• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

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

bigrizz

Member
Joined
Apr 27, 2023
Messages
12
Likes
9
Location
Australia
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?
 

robwpdx

Active Member
Joined
Aug 8, 2020
Messages
268
Likes
372
You have a switching (class-d) amplifier, fed by a switching power supply. A smart plug is switching. If the smart plug is capable of dimming, it does more switching - 120 times a second (SCR circuit.) If it is only capable of on or off, it does less switching. I'm pretty sure you will be fine running it on a smart plug from first principles.
 
OP
B

bigrizz

Member
Joined
Apr 27, 2023
Messages
12
Likes
9
Location
Australia
You have a switching (class-d) amplifier, fed by a switching power supply. A smart plug is switching. If the smart plug is capable of dimming, it does more switching - 120 times a second (SCR circuit.) If it is only capable of on or off, it does less switching. I'm pretty sure you will be fine running it on a smart plug from first principles.
I saw another post here on ASR about a somewhat similar topic here. This person suggests that switching power to the SMPS on and off affects its life. Not sure of the source of their information.
 

robwpdx

Active Member
Joined
Aug 8, 2020
Messages
268
Likes
372
I saw another post here on ASR about a somewhat similar topic here. This person suggests that switching power to the SMPS on and off affects its life. Not sure of the source of their information.

I would doubt that. Generally component failures follow a bathtub curve - infant mortality, a long period of very low failure rate, then increasing end of life failures.

Capacitors are in circuits to be used. On the input of a SMPS are usually inductors and capacitors to keep EMI from flowing back into the line, and on the output to get the DC back to DC. The high frequency switches are going to have high rise time "inrush" currents at their drive frequency every cycle by design. They don't have large capacitors to "charge up" with "inrush" current because the switching frequency is high. It is true the lower temperature your capacitor, or any electronic component, the longer time to end of life.

That article may have been inspired by analog supplies and tube amps turning on, thermally stressing the tubes, or those giant 10,000 uF capacitors on analog amplifier power supplies charging up.
 
OP
B

bigrizz

Member
Joined
Apr 27, 2023
Messages
12
Likes
9
Location
Australia
I would doubt that. Generally component failures follow a bathtub curve - infant mortality, a long period of very low failure rate, then increasing end of life failures.

Capacitors are in circuits to be used. On the input of a SMPS are usually inductors and capacitors to keep EMI from flowing back into the line, and on the output to get the DC back to DC. The high frequency switches are going to have high rise time "inrush" currents at their drive frequency every cycle by design. They don't have large capacitors to "charge up" with "inrush" current because the switching frequency is high. It is true the lower temperature your capacitor, or any electronic component, the longer time to end of life.

That article may have been inspired by analog supplies and tube amps turning on, thermally stressing the tubes, or those giant 10,000 uF capacitors on analog amplifier power supplies charging up.
Thanks Rob. Sounds reasonable. I don't have the knowledge to argue otherwise, that's for sure! I wouldn't be turning it on and off all that often anyway. Max once a day on average I'd say. Out of curiosity, I plugged in the power supply to a smart plug I have that does power monitoring to see what kind of power it's drawing without any music playing. It seems to run about 6.5W at idol. If I was to leave it running 24/7, it'd amount to about $1.20 (Australian dollars) a year in cost. The case seems to run around 32 degC (about 90 degF) at idol so it'd be a fair bit warmer inside the enclosure would be my guess. So the temperature is more the issue than the cost to run it and the long term effect that might have on the life of the amp.
 
OP
B

bigrizz

Member
Joined
Apr 27, 2023
Messages
12
Likes
9
Location
Australia
Ok, I thought I'd test it out now I have it plugged into the smart plug. Interesting behaviour. Turning the power supply off then on after about 10 seconds with the smart plug while the switch on the amp is set to 'on' results in a 'click' 'click' 'klang' from the amp and no power on. The 'klang' is a different sounding 'click' like a different relay activating. I have to cycle the amp power switch for the amp to turn on. Seems to be some form of protection switching going on in the amp preventing it from powering up. The volume on the amp is set to about a quarter. Didn't expect that. Seems my plan has been foiled.
 

gafortiby

Member
Joined
Apr 21, 2023
Messages
36
Likes
43
Ok, I thought I'd test it out now I have it plugged into the smart plug. Interesting behaviour. Turning the power supply off then on after about 10 seconds with the smart plug while the switch on the amp is set to 'on' results in a 'click' 'click' 'klang' from the amp and no power on. The 'klang' is a different sounding 'click' like a different relay activating. I have to cycle the amp power switch for the amp to turn on. Seems to be some form of protection switching going on in the amp preventing it from powering up. The volume on the amp is set to about a quarter. Didn't expect that. Seems my plan has been foiled.
Interesting. What if you power cycle it very slow? Wait a whole minute?
 
OP
B

bigrizz

Member
Joined
Apr 27, 2023
Messages
12
Likes
9
Location
Australia
Interesting. What if you power cycle it very slow? Wait a whole minute?
I just tried it and yes, that works! I waited a minute or so and then powered up from the wall and it turned on fine. That must be the secret. I just have to make sure I don't power cycle too quickly. In normal use, that shouldn't be an issue. Thanks for the suggestion.
 

Sokel

Master Contributor
Joined
Sep 8, 2021
Messages
6,501
Likes
6,662
Maybe *just maybe as it can vary* we shouldn't carelessly suggest stuff without measuring them.
Best would be to measure it at place and as it sits.
Example:

No smart switch:
no smart.PNG

With smart switch:
smart.PNG

both for easy comparison:
both.PNG
 

Sokel

Master Contributor
Joined
Sep 8, 2021
Messages
6,501
Likes
6,662
If only I owned the tools to be able to do such testing. :(
Any decent interface along with software like the one you see above or REW can help you identify stuff like this,it doesn't have to be state of the art,just a help tool.
And considering the cost of a nice rig 200-300 euros is a minor expense and most importantly helps you fix stuff otherwise only under suspicion.
 

gafortiby

Member
Joined
Apr 21, 2023
Messages
36
Likes
43
I just tried it and yes, that works! I waited a minute or so and then powered up from the wall and it turned on fine. That must be the secret. I just have to make sure I don't power cycle too quickly. In normal use, that shouldn't be an issue. Thanks for the suggestion.
Thanks! — I plan to use it through a smartplug as well, but I would only power cycle once a day. I just need to turn it on when I start work and turn it off when I leave the office. Sounds like it will work fine in that usage. :)
 

WinWiz

Member
Joined
Jan 30, 2021
Messages
98
Likes
35
How does Bluetooth behave when the power is switched at the wall socket?
If my wife pair her iPhone and turns the wall socket off without unpairing her phone. Will I then be able to pair my android phone after turning the wall socket on?
Or will I also have to press and hold the amps power button to clear Bluetooth pairing before I can pair with my phone?
 

Fosi Audio

Senior Member
Audio Company
Forum Donor
Joined
Sep 10, 2021
Messages
328
Likes
1,626
How does Bluetooth behave when the power is switched at the wall socket?
If my wife pair her iPhone and turns the wall socket off without unpairing her phone. Will I then be able to pair my android phone after turning the wall socket on?
Or will I also have to press and hold the amps power button to clear Bluetooth pairing before I can pair with my phone?
If your wife's iPhone is not nearby when you turn the wall socket on again, you can pair your Android phone.
 
D

Deleted member 48726

Guest
It should work fine. Power on/off from the wall outlet is the same as flicking the power switch on the unit. The smart plug is doing exactly that via its internal relay.
 
Joined
Jun 26, 2023
Messages
2
Likes
0
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:

Hello XXXX,
Thank you for reaching out to us, I hope you are doing well.
The switch on the power amplifier is designed to deactivate the mute circuit rather than cutting off the power supply to the amplifier.
It will make a popping sound if you don't use a physical on/off switch, it won't damage your speakers, and you can use it with confidence.
Any problem, pls feel free to contact me again. Wish you a lovely day:)
 
Top Bottom