2 Failed Fosi v3s or an Electrical Issue?

[Connor1a]

So I’ve had 2 failed Fosi v3s. Here’s the situation.

I bought a pair of Fosi v3s bundled with a 48v/10a shared power supply. The power supply came with a line filter and a y-cable to feed the two monoblocks. The power supply, filter, y-cable and 2 monoblocks were sold as a set by Fosi.

I rent a circa 1940s house. Of potential interest here is that the wiring has been retrofitted in some rooms with GFCI receptacles to allow grounded plugs to be used without running grounding wires to all of the receptacles (only some). I’m not an electrician. I was told that the GFCI receptacles are a valid approach in such a circumstance as long as the “load differential” back to the main is [something I don’t recall] and a GFCI receptacle in the circuit is actually grounded. I have surge suppressors on every plug.

Back to the Fosis, I unboxed the 2 monoblocks, installed them neatly, attached speakers, powered them on and voila, music. Everything ran fine until I powered off the amps at the end of the day. The next AM I went to power on both amps and was treated to a meaty “POP” from the right channel amp. There was a whiff of ozone and no sound from that channel. The left channel amp was fine. I did a bit of powering on / off and channel switching. The right channel amp was dead. There was a rattle inside the enclosure. So I boxed everything up and shipped it back off to Amazon.

4 days later I received a replacement set of electronics. I set them up in exactly the same manner, enjoyed the sound for a day, powered them off until the next AM, and “POP” the right channel amp fried again. Exactly the same set of circumstances / the same ozone / the same failure.

Meanwhile, I’ve been running several other devices off the same receptacle including a grounded Class A/B amp and TV without issue... I’ve had various transformers on the receptacle. For months. I haven’t blown a circuit on the panel or the surge suppressor. Nothing else on the same receptacle has exhibited any ill effects whatsoever. But… It’s exceedingly strange that the event happened twice. Again, both times on the right channel amp only. The left channel amp continued working fine. I swapped the amp from one end of the y-cable to the other. Both worked. I’m stumped…

I’m just about to plunk down a wad of cash on a new NCx500 amp. I’ve described this to the manufacturer. They couldn’t explain the situation and don’t think a grounding issue would affect their kit, but I can’t shake the idea that the funky electrical in the house is causing an issue. It “shouldn’t”, and I’m not an electrician or a licensed engineer, but it’s too much of a coincidence. Would you guys have any ideas?

Thanks so much as always.

 

[terryforsythe]

Would you guys have any ideas?

To start, check the voltage with a multimeter. If you don't have one, they are not too expensive these days.

 

[Connor1a]

To start, check the voltage with a multimeter. If you don't have one, they are not too expensive these days.

Voltage at the receptacle? Can do. I need to find my multimeter. Will revert.

 

[terryforsythe]

Voltage at the receptacle?

Yes.

 

[Speedskater]

a GFCI receptacle on a 2 wire AC circuit, performs it's safety function, but it does not provide a Safety Ground path back to the Neutral to trip the circuit breaker in case of a Ground Fault (short circuit to chassis).
Rather than a DMM multimeter, a Kill-a-Watt meter is a better & safer AC power line tool.
Nor does the 2 wire GFCI receptacle provide a path back to the Neutral for noise and leakage currents.

 

[DVDdoug]

Is the power supply from Fosi, or a 3rd party?

The power supply might put-out a higher-voltage spike when switched-on. (I've seen that once and it was on a high-end lab-style power supply!) It might be too-quick to show up on a meter. Or it may just be out-of-spec.

"Old wiring" in your house won't usually cause an over-voltage surge, and if was too high you'd (probably) see your lights getting brighter or changing in brightness. The exception is some non-dimmable LED lights that work at constant brightness from 80-280V, or something like that.

But if you have an open neutral (or a flaky neutral connection) to your house you'll get higher voltage on one phase and lower voltage on the other phase. But you'd notice that with your lights, etc. I knew someone that happened to, and half of the light bulbs (and maybe some other stuff) were blown.

 

[Connor1a]

To start, check the voltage with a multimeter. If you don't have one, they are not too expensive these days.

So the tester shows 122 VAC with an Open Grd Fault.

 

[Connor1a]

Is the power supply from Fosi, or a 3rd party?

The power supply might put-out a higher-voltage spike when switched-on. (I've seen that once and it was on a high-end lab-style power supply!) It might be too-quick to show up on a meter. Or it may just be out-of-spec.

"Old wiring" in your house won't usually cause an over-voltage surge, and if was too high you'd (probably) see your lights getting brighter or changing in brightness. The exception is some non-dimmable LED lights that work at constant brightness from 80-280V, or something like that.

But if you have an open neutral (or a flaky neutral connection) to your house you'll get higher voltage on one phase and lower voltage on the other phase. But you'd notice that with your lights, etc. I knew someone that happened to, and half of the light bulbs (and maybe some other stuff) were blown.

The manufacturer was Hunt-Key. A fairly beefy brute.

Funny enough, all my lighting is actually either Hue or no name led so were there a phasing issue I would most likely not see it in my lights.

I did test several plugs in the house though. There are a set which are correctly grounded (or at least are being tested as grounded per a Klein socket tester). However, the offending socket comes back with a ground fault (solid red light).

Could that out of phase theory contribute to why only the right channel amp would toast? It’s the damnedest thing. It’s odd that its only happened on this power supply. Could it be the y-cable somehow splitting that power?

 

[NTK]

A similar problem is reported here. See this post and ones preceding and following it:

Fosi Audio V3 Amplifier Review

Hi Finn. This PCB (XLR TO RCA) exists at ALIEXPRESS: search by photo -> It requires a PSU as you see. The other solution but without power supply is to use de-symmetrizing transformers but the cost of the PCB is 5 to 10 times higher -> The advantage of the latter is that it ensures...

www.audiosciencereview.com

 

[Sokel]

PSU's like that are usually protected by lots of issues if certified,etc.
Can you measure it while is working and while turning off your gear?

 

[terryforsythe]

So the tester shows 122 VAC with an Open Grd Fault.

The voltage is a bit on the high side, but should not be enough to kill a properly designed amplifier.

If you don't have a ground wire, the open ground fault will show up. Not much you can do about that without running a ground wire. Nonetheless, ground typically is used for safety, and shouldn't affect the amplifier. A little more noise may come through if the power supply is using class-Y capacitors L-G and N-G.

 

[Connor1a]

PSU's like that are usually protected by lots of issues if certified,etc.
Can you measure it while is working and while turning off your gear?

Unfortunately no. Everything has been returned.