Fosi Audio V3 Amplifier Review

[Down South]

I'll keep that in mind, heat seems to maybe be the cause or contributign factor here as its back to normal today and the temperature has dropped 10c from the abnormally high temperatures we had yesterday in the UK. Of course, it could be completely unrelated.

You can use the V3s on their side. I removed the attractive orange pieces and use a computer fan undeath, Takes care of the heat problem. This what I did on the hybrid h/amp. The mosfets used to create a lot of heat as did the power resistors directly underneath, so I removed the bottom plate and raised the power mosfets - voila the internal temps were dramatically lowered.
Commercial equipment makers know full well that the life of resistors and caps is shortened by using them inside cramped and poorly ventilated boxes. This research was done in the 1950's. Unexpected was the bonus of a slightly sweeter sound. In the early days of hi-fi people weren't constantly changing equipment, they bought gear to last. This is the 'disposable' society.

 

[buyman]

Has anyone replaced the pot on one of these? Mine's developed a channel imbalance seemingly overnight, and I have to assume that it's the pot to blame.

Not yet. I have the same issue with a unit and was in contact with support. The hoops they sent me through made me give up in the end, and just order a new V3 while it was in sale. I want to desolder the pot but I didn't take the time yet. And I might have to find the spare parts ordered from Aliexpress first. I think also the second unit has a inbalanced pot, so I probably will change to other brands if they have something similar available.

 

[Mordor]

I have a pc fan 140mm, conected to a USB 5v port.......easy peasy.

 

[Karls_speaker_works]

Picked up the 48V version on Ebay for $85 shipped this past week. Swapped it out for the fixed gain 85W mosfet amp I was using for the rear overhead Atmos speakers. I was forced to use an external amp since I maxed out the 9 amps in my X3800H. I had initially used an older Musical Fidelity 85W/ch amp for this duty that I had sitting around, but I got tired of the "pop" when the relax turned on the power amp, then listening to the caps discharge shortly after the amp was turned off. Besides that it has a decent amount of bias current which was a waste of idle power. I popped this amp in (full gain) and rechecked the SPL - just 2dB less gain compared to the class AB amp, not bad. I have no idea how to do a listening test with overhead speakers, but I hear nothing anomalous. I will re-cal the setup with the new amp just in case there is any hf gain due to in-ceiling (monoprice) speakers are rated at 8 ohms. Perhaps they will need a little less boost up top - we'll see.

 

[buyman]

I finally managed to desolder my potentiometer and measure it externally. Unfortunately, my (also chinese) spare parts are not really better than the original one.

Finding a drop in replacement is quite hard. 50k stereo potentiometer with Rotary Switch, 15mm grooved knob ...
Aliexpress had some (now I can't find them right now), and I found two more:

50K Stereo Volume Control with Switch [6510] : Sunrom Electronics

Potentiometer axial stereo 50K lin with switch | electronic-studio.c

electronic-studio your electronics shipping! Potentiometers with switch

electronic-studio.com

But I doubt, the quality will be better.

Alps also has something, but with the wrong Knob and resistance:

RK0971221Z0X Product information | RK097 Series | Rotary Potentiometer (Metal shaft type) | Potentiometers | Products Search | Products & Technologies | Alps Alpine

RK097 Series RK0971221Z0X Type : Metal shaft multi-ganged type ･ Size : 9mm size ･ Number of resistor elements : Single-unit, Dual-unit ･ Attached switch : Without/Rotary switch/Push-on switch

tech.alpsalpine.com

10k will limit the max. Volume, so no. Or Change the input voltage divider from 47k to 10k, but also with less input impedance.

I could add a dedicated On/Off Switch to the front and just use a normal 6-pin potentiometer. Or wire some bigger poti via the dead bug method and have far more options. As I currently have 2 units here, I can play arround with potis and tweaks easily. I don't want to loose the conveniece of the knob to adjust the volume. My USB-DAC has volume control, but only via touchscreen or remote. Not very convenient. Other than that, I could also use the shortcuts on my keyboard, but a physical knob is far superior in my opinion.

Would you have any suggestions for a drop-in replacement of the poti? Or I might just go the heavier modding route (or look for a different amplifier in the future).

 

[rongon]

If you turn the volume control all the way up, is there still a channel imbalance?

 

[Count Dacula]

 

[Joe Smith]

If using a preamp, can just leave the v3 pot on full and control volume using the preamp pot…

 

[Count Dacula]

Yes, I'd rather not reply upon that cheesy DAC-Pre to provide much signal current, just the minimal level to get up off the noise floor, but before distortion kicks in. The V3 has definitive instrumented tests that the gain is clean, but I never have a bad experience with a "balanced" approach.

On my main systems, that use a nice headphone DAC, I never run it flat out because that would exceed 2v and theoretically overdrive the next component, a preamp. For that reason, I'm used to doing it with a "2-pot" approach, but I'm open to ideas. Running my pre flat out and attenuating it with a (better) DAC seems feasible too, so there's a thing to think about.

 

[Angst92]

It seems one channel on the amp is mid failure, and my issue previously wasn't the pot. The volume level of the right channel is currently all over the place with occasional pops and no output apart from static. It's a couple of months outside the amazon warranty coverage but still within the supposed 24month manufacturer warranty so ive emailed Fosi, but I won't hold my breath.

Edit: Bought some op-amps to see if it's just one of those failing since its just one channel.

 

[Angst92]

It seems one channel on the amp is mid failure, and my issue previously wasn't the pot. The volume level of the right channel is currently all over the place with occasional pops and no output apart from static. It's a couple of months outside the amazon warranty coverage but still within the supposed 24month manufacturer warranty so ive emailed Fosi, but I won't hold my breath.

Edit: Bought some op-amps to see if it's just one of those failing since its just one channel.

For anyone else that has this issue, It seems I have resolved it by swapping the socketed NE5532P opamps. Looking around while doing it I couldn't see any over obvious signs of failure like scorch marks etc.

 

[buyman]

I finally managed to desolder my potentiometer and measure it externally. Unfortunately, my (also chinese) spare parts are not really better than the original one.

Ok, I was wrong about that part. I updated my measurement setup for the potentiometer with small clamp test probes from a logic analyzer rather than directly measuring it on the pins.

The potentiometer of my first bought V3 was complete garbage, no consistent readings between 0 and arround 90° and kombinations like 350ohm on one channel and 2000 on the other. From arround 90° turning angle on, it was getting better up to the point where I'd say it was usable.

Nevertheless I swapped it out with one of my spare ones (measured and took the best ones) and I'm very happy I did it: no more scrathing noises, consistent low volume control, even smoother operation.

I also decided to desolder the poti from the 2nd unit. This time the potentiometer was orange like in the post above, the first one was green/blue. It measured quite fine desoldered, so no obvious big deviations between the two channels. As it was prone to scrating, I still swapped it out with another spare part. But this unit I haven't tested yet, so I can't say if it has improved or not. I'd assume the scratching noises are gone, but the L/R balance to be similar at best, maybe even slightly worse.