Power Amplifier LJM L20SE

[Eliseu]

Electronic Schema Power Amplifier LJM L20SE

Electronic schema and analysis

Schema: Amplif_L20SE.pdf - Google Drive

Project: Amplif_L20SE.ms14 - Google Drive

I am not marketing this product and I am not the author of the project. I did the schematic circuit for analyzing and sharing information.

 

[wdebelg]

I bought one on aliexpress and also tried to solve the puzzle. What I found is identical except for one detail: I can't find the 33k resistor between VEE and the base of the 2N5401pre-driver: your schematic counts 29 resistors, the actual board only 28. (at least, the version I received).

 

[wdebelg]

continued...

I just found out how to attach...

 

[Ketje]

There is a resistor much to small, pulls the input stage out of balance.
Mona

 

[ivanlukic]

This thread should be in Solid State section.

 

[odisy]

I think its a perfect amplifier ,can outperform commercial ones of many 1000 .Of course needs coupling input capacitor ,adjustable bias current at 25ma per transistor and nothing else.At 35-0-35 AC don't need to change the value of 150 Ω resistor ,maybe at higher power supply.

 

[odisy]

Needs big heat sinks and the output inductor with the parallel 10Ω resistor like every amp.

 

[coldrunning2002]

I had a quick look at the circuit.

* What is the phase and gain margin?
* Where is the short circuit protection?
* HDS662 has to temperature compensate 6 VBE's
* current source with 270 Ohm resistor and 2N5401 will not be stable with severe ambient temperature changes!
* where is the offset-null trimming?
* where is the quiescent current trimming?
* 1n4004 are not very fast diodes for freewheeling transients!
* 1mF capacitor in the feedback path ?

 

[XPZMIePKdFlkA]

Location of the original L20SE thread

The original L20SE thread, started by LJM (the board designer), may be found at:
http://www.diyaudio.com/forums/solid-state/199093-l20-amp-use-only-two-njw0302g-5.html#post3601502

 

[Eliseu]

I'm sorry

I bought one on aliexpress and also tried to solve the puzzle. What I found is identical except for one detail: I can't find the 33k resistor between VEE and the base of the 2N5401pre-driver: your schematic counts 29 resistors, the actual board only 28. (at least, the version I received).

You are correct, this resistor does not exist, there are only 28 resistors.

 

[Eliseu]

Electronic Scheme Power Amplifier LJM L20SE

Electronic schema for analysis

 

[Eliseu]

Test 1

IN 1vp 1Khz - OUT 4ohms 82w - THD 0.011

 

[Eliseu]

Test 2

IN 1.7vp 1Khz - OUT 4ohms 237w - THD 0.019

 

[Eliseu]

Image

Images

 

[Eliseu]

Image

Images

 

[andrewlebon]

Hi Eliseu
greetings very nice build is it possible to post correct schematic
warm regards
Andrew

 

[ivanlukic]

Eliseu,

Thermal grease is not used with rubber washers. Just bare washer between transistor and heatsink.

 

[Eliseu]

Eliseu,

Thermal grease is not used with rubber washers. Just bare washer between transistor and heatsink.

Good observation! In the last modification in the project I took out the folder. Soon I'll be posted. Thank you!

 

[Eliseu]

Hi Eliseu
greetings very nice build is it possible to post correct schematic
warm regards
Andrew

Yes. The original has been corrected and the project has been added. It's at the beginning. Page 1.

 

[Eliseu]

Original circuit

circuit, response and fourier curve.