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Would it be ok to control power to a Fosi Audio BT20A Pro with a smart plug?

gafortiby

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I can confirm that for Fosi Audio V3 unit, I cannot hear any pops when I control power by plug. in fact there is some kind of relay in the device that clicks on separately after I power the AC so it internal power is controlled via that relay.
 
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Deleted member 48726

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Fwiw, I'm an owner of Fosi TB10A (https://fosiaudioshop.com/products/home-audio-amplifier-receiver-tb10a). As far as I can tell, it's the same amp minus the bluetooth connectivity. I bought it for the exact same use case – hiding it in my cabinet where it's hooked up to an airport express for audio input over Airplay and I was intending to power it on/off using a smart outlet so that it could be off when not in use, but ready to play as soon as I turn on the lights in the room where the speakers are.

I have the exact same solution running perfectly in one of our restrooms using a small amp from Nobsound, but that is too weak to power my larger speakers for this setup, so I decided to go for this Fosi amp.

To my disappointment, the speakers make loud pops whenever the power is cycled on the Fosi amp. Reading here where they claim that they have tested this scenario for BT20A, I decided to reach out to them and ask if there's a difference between the amps or if I have a faulty unit.

Turns out that the power switch is not actually a powerswitch at all – it's just a toggle for the onboard mute function. So I think their above answer that this works is completely false.

I think I'm going to have to turn a blind eye to this, ignore the constant (albeit small) power draw and leave it on at all times. I do not enjoy the sound effects of turning the lights on. :)

Here's their email for reference:
That's a very odd way and not what you'd expect from a power button..
 
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Fwiw, I'm an owner of Fosi TB10A (https://fosiaudioshop.com/products/home-audio-amplifier-receiver-tb10a). As far as I can tell, it's the same amp minus the bluetooth connectivity. I bought it for the exact same use case – hiding it in my cabinet where it's hooked up to an airport express for audio input over Airplay and I was intending to power it on/off using a smart outlet so that it could be off when not in use, but ready to play as soon as I turn on the lights in the room where the speakers are.

I have the exact same solution running perfectly in one of our restrooms using a small amp from Nobsound, but that is too weak to power my larger speakers for this setup, so I decided to go for this Fosi amp.

To my disappointment, the speakers make loud pops whenever the power is cycled on the Fosi amp. Reading here where they claim that they have tested this scenario for BT20A, I decided to reach out to them and ask if there's a difference between the amps or if I have a faulty unit.

Turns out that the power switch is not actually a powerswitch at all – it's just a toggle for the onboard mute function. So I think their above answer that this works is completely false.

I think I'm going to have to turn a blind eye to this, ignore the constant (albeit small) power draw and leave it on at all times. I do not enjoy the sound effects of turning the lights on. :)

Here's their email for reference:
Drilled deeper into wether BT20A has the same behavior and got this answer from Fosi support:

Hello XXXXX,
Thank you for the answer.
BT20A behaves the same way, we continually keep our product improved/updated.
Please take a look at model V3, it is specialized REAL-OFF technology that ensures the cleanest shutdown.
https://fosiaudioshop.com/products/...i-fi-stereo-audio-amplifier-with-tpa3255-chip
Please let us know if there is anything else we can do to assist you.

<sarcasm>Great thing that V3 includes this amazing new functionality of REAL-OFF!</sarcasm>

For me, that amp is unfortunately not what I'm looking for as I want/need the EQ knobs of the prior versions.

I'd be happy to get recommendations if anybody is aware of an amp that:
  • Has the same compact form-factor
  • Can deliver at least 2x100W
  • Has a physical on/off switch (with REAL-OFF functionality) that remembers it's state even if power is completely lost
  • Does not pop the speakers when power is cycled and power switch is set to ON
  • Volume setting that keeps its state when power is lost (ideally physical knob, but not necessary)
  • Basic EQ settings that allows tuning of base/treble, state kept when power is cycled
  • Line in via 3,5mm or RCA
 

Starbomba

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Jul 19, 2023
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I can confirm that for Fosi Audio V3 unit, I cannot hear any pops when I control power by plug. in fact there is some kind of relay in the device that clicks on separately after I power the AC so it internal power is controlled via that relay.
With the very scientific and accurate method of plugging the amp and unplugging it, i can confirm for my BT30D Pro does not send any pops to my speakers. I can also hear a relay going in and out, assuming it does something to prevent current inrush or some other protection.

I also think the switch is a "mute" switch, and it makes sense. There's no way such a puny switch can handle 150W+ of power on those amps (or whatever the power supply is rated for). It is definitely a "soft-off" switch, pretty much like TVs and other modern stuff, not a hard power cutoff switch.
 

Martinvb

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Drilled deeper into wether BT20A has the same behavior and got this answer from Fosi support:



<sarcasm>Great thing that V3 includes this amazing new functionality of REAL-OFF!</sarcasm>

For me, that amp is unfortunately not what I'm looking for as I want/need the EQ knobs of the prior versions.

I'd be happy to get recommendations if anybody is aware of an amp that:
  • Has the same compact form-factor
  • Can deliver at least 2x100W
  • Has a physical on/off switch (with REAL-OFF functionality) that remembers it's state even if power is completely lost
  • Does not pop the speakers when power is cycled and power switch is set to ON
  • Volume setting that keeps its state when power is lost (ideally physical knob, but not necessary)
  • Basic EQ settings that allows tuning of base/treble, state kept when power is cycled
  • Line in via 3,5mm or RCA
Fosi BT20A Pro checks all boxes (that is, when powered by the 48V 5A power adapter). It also has a true sub out channel, which is volume sensitive.
 

mlieber507

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Apr 11, 2021
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Hi everyone. I just took delivery of a Fosi BT20A Pro with a 48V power supply. My intended use is to power some ceiling speakers from a channel on a Nuvo multizone amplifier located in a cupboard. The Nuvo has channels with pre-outs, so I can control the volume from the Nuvo but I can't control the power of the Fosi remotely. I'm not too keen to leave the Fosi permanently on so I was going to put a smart plug behind the Fosi and control power to it that way. I read a review by someone on Amazon of a similar Fosi amp who commented that the power supply is always on and the switch on the Fosi doesn't actually switch the amp off but puts it in a standby mode. His comment was that switching the power supply on and off at the wall would shorten the life (not clear if it shortens the life of the amp or the power supply). Something to do with the inrush current?

What are people's thoughts on this? Do you see any issues leaving the Fosi on at its switch and switching power at the wall? I could potentially switch the power between the power supply and the Fosi with a smart relay, so the power supply is permanently getting power. Would that be better?
Some Fosi amps do not suppress pops if you turn them on and then apply power. However at least one, the V3, will not pop when you apply power with the amp turned on. Unless someone has experience with this with a BT20A Pro, you can always buy it from the big A, try it, and return it if get a pop.
 
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Deleted member 65547

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Everything in my house is managed by home automation and nothing has ever had a problem. Maybe it would have been different with the equipment of the past, or the new ones of poor quality (but REALLY poor), extremely sensitive to spykes, but now everything is suitable for being unpowered when not in use.
 
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Deleted member 48726

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Everything in my house is managed by home automation and nothing has ever had a problem. Maybe it would have been different with the equipment of the past, or the new ones of poor quality (but REALLY poor), extremely sensitive to spykes, but now everything is suitable for being unpowered when not in use.
Of course it is. It shouldn't be a problem. You, flipping the main power switch on the amp, is the same as if some home automation wifi controlled relay does the same.
 
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Deleted member 65547

Guest
Of course it is. It shouldn't be a problem. You, flipping the main power switch on the amp, is the same as if some home automation wifi controlled relay does the same.
Not exactly.
The amplifier switch, which is always ON, is located downstream of the power supply.
So if the power supply is not of good quality a spyke at its input propagates towards the low voltage part and therefore to the amplifier.
Modern switching power supplies do not create this kind of problem.
 

TurtlePaul

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Amir measured the BT20A and did a power on test. It looks like it has a thermistor to limit inrush current. Therefore, using a smart switch should be fine.
 
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Deleted member 65547

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Amir measured the BT20A and did a power on test. It looks like it has a thermistor to limit inrush current. Therefore, using a smart switch should be fine.
Using smart switches with Fosi power supplies does not create any problems, but this is now true not only for Fosi but also for everyone else.
However, the temperature limitation has nothing to do with it, nor does the current limitation.
Spykes are short overvoltage transient, which do not cause excess temperature or current but if excessive can damage semiconductor junctions or the dielectric of capacitors.
 
D

Deleted member 48726

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Not exactly.
The amplifier switch, which is always ON, is located downstream of the power supply.
So if the power supply is not of good quality a spyke at its input propagates towards the low voltage part and therefore to the amplifier.
Modern switching power supplies do not create this kind of problem.
Yes. Exactly. This is not an issue. If the power brick can't handle the in-rush it's faulty. How else are you gonna connect the thing to the wall outlet.if it can't handle that.
 

restorer-john

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Yes. Exactly. This is not an issue. If the power brick can't handle the in-rush it's faulty. How else are you gonna connect the thing to the wall outlet.if it can't handle that.

SMPS supplies can have enormous turn on currents, even small ones. I'm sure you've experienced a pop/arc sound when plugging in a large laptop supply- that's the inrush current to the supply- not the connected amplifier.

Power cycling SMPSs is never a great idea, but leaving them on isn't either. You can't win, especially if there's no inrush limiter/ptc in the SMPS.
 
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Deleted member 48726

Guest
SMPS supplies can have enormous turn on currents, even small ones. I'm sure you've experienced a pop/arc sound when plugging in a large laptop supply- that's the inrush current to the supply- not the connected amplifier.

Power cycling SMPSs is never a great idea, but leaving them on isn't either. You can't win, especially if there's no inrush limiter/ptc in the SMPS.
Of course. That's my point. -What are you gonna do? It better be made for it.
 

popej

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It is not the kind of electronics, that I know much of, but some ideas come to my mind :)

Smart plug should turn on devices when AC voltage cross 0V, I guess. Then switching on should be as easy as possible, not the random spike like when using mechanical switch or plugging in.

Any modern SMPS should use power factor correction and PFC circuit can include protection against excessive inrush current.

Smart plug takes power itself, maybe less than idle SMPS, but better to check, if you want to use smart plug to reduce power consumption.
 
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Deleted member 65547

Guest
Yes. Exactly. This is not an issue. If the power brick can't handle the in-rush it's faulty. How else are you gonna connect the thing to the wall outlet.if it can't handle that.
Exactly. If the power supply was not able to manage the spyke it would not be possible to connect it to the electrical network by keeping the load power switch (in this case the amplifier) on ON, because it would be necessary to first connect the power supply and then turn on the load, therefore this component would not have been managed via home automation.
It can still happen with "linear power supplies" because if not well designed it is easy for a spyke on the transformer primary to propagate towards the output.
In the past it was like this, but not anymore because everything is designed taking into account management via home automation.
 
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Deleted member 65547

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Smart plug should turn on devices when AC voltage cross 0V, I guess.
There is the possibility of having "zero cross" activation using electronic relays (triacs), but this is not the case with common home automation, which uses common mechanical relays.
 

popej

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I expected solid state relay, but maybe they are too expensive yet?
 
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Deleted member 65547

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No it doesn't cost much, in fact for power applications it costs even less than the corresponding mechanical one.
However, it requires a heat sink, which is expensive, takes up space and requires assembly in relatively free air, and if you want zero crossing activation you need management electronics that are not complicated but still more complex than the simple "ON/OFF" which drives the mechanical relays.
But above all it is not normally necessary to resort to this strategy
 
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