Fosi BT20A Pro High Temperature Issues...

[John in CH]

ASR Newbie here.

I have three BT20A Pro amps. One was purchased with the Fosi provided standard power supply (can't remember if it was 32v or 36v). Two were purchased with Fosi provided 48v power supplies.

When idling or running on the standard power supply the amp is just slightly warm to the touch. But when simply idling (or playing) on 48v they become so hot that I'm reluctant to touch them. I swapped the PS's around to see if the heating problem was due to the amps or due to the PS voltage. The heating issue clearly followed the 48v supplies. Based on this exercise it is clear to me that 48v causes extremely high idling temperatures. Whereas idling or running on the standard (32v or 36v) supply the case temps are just slightly above ambient.

I then noticed that 48v idling temps would drop to ambient if I simply unplugged one of the two RCA input cables. Didn't matter if it was left or right side. With both RCA's connected, idling temps would soar to "do not touch" territory. But disconnecting one RCA would cause idling temps to drop again.

I tried this on all three amps and identical behavior was observed on all of them.

My audio source is a Denon DNP-800NE Music Streamer which passes through a Fosi P1 tube preamp (Denon > P1 > BT20APro).

Same high temp behavior is observed when connected directly to the Denon (ie without the P1 in the loop: Denon > BT20APro) and persists whether the Denon or the P1 are powered on or off.

This got me to thinking that the RCA's from the P1 and/or the Denon may have a shared ring/ground (I have not yet confirmed this as several other probjects are taking the priority at the moment).

Question: Could such shared ring/ground on the RCA cables cause the BT20A Pro to run such high temps when running on 48v PS? But not on the lower 32v/36v PS?

Has anyone else observed similar behavior with their BT20A Pro on 48v? And does unplugging one of the RCA's cause the idling temps to drop?

Rgds...
- John

 

[Pecrow]

Hi john,
Yes, i too have a 48v psu connected and my bt20a pro gets very hot. I havent measured the case temp but it must get to 60c even when its idle. I’m considering ordering a 32v psu so that i dont fry the amp. No rca connected, just a bt connection to my phone.

 

[RayHs]

My BT20A Pro also gets pretty warm with a 48V power supply (at least 10° F) over the 32V one even with no signal.

 

[HarmonicTHD]

My BT20A Pro also gets pretty warm with a 48V power supply (at least 10° F) over the 32V one even with no signal.

View attachment 346282View attachment 346281

Where is the issue? Why would 95F be not good?

 

[RayHs]

I don't think it's an issue other than perhaps longevity, the case is obviously doing it's job as a heat sink. I also have a V3 and you can not even feel a temp at 32V but does feel warm at 48V.

 

[Deleted member 48726]

It would be interesting to see which components inside contribute most to the heat. To assess if it is damaging in short or long term.

 

[RayHs]

Hooking the power supplies to a Kill A Watt, am seeing a 0.22A draw on the 48V GaN power supply vs 0.07 on the 32V both at idle connected to the BT20A.

With the power supplies disconnected from the BT20A am showing 0.04A draw on the 48V GaN and 0.0 on the 32V.

 

[HarmonicTHD]

It would be interesting to see which components inside contribute most to the heat. To assess if it is damaging in short or long term.

I guess for 100 bucks, once it dies, one simply buys a new one. That´s about dinner with your loved one. No? The infrared camera the OP took the pictures with, was probably more expensive.

 

[Deleted member 48726]

I guess for 100 bucks, once it dies, one simply buys a new one. That´s about dinner with your loved one. No? The infrared camera the OP took the pictures with, was probably more expensive.

And so?
Isn't it interesting regardless of price?
It's quite inconvenient when it dies I imagine and 100 dollars is a considerable amount for some people.

 

[Chr1]

Time to drill some holes in the casing methinks...

 

[Deleted member 48726]

Hooking the power supplies to a Kill A Watt, am seeing a 0.22A draw on the 48V GaN power supply vs 0.07 on the 32V both at idle connected to the BT20A.

With the power supplies disconnected from the BT20A am showing 0.04A draw on the 48V GaN and 0.0 on the 32V.

Is that 230 V bricks?

 

[RayHs]

Is that 230 V bricks?

120V

 

[RayHs]

Interesting thing is when hooked up to the V3 with no signal am seeing 0.19A draw on the 48V GaN and 0.03A draw on the 32V. Am guessing the Bluetooth adds a fixed ~0.03A draw on the BT20A.

 

[John in CH]

Hooking the power supplies to a Kill A Watt, am seeing a 0.22A draw on the 48V GaN power supply vs 0.07 on the 32V both at idle connected to the BT20A.

With the power supplies disconnected from the BT20A am showing 0.04A draw on the 48V GaN and 0.0 on the 32V.

As mentioned in the OP, my experience is that 48v temps rise significantly when both left and right channels (signals) are connected. With just one channel (left or right) connected, idle temps fall to just slightly above ambient.

I wonder if Kill A Watt would reveal an amperage draw difference in scenario above? Rgds... - John

 

[RayHs]

With the 48V GaN supply on the BT20A and no signal from source, I see the same draw on the Kill A Watt with one or two channels connected but the temp is 4° F cooler when one of the channels is disconnected.

 

[rj2wells]

It would be interesting to see which components inside contribute most to the heat. To assess if it is damaging in short or long term.

It's damaging to my electric bill. I use this amp a few times a week, I don't need it running an electric fever 24/7. I also long term worry about fire risk when something stays hot indefinitely.

I solved it for myself by using a power bar with a 12v relay trigger, driven by my WIIM. It's now totally powered off when not in use, but I shouldn't have to do that.

@Fosi Audio should fix this in future versions, there's no good reason for it to draw so much power when idle.

 

[RayHs]

One other thing I noticed with the BT20A is that I'm measuring 10.7mV DC on the speaker outputs even with no signal while the V3 shows just 0.1mV DC.

 

[burkm]

I don't think there ever is the danger of a "fire hazard" as long as the amp does not implode or explode.
It does shorten the life expectancy of electrolytic capacitors and even resistors, because they do have a temperature conforming life.
Fosi Audio chose a fanless future for their class D amps without a separate heat sink. They use the whole aluminum cabinet as a heatsink, which causes the cabinet to get hotter...
This might lower the temperature of the class D amp chip itself, but it causes a higher temperature for the cabinet, which replaces the heat sink.