• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Review and Measurements of L20.5 Loudspeaker Amp

YMY

Member
Joined
May 11, 2019
Messages
16
Likes
24
Location
SHANGHAI CHINA
#1
New to the forum. budget stereo speaker amp Measurements
To be honest,it comes to my mind for a long time that i want to introduce this array of products,but it was put on hold for a variety of reasons,it's my honor to have a brief introduction.
introduce the L20.5 amplifier & which was designed for the monitor speaker
This array of power amplifier prototypes started being created in 2003(maybe more earlier) in Sichuan province of China.
The designer paid more attention on scientific data of AP(audio precision),however,it still has some shortcomings--that will be mentioned later.
SO..the mother board must be MODification,finally can be use,Warning!!Must remember don't use switching power supply at any time&Please don't use pre-amplifier
“science datasheel”
8Ω 200 W 4Ω 400 W CLASS-AB
frequency response 20-25 Khz -0.15 DB 20 Khz-0.05 DB 10 Hz -0.7 DB
AP TEST (8Ω)1-50 W
THD+N 50 HZ 10 W(9 Vrms) <0.0007
THD+N 1 Khz 10 W(9 Vrms) <0.001
THD+N 10 Khz&20 Khz 10 W(9 Vrms) <0.0008
THD+N 50 W(20 V rms) 1 Khz <0.0015

IMD+N 50 W <0.0015
output impedance L 20.5=0.02Ω(theory)=damping factor:8Ω 400 4Ω 200
L 20=0.004Ω
SR:35
Unfortunately,the seller himself demostrated a very wrong way to use AP..which led to the master design error and insisted on the wrong AP test method,we have different views,so we could not communicate with each other,fortunately,my friend is an experienced university professir who is very interested in this product and makes a simple MODification (feedback) I'll show you how to MOD the motherboard later.
最后:price
QQ图片20190513124313.jpg











@@RT6MD{0HX{@W_0%GU%XFN.jpg
]1577)39DK]6M9%S55DVJ@I.jpg
9_690$CQGD[$9D8$((85Y{C.jpg





130DFC4AAAAA1DF82317D2D3CE849556.jpg
W5JBZ8V@P}O0DS$V`2F1WFK.jpg
3HJ02XUO9F}XPS6FE{0(DF1.jpg






MODification


MF2D2NJCMC1HF1Q~]TM)O1F.jpg


W4DN[T9GLV87{6N]{X1ZZ]5.jpg

41V0@Z%N}(XS%J8CU(%2(5P.jpg

simple mod complete

XIDI@OWPH]K9B{D]2}701Y7.jpg
7OC3]{JZ7}LY(L)]NZ8HF@8.jpg

Special thank Dr. Yi &Chloe


----------------------------------------------------------------05 13 2019 Shanghai China---------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
 
Last edited:

maxxevv

Addicted to Fun and Learning
Joined
Apr 12, 2018
Messages
737
Likes
532
#2
Those are pretty decent numbers for something at that price bracket.

How do they measure in the 100-200W range ?
 

maty

Addicted to Fun and Learning
Joined
Dec 12, 2017
Messages
843
Likes
344
Location
Tarragona (Spain)
#3
Last edited:

maxxevv

Addicted to Fun and Learning
Joined
Apr 12, 2018
Messages
737
Likes
532
#5
I was referring to the measurement results of the module in the 100~200W range.

Your online translator must have thought I was asking how you loaded the module to test at that power range instead.

In any case, its pretty impressive for something in that price range. And as far as I understand of your comment, it works best in Class A or Class AB but not in Class D setup ?
 

YMY

Member
Joined
May 11, 2019
Messages
16
Likes
24
Location
SHANGHAI CHINA
#7
I was referring to the measurement results of the module in the 100~200W range.

Your online translator must have thought I was asking how you loaded the module to test at that power range instead.

In any case, its pretty impressive for something in that price range. And as far as I understand of your comment, it works best in Class A or Class AB but not in Class D setup ?
We'll try it later.
I do have translation software like Google Baidu, but it's a little hard to use.:p
 

maty

Addicted to Fun and Learning
Joined
Dec 12, 2017
Messages
843
Likes
344
Location
Tarragona (Spain)
#11
Then we need a new L20.5 version or new amp with the best of the two. And global feedback < 29 dB to get sound more 3-D as defend some knowledgeable diyers and builders.

Problem, ljm_ljm is now in other more lucrative things I read.

Well, that is why I will keep the one what I have, now that sounds so good!
 
Last edited:

YMY

Member
Joined
May 11, 2019
Messages
16
Likes
24
Location
SHANGHAI CHINA
#12
LJM said : L10 was the worst amplifier he ever made,L20 V10 have a bit of magic dust here and there(means some warm coloration,but thd+n remained at 0.002)
we test..

L20 V10 THD+N:0.1:facepalm:


PRO2(headphone amp) THD+N: over 0.5:rolleyes::oops:???
Finally, I want to say... I can't hear the obvious distortion
 

YMY

Member
Joined
May 11, 2019
Messages
16
Likes
24
Location
SHANGHAI CHINA
#13
LJM said : L10 was the worst amplifier he ever made,
L20 V10 applied a bit of magic dust here and there(means some warm coloration:rolleyes:,nonetheless,thd+n still at 0.002)



but we test THD+N: 0.1 (L20 V10) maybe it's wrong,i can't remember clearly.;)



LJM PRO2(headphone amp) THD+N: over 0.5:facepalm:???
QQ图片20190612205036.jpg
 

YMY

Member
Joined
May 11, 2019
Messages
16
Likes
24
Location
SHANGHAI CHINA
#14
LJM MX50X2 test
50W(20V) 8Ω THD+N
50HZ 0.0014
1KHZ 0.0016
6.6KHZ 0.0049
10KHZ 0.0088
20KHZ 0.04:)
DF(damping factor) over 2500:eek:
mmexport1560346818630.jpg
mmexport1560346833870.jpg
mmexport1560346831460.jpg
mmexport1560346828883.jpg
mmexport1560346825684.jpg
mmexport1560346821588.jpg
 

YMY

Member
Joined
May 11, 2019
Messages
16
Likes
24
Location
SHANGHAI CHINA
#19
Okay. Do you have such graph for this amp? Looks a steal if it has this much power.
You can see the details of the modifications in picture 9

Sorry, I have no AP and I am not a professional in this field.
Dr. Yin having a meeting in Shanghai (today) about university recruitment,he is very busy.

But I can make speakers, have measuring tools and use software simulators.
This year I have a crazy plan. I want to buy all the cheap speakers in China and test distortion

coming sooooon!
 

Attachments

Top Bottom