Pre request in my review of Hifiman EF2A and kind permission from its owner, this is the teardown review of the unit.
Let's start with the main board's top view:
The heart of the unit is the now quite obsolete TI/Bur-Brown PCM2702 DAC chip. It came out circa year 2000 and only supports 16 bit audio at 32, 44.1 and 48 kHz.
The unit has analog input which I think goes through the OPA264 op-amps.
Surprising to see is the Philips TDA1308 headphone amplifier.
It is being used apparently to then drive the tubes. In other words, half-way through the signal flow we already have our headphone output but then we choose to mess with it with later stages. The headphone amp likely has nice gain and hence the reason it over-drove and clipped the input stage when using USB DAC.
The output of the headphone amp goes into pair of pentode tubes. The one that I have reportedly has aftermarket 5654RT pentode tubes.
A few beefy TO-220 2SC/2SA complimentary power transistors drive the headphone output:
No wonder this thing has lots of power.
Capacitors appear to be top brand names from Nichicon and United-Chemi-Con:
The markings seem genuine. And so do the markings on other parts. The could still be counterfeit but if they are, it is not easy to see.
Not so good is seeing hand modification instead of spinning the PCB board and fixing the design issue:
I am sure pulling the leg of that transistor way to the right over the other parts is against the Geneva convention for humane treatment of electronic parts.
Outside of that, the top side seems fine. It is the bottom side that gives me pause:
This thing screams dirty, sloppy, cheap, PCB and construction. You can see those white stains. And lots of mods with resistors and such hand soldered there.
Worst example is hand soldering tiny surface mount parts to what is a through-hole design:
All of this can be cleaned up with revising the PC Board and including the small few changes needed to mount things properly. Instead, they are paying people to sit there and hack the thing manually. Cheap labor is no doubt the enabler.
Here is the transformer feeding the thing:
It produces AC which is then rectified and regulated internally.
Conclusion:
The design here while following the typical hybrid tube architecture (tube buffer but transistor output) but also odd choices like headphone amplifiers driving the tubes. The choice of super obsolete, 16-bit DAC is pretty bad. They must be getting these for pennies or something.
The level of hand modification is excessive and the back of the board quite ugly.
Clearly this is not something to be proud of. On the other hand, it is what it is for the price.
As always, questions, comments, corrections, etc. are welcome.
Let's start with the main board's top view:
The heart of the unit is the now quite obsolete TI/Bur-Brown PCM2702 DAC chip. It came out circa year 2000 and only supports 16 bit audio at 32, 44.1 and 48 kHz.
The unit has analog input which I think goes through the OPA264 op-amps.
Surprising to see is the Philips TDA1308 headphone amplifier.
It is being used apparently to then drive the tubes. In other words, half-way through the signal flow we already have our headphone output but then we choose to mess with it with later stages. The headphone amp likely has nice gain and hence the reason it over-drove and clipped the input stage when using USB DAC.
The output of the headphone amp goes into pair of pentode tubes. The one that I have reportedly has aftermarket 5654RT pentode tubes.
A few beefy TO-220 2SC/2SA complimentary power transistors drive the headphone output:
No wonder this thing has lots of power.
Capacitors appear to be top brand names from Nichicon and United-Chemi-Con:
The markings seem genuine. And so do the markings on other parts. The could still be counterfeit but if they are, it is not easy to see.
Not so good is seeing hand modification instead of spinning the PCB board and fixing the design issue:
I am sure pulling the leg of that transistor way to the right over the other parts is against the Geneva convention for humane treatment of electronic parts.
Outside of that, the top side seems fine. It is the bottom side that gives me pause:
This thing screams dirty, sloppy, cheap, PCB and construction. You can see those white stains. And lots of mods with resistors and such hand soldered there.
Worst example is hand soldering tiny surface mount parts to what is a through-hole design:
All of this can be cleaned up with revising the PC Board and including the small few changes needed to mount things properly. Instead, they are paying people to sit there and hack the thing manually. Cheap labor is no doubt the enabler.
Here is the transformer feeding the thing:
It produces AC which is then rectified and regulated internally.
Conclusion:
The design here while following the typical hybrid tube architecture (tube buffer but transistor output) but also odd choices like headphone amplifiers driving the tubes. The choice of super obsolete, 16-bit DAC is pretty bad. They must be getting these for pennies or something.
The level of hand modification is excessive and the back of the board quite ugly.
Clearly this is not something to be proud of. On the other hand, it is what it is for the price.
As always, questions, comments, corrections, etc. are welcome.