Fosi Audio Box X5 Phono Preamp Review

[amirm]

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.

 

[sapphari]

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.

 

[SIY]

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.

 

[AudioSceptic]

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.

 

[early rejecter]

Looks like a nice little unit, especially given the price, but does anyone else find the placement of the grounding post somewhat odd?

 

[renaudrenaud]

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.

 

[amirm]

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.

 

[Wiredforsound]

Could Fosi please inform us on its loading specifications.
For future generations. Smiling emoji

Above video states impedance MM 47k ohms

Capacitive?

 

[early rejecter]

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.

 

[antcollinet]

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.

 

[restorer-john]

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.

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.

 

[JeremyFife]

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 .

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.

 

[restorer-john]

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.

 

[cfwotzka]

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...

 

[antcollinet]

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.

 

[cfwotzka]

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

 

[morillon]

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?
;-)

 

[Raticosa]

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.

 

[morillon]

already said...
but if fosi adopted a low capacitance between 0 and 100 pico*... will eventually remain manageable..
we will see if they intelligently ( cap and lf filter) enrich their future "x6"**
;-)
* examp styro or mica solder in rca inside ;-)
**moreover, this type of adjustment is often found on the internal strap or dip requiring opening, could be an approach for the "x6" without so many "physical" modifications ;-)

waiting ;-))

 

[DSJR]

Only read the first two pages so far, but I'm still cautious as regards hf overload margine, bearing in mind cheaper pickups tend to have hf peaks still, rather than deep suckouts as in pre-digital days... A 3 or 6dB peak at 10 - 15k isn't uncommon and this may well eat away at hf overload margins - perhaps?

Still, phenominally cheap and with MC input too.

I'd also suggest a mandatory lf filter below 15 - 20Hz though, as this thing will usually be used with cheaper turntables and not necessarily set up or sited properly (so many pictures I see of modern vinyl systems often set up as a shrine to 'audio' make the little remaining career audio-dealer in me cringe I'm afraid...