Poor SNR and THD+N with 3 different TPA3255 amplifier boards - are there any good ones out there?

[Mark185]

I am attempting to build a 6 channel amplifier to use for a triamplified active speaker based on the NHT 3.3. (I bought the drivers from an NHT engineer shortly after the company was purchased by Recoton over 10 years ago.). I have some Marchand active crossover boards purchased at same time as the NHT drivers.

I was thinking that the proliferation of TPA3255 amplifier boards on Ebay and Amazon would result in me finding something useful for my project. I have purchased 3 different boards with different designs in terms of capacitors and heat sinks. 2 of the boards are dual TPA3255 designs. All 3 measure terribly with low SNR and high THD+N. I am using a Quant Asylum QA403 and a 4 ohm load bank with low inductance Vishay resistors. I have tested many commercial amplifiers with this setup so I know my equipment and methods are good.

So my question is "Are all of these generic TPA3255 amplifiers garbage?" I am thinking at this point to just use some commercial mini amps such as Aiyima A07 Max or Fosi V3.

Does anyone know of a good TPA3255 board for a DIY build like mine? Here are some of the measurements I got so far.

 

[mcdn]

With TPA3255 boards the main source of distortion should be output inductor saturation. Unfortunately the inductors are the most expensive part by far, so vendors do cheap out on them.

The other source of distortion is the power supply. What you show does look a bit like clipping. Are you sure your supply is capable of delivering the necessary current?

As for brands - 3e Audio have been very reliable as many builders here can attest and many reviews here show, but they're not cheap, see their aliexpress listings. That said their website is no longer active, so it would be good to get some more recent experiences.

 

[TurtlePaul]

I bought a 3e Audio A7 last week. I also own a Fosi v3. Both are good amps. I agree with the previous poster, the output inductors in both the e3 and Fosi are an order of magnitude more expensive than the cheapest available options. I also believe that post filter feedback and some of the more expensive output filter cap options require more filter caps and higher power filter components. Understandably the cheapest generic boards optimize for cost instead of output filter performance. Your examples are also showing terrible power supply filtering while high end options have power factor correction and GAN components.

 

[NTK]

The TI class-d amplifier LC output filter application report showed examples of the effects of different inductors on THD+N. (Fig 29 horizontal axis label seems to be incorrect and should instead be frequency in Hz, not output power.)
https://www.ti.com/lit/pdf/SLAA701

 

[Mark185]

I wish I could find 3e Audio boards for sale to US customers. No luck so far. I have a 3e Audio A7 stereo amp in my basement home theater driving my main L-R tower speakers. I have a Yamaha AVR with preamp outputs. All of this to say, I really like the 3e design. I just did not want to shell out the $$$ for 3 of them to do the triamp speaker. I may do that if I don't find a decent DIY option.