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Fosi Audio Box X5 Phono Preamp Review

Rate this phono stage:

  • 1. Poor (headless panther)

    Votes: 4 2.0%
  • 2. Not terrible (postman panther)

    Votes: 8 4.0%
  • 3. Fine (happy panther)

    Votes: 35 17.5%
  • 4. Great (golfing panther)

    Votes: 153 76.5%

  • Total voters
    200
Very nice work. Credit where credit's due in spite of competition!

I'm guessing from my own experiments with similar results that this is based on an NJM4580 front end.
In this video, the board is seen as of about 13:15, on for the next 4 minutes. There's an NE5532 (socketed)*, and also elsewhere, two surface-mount OPA 1612s. Looks like a single-side board and there doesn't seem to be any other op-amp.


*Someplace on the site for the X5, Fosi states: "Replace with DIP8 dual discrete op-amps, meeting your pursuit of a personalized audio experience."
 
It's a simple 'how to'. Not really documentation.

You know, I think it's funny that we have a phono stage being judged on its superior SINAD, which you're extremely unlikely to get to hear because the surface noise from any record is going to absolutely bury the noise from the preamp. This preamp has really really low noise, which is great, but it lacks important features such as variable loading for MC cartridges and any useful documentation that would be helpful for cartidge-tonearm-cable matching.

Phonograph playback is an electro-mechanical system. The final quality of that playback system is going to be far more dependent on the cartridge-tonearm-turntable performance than on the performance of the phono correction/preamplifier stage. Unless there is something horribly wrong with the phono stage in use, I seriously doubt anyone with a U-Turn Orbit turntable is going to hear the difference between its built in phono stage and this Fosi Audio wonder preamp.

Had Fosi included capacitance and impedance loading options, I would think differently. Since phono cartridges definitely sound different into different C and Z loads, that would have made the product more useful and widely compatible.

Grado carts sound very good into 10k ohm load.

AT carts do not like high capacitance loads. 250pF max, I'd say, and that would include the roughly 150pF to 200pF from the tonearm wiring and turntable to preamp interconnect cable.

Vintage Shure, Stanton and Pickering MM cartridges tend to be higher in coil inductance (L) and internal series resistance (Rseries) and are supposed to work better into higher C loading. Some say they sound better into a higher than 47k load at the preamp input.

The Denon DL110 HOMC cartridge works well into as low as 1.5k ohms (its Zout is only 150R or so). It sounds more harsh and brittle into the standard 47k ohm load. More pleasant (to my ears, at least) into 1500 ohms.

The Denon DL103 MC cart works best into about 400 ohms (its Zout is about 40 ohms). However, many more expensive MC carts have Zout of 10 ohms or less, and those work well into a smaller 100 ohm load.

Unlike digital sources, there is no standard for C, L or Z in phono preamps, other than the 47k ohm input loading for MM carts. There's no standard at all for MC carts.

Anyway, it's fun to kibbitz about audio gear.
These are great points ...

If Fosi can produce such a low noise phono pre-amp then maybe they can really disrupt with the many fundamental features you mention both for MM and MC, and more ...

Low bass cut off is essential in my book < 20hz, and it gets far harder with higher gain for MC... etc.

They got good headroom too ... but too much gets lost in the great SINAD headline when you think about it further as you have.

And before everyone gets carried there are great boxes with subsonic filtering and mono switches for not much more price wise.
 
There is absolutely no excuse to not provide the data as it is available anyway and making a PDF document takes no more than maybe one hour of work (less if you have templates to build on). If the data isn't available in house, all bets are off.
This site wouldn't exist if people did what you are asking. Today, specs are reduced to just physical dimensions on some audio products! Yes, a few still provide detailed specs but even those lack the sweeps and such. So you better not put this at the feet of Fosi much less for such a low cost device. The data you want is provided in the review and if not, you are welcome to get one and produce the rest.
 
I'm with you on this one KSTR. It's on the manufacturer to post basic specs on their products so that the products can be applied appropriately. This site should still exist even if they all did, because independent verification is still valuable. I'm surprised to see the manufacturer defended in this situation.
 
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Measurement of load for MM (particularly) is needed. Ditto noise with an actual cartridge attached for reasons I posted about (and provided data for) a couple years ago.

For the S/N freaks out there, remember that, putting aside mechanical issues, cartridges have Johnson noise, and at higher frequencies where the inductance becomes a significant part of the source impedance, there's increased Johnson noise from the input resistance. Again, I've posted data showing this.

edit: Here's an example of the rise in noise in the upper octaves that is NOT captured using Amir's testing regime.
1736812536959.png
 
Won't most of the result there be dependent on the quality of the test record, on the deck, and on the cartridge. Far more so than the phono pre
Yes, Milosz said
I STILL want to see measurements of actual vinyl playback. I WANT TO KNOW THE ACTUAL PLAYBACK SINAD from a test disc!
and I expect this will swamp the performance of any phono preamp. Of course, you could be unlucky and FR deviations might add, for instance.
 
Looks like a nice little unit, especially given the price, but does anyone else find the placement of the grounding post somewhat odd?
 
Looks like a nice little unit, especially given the price, but does anyone else find the placement of the grounding post somewhat odd?
Agree with you but it is probably just a question of priority: performances, price then add what you want.

If the priority is to have the grounding post near the RCA I am pretty sure you will find more expensive and less performant phono preamp. As a compromise, in my system of values, This unit is on the top list.

I am pretty sure Fosi will produce some X6 or X7 sooner or later and it will be a better compromise.
 
Looks like a nice little unit, especially given the price, but does anyone else find the placement of the grounding post somewhat odd?
It is right next to negative power supply connection so electrically, it is in the right place.
 
Could Fosi please inform us on its loading specifications.
For future generations. Smiling emoji

Above video states impedance MM 47k ohms

Capacitive?
 
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It is right next to negative power supply connection so electrically, it is in the right place.
In that case perhaps a better question would’ve been whether the placement of the RCA inputs is somewhat odd? Not a big deal of course, and certainly wouldn’t prevent me from buying one, just have never come across an arrangement quite like that.
 
Yes, Milosz said

and I expect this will swamp the performance of any phono preamp. Of course, you could be unlucky and FR deviations might add, for instance.
So not much point in repeating that test with every preamp, since it tells you nothing about the performance of that preamp in general. The results are either simply dominated by the upstream components, or it shows a variance that only applies with those particular upstream components and their setup, and doesn't tell you anything about the general performance of the preamp.
 
Looks like a nice little unit, especially given the price, but does anyone else find the placement of the grounding post somewhat odd?

Absolutely it is a bit odd, however, they have simply run a flying lead from the GND to the rear panel in probably the easiest place to put it.

1736843465274.png


It is right next to negative power supply connection so electrically, it is in the right place.

Got nothing to do with it. It's an AC supply remember.
 
Hello ASR community !

My friends gift me a audio-technica at-lp60x, my first turntable ! Is this pre-amplifier a good investiment from the internal pre-amp from my turntable ?

Sorry my english is not perfect :D.
Hi, that's a nice gift, enjoy.

It's not likely that an external phono stage will be a big improvement though, I wouldn't spend money there first.

Improvements to your sound will come from your speakers, or adjusting your speakers in your room.

Do you have other sources of music? If not, something like the WiiM Mini streamer is a very good idea - cheaper than the Fosi and gives a great alternative to vinyl.

Open a new thread if you want to explore this more.
 
In that case perhaps a better question would’ve been whether the placement of the RCA inputs is somewhat odd?

The thing is tiny. Just enough room to do what they have done. And they seem to have done a good job. I have no complaints about the look of the build. A whole lot of regulation and more regulation all because they started with half wave rectification and an AC plugpack, but there's good reasons for that in terms of cost.
 
So not much point in repeating that test with every preamp, since it tells you nothing about the performance of that preamp in general. The results are either simply dominated by the upstream components, or it shows a variance that only applies with those particular upstream components and their setup, and doesn't tell you anything about the general performance of the preamp.
I consider your comment to be something said in general and not particular dedicated to the Box X5 discussed here...
 
I consider your comment to be something said in general and not particular dedicated to the Box X5 discussed here...
Thanks for your observation, though I am not sure what your purpose was in making it.

It relates to the Box X5 in that someone requested those tests for this product. My reply is to point out why that makes no sense. Specifically for this product. As you rightly point out it also applies for any other.
 
Thanks for your observation, though I am not sure what your purpose was in making it.

It relates to the Box X5 in that someone requested those tests for this product. My reply is to point out why that makes no sense. Specifically for this product. As you rightly point out it also applies for any other.
Sorry, but perhaps only now I understand your comment and fully share your opinion
 
Measurement of load for MM (particularly) is needed. Ditto noise with an actual cartridge attached for reasons I posted about (and provided data for) a couple years ago.

For the S/N freaks out there, remember that, putting aside mechanical issues, cartridges have Johnson noise, and at higher frequencies where the inductance becomes a significant part of the source impedance, there's increased Johnson noise from the input resistance. Again, I've posted data showing this.

edit: Here's an example of the rise in noise in the upper octaves that is NOT captured using Amir's testing regime.
View attachment 420882
Which generator should be adopted and adapted then?
;-)
 
Great performance at a cheap price.. but as someone already said, the input capacitance, for both MM and MC cartridges, is as much as important as the input resistance... as an example, I replaced the input capacitance (220pF) of my Marantz PM 6007 phono input board with some smaller 47pF because the original 220pF, in addition to another 100pF of the (good) RCA cable, made an annoying magnification of the high frequencies around 12/13kHz (frequency response verified with two different LP test vinyl with frequency sweep and pink noise), now the frequency response is almost flat.

In conclusion: the best "cheap" phono preamps (as the Schiit Mani 2) have the possibility to change the input capacitance to adapt the frequency response to your cartridge output impedance. I would never buy this phono preamp because of missing specs about its input impedance.
 
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