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Comments and tests on a LM audio MIN400A China made Purify inspired amplifier.

Abrise

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Comments and tests on a LM audio MIN400A China made Purify inspired amplifier.
This post is not an incentive to follow in my footsteps but is for informational purposes. I’ll try to point out facts only.

Where I live, I am a French expat in Thailand, there is not many high-level products tested on ASR locally available besides Topping or SMSL products. I already have the excellent Topping PA7, but for my last amplifier I wanted something excellent but different. Buying and having it shipped from the west from Audiophonics, VTV, Buckeye or the likes is long and complicated. Moreover, guarantee is almost impossible to claim cross continent anyway because of shipment time, cost and custom issues. So, I have just purchased for 620€ including transportation on AliExpress, a Purifi like based amplifier. The device is also for sale elsewhere on Aliexpress for twice this price!
The original offer is on Taobao https://item.taobao.com/item.htm?sp...XzChad&id=662513179130&ns=1&abbucket=4#detail , it’s at a similar price but if you are not Chinese you cannot buy easily on Taobao .

There is already a thread on this product, but it has turned into politics and philosophy, a bit limit on ASR. No facts of manufacturer misbehavior have been proven although this thread is up for more than a year now. https://www.audiosciencereview.com/forum/index.php?threads/chinese-purifi-1et400a-clone-amp.36470/

This amplifier is extremely well placed into @Matias list https://docs.google.com/spreadsheets/d/1ZlTOYxmPs938gqHjtDABkWS-MApu7uJjzIGnJ2Elm6Y/edit#gid=0

There has been an extensive testing with superb results https://www.l7audiolab.com/f/min400a/ However these results, certainly honestly obtained, are -at least as it is presented by the vendor -misleading to the normal reader as you’ll understand later.

I will make a few tests to check if my unit is at par with the one tested by l7audiolab. I think that the manufacturer has low volume and although he says that he controls all units shipped, I better check myself. Also, there is a small difference as I choose the unit with a small form factor and with a passive volume knob.

Purchase and transportation

This experience has been quite stressful. At payment I wasn’t given the choice of shipment. Parcel was supposed to arrive 13 days after payment. But the shipment took place 13 days after the payment. Contact with seller was inexistent. I thus started to be scared a little bit. In 20 years of practice, I have never been scammed with AliExpress but usually I choose well known shops. At last, it is shipped. But it’s going first to Japan. What?... To summarize the parcel travelled from Hong Kong to Japan to China to Indonesia to Singapore to Thailand to…Home. Strange Fedex logistics. All together 23 days from purchase to final delivery. Usually, it takes a week or two. By the way 23 days is no longer than having things shipped from Europe.


Manufacturer specs

Power at 1% distortion: 200W*2 8 ohms, 350W*2 4 ohms
Distortion: less than 0.00025% at 1kHz 100W i.e. -112dB
SN: above 125dB, measured 127dB.
Frequency response: 20-20hKz - 0.02dB.
Manufacturer writes that the connection board and power supply unit are his design. The buffer which can be disabled is 14dB gain.
Iddle power is 16W



Unpacking

I weighed the parcel when it arrived and took a video of the opening. The shipment box is the only box. There is no manual neither plug cable inside.

Here is a photo.
1699366892902.png






First tests

My test equipment is: SMSL-D6S xlr output as the DAC, 4x2 Ohms 200W resistors as the dummy load and voltage divider when necessary, E1DA cosmos class B, Topping HS02 isolator, Surface Pro PC with REW. This setup is good enough to make valid measurements for the expected results. (at least 10dB better.)

And the first result is …

At 5W 4Ohm THD+N of 97dB. A SINAD of 97dB puts the amp into the excellent category inside @amirm scale. However, I was disappointed as I was waiting for SOTA values as per L7Audiolab measurements 10dB better.
1699366965697.png





To better understand the amp I have made a lot of other tests but to make a long story short here are just 2 other graphs

THD+N vs level BW 20kHz showing a max power of 170W at 8 Ohms. Read 500Hz not 500kHz
1699366992311.png




And this more than acceptable multitone test at 5W 8Ohms around 18bits
1699367007595.png






But why am I so far from the manufacturer specs and L7Audiolab tests ?

After a sleepless night, I decided to disable the buffer. Getting 14dB less gain and a DAC with an output of 5V only, the amp will not be very powerful. To do this I have to take out the 2 amplifiers mini boards and change the position of 4 jumpers.

Immediately I could see the difference in test results: 10dB improvement! I went back to l7Audiolab test and realize that to get 5W on 4Ohms he puts 1.05V at the amp input and to get 150W on 8 Ohms he puts 7.94V. Thus, there is no input buffer in his device under test. And the natural gain of the amp is 4.3 or 12.6dB. I believe that the absence of input buffer should have been written clearly in the report text.

Here are the culprits perverting the signal, they are supposed to be OPA1612 but the marking is erased.
1699367125677.png



With a max of 5V at my DAC level I will get a max of 115W on 4Ohms or 55w on 8 Ohms. It might be enough, I don't know.

Tests without the input buffer

5W 4Ohms 1kHz spectrum analysis shows now excellent results SINAD of 106 dB within 2dB from l7Audiolab testing
1699367199162.png




Multitone test at 5W 4Ohms almost 19 bits very nice.
1699367220352.png




Frequency response 5W 4Ohms Is excellent
1699367239400.png




Another test at 90W close to the max I can go with no buffer. THD+N 97dB excellent but was expecting even better
1699367306105.png






So now I have to choose among

1/Keeping the amplifier without the buffer and get a more than excellent device but limited at 115W 4 Ohm

2/Put back the existing buffer amplifier and getting an excellent amplifier with quite a lot of power.

3/Replace the buffer amplifier by a better one.

For this last alternative I need support.
-does it make sense that the input buffer causes a damage of 10dB to the specs ?
-would it make sense to replace the small modules by another amp and which one?
 

MaxwellsEq

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Comments and tests on a LM audio MIN400A China made Purify inspired amplifier.
This post is not an incentive to follow in my footsteps but is for informational purposes. I’ll try to point out facts only.

Where I live, I am a French expat in Thailand, there is not many high-level products tested on ASR locally available besides Topping or SMSL products. I already have the excellent Topping PA7, but for my last amplifier I wanted something excellent but different. Buying and having it shipped from the west from Audiophonics, VTV, Buckeye or the likes is long and complicated. Moreover, guarantee is almost impossible to claim cross continent anyway because of shipment time, cost and custom issues. So, I have just purchased for 620€ including transportation on AliExpress, a Purifi like based amplifier. The device is also for sale elsewhere on Aliexpress for twice this price!
The original offer is on Taobao https://item.taobao.com/item.htm?sp...XzChad&id=662513179130&ns=1&abbucket=4#detail , it’s at a similar price but if you are not Chinese you cannot buy easily on Taobao .

There is already a thread on this product, but it has turned into politics and philosophy, a bit limit on ASR. No facts of manufacturer misbehavior have been proven although this thread is up for more than a year now. https://www.audiosciencereview.com/forum/index.php?threads/chinese-purifi-1et400a-clone-amp.36470/

This amplifier is extremely well placed into @Matias list https://docs.google.com/spreadsheets/d/1ZlTOYxmPs938gqHjtDABkWS-MApu7uJjzIGnJ2Elm6Y/edit#gid=0

There has been an extensive testing with superb results https://www.l7audiolab.com/f/min400a/ However these results, certainly honestly obtained, are -at least as it is presented by the vendor -misleading to the normal reader as you’ll understand later.

I will make a few tests to check if my unit is at par with the one tested by l7audiolab. I think that the manufacturer has low volume and although he says that he controls all units shipped, I better check myself. Also, there is a small difference as I choose the unit with a small form factor and with a passive volume knob.

Purchase and transportation

This experience has been quite stressful. At payment I wasn’t given the choice of shipment. Parcel was supposed to arrive 13 days after payment. But the shipment took place 13 days after the payment. Contact with seller was inexistent. I thus started to be scared a little bit. In 20 years of practice, I have never been scammed with AliExpress but usually I choose well known shops. At last, it is shipped. But it’s going first to Japan. What?... To summarize the parcel travelled from Hong Kong to Japan to China to Indonesia to Singapore to Thailand to…Home. Strange Fedex logistics. All together 23 days from purchase to final delivery. Usually, it takes a week or two. By the way 23 days is no longer than having things shipped from Europe.


Manufacturer specs

Power at 1% distortion: 200W*2 8 ohms, 350W*2 4 ohms
Distortion: less than 0.00025% at 1kHz 100W i.e. -112dB
SN: above 125dB, measured 127dB.
Frequency response: 20-20hKz - 0.02dB.
Manufacturer writes that the connection board and power supply unit are his design. The buffer which can be disabled is 14dB gain.
Iddle power is 16W



Unpacking

I weighed the parcel when it arrived and took a video of the opening. The shipment box is the only box. There is no manual neither plug cable inside.

Here is a photo.
View attachment 324604





First tests

My test equipment is: SMSL-D6S xlr output as the DAC, 4x2 Ohms 200W resistors as the dummy load and voltage divider when necessary, E1DA cosmos class B, Topping HS02 isolator, Surface Pro PC with REW. This setup is good enough to make valid measurements for the expected results. (at least 10dB better.)

And the first result is …

At 5W 4Ohm THD+N of 97dB. A SINAD of 97dB puts the amp into the excellent category inside @amirm scale. However, I was disappointed as I was waiting for SOTA values as per L7Audiolab measurements 10dB better.
View attachment 324605




To better understand the amp I have made a lot of other tests but to make a long story short here are just 2 other graphs

THD+N vs level BW 20kHz showing a max power of 170W at 8 Ohms. Read 500Hz not 500kHz
View attachment 324606



And this more than acceptable multitone test at 5W 8Ohms around 18bits
View attachment 324607





But why am I so far from the manufacturer specs and L7Audiolab tests ?

After a sleepless night, I decided to disable the buffer. Getting 14dB less gain and a DAC with an output of 5V only, the amp will not be very powerful. To do this I have to take out the 2 amplifiers mini boards and change the position of 4 jumpers.

Immediately I could see the difference in test results: 10dB improvement! I went back to l7Audiolab test and realize that to get 5W on 4Ohms he puts 1.05V at the amp input and to get 150W on 8 Ohms he puts 7.94V. Thus, there is no input buffer in his device under test. And the natural gain of the amp is 4.3 or 12.6dB. I believe that the absence of input buffer should have been written clearly in the report text.

Here are the culprits perverting the signal, they are supposed to be OPA1612 but the marking is erased.
View attachment 324608


With a max of 5V at my DAC level I will get a max of 115W on 4Ohms or 55w on 8 Ohms. It might be enough, I don't know.

Tests without the input buffer

5W 4Ohms 1kHz spectrum analysis shows now excellent results SINAD of 106 dB within 2dB from l7Audiolab testing
View attachment 324609



Multitone test at 5W 4Ohms almost 19 bits very nice.
View attachment 324611



Frequency response 5W 4Ohms Is excellent
View attachment 324612



Another test at 90W close to the max I can go with no buffer. THD+N 97dB excellent but was expecting even better
View attachment 324613





So now I have to choose among

1/Keeping the amplifier without the buffer and get a more than excellent device but limited at 115W 4 Ohm

2/Put back the existing buffer amplifier and getting an excellent amplifier with quite a lot of power.

3/Replace the buffer amplifier by a better one.

For this last alternative I need support.
-does it make sense that the input buffer causes a damage of 10dB to the specs ?
-would it make sense to replace the small modules by another amp and which one?
This pops up quite a lot. Some excellent SINAD scores are for amplifiers with low gains. Ideally, something in the high 20s should be used.

Inevitably, noise is higher with more gain and it's easier to drive the amp into clipping.
 

AnalogSteph

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SINAD with the buffer in looks to be just about entirely noise-limited, and at 98 dB ref. 5 W / 4 ohms seems low enough to give inaudible hiss levels with just about any speaker. Noise output translates to about 59 µV. That would be 2.75 µV, input-referred.

D-6s output dynamic range is specified to be 129 dB for XLR at a maximum of 5 Vrms out. That's an output noise level of 1.77 µV, quite possibly A-weighted so it may well be >2 µV 20 kHz flat. This is getting very close to the above figure, suggesting that DAC output noise may actually be a limiting factor.

If you do not happen to have any XLR attenuators handy, try an unbalanced connection instead. D6-s output noise should be 3 dB lower there, and with your isolator you should be able to avoid ground loops.

BTW, props to the Cosmos ADC for apparently handling a Class D amplifier without a steep lowpass in front. That's traditionally a good way of upsetting an analog input stage.
 

kemmler3D

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Thanks for doing the measurements! But, all things considered, these amps are like $800 on Ali Express and you can get a real 1ET400A for $1100 in the US. If I were in the market I'd go for the real thing, but in other regions I might be tempted by this one.

As for replacing the buffer stage... I would be interested to see what happens if you do, but personally I can't offer any tips on how to go about it...
 
OP
A

Abrise

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Thanks for doing the measurements! But, all things considered, these amps are like $800 on Ali Express and you can get a real 1ET400A for $1100 in the US. If I were in the market I'd go for the real thing, but in other regions I might be tempted by this one.
Right. If I were living in Europe or US I would go for the real thing although more expensive.
As for replacing the buffer stage... I would be interested to see what happens if you do, but personally I can't offer any tips on how to go about it...
I don't know what chip they have on the small boards as they erased the marking. i have ordered real opa1612. I will see if it makes a difference.
 
OP
A

Abrise

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SINAD with the buffer in looks to be just about entirely noise-limited, and at 98 dB ref. 5 W / 4 ohms seems low enough to give inaudible hiss levels with just about any speaker. Noise output translates to about 59 µV. That would be 2.75 µV, input-referred.

D-6s output dynamic range is specified to be 129 dB for XLR at a maximum of 5 Vrms out. That's an output noise level of 1.77 µV, quite possibly A-weighted so it may well be >2 µV 20 kHz flat. This is getting very close to the above figure, suggesting that DAC output noise may actually be a limiting factor.

If you do not happen to have any XLR attenuators handy, try an unbalanced connection instead. D6-s output noise should be 3 dB lower there, and with your isolator you should be able to avoid ground loops.

BTW, props to the Cosmos ADC for apparently handling a Class D amplifier without a steep lowpass in front. That's traditionally a good way of upsetting an analog input stage.
Thank you for your interesting comments
Regarding the steep low pass in front of the cosmos , it is certainly recommended but I don't have one. My measurements are quite stable so I hope it does not upset to much the analog stage. My measurements on the topping pa7 were extremly closed to @Amir measurements so they gave me some confidence.
I have a XLR attenatuor but better when I first tested this MIN400A with the input buffer I disable the volume potentiometer thinking it might add noise. But it is just the opposite, with the volume knob I can reduce the input buffer gain. I thus made a few more test with a total gain of 18dB which for 5v input gives exactly the max power of 200W 8 Ohms.
Here is the quite good result on 8 ohms. THD+N -105dB. I am not complaining!
1699927113101.jpeg



There is another cause of error that I want to analyse further before concluding and finish my tests on this amp. It is the 4*2 Ohms dummy load. I think the error is small when measuring and powering on 8 Ohms but there is 3rd harmonic added when I measure on 2 ohms and powering on 8 ohms for instance. There is some explanation on the ASR dummy load thread. As I have finished to renew all my setups and this is the last amplifier I am buying, I will not invest in a new dummy load and limit my tests to those where the dummy load is not a problem, like on 8 Ohms only. This effect was not seen on all my old amplifiers which were below 90 sinad and neglectable on the Topping pa7 with its 102 SINAD.
 

renaudrenaud

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Do you think there is any hearable difference between the different amps and their different SINAD? Or even the same amp, with and without the buffer?
 
OP
A

Abrise

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Do you think there is any hearable difference between the different amps and their different SINAD? Or even the same amp, with and without the buffer?
I will probably not make any difference during blind test. I just like ta get the best from my toys. It's a kind of game. Just being sure that our tools are completely transparent.
 

renaudrenaud

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I will probably not make any difference during blind test. I just like ta get the best from my toys. It's a kind of game. Just being sure that our tools are completely transparent.
It's a question for me. I bought a Fosi BT20A pro for 50€ and use it on high efficiency speakers. The results are impressive for me. I wonder if I would be able to hear any difference with a Topping LA90 @120 dB SINAD. I guess I will buy one sooner or later because I am too curious, but I am not sure I will be able to hear any difference.
 

mocenigo

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Thanks for doing the measurements! But, all things considered, these amps are like $800 on Ali Express and you can get a real 1ET400A for $1100 in the US. If I were in the market I'd go for the real thing, but in other regions I might be tempted by this one.

I wonder whether this is actually a real 1ET400A module. In bulk or “from the factory” they easily cost much less than the price on the Purifi web site. Bulk is of course fine, while night runs are not.
 

Snoopy

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With all the manufacturers in the EU/UK/US that have great support and are not much more expensive, i don’t get why someone would buy a amp like this from china.

Especially if you end up messing around with the internals bring the performance up to a competitive level.
 

mocenigo

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With all the manufacturers in the EU/UK/US that have great support and are not much more expensive, i don’t get why someone would buy a amp like this from china.

Especially if you end up messing around with the internals bring the performance up to a competitive level.

For somebody in the south east of Asia it would probably be great. In Europe I have been a customer of @Apollon Audio and have been very satisfied.
 
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