TPA3255 Reference Design Class D Amp GB

[Kay Pirinha]

xrk, you've been sending me a board some weeks ago. You remember? What's the difference between that one and those of current production? What do I need to take notice of when populating it?
Best regards!

 

[xrk971]

The main issue is to put a piece of Kapton or other insulator over the tab (pin 4) of N151 - the 3.3v LDO to isolate it from GND. Else there is a short. Otherwise the board is functionally fine. Take note of silkscreen typos on the Wxxx pads on the bottom. There, just follow my photograph and marked up diagram to connect solder pads for stereo BTL. I assume that’s the mode you want. Also, taken note that PVDD positive are the two pins closer to the TPA3255.

So ignore the ++ and - - on the Vdd (X221) connector on diagram below, however other notes are correct:

Here is photo of how to connect Wxxx jumpers (follow red rectangles) for stereo BTL with balanced inputs, use a low value 1210 resistor if you don’t have any 0R jumpers or a small piece of wire works too; red circles indicate pad number 1:

 

[xrk971]

Buy some red and black nail paint to add correct coloured dots over the incorrect markings.

Great idea. Actually, an extra fine black Sharpie will do the trick with no scraping required.

Thanks,
X

 

[Eva]

I bought one of these 800w 48v SMPS designed for LED lighting from Aliexpress a few months ago. I set its internal switch to 120VAC input (220VAC is an option), and wired it to an EIC socket with earth ground.

I connected it to the amp, not expecting much as I had already tested out a much more expensive Connexelectronic 800w SMPS ($150) and was dissappointed with the excessive added hash noise.

Well the cheap $44 one from Aliexpress surprised me. It is not noisy at all, and in fact, is close/idenmtical to the 12v battery and DC step up in terms of low noise performance.

Here is a photo of the setup shown connected to speakers for listening:

Here is a closeup of the inside of one of these SPMP from venfor AIFENG on Aliexpress. I had to disconnect the internal fan cable and let it run naturally cooled for now. The fan was way too noise and this deserves a better fan. At normal volumes, it is not even warm without a fan:

Here is the measured FFT for 8.12Vrms into 3.3ohm load:

Here is the FFT fo 4.36Vrms (graph label is incorrect) into 3.3ohm load:

Has anyone noticed the transformer labelled "48V 1000W" which does not have creepage or clearance between primary and secondary windings, as mandated by safety regulations and routinely implemented with margin tape or triple insulated wire or split windings? A Chinese Special.

 

[xrk971]

You mean my $44 Chinese made SMPS doesn't have UL/CE required double insulated isolation between the mains and output? 😉

I do not know how SMPS like this work, but the transformer looks very similar to other UL-certified SMPS of same rating that I have. Could the double insulation or margin tape be embedded underneath the external copper windings?

 

[29285]

Using triple isolated wire on the secondary side (furukawa TEX-E) you can omit isolation layers.

 

[xrk971]

I just got some THaT1646 SE to balanced converters from Sparkfun. Nice easy to use units.

I made some +/-15v power supplies from a +/24v DC-DC (5v to 12v input) with LC filter and LM7815/7815 regulators.

Driving signal from headphone output of Focusrite. Works well and sounds great. Silent - no added hiss or hum at speaker cone.

 

[manudrz]

Ok, so if I buy at ETSY will the TPA already be soldered ?

 

[xrk971]

No, but the TPA3255 is the easiest part to hand solder of all the parts as it has exposed pins. Also, it’s on the bottom side and is the last part to be installed after topside is fully populated with all SMT. If you have not done other SMT projects before, this is not something I recommend for a SMT soldering beginner. It really should be done with paste and hot plate / hot air techniques.

 

[manudrz]

Ah OK, I thought an option would be available but I think I'll have to try it. I'll let you know...😛

 

[xrk971]

Thanks for your order manudrz!

 

[xrk971]

New boards completed manufacturing and are undergoing automatic optical inspection. Should ship out to USA tomorrow.

 

[xrk971]

Boards have arrived. I put a black dot with a sharpie over the incorrect Vdd polarity markings. The revised 3.3v LDO pads look good.

 

[tubo]

Hi Xrk971

Any chance you will offer a completely assembled unit?

 

[xrk971]

Maybe in the future. I am looking into getting these professionally assembled by a factory but that won’t be for a while.

 

[grahamgraham]

With respect to safety and heat dissipation, will the PSU you used have enough internal safety mechanisms to operate without a fan given decent ventilation? Did you find a fan that was quieter?

 

[xrk971]

I haven’t tested the 800w SMPS at full 150w per channel yet without a fan, but I think they have internal temp shutdown built in. The temp is auto speed controlled I know that. It speeds up when load is increased. But the main thing is, the chassis is quite a massive natural heatsink and currently is not even warm at normal volume levels up to 20w levels. If you are going to use it continuously at 300w, then probably will need a fan. I have Noctua’s that are silent but have not bothered to swap them in yet. Another option is simply adding a series resistor to the 12v lead to slow it down.

 

[xrk971]

Let me attach the main TPA3255 thermal pad to a full size heatsink as intended, and do test at full power (150w per channel) and see how hot the SMPS gets. I have a 200w 4ohm wirewound load resistor but it’s not good for measuring distortion as it introduces a lot of distortion to a measurement. It’s good for power testing to check for clipping levels though.

I think a 5w 33ohm resistor in series with the stock fan motor lead might work wonders to reduce the fan noise.

Btw, those of you who have ordered the new boards, I’ll ship them out tomorrow.

 

[wineds]

I haven’t tested the 800w SMPS at full 150w per channel yet without a fan, but I think they have internal temp shutdown built in. The temp is auto speed controlled I know that. It speeds up when load is increased. But the main thing is, the chassis is quite a massive natural heatsink and currently is not even warm at normal volume levels up to 20w levels. If you are going to use it continuously at 300w, then probably will need a fan. I have Noctua’s that are silent but have not bothered to swap them in yet. Another option is simply adding a series resistor to the 12v lead to slow it down.

Can you add a link to the power supply please?

 

[xrk971]

I got the 800w 48V unit here. $44 including shipping as I recall. There is a pot to adjust voltage and I increased it to 50v.

AliExpress