The TPA Class D audio chip range from Texas Instruments, although been on the market for a while is making a huge impact in the audio industry. Interestingly enough TI always used to focus on the analogue and microprocessor/embedded industries so I am not surprised that they would come into this spectrum of products competing head on with ICE, Hypex and International Rectifier, now Infeon.
My experience with these TPA chips comes in through TEMU purchases, shipped to South Africa, the products being:
TPA 3110 XH-A232
TPA 3116
TPA 3225
Power Output
Most of the reviews I have read and watched on YT including Reddit posts imply that the power outputs are vastly overrated along with in some cases heatsinks not designed for the Class D output stage. Some of these modules do not even have filter capacitor outputs. Also, claims of very high distortion.
Here is my take on this.
Sadly there is and will always be this thing about Fake News and this applies just as easily to these modules and the recommended power supplies. Trust team marketing in this case, not from TI but the manufacturer. Showing a supply voltage requirement of 50V is one thing but having 35V filter capacitors across the supply is another. TEMU do advise to stick to the +35V power rail though.
A very simple calculation to get power output of any amplifier is to use the formula Vcc^2 / 8RL where Vcc is the rail supply and RL is the Load Resistance in Ohms.
The famous Power Output formula based on supply rail and load impedance.
Or how about this to explain further:
Power Output – another view
Into an 8 Ohm load we get a current of 12.726 / 8 = 1.6A. This is equal to 20W dissipation across the load based on the RMS or 0.707 * 18V. This does not take into account any losses e.g. switching in drop across the MOS or BJT devices. As most will know, this is where our Class A amplifiers turn into heaters and Class D perform a lot more efficiently.
So in theory the TPA3255 should give one about 160W with a 36V supply into a 4 Ohm load. (the manufacturer states 600W into a 2 Ohm load in parallel bridge tied load mode (PBTL) at just over 50V.
The commercially available TB10D manufactured by Fosi Audio comes with a 32V 5A supply so to increase the output performance one will need to increase the supply rail voltage along with the current handling capacity of the PSU as well as additional heatsinking or a cooling fan. In my case I’m using a 12V 40A supply, a boost device to +36V rated at 1200W. (about 30A but at 480W, max 15A). The reason for the +12V supply is to run this module off a car battery or Li-Ion/LiFePO4 batteries. Fun on the beach anyone? I am in the process of adding a phono stage, DAC, Bluetooth and tube buffer, just for the fun of it. Nowadays it’s cheaper to buy a complete module than do your own design and have the PCB made up etc. (Details hopefully posted here by 19th May).
Power Supplies for Class D
There was a question posed about power supplies and class D which Paul McGowan, PS Audio, answers straight and to the point, as always:
You may be interested to know that a lot of manufacturers now bring out class AB amplifiers with switching supplies, as I mentioned in a previous article. This also reduces shipping costs. I had a Harmon Kardon which used an SMPSU.
So do these units actually deliver the rated power?
No, because in most cases the user is not testing with a proper PSU and secondly one needs to check the input drive BEFORE the amplifier starts distorting to give a qualified reply. BUT, why reinvent this wheel when Eddie Aho, Kiss Analogue, does the testing for you.
TPA Class D, actually all things Class D – Things to be aware of:
The heatsinking, although Class D and it’s supposed high efficiency, it is not 100% so you will have heat. Longevity calls for more heatsinking or a fan.
Watch those supply rails and filter capacitor voltage ratings.
Quality of the inductors at the outputs – I cannot say if there are shortcuts being taken in this area but it is crucial that the filter components are of the highest quality to reduce total harmonic distortion and noise. That and current handling capacity, its all very fine and well that the manufacturer states these very impressive output figures but those inductors seem to have very fine wire – 300W one needs wire capable of handling a minimum or 10A and this needs to be kept cools as well so the SWG/AWG rating is very important.
Overtemperature shutdown and undervoltage lockout circuitry are very important in all classes of amplifier, but more so, undervoltage is not healthy for the Class D audio amplifier.
Like tube output stages, it is not recommended to run a class D amplifier without a load because it forms part of the damping circuit at the output of the LC filter. The very high voltages which can be generated will cause breakdown of the switching devices and/or filter capacitors.