Is it ok to keep a cheap class-D amp always turned on?

CowCat

Member
2019-04-05 12:12 am
I have a chinese generic TPA3251 amplifier(~39 US dollars) and a chinese generic TPA3255 amplifier(~41 US dollars). I have a chinese 32V 5A adaptor for each amplifier.

I'm thinking about hooking one of them to Raspberry Pi and keep it always turned on.

How long would it last? How long would it sound good if it's left powered on?
 
My worry would not so much be the amplifier as the power supply. Each year a considerable number of power supplies, often when in stand-by mode, have a sudden break-down and catch fire. Chinese or not, it happens quite frequently. It even happened for a neighbor of mine that their well-reputed brand television caught fire. Made quite a mess in the living-room.
I do not leave electrical gear on when I leave the house for more than a short time. When I exceptionally leave for days, I turn all supplies off except for the heating control, alarm systems, freezers etc.
 
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Anything that runs hot is aging faster. In many of the cheaper modules the output inductors run hot because they are rather undersized for the task. And ferrite inductors deteriorate with high temperature, becoming more lossy and thus accelerating the process.

I'd power down when not in use unless the inductors are running cool to the touch.
 
My worry would not so much be the amplifier as the power supply. Each year a considerable number of power supplies, often when in stand-by mode, have a sudden break-down and catch fire.

The problem with repeatedly disconnecting these SMPS bricks is the large current inrush that happens when you reconnect them. Those first few cycles of AC can carry quite a load of current and that will shorten the life of the power supply quite noticeably.

They are actually designed to be plugged in and powered on continuously.
In fact, powering them down and back up repeatedly could well be the cause of the catastrophic failures you mentioned.

This problem is further exacerbated by the bulk capacitors in the amplifier itself. Generally they are left charged all the time power is connected. Add this inrush of current to that of the brick itself and you have a power supply killer.

I ran into this first with PC power supplies... they are designed to be powered up all the time. A couple of my computer clients were turning them off, via the babysitter switch on the back, every time they shut down their computer. When they came to me their complaint was that power supplies were only lasting a few months. So I replaced the supply and told them to stop turning off the back switch... Haven't hear from them since.

Plug it in, hook up the amp and power supply and leave it that way. Use the front panel switch on the amp to turn it on and off.
 

CowCat

Member
2019-04-05 12:12 am
Douglas Blake, thanks for clarification.

Is it a good idea to turn the amp off when I don't use it? Or, does the amp not care whether it's always turned on?

As far as I know, the amplifier power switch is actually a mute switch which just cuts off electricity to amplifier chipset.
Even if I turn off the mute switch, the main capacitor of the amplifier is probably still powered by the power source.
 
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Douglas Blake, thanks for clarification.

Is it a good idea to turn the amp off when I don't use it? Or, does the amp not care whether it's always turned on?

As far as I know, the amplifier power switch is actually a mute switch which just cuts off electricity to amplifier chipset.
Even if I turn off the mute switch, the main capacitor of the amplifier is probably still powered by the power source.

Leave it powered but "off" ... the mute and standby will disable output and place the chip in a very low power stated.
 
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CowCat

Member
2019-04-05 12:12 am
Douglas Blake, the chip is already in a low power state when there is no sound. When there is no sound or quiet sound, the temperature of the metal amp case is below 37 degrees celcius which is my core body temperature.

I think the temperature of the capacitor is more important because the chip will outlast the capacitors.

rayma, Thermal paste was used by the manufacturer to conduct heat to the heatsink. How long would it take to dry out? It's hard to believe that it will dry out when it's under a heatsink.
 

rayma

Member
2011-04-29 8:37 pm
Thermal paste was used by the manufacturer to conduct heat to the heatsink. How long would it take
to dry out? It's hard to believe that it will dry out when it's under a heatsink.

I've seen plenty of electronic assemblies with dried out thermal paste. Depends on the hardware details
and quality of the paste, but I'd certainly do an inspection once a year in critical equipment.
 
I wouldn't worry about the sound quite so much as a power supply failing catastrophically and burning the house down

Years ago I used to leave my amp on, luckily I was in when the transformer caught fire, never again. If the OP wants to risk his life or property that's fine, let's hope innocent people don't suffer if the worst happens.

I used to leave it on because I was stupid enough to believe audiophile BS, what other reason is there?
 
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Douglas Blake, the chip is already in a low power state when there is no sound. When there is no sound or quiet sound, the temperature of the metal amp case is below 37 degrees celcius which is my core body temperature.

If the standby function is properly implemented the PWM drivers are off and the output is in a high impedance state. There is practically 0 power dissipation.

I think the temperature of the capacitor is more important because the chip will outlast the capacitors.

That's quite possible... but working with the TPA3116 extensively of late, I've never noticed any warmth on the bulk capacitor, ever.

rayma, Thermal paste was used by the manufacturer to conduct heat to the heatsink. How long would it take to dry out? It's hard to believe that it will dry out when it's under a heatsink.

Actually it's supposed to dry out. The oils are only there to ensure the compound flows and is distributed evenly under pressure between the part and sink.
 
Years ago I used to leave my amp on, luckily I was in when the transformer caught fire, never again. If the OP wants to risk his life or property that's fine, let's hope innocent people don't suffer if the worst happens.

I used to leave it on because I was stupid enough to believe audiophile BS, what other reason is there?

Not On on... on as in still connected and plugged in but off as in low power standby mode. That's what the little button on these things does now... it simply puts the amp in low power standby.

Connecting and disconnecting these modern brick style SMPS supplies generally results in blowing the input rectifiers after a few inrushes of current. They are designed to be left on all the time. I have 4 of them within a couple of steps of me. All have beein pluged in and running for more than 4 years without even a hint of trouble. I've also sold a couple of dozen of these things as "soundbar killers" and so far not one problem with power supplies.
 
Unless the equipment is needed 24/7 instantly, just shut the damn thing off when done using it.
I enjoy my lowered electric bill by turning stuff off that I'm not using.
It's a no-brainer.

Define "Off" in the context of these new class D amplifiers...

Turning off the AC as in from a power bar, risks massive inrushes of current that can damage an SMPS supply.

In most new equipment "Off" means... Power Supply on, Amp in standby.

In this state the SMPS supply is at the ready but no current is flowing. The amplifier is powered with it's bulk capacitors charged, but the output stage is disabled and in a high impedance state... and yes, it's done that way to avoid the huge inrushes of current I've been talking about.
 

CowCat

Member
2019-04-05 12:12 am
So, if I left the amp always on, would the capacitors be the first things that die? That might take anywhere between 2~10 years if the capacitors were cheap fakes.

What kinds of damages should I expect from leaving it always on?
 
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