Hi first post, I just wanted to share my experience with a $2 headphone amplifier PCB from AliExpress,
I was looking round for a cheep amp that I could connect up to my phone to give it a little bit of power so it would drive some cheep cans (Behringer HPS3000) anyway's I stumbled across a listing for a very basic circuit that used a TPA6120 quite an impressive IC, I had a quick look a the data sheet and the PCB layout appeared to match the manufacturers default circuit diagram. The tpa6120 needs no output coupling capacitors, so basically the PCB is just a few resistors and some filter caps for the power.
I got the hole thing wired up (after wireing the input to the output pins swearing at it and starting again) I got the little amp to start cooking. Quite literally I burned my thumb on the IC and had to mount a heat sink on the little fella to stop him burning up.
So my assumption was that it was oscillating. so I worked my way though the circuit drawing a circuit diagram while comparing to the data sheet. I'm very amateurish so this took a lot longer than I really expected it to, nothing! could not find a thing wrong with the wireing of the input, feed back or output.
By this stage I'm really doubting myself, maybe this IC needs to be mounted to a heat sink ? Maybe it's a fake IC ? Maybe I'm just a idiot ?
I found the manufacturer of the IC actually offers feedback on circuits, wow amazing ! surely they can help me because I have to get to the bottom of this now, but first I might as well draw a diagram of the power to the IC so I could upload an image of that too.
2 surface mount ceramic caps and 2 electrolytic capacitors so simple! The first electrolytic had the postive wired do the positive supply, and the 2nd capacitor had its positive wired to the negative supply.... Wait WHAT ! hours and hours I've spend on this, and all it was was a cap wired backwards !! /smashes head into table .
I don't know what the moral of the story is. But I had to post this somewhere and now I need a strong whiskey
I was looking round for a cheep amp that I could connect up to my phone to give it a little bit of power so it would drive some cheep cans (Behringer HPS3000) anyway's I stumbled across a listing for a very basic circuit that used a TPA6120 quite an impressive IC, I had a quick look a the data sheet and the PCB layout appeared to match the manufacturers default circuit diagram. The tpa6120 needs no output coupling capacitors, so basically the PCB is just a few resistors and some filter caps for the power.
I got the hole thing wired up (after wireing the input to the output pins swearing at it and starting again) I got the little amp to start cooking. Quite literally I burned my thumb on the IC and had to mount a heat sink on the little fella to stop him burning up.
So my assumption was that it was oscillating. so I worked my way though the circuit drawing a circuit diagram while comparing to the data sheet. I'm very amateurish so this took a lot longer than I really expected it to, nothing! could not find a thing wrong with the wireing of the input, feed back or output.
By this stage I'm really doubting myself, maybe this IC needs to be mounted to a heat sink ? Maybe it's a fake IC ? Maybe I'm just a idiot ?
I found the manufacturer of the IC actually offers feedback on circuits, wow amazing ! surely they can help me because I have to get to the bottom of this now, but first I might as well draw a diagram of the power to the IC so I could upload an image of that too.
2 surface mount ceramic caps and 2 electrolytic capacitors so simple! The first electrolytic had the postive wired do the positive supply, and the 2nd capacitor had its positive wired to the negative supply.... Wait WHAT ! hours and hours I've spend on this, and all it was was a cap wired backwards !! /smashes head into table .
I don't know what the moral of the story is. But I had to post this somewhere and now I need a strong whiskey
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@kn0ppers I don't think I would be that unfair to it, they have made efforts to shorten tracks were critical. Ie the ceramic capacitors (filtration) are about 3mm away from the IC's pin's, and the feed back circuit is as short as it can be.
However I've not studyed the reference design manual, so maybe I'm missing something that you can see.
Looking on the outputs. that looks ok to me too I've got about 4.4mv of DC offset with no load and 1.6mV with a 64 Ohm load.
I suspect due the huge screwup with the capacitor being installed reverse polarity this board is a reject (someone has probably stolen them out of a bin lol ) and that's how it ended up on AliExpress and eBay.
However I've not studyed the reference design manual, so maybe I'm missing something that you can see.
Looking on the outputs. that looks ok to me too I've got about 4.4mv of DC offset with no load and 1.6mV with a 64 Ohm load.
I suspect due the huge screwup with the capacitor being installed reverse polarity this board is a reject (someone has probably stolen them out of a bin lol ) and that's how it ended up on AliExpress and eBay.
Capacitors could be closer, feedback loop shorter, ground plane under capacitive sensitive nodes should be cleared. Those are the 3 most obvious criticisms from my point of view. Grounding layout also doesn't seem very thought out, but I might be wrong and all of this pure overdramatisation 
Edit: You can find the evaluation board I meant by searching for "SLOU169"
Edit: You can find the evaluation board I meant by searching for "SLOU169"
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IC just warm, using +/- 11V. Just the noise when no signal.
Yes +Cap connected to vcc-
@kn0ppers : i just use hot air solder @410 Celcius
The amp works.
I replaced the SMD 100uF capacitors with TH caps Sanyo 470uF/25V CZ.
There is no hiss on mine, powered with +/-12V linear regulated PSU.
But the PCB is too small, I think, and it is getting hot.
The amp drives well low impedance headphones - mine are Austrian Audio Hi-X15, which are 25ohm.
I'm not impressed with the sound, so I use the headphones directly connected to my Audient Evo 8 interface.
I replaced the SMD 100uF capacitors with TH caps Sanyo 470uF/25V CZ.
There is no hiss on mine, powered with +/-12V linear regulated PSU.
But the PCB is too small, I think, and it is getting hot.
The amp drives well low impedance headphones - mine are Austrian Audio Hi-X15, which are 25ohm.
I'm not impressed with the sound, so I use the headphones directly connected to my Audient Evo 8 interface.
Here's another version found on Amazon, choice of assembled or loose parts:
https://www.amazon.com/dp/B09ND6RD9...PYQUVYKXP&ref_=list_c_wl_lv_ov_lig_dp_it&th=1
https://www.amazon.com/dp/B09ND6RD9...PYQUVYKXP&ref_=list_c_wl_lv_ov_lig_dp_it&th=1
