Switching supply for power amplifier

[Pimpom]

If anyone has used or is using a generic switching power supply for a power amp, could you please share your thoughts and experience?

Specifically, I'm thinking of using a general purpose SMPS to power a Chinese-made Class D TDA7498E module. The aim is to get a good PA-level quality rather than the highest of hi-fi. The PSU I'm thinking of is a generic type meant for LEDs, CCTV and the like. If there's nothing seriously wrong with the idea, I'd over-spec the PSU rating by about 50%.

The TDA7498E is rated at 2x160W into 4 Ω at 36V for 10% THD (2x125W at 1% THD). A suitable PSU would be, say, a 36v 15A unit. Here's one example each of the modules:

Best price 36V 15A 540W Universal Regulated Switching Power Supply for CCTV Led Radio Free shipping-in Lighting Transformers from Lights & Lighting on AliExpress
TDA7498E 2X160W Dual Channel Audio Amplifier Board, Support BTL Mode 1X220W Single Channel, DC 24V Digital Stereo Power Amp Modu on AliExpress

 

[nigelwright7557]

For power amplifiers I prefer simplicity and robustness so stick to mains transformer/bridge/smoothing setup.

Having said that not had many problems with my PC SMPS.
The fan vent eventually blocked up with dust and the power supply overheated and shut down. Luckily it shutdown rather than just meltdown.

 

[Pimpom]

For power amplifiers I prefer simplicity and robustness so stick to mains transformer/bridge/smoothing setup.

Thanks for the quick reply. The question of robustness is one of my main reasons for asking here. I've built a few audio amps, all linear types of my own design with discrete parts except for some simple ones using low to medium power ICs. They all use transformer-rectifier supplies, some low-power ones with regulated supplies. I've occasionally wound my own transformer.

This will be my first venture into Class D and SMPS. I suppose my reasons are the same as everyone else's for using them - reduction of size, weight, heat and, in some cases, cost.

So, what factors should be kept in mind in using this kind of combination of amp and PSU modules? Are these types of PSU prone to sudden meltdown? Is noise a problem? Anything else to consider?

 

[nigelwright7557]

With SMPS you cant put big capacitors on the output or it overloads them on power up.
They also have a tendency to high frequency (from switching) noise.
There is simply a lot more to go wrong on SMPS.
If they do go wrong they are often hard/expensive to fix.
A transformer is usually pretty bullet proof unless you do something really stupid.

 

[Osvaldo de Banfield]

Every SMPS has a limit for the current than can be sourced from it, so it is by far, more reliable. Also, they are voltage regulated, so the impedance is so low that big caps at their output never is necessary.

Also, catastrophic failures always occur in their high voltage section, in the primary of the transformer, so, NEVER a load will be destroyed using them, provided they are used according to the manufacturer's parameters. I had repaired and designed several of them, and I have experience with them.

 

[Pimpom]

...... Also, they are voltage regulated, so the impedance is so low .....

Another reason for using SMPS. With a regulated power supply - linear or switched - the maximum peak and sustained power outputs of the amplifier are virtually the same, although not everyone will consider this important for audio.

I think I should further clarify the follow-up question in my second post. When I asked "Are these types of PSU prone to sudden meltdown?", I meant those intended primarily for other applications like lighting and may not be of very high quality. The demands of such other applications may be different from those of an audio amplifier.

 

[Osvaldo de Banfield]

Some kinds of SMPS's will not perform well in audio applications, mostly in class AB or B. This is because most of them , of the half/full bridge or forward converters, have a filter internal to the SMPS that has (Because they need) choke input filter post rectifying the pulses, to get the average value of the PWM, not the peak. So, as this filter (Inductor together to the output cap's) conform a low pass filter that has slow time constant, making them slow to respond to sudden changes in the load current. Those derived from the flyback topology (1 or 2 switches) hasn't that filter, and are the most appropriate ones to audio job.

 

[Pimpom]

Understood. I haven't opened and analyzed any of the type of SMPS that are widely available for driving LEDs, so I have no idea which topology is used. I do know that computer PSUs commonly use half/full bridge types with inductor input filters.

I have designed and built from scratch a very few switching supplies. But they were mostly low power ones, the highest-powered being a 24V 10A unit custom-built for a local firm some 10 years ago. I live in a very remote place and I did those few builds out of necessity. I'm no expert at it and would rather avoid doing such one-off designs, especially since they are now more easily available online.

 

[Osvaldo de Banfield]

It is usually unknown the topology of the SMPS unltil you have at hand, and can disassemble and see how it is composed. Nor usually can you know the switching frequency, but perhaps you can choice the highest switching freq. available, because it will have lower inductor value and higher BW than one of lower one, independently of the topology.

I would choice one of the flyback type, but find one over 200W is difficult to get.

 

[wg_ski]

Another reason for using SMPS. With a regulated power supply - linear or switched - the maximum peak and sustained power outputs of the amplifier are virtually the same, although not everyone will consider this important for audio.

That is only true if the supply can deliver the peak current required by the amplifier. Even with a sine wave, the peak current drawn is approximately a factor of 3 higher than the average. If it is not designed to do this, and only sized for the average demand, it will intermittently go in and out of current limit when operating at high levels and low frequency. Lighting power supplies would be the worst in this regard, as they would normally go into limit just above rated power. If you used one that put out 3X the audio power, it would be very reliable as your average demand would be way less than its typical operating mode. But big switchers can get expensive.

 

[jan.didden]

Hypex has SMPS which are designed for higher short term peak currents than the current limit. They were developed for their Ncore amplifiers.
I routinely use their 400W +/46V and never had any issues. Also have +/-22V aux voltage outputs you can use with a regulator for any opamps in the system.
They are pretty cool ;-)

Jan