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Comment by Hydraulix989 | Hacker News Reader

I built this project myself last spring. That 3e-Audio TPA3250 board isn't sold anymore, so I built my own custom variant amplifier using similar parts with a TP3251:

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.

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There is no way DIY diode bridge and filtering caps on a separate board could make a slightest difference here, in fact high frequency noise from the power supply could only be filtered right near the chip. But leveling up an amplifier, to a 4 times more powerful as you did, would make a significant difference in sound.

TPA3251 is the best on all performance

I would suspect imagine that putting a power supply like this in the same enclosure could introduce unpleasant noise. There will be a big current spike every half cycle when the rectifier starts conducting. The power factor will be awful, and I can easily imagine 120 Hz and its harmonics coupling somewhere you don’t want them. Not to mention that you might be able to hear the power supply buzzing.

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.

If Apple or Dell sold 36V 10A power bricks, then maybe.

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.

Apple or Dell? I would start with Meanwell if I were trying this.

In fact there is a way or two.

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.

Very pretty! Thanks for showing it. What I'm going to say I hope will be taken as constructive, for those who are a bit more OCD about their electronics.

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

This level of free electronics review is awesome, thanks from a software guy with more solder than sense.

Glad I'm not into power or audio electronics. :)

I hope I haven't put you off for life! :)

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.)

- There is only one lug, see photos.

- Polyester caps are AC rated

- Transformer is 300VA

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