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Fosi Audio V3 Mono Amplifier Review

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 7 1.4%
  • 2. Not terrible (postman panther)

    Votes: 12 2.4%
  • 3. Fine (happy panther)

    Votes: 100 20.0%
  • 4. Great (golfing panther)

    Votes: 382 76.2%

  • Total voters
    501

TonyJZX

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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

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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

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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

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Feb 19, 2024
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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:


Also vintage markets should have tons of cheap preamplifiers.
 

AndyLu

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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.
 
Last edited:

EddNog

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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:

This works too:

-Ed
 

Sean B

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Apr 18, 2024
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Anyone looking for a good budget pre amp for these monos I can recommend this for a few reasons, but xlr, a nice phono in with a remote and compact form factor are worth a mention. Oh, sub out and Bluetooth too!

I’ve been running a pair of ZA3’s from it and all I can say is they’re a match.
 

Bleib

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Anyone looking for a good budget pre amp for these monos I can recommend this for a few reasons, but xlr, a nice phono in with a remote and compact form factor are worth a mention. Oh, sub out and Bluetooth too!

I’ve been running a pair of ZA3’s from it and all I can say is they’re a match.
Wait, no XLR input?
 

TonyJZX

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ironically they make a matching dac with xlr out...
 

DavidM1

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Feb 7, 2023
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Well done Fosi for responding so quickly and effectively to the issue that arrived on the first day of the launch. I imagine there were a few tense moments at Fosi and also some nervousness from those who’d registered for 10A supplies.

A benefit of Kickstarter product launches is that it’s not too late to save the day when a problem comes up. No customers have actually been charged and products haven’t shipped. I’m glad to see Fosi’s proposed solution and the speed at which it arrived.
 

Cal_Cobra

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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.
A pair of VU meters, complete with the driver board costs all of $5 USD on AE. The wholesale cost of goods is even cheaper, so the cost to add VU meters seems insignificant.
 

Cal_Cobra

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I want the Op amp.
Same here, and I think we'll get it, it's been what 24 hours since the Kick Starter campaign opened and it's already funded to $210K out of the $300K

I just hope they include a pair of opamps per mono block.

Do you get all the tool kit, cables and opamps if it hits $300K?
 

TonyJZX

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A pair of VU meters, complete with the driver board costs all of $5 USD on AE. The wholesale cost of goods is even cheaper, so the cost to add VU meters seems insignificant.
they suddenly added the MC101 that no one asked for so i reckon they could add VUs and trim knobs on the next one

 

Kimbrough Xu

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Same here, and I think we'll get it, it's been what 24 hours since the Kick Starter campaign opened and it's already funded to $210K out of the $300K

I just hope they include a pair of opamps per mono block.

Do you get all the tool kit, cables and opamps if it hits $300K?
Just one pcs, if it hits $300K, we will get all the 3 according to the campaign.
 
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