https://photos.app.goo.gl/gPH8VZiaGRiNYWfL6
It sounds MUCH better than my existing cheap vendor Fosi TPA3116 did -- the cheap vendor ones don't use quality components, especially for the power supply, so you're not going to see the expected performance.
That power supply board (diode bridge + filtering caps) was designed with a friend in KiCAD and fabricated by JLCPCB (I have a few boards leftover). The speakers are also DIY -- Hivi 3.1 with cherry wood veneer!
I showed article author Zorpette my work, and he gave it his blessing =)
EDIT: If you do try to build this, be VERY careful around the high-voltage power supply electronics.
The extra resistance (2 to 10 milliohms probably) of the wire between the two boards, together with the smoothing capacitors on the downstream board, acts as a low pass RC filter.
Also the capacitors on the PS board may be low-inductance types, and filter HF noise more effectively than the caps on the amplifier module.
Having the diode bridge further away from the amp module's inputs means the antenna action of the rectifier's leads is less effective: the RF power of over-the-air rectification transients at the inputs is reduced by the square of the distance.
The layout of the amp as shown is good, except that I'd shorten and cable-tie wires to help prevent hum loops.
Get a nice AC-DC converter brick and call it a day. If you want to be fancy, stick a linear regulator on the output.
The ones that I've seen don't put out their claimed current, lose regulation badly at high load, and put a lot of hash on the DC rails. Seriously ugly. Opening them up, the circuit design often looks like it comes from the 1980s. Physical design usually doesn't meet standards for HV separation and creepage.
Rather than a linear regulator, lots of filtering (a few 100nF ceramics and a few millifarads of smoothing) would help. And a high-powered TVS or two for when the power brick dies, as it will.
Safety: -
The mains safety earth (chassis bolt) should only ever have one lug: the mains input earth. Put a separate bolt an inch or so away from the mains safety earth bolt for the chassis connection of the bridge centre ground. (People have killed themselves doing repairs by ignoring this, and having faulty mains wiring.)
Fuses on the transformer secondaries are recommended if the transformer is expensive. If the bridge rectifier or an amp output stage fails, it'll almost certainly fail short, and the transfomer will heat up until its internal thermal fuse melts -- or if there isn't one, until it catches fire.
Likewise fuses on the DC rails will help protect the expensive smoothing capacitors from amp failure. (Yes, the TPA3251 has built-in protection - but that might also be damaged by the surge that caused the output stage to fail.)
I hope the polyester cap across the transformer secondary is X2 class.
Other points:-
A snubber across the mains switch will reduce arcing on switch-off and prolong the life of the switch. 10R-50R 3W in series with 100nF, X2 class, will do it. (The wattage rating is a proxy for both voltage rating and surge current rating.)
From the scale it looks like the transformer is a 120 or 160VA model. That's seriously undersized for an amp module rated at 350W (circa 550 VA with a traditional mains-frequency transformer). Transformer secondary fuses are strongly indicated.
OTOH, going up to a 500VA toroidal transformer means you'd need a soft-start circuit to prevent your house circuit breakers popping on start-up, from the initial transformer saturation inrush current.
I'm amazed you don't get RF interference with all that length of unshielded wire on the input side. I just have to leave one inch unshielded to be plagued with EMI - unless I use filters on the input terminals (100R / 220pF RC filter).
You don't have DC blocking on your volume control. I guess none of your sources have any DC offset. If not, changing the volume will be scratchy.
References: -
1. Bob Cordell, Designing Audio Power Amplifiers.
2. Doug Self, Audio Power Amplifier Design 6e.
3. Rod Elliott, sound-au.com. "Designing Linear Power Suppplies part 2" https://sound-au.com/power-supplies.htm
4. Idem, "Transformers - The Basics, part 2". https://sound-au.com/xfmr2.htm
Glad I'm not into power or audio electronics. :)
It can be fun and rewarding to buid your own.
Your amp will be fine as long as you use it for lounge-room listening. Just don't use it in pro situations, e.g. a wedding reception or large party (50+ people). Please!
(But if that cap across the transformer secondary is only DC rated, not AC, you can expect it to explode. Might take a couple of years, if you're lucky. I had one last five years before I learned about "X-class" mains rated capacitors.)
- Polyester caps are AC rated
- Transformer is 300VA
AB would be more likely than A, but I can't imagine finding them even in a large flat screen TV since they are inherently less efficient and require larger power transformers which make them fairly heavy and bulky. You only really find non switching amps these days when people want to sacrifice some of that convenience for some nicer sound.
There's not really a good reason to use non-class D in any mobile application today. As few as 10 years ago I thought Class D = garbage you settle for if you must, I've heard some incredibly good Ds that have made me completely change my mind
I’ve done some unscientific blind tests with nice modern class Ds on people who avowedly think all digital amplification is trash. 9 times out of 10 the reaction has been something like “hmm, how lovely, now when are you going to show me the digital amp?” After I tell them what it is, it becomes “oh yeah, I can hear it now. It’s fine I guess for casual listeners but clearly lacks X.”
People consistently report higher levels of satisfaction with more expensive wine versus cheaper one, even if it’s just the same wine rebottled. They’re not lying, our perceptions and preconceived notions genuinely affect the we experience reality.
I have noticed different headphones and using a class AB headphone amp vs builtin switching amps can significantly impact how long I can listen for... But that anecdotal correlation is not enough for me to assign blame to switching amps, it might just be crap switching amps... or switching amps with not enough headroom. The problem is class D is always used for cheap low power devices, so most bad experiences are inevitably going to strongly correlate with class-D - whether or not it's attributed to the fundamental property of switching vs just being a bit ... shit.
The victory of class D is now total; extremely low distortion numbers can be achieved without heroic board layout or expensive passives made of unobtanium. All available in the tiny packages of AirPods, smartphones etc. And power levels in the tens of watts can be done with a single chip.