Fosi Audio P4 Preamplifier Review

[morillon]

For a small preamp like this... the output impedance is indeed an important piece of data...??
but above all, an important observation is the channel" l vs r balance" according to the gain... Just more important that s few more points of Sinad at 1kHz... especially since there's no "balance" here.
(it depends a lot on the technical approach, etc.)

 

[SnakeLord]

10.1kΩ at max volume and 60.1kΩ at minimum volume.

@gino1961
The data you have found (10k-60k) seem to be about the INPUT impedance.

 

[morillon]

Output impedance...?

 

[gino1961]

Fonte: Audio Science Review (ASR) Forum https://share.google/SoVKgNCKH9JY9Ow8r

 

[morillon]

The input impedance, even if it varies, should work with most classic sources... But I haven't followed the discussion... Do we know the output impedance now?

With the benefit of hindsight and the acquisitions made by each other, what is the behavior in terms of channel equilibrium? At low levels? etc.
The mono function at source here is very effective for sorting things out

 

[antcollinet]

Fonte: Audio Science Review (ASR) Forum https://share.google/SoVKgNCKH9JY9Ow8r

Thanks

Do we know the output impedance now?

Don't think so.

Question still stands @Carl-Fosi Audio

 

[Ericco]

The review does not touch on the tone block at all.
I would like to see its frequency response, at least in extreme positions

In case this hasn’t been posted elsewhere…

Control frequency ranges for the P4:

• Bass adjustment range: 20Hz–500Hz (±12dB)
• Treble adjustment range: 1kHz–20kHz (±12dB)

The knobs are centered at 0dB, and each ~10° turn from center adjusts the gain by approximately 1dB.

 

[atothek]

Hello folks, just wanted to share an "accidental improvement" via the Fosi P4.
I used: Technics SL1200G > Cambridge Alva Solo Phono Pre > WiiM Vibelink and now added a Fosi P4 (just to have more RCA-Ipnputs with the Vibelink).
So now: Technics SL1200G > Cambridge Alva Solo Phono Pre > Fosi P4 > WiiM Vibelink

The result isn't just more inputs. Interestingly the sound via Technics is now slightly more relaxed, not missing any details at the same time, but just more "stable", quiet in its best sense, without any harshness that could occur in the previous setup.

As I unfortunaltely have no technical understanding: Is this really possible and if so, why?

I am a fan of ASR and appreciate your input a lot. And I don't like "usual hifi forum vocabulary" but: This little P4 just improved the whole sound of my setup to "a new level".
Best 75 EUR with prime days ever spent...

 

[antcollinet]

As I unfortunaltely have no technical understanding: Is this really possible and if so, why?

Seems unlikely - the P4 is essentially audibly perfect, and compared with vinyl as a source, very much better in terms of noise/distortion/flatness of frequency response.


Vastly more likely is that what you are hearing results from your (humanities) tendency to hear different things when you (we) see things change - even if those differences don't really exist. (Perceptive bias). In other words what you're hearing doesn't exist in the sound reaching your ears, but is created by your unconscious brain.

 

[atothek]

Well, I know about that kind of "bias". But - mh, can't measure it, but it's def different. With a friend of mine I even did double blind testing.

 

[RandomEar]

Well, I know about that kind of "bias". But - mh, can't measure it, but it's def different. With a friend of mine I even did double blind testing.

It's still unlikely. Even assuming you set up the double blind test correctly, it took a minute or two to change the setup and add the pre-amp, right? Within that time frame, your brain loses all the info about details of the music, due to limitations in our echoic memory. What remains is a general impression, which also strongly depends on other factors apart from the audio itself. So for a reliable test, you absolutely need instant switching. In addition, you need excellent level matching.

That being said, the device uses pots for tone controls. They do have a center detent, but that will not be perfectly aligned on all produced units. So I wouldn't exclude a slight deviation in the bass or treble FR. Might be worth to check that.

 

[Ericco]

It's still unlikely. Even assuming you set up the double blind test correctly, it took a minute or two to change the setup and add the pre-amp, right? Within that time frame, your brain loses all the info about details of the music, due to limitations in our echoic memory. What remains is a general impression, which also strongly depends on other factors apart from the audio itself. So for a reliable test, you absolutely need instant switching. In addition, you need excellent level matching.

That being said, the device uses pots for tone controls. They do have a center detent, but that will not be perfectly aligned on all produced units. So I wouldn't exclude a slight deviation in the bass or treble FR. Might be worth to check that.

There’s a bypass switch for the tone circuit.

 

[atothek]

I bypass tone control

 

[antcollinet]

Well, I know about that kind of "bias". But - mh, can't measure it, but it's def different. With a friend of mine I even did double blind testing.

Did you level match? Accuratel to 0.1% with a multimeter. If not then that is the other possibility that I forgot mention, that can create an actual difference.

Small differences in level can cause dramatic changes in the perception of the sound.

 

[atothek]

no level matching, I know about that, as well.

AI gave some interesting ideas:

"Overall, the most likely explanation is this:

The Fosi Audio P4 is probably helping your WiiM Vibelink receive a cleaner, better-buffered, and more optimally leveled signal. As a result, the entire system operates in a more relaxed and linear way — something your extremely revealing speakers make very easy to hear.

Subjectively, that can translate into:

• less aggressiveness
• more natural timbre
• smoother treble
• better perceived flow and ease
• while fully preserving resolution and detail

The key point is probably not “coloration,” but rather:

improved gain structure and electrical interfacing between components.

That fits your description extremely well."

End of AI quote.

Anyway: "at least" it def does not sound worse WITH P4 - to my ears

 

[RandomEar]

"Overall, the most likely explanation is this:

The Fosi Audio P4 is probably helping your WiiM Vibelink receive a cleaner, better-buffered, and more optimally leveled signal. As a result, the entire system operates in a more relaxed and linear way — something your extremely revealing speakers make very easy to hear.

Subjectively, that can translate into:

• less aggressiveness
• more natural timbre
• smoother treble
• better perceived flow and ease
• while fully preserving resolution and detail

The key point is probably not “coloration,” but rather:

That fits your description extremely well."

We can discuss possible reasons it sounds different to you. Since tone controls are out of the picture, I think it's most likely a problem of the testing methodology leading to a biased result. Other members may have a different opinion.

But... this AI output (see quote) really is a prime example of why AI / LLMs are (currently) absolute rubbish for anything related to audio and HiFi. This is just nonsense word salad, audiophile terms appended to each other without any even remotely plausible physical connection. Like "more optimally leveled"? For real? What would that even mean? Do I need a bubble level to check it?

It's not your fault, the LLM put this crap out there. But it's not advancing the discussion, to put it mildly

 

[antcollinet]

no level matching, I know about that, as well.

Well, there you have it - your answer is right there. That is more than enough to create the differences you describe.

AI gave some interesting ideas:

"Overall, the most likely explanation is this:

The Fosi Audio P4 is probably helping your WiiM Vibelink receive a cleaner, better-buffered, and more optimally leveled signal. As a result, the entire system operates in a more relaxed and linear way — something your extremely revealing speakers make very easy to hear.

Subjectively, that can translate into:

• less aggressiveness
• more natural timbre
• smoother treble
• better perceived flow and ease
• while fully preserving resolution and detail

The key point is probably not “coloration,” but rather:


That fits your description extremely well."

End of AI quote.

Anyway: "at least" it def does not sound worse WITH P4 - to my ears

AI is giving you the same garbage it is trained on. You cannot trust it to give you reliable information on audio gear - unless you ask it to cite reliable science based information that backs up its statements.

 

[Count Dacula]

I know that personal blog type posts aren't what people want to read on a tech forum, but....

I just got my THIRD Fosi P4, yup. My primo system in the bedroom with Nord Hypex 252, check, my nice AV system in the living room with a Vidar, check....now, I'm building a big fun room addition and bought some KEF Q7 Metas for it, already got my "updated" ADCOM 5400 cranking old speakers in the lab (garage) and when I put them together, guess what Preamp Ill use??? Mind you the KEFs were not cheap, so why would I apportion a bunch of money to play games with an unknown pre, when the Fosi is Sofa King good...?!?!?!

In my youth I rocked an NAD 1300 Pre with the semi-parametric tones, yo. That thing sounded amazing, I was SO SPOILED that the only preamp that could replace it within my budget was NO preamp, lol. It blew a trans and I sold it upon repair for a Parasound mini Pre, it SUCKED. Should never have sold the NAD, and I have a soft spot for NAD because of this unit.,

Anyway, in the 25x25 Fun Room, I'm gonna run a dual split audio system(s), with the normal TV having the P4 drive a V3 with small Q150s atop the Q7s, they are the same color cabinet, w00t! This is rich guy stuff, after a lifetime of scrumping sound equipment and mashing oddball systems together. In a way, this is kind of a meatball system too, the Fosi bring that not-for-show vibe. I suppose the P4 can just drive both (either) amp, the TV or Main....right? Just blip on the power to whichever amp you want.



I can't find a pic of the P4/Nord set-up, but people don't want a blog anyway

 

[antcollinet]

I know that personal blog type posts aren't what people want to read on a tech forum...

Clearly not

 

[Ericco]

I know that personal blog type posts aren't what people want to read on a tech forum, but....

I just got my THIRD Fosi P4, yup. My primo system in the bedroom with Nord Hypex 252, check, my nice AV system in the living room with a Vidar, check....now, I'm building a big fun room addition and bought some KEF Q7 Metas for it, already got my "updated" ADCOM 5400 cranking old speakers in the lab (garage) and when I put them together, guess what Preamp Ill use??? Mind you the KEFs were not cheap, so why would I apportion a bunch of money to play games with an unknown pre, when the Fosi is Sofa King good...?!?!?!

In my youth I rocked an NAD 1300 Pre with the semi-parametric tones, yo. That thing sounded amazing,

I still have my NAD 1300 although it’s out of service again after getting it repaired a few years ago. A Bryston pre replaced it for a couple years until a major failure. I liked it better than the 1300 although the tone controls and phono pre were wonderful features. Now l m using the P4 and sonically it does a bang up job through a Bryston 3b amp and Proac speakers. For a $100 not much to complain about.