This is a great success to apply volumio with 9038pro. I implemented all my knowledge to make it for home or car use with auto safe shutdown, output delay leech and it spent 3 months to finish. It used 12v supply and convert 5v, 9v and 18v. For the control part I used wemos mini to control switch on off when it detects power on. Moreover, because wifi is sucked if using ssd, I added a 4g wifi routIer board to connect pi4 to LAN port on the board and disabled pi4 wifi so that I can connect internet radio and also my mobile can access internet.
For the 9038pro, I used tps7a4700 and tps7a3301 also for powering opa838 op amps. All audio note cap, 100mhz ocxo, creating best sound reproducing. It supports both RCA and balanced output. But for this board the balanced output hasn’t passed the LPF op amps. The USB interface I used unknown China brand with supports up to pcm1536 and dsd1024.
The 1st version had been taken by my friend instantly and this is the 2nd version with dsi monitor, of cause the case is modified by factory. All ports are standardized in xlr format for easier implementation and flexibilities.
Because the dac board is tiny, the balance output doesn’t have LPF included. I tested to put a pre amp board and replaced the op amp to a headphone amp TPA6120A2 to the balance. Which pinout is same as dual op amp but only hotter needs more current. What a surprise the sound is professionally great and LOUD enough for most of headphones. Most important is the price is also magically cheap, around $15 in total. I really like this setting coz the preamp board is quite direct with no bypass cap, directly amplified my opa828 sound with not much affection.
Besides, all the op amp I tried the best is opa828 at this moment. Which produces wide and depth and most Noble sound quality than all I tried. It is a great value compare with muse01 or opa627, around $7 each. If you make a preamp, try it with no doubt.
4g router turns out totally solved ssd/wifi issue. Plugged 4g USB router b4 boot, pi generated a USB LAN so my mobile or wheel control and access the pi. It is not necessary working too much in Linux wise.
The only problem now…
Is it possible the enable the HDMI0 and 1 at the same time with different resolution for volumio?
As sticking on my plan the PASS A3 class a amp has been borned but I’ve just completed 50% coz this is a mono block. Powering it with a 200va R-transformer with 70000uf CRC circuit. Happy to show with you guys.
