Sorry about my English.
I dont think there was a serious problem with V2 amp.According to Murrel,I replaced 4 capacitors with higher voltage rate capacitors and everything is back to normal.Hump is still there but it was reduced a lot.In my opinion,the V2 amp has a better quality than V3.
To people who is using V2 amp,I want to shared something I did to improve my v2 amp.After playing around with my V2,I did a test with the power supply board.I set the volume to 1 oclock and played "3 types of bass " song.I used a mulimeter to measure the voltage drop beetween 4 capacitors.At the deepest bass note in the song(about 3 seconds), the voltage droped down from 75v to 68v.
At that time,the output of the MFW15 was funny(strange noise appeared) and the bass was like uncontrolled.By doing that I know the power board did not provide enough power for the amplifier module-->distortion.I looked at the values of 4 no name filter capacitors on power supply board(1500uf each,3000uf for each channel) which are way too small.I think to reduce the cost of the amplifiers,they chose to use no name low value capacitors.
So i bought 4 3300uf 100v nichicon capacitors from digikey to connect to 4 originals capacitor in parallel.The total capacitance at this time is ~10000uf for each channel. Doing a test again(volume was set to 1 oclock),now the voltage droped down from 75v to 72.5 at deepest note in the song.Moreover,the MFw15 now not only can shake my wall but also shake my couch freaking hard which I could not feel before.My wife sat next to me on the couch also felt that . The output at the hardest note is clean and very stable.In addition, is the hump now is barely heard (deadly silent). Im really impressed with the MFW 15 after adding more capacitor.
I also replaced the red cheap output capacitor on the audio board with a 3.3uf 400v Jentsen audio cross cap which makes the output now is not muddy at before but faster and more musical.I am not an audiophile but I can hear the difference.
I also move all the wires(from controller and driver) far away the transformer.The electromagnetic from transformer will interfere with the audio signal,which caused hump.Those people who still get hump after replacing 4 caps should check this.
In conclusion,the total cost for this upgrade is under 30 bucks and it makes a huge different in sound quality.In the future,I may add more capacitors for the power board to make less voltage drop as much as possible.
Disclaimer: I will NOT be held responsible for you damaging your amplifier. I am not responsible of you get hurt.Do it at your own risk.Do NOT try this at home.It should be performed by a professional.