Fosi Audio V3 Mono Amplifier Review

[Cal_Cobra]

Interesting that many measurements and tests are still there even though those aren’t practical in real world used case, its a big debatable topic here on ASR but I am not going there.
Appreciate what you said but IT change management process made me learn the need of testing in every way possible, every possible issues if possible.
You never know how creative a user could be using what they buy .

And even with a UE/UI testing process, bugs, glitches, user oddities, etc., still remain the norm. I've worked in tech, interfacing with engineering, and manufacturing for decades [albeit far more complicated devices, some with 32 layer PCBs), and even the best thought out and tested products, still encounter challenges upon release.

Thus far Fosi Audio appears both receptive to "criticism" as well as exhibiting a great desire to satisfy their customer base by building products demanded by audio enthusiasts at bargain basement prices.

 

[Anton D]

I never realized how many people are unfamiliar with the old fashioned power amplifier thing.

Makes me feel so old!!

 

[36mbbj]

Add BLUE back-lit VU meters and we have a winner

Whilst it would be nice eye candy, it would add to the cost of the end product without any audible benefit. We are talking about a low-cost true dual-mono power amp, the key words here being "low" & "cost". If not having VU meters is the price to have a very decent (to put it mildly) power amp that sells for what a NAD 3020 used to sell for, I'm willing to sacrifice the eye candy. Sometimes, less is truly more.

It feels like you're on the same wavelength as us! We've recently begun exploring a similar solution – housing multiple amplifier boards within a single chassis and incorporating an internal power supply

@Fosi Audio : glad to hear I'm not the only one that thought of that! I'll probably remind you of the very obvious, but from my years in the hobby, I've observed how the power supply is a very critical part of amplification. A badly-designed or underspec'd power stage can turn an otherwise stellar amplification design into, well, cr\*p. There's a reason why very expensive audio gear has sizeable power supply stages - my current power amp has beer can sized capacitors and a toroidal transformer the size of a Christmas pudding, for example.

I'd also add: if you are considering making a traditional looking power amp, a matching pre-amp would be in order to provide a complete solution. Methinks a simple & clean full analogue design with an optional & upgradable internal DAC, maybe with a similar phono stage (internal, optional & upgradable) to complete the picture as they say, sold for a similar price to the power amp, could be a hit in the market.

 

[TheBatsEar]

I have a WiiM too, but just in case the device resets itself or something else bad happens, you suddenly blow your speakers up with so much watts.

Collect 10 documented cases where this led to damage of property. In other words: sometimes we suffer more in our minds than reality.

 

[AndyLu]

I have a WiiM too, but just in case the device resets itself or something else bad happens, you suddenly blow your speakers up with so much watts.

It looks like an 'old fashioned' power amp seems like a new concept to you (correct me if I am wrong).
Power amplifiers without volume control are nothing new and pretty standard. They are supposed to be used with a pre-amp with a rotary volume control and/or an old fashioned potentiometer. People are using them this way for decades already. As far as I understand Fosi made these mono blocks on purpose without volume control because users asked for it.
You may not be the intended use case or maybe (while it can be used for this purpose) a WiiM is not the most appropriate?

No offense but to quote @Anton D your post "makes me feel old" too

 

[36mbbj]

I never realized how many people are unfamiliar with the old fashioned power amplifier thing.

Makes me feel so old!!

You might be horrified to realise how many young people never heard or even just saw a proper sound system, with real loudspeakers... or never realised you could sit down and actually listen to music without doing something else at the same time.

For too many, if it's not listening to music through earbuds as they are riding mass transit, it's bringing out a battery powered portable speaker thing as they are busy with something else, because they have to be "productive" or "efficient". I've lost count of the number of jaws that had to be picked off the floor after I make them sit down in my music room and tell them to shut it as I put on some music. "Just listen" I tell them and you can just see from the expression on their faces that they never heard music played through a proper hi-fi setup. Even music they thought they knew becomes something totally new to them, they're hearing things they never heard before.

I too feel old when they look at my music collection and they say "all of this is music?".

 

[great04]

Looks very good regardless of price. If you are going to need 2 of them, Just make sure to get separate power supplies. I heard they are bundling 2 of them with just one 48 V 10 AMP power supply( instead of 5 amp)which will probably defeat the benefits of the design of this product. Question, the XLR/TRS input is it really a Balanced input? Or just for purpose of more flexibility or amount of inputs?

What is the difference between separate 5A power supplies and on 10A supply? What is the design benefit you mentioned? Thanks

 

[TonyJZX]

the problem then is that there's a hole in the marketplace for a suitable priced preamp to match these units

the fact that people are out there searching and not finding much says it all

 

[Rafaille]

the problem then is that there's a hole in the marketplace for a suitable priced preamp to match these units

the fact that people are out there searching and not finding much says it all

Depends on what you call a preamp. If no phono stage is needed then pretty much any modern DAC with volume control will do. No hole in the marketplace there.

 

[Sokel]

the problem then is that there's a hole in the marketplace for a suitable priced preamp to match these units

the fact that people are out there searching and not finding much says it all

If we're talking about a preamp with a precise,motorized analog pot who can last a long time and not glitch and burn gear and ears the pot alone can go half the price of the mono's,just as a component.
Relay based ones relay heavily on the relay's quality,which is no cheap either for the nice ones.

And all the above without even putting them on the PCB,in a case with connectors,PSU,etc.
It's not going to be easy.

 

[Adrian Parker]

I'm glad to respond to all your concerns above.

1. V3 Mono employs a unique cooling design. We closely attach the amplifier chip's heatsink to the chassis, effectively turning the entire chassis into a radiator. Additionally, we have included vent holes on both sides of the chassis to enhance air circulation. Since the chassis serves as a radiator, its surface temperature may seem a bit high. However, this indicates that the heat from the TPA3255 amplifier chip is being effectively transferred to the chassis, allowing the V3 Mono to stably maintain high power output continuously. So, there is no need to worry.

2. We are currently resolving this issue. If it is not perfectly resolved, we will offer you the dual power supplies set instead.

3. The standard op-amp in V3 Mono is the NE5532, which is known for its ability to reproduce sound in a true and natural manner without altering the original timbre. If your DAC or preamp already has tone-tuning functions, there is no need to roll the op-amp. The design of replaceable op-amps is particularly favored by many DIY enthusiasts. Among our fans, many users opt for renowned op-amps like the Sparkos SS3602, Burson V7/V6/V5i, and MUSES02. They enjoy experimenting with different op-amps to experience various sound signatures, which they find quite intriguing.

4. Yes, you can add more sets if needed. Please leave a message for our team on Kickstarter, and my colleague will guide you on how to add them.

5. V3 Mono is designed as a power amplifier; hence, it is typically used in conjunction with a preamp. You can connect a subwoofer to the preamp to setup your system.

Thanks for the prompt updates. It is appreciated:.
1 Understood.
2 I would even be happy to pay difference for 10A power supplies if it means reduced heat, or have one of each of 5A and 10A. I am looking to bi-amp, and drive some very large 8Ohm speakers, and need all the power I can get-when needed. 10inch sub and 2.5 Mid + Tweeter
3 I am still confused over opamps. How many in each V3 amp, and how many needed if I use XLR? Also my Leema Pre amps do not have tone controls. Would this mean an opamp 'roll' would help?
Will Sparkos Pro fit? I know they are crazy expensive, but knowing if they fit is the question. Also are they suited to a power amp? Everything I have seen on the SS3602s has been great, so would be the obvious choice - but still expensive. Can other readers suggest best alternatives?
4 I have doubled* my order Which has also doubled postage, this cannot be right?
- *Do we get free T shirts for doing that? How nice would that be
5 OK. My preamp has no sub out , line or XLR - not sure both will work together, if they do then problem solved, gain differences can be solved by 'volume' controls on sub.
Pre release I did ask for V3 mono to have sub out - as stereo V3 does. Shame.

 

[EddNog]

Depends on what you call a preamp. If no phono stage is needed then pretty much any modern DAC with volume control will do. No hole in the marketplace there.

You say this, but the way some of these DACs is built, using the volume control is not practical. For example, I used to use an SMSL DO100 DAC and if I relied on the volume control in it, there was loud cracking noises from the speakers every time the sample rate changed from song to song. That makes using the DAC itself for volume control impractical in real use. The only way to eliminate or mitigate that problem was to turn down the volume at the amplifier, an option that is there with an integrated amp or a power amp with variable gain (like the GCC-100 I was using before) or volume attenuator (like the Fosi ZA3), but setting gain/volume down and using a much higher volume range/setting at the DAC, but with a power amp with no attenuator or variable gain control, you cannot avoid this on DACs with that sort of noise when changing sample rates.

-Ed

 

[EddNog]

Thanks for the prompt updates. It is appreciated:.
1 Understood.
2 I would even be happy to pay difference for 10A power supplies if it means reduced heat, or have one of each of 5A and 10A. I am looking to bi-amp, and drive some very large 8Ohm speakers, and need all the power I can get-when needed. 10inch sub and 2.5 Mid + Tweeter
3 I am still confused over opamps. How many in each V3 amp, and how many needed if I use XLR? Also my Leema Pre amps do not have tone controls. Would this mean an opamp 'roll' would help?
Will Sparkos Pro fit? I know they are crazy expensive, but knowing if they fit is the question. Also are they suited to a power amp? Everything I have seen on the SS3602s has been great, so would be the obvious choice - but still expensive. Can other readers suggest best alternatives?
4 I have doubled* my order Which has also doubled postage, this cannot be right?
- *Do we get free T shirts for doing that? How nice would that be
5 OK. My preamp has no sub out , line or XLR - not sure both will work together, if they do then problem solved, gain differences can be solved by 'volume' controls on sub.
Pre release I did ask for V3 mono to have sub out - as stereo V3 does. Shame.

Just in regards to the op-amps, there are three in each V3 Mono. One near the back does the job of converting RCA/single-ended input signals to balanced in order to function with the balanced architecture of the amplifier, so if you’re using XLR, that op-amp does not come into play. Towards the front of the amp, there are another pair of op-amps, and they both play into actual amplification, so if you’re going to roll for sound, you would play with those. Fosi told me they don’t need to match, and you can change just one if you wanted, and to feel free to experiment. Personally, I plan to stick to trying matching pairs there. As to spacing, it is hard to tell from images if the Sparkos SS3602 will fit there. The Burson V7s will fit, and that’s what I plan to run there. The one on the back for converting single-ended input to balanced does appear to have the room for the SS3602.

-Ed

 

[AndyLu]

Thanks for the prompt updates. It is appreciated:.
1 Understood.
2 I would even be happy to pay difference for 10A power supplies if it means reduced heat, or have one of each of 5A and 10A. I am looking to bi-amp, and drive some very large 8Ohm speakers, and need all the power I can get-when needed. 10inch sub and 2.5 Mid + Tweeter
3 I am still confused over opamps. How many in each V3 amp, and how many needed if I use XLR? Also my Leema Pre amps do not have tone controls. Would this mean an opamp 'roll' would help?
Will Sparkos Pro fit? I know they are crazy expensive, but knowing if they fit is the question. Also are they suited to a power amp? Everything I have seen on the SS3602s has been great, so would be the obvious choice - but still expensive. Can other readers suggest best alternatives?
4 I have doubled* my order Which has also doubled postage, this cannot be right?
- *Do we get free T shirts for doing that? How nice would that be
5 OK. My preamp has no sub out , line or XLR - not sure both will work together, if they do then problem solved, gain differences can be solved by 'volume' controls on sub.
Pre release I did ask for V3 mono to have sub out - as stereo V3 does. Shame.

About your point 5:
The V3 mono blocks are power amps. Power amps by definition only have speaker outputs and no dedicated sub outs. The stereo V3 you are talking about is an integrated amp (that means a pre-amp and a power amp in one box). Pre amps can have sub-outputs, hence the stereo V3 has them. Power amps are only meant for speakers. So even if you asked for sub-outs on the V3 mono blocks, that is not the place for them. To say that is a 'shame' is a bit misplaced because this is not something you can blame Fosi for. As far as I know there are no dedicated (without volume control) power amps on the market with dedicated outputs for subs. Of course there are subs (like Rell) which accept speaker outputs from power amps, but that is a whole other subject.

 

[TonyJZX]

Depends on what you call a preamp. If no phono stage is needed then pretty much any modern DAC with volume control will do. No hole in the marketplace there.

you put your trust in a 'modern dac'

you can have a famous topping moment

 

[Adrian Parker]

Re Opamp Rolling for V3. Reading the collective wisdom of my friendly AI assistant I would deduce that 95% of the impact of rolling am opamp would be tonal at XLR input (see below) and actually not worrying so much about over investing in output opamps :-


When it comes to Class D power amplifiers, there are some notable differences that can impact the relevance of changing opamps:

1. Efficiency and Design:
   • Class D amplifiers are known for their high efficiency. They use pulse-width modulation (PWM) to switch the output transistors rapidly between fully on and fully off states.
   • The output stage of a Class D amplifier primarily consists of power MOSFETs or IGBTs (Insulated Gate Bipolar Transistors).
   • Opamps play a minimal role in the output stage of Class D amplifiers. The primary focus is on the switching behavior and filtering.
2. Signal Processing and Feedback:
   • Class D amplifiers typically have a separate input stage (often analog) where opamps are used for signal processing.
   • Opamps in the input stage handle tasks like gain adjustment, filtering, and sometimes feedback.
   • Upgrading opamps in the input stage can influence the overall sound quality, especially in terms of clarity, tonal balance, and noise.
3. Output Filtering:
   • Class D amplifiers require output filters to convert the PWM signal back to an analog audio waveform.
   • These filters are often passive (inductors and capacitors) and play a crucial role in shaping the output signal.
   • Opamps are not directly involved in the output filtering process.
4. Noise and Distortion:
   • Opamps in the input stage can affect the noise floor and distortion levels.
   • However, the impact on the final output largely depends on the overall design and quality of components.
   • Class D amplifiers are inherently low-distortion due to their switching nature, but opamp choices can still matter.
5. Listening Tests:
   • As with any audio component, the best approach is to listen and compare.
   • Some audiophiles report subtle differences when changing opamps in Class D amplifiers, while others may not notice a significant change.
   • Factors like the rest of the audio chain, speakers, and personal preferences play a role.
6. Safety and Compatibility:
   • Ensure that any opamp replacements are compatible with the amplifier’s voltage requirements and pinout.
   • Follow safety precautions when modifying electronic equipment.

In summary, while the impact of opamp changes in Class D power amplifiers may be less pronounced than in pre-amplifiers, it’s still worth experimenting if you’re curious about fine-tuning your audio system. Remember that the overall design, output stage, and filtering matter significantly in Class D amplifiers.

 

[Adrian Parker]

About your point 5:
The V3 mono blocks are power amps. Power amps by definition only have speaker outputs and no dedicated sub outs. The stereo V3 you are talking about is an integrated amp (that means a pre-amp and a power amp in one box). Pre amps can have sub-outputs, hence the stereo V3 has them. Power amps are only meant for speakers. So even if you asked for sub-outs on the V3 mono blocks, that is not the place for them. To say that is a 'shame' is a bit misplaced because this is not something you can blame Fosi for. As far as I know there are no dedicated (without volume control) power amps on the market with dedicated outputs for subs. Of course there are subs (like Rell) which accept speaker outputs from power amps, but that is a whole other subject.

Good to know. FYI I make my case on the basis that my power amps all have line out - suitable for daisy chaining (bi amping), or subs.

 

[Dr. Noooooo]

You say this, but the way some of these DACs is built, using the volume control is not practical. For example, I used to use an SMSL DO100 DAC and if I relied on the volume control in it, there was loud cracking noises from the speakers every time the sample rate changed from song to song. That makes using the DAC itself for volume control impractical in real use. The only way to eliminate or mitigate that problem was to turn down the volume at the amplifier, an option that is there with an integrated amp or a power amp with variable gain (like the GCC-100 I was using before) or volume attenuator (like the Fosi ZA3), but setting gain/volume down and using a much higher volume range/setting at the DAC, but with a power amp with no attenuator or variable gain control, you cannot avoid this on DACs with that sort of noise when changing sample rates.

-Ed

To my understanding simplest “preamp“ can be just a passive attenuator / voltage divider, easy to DIY or maybe get some cheap assembled device from Aliexpress or alike. See for instance:

Simplest Passive Preamp design

Hi, I am looking for a simple pre amp/attenuator design to use between a DSP and power amp. DSP(MiniDSP HD) out put is 2V RMS and the amplifier is Adcom GFA 545 II. Purpose is to protect the amplifier and woofers as a second level of protection. Is it possible to do this using a passive...

www.diyaudio.com

Also vintage markets should have tons of cheap preamplifiers.

 

[AndyLu]

Good to know. FYI I make my case on the basis that my power amps all have line out - suitable for daisy chaining (bi amping), or subs.

I don't know what power amps you have, but in your case I assume that they are integrated amps and not pure power amps. If they have line out and/or sub out there is also some form of pre-amp built in (with or without a volume control). To add to the confusion a lot of manufacturers nowadays call their amps 'power amps' even if they basically are integrated amps (one example that springs to mind is Topping with it's PA* range of integrated amps where PA stands for Power Amp).

To avoid confusion: in the case of the Fosi V3 mono blocks: these are pure power amps without a built in pre-amp. So no volume control, no line out, no sub out. Only speaker out.

 

[EddNog]

To my understanding simplest “preamp“ can be just a passive attenuator / voltage divider, easy to DIY or maybe get some cheap assembled device from Aliexpress or alike. See for instance:

Simplest Passive Preamp design

Hi, I am looking for a simple pre amp/attenuator design to use between a DSP and power amp. DSP(MiniDSP HD) out put is 2V RMS and the amplifier is Adcom GFA 545 II. Purpose is to protect the amplifier and woofers as a second level of protection. Is it possible to do this using a passive...

www.diyaudio.com

This works too:

Amazon.com

-Ed