 1K on the schoolies amp....seems to me on different places???
And instead of the 10 ohms on the schoolies amp it should be shorted???

chermann 19th August 2019 11:37 AM

Hi Rabbitz

I have the amp as you posted in #857

my uncoverd topics are: (from left to right)

the 10µF input cap is wrong polarized- but nevertheless we should use a foil cap.
the 47µF is the electrolytic cap for the PIN 2: at the other schematic´s its a 22µF non bolarized cap.
right/upper corner: the 3R3 is marked on the pcb but it should be a 1R resistor. 1W minimum
the supply electrolytic caps are not correct (100µF) because it should be 220µF at minimum on the supply
all other part i measured with my LCR meter and they are ok.

btw: at my kids the 1M and the 10R are missing - i claimed the seller....will see..
wating for power supply and then start with tests...


chris

rabbitz 19th August 2019 01:36 PM

Quote:

Originally Posted by kurtvisti (https://www.diyaudio.com/forums/chip-amps/341675-ebay-mono-lm1875-kit-post5888922.html#post5888922)
I have off course compared the 2 schematics.
What about R3 on the P72 and the 1K on the schoolies amp....seems to me on different places???
And instead of the 10 ohms on the schoolies amp it should be shorted???

R3 and the 1K are in the same place just before pin 1 on the chip. The location of the 330pF cap makes no difference for this resistor. The 10R is a ground lift resistor which sits between signal ground and power ground and can help reduce hum but have not seen it used on any of the Chipamps I've build but have on plenty of SS amps.


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