Post by 24century on Nov 17, 2017 20:23:58 GMT -5
Hi MAC, thanks again for the help with my JBL woofer, I believe it is fully resume to working stage after 2 days test 
!
Bought a DAC board about 2 years ago, never get it work even one time, had to get a transformer and power supply since it takes dual DC and one set of AC
similar item see link
Background:
1. back in year 2015, 4490 DAC chip was a big thing, not too many finished product on the market, it is the top rated Valet Sound product series of AKM
2. there are 2 mode for the chip, parallel: play FLAC or DSD (D2P) mode
serial: DSD (DoP mode)
for people who doesn't understand DSD and different modes, DoP (DSD over PCM) will push DSD full stream to the DAC Chip (4490) via USB and mode signal 4490 will accept the signal under serial mode and determine what mode is to play, in D2P mode, 1 bit to 24 bit process will be fully handled by the DAC chip, user will get much pure music output to loudspeakers, more accurate voice & instrument phase to original, clear sound
3. Appear to be factory release the PCB board and component to seller, seller did SMD component soldering and sell as DIY kit to buyer
seller's SMD soldering skill wasn't great and left a short somewhere and I have never get it work even one time
4. newer version ignored the transistor (NPN) control & signal switch (Fujustu A5W-K) part to make it simple and easy
Reason to pick it up now: Believe this guy can do D2P, not too many DAC board has ability to switch between DSD Native and D2P, although this one wasn't automatic (done by jumpers)
Current stage:
preparation mode
a. found the short caused by one SMD capacity, will clean the board by removing some solder left by seller
b. ordered upgrade Op-Amps and they are on the way
c. will get new power supply next week
d. DAC part feels OK by previous test
Question I have so far:
1. Does the quality and class of Op-Amp component on LPF (active low-pass filter) really effect the sound quality?
2. how do I test the switch part to tell the status? Think the pre-amp part will be in idle mode when no audio signal detected to mute the output controlled by Fujustu A5W-K relay
more info and picture will put tomorrow with IC models and detail
