Fosi Audio Box X5 Phono Preamp Review

[Huey2001]

If such a brick outputs AC, i.e., alternating current, then it's never a power supply, but a simple transformer without any electronics.
Such a transformer is always wound for a specific voltage range and certainly never for 120 and 240 volts.
The exception is transformers with an additional switch, like those found on some devices. In these cases, two separate windings of the transformer are connected in series (220/240V) or in parallel (110/120V).

Of course, switching power supplies are often designed for wide voltage ranges, e.g., 90-265 volts, but never transformers.
I'm appalled that Fosi is giving out incorrect information on this.


The images in the shop are wrong if you mean the 16V/1A AC power supply for the BOX X5. You probably only ordered the replacement power supply.
And as mentioned above, it's not a power supply with direct current, but only a transformer that outputs alternating current.

Hm, that would be a shame. Also bad they show wrong picture: quite misleading…
Well, let’s wait first. Guess it can be returned if it is simply same replacement…

 

[Roland68]

Hm, that would be a shame. Also bad they show wrong picture: quite misleading…
Well, let’s wait first. Guess it can be returned if it is simply same replacement…

Or you can resell it; it also fits many Pro-Ject and other turntables with 16V AC.

 

[cfwotzka]

All manufacturers supply very basic transformers with these AC bricks.

Two points to note:
The hum could be caused by the transformer not being wound tightly enough and/or not being potted, i.e., normal 50/60 Hz mains hum. This shouldn't have any electrical effect, but it's definitely not a sign of quality.
The hum could also be caused by a DC component in the mains voltage, which you can measure. This can have a negative impact, but there are DC filters/blockers available. Please don't use expensive audio equipment; it only contains components costing a few euros.
And only use filters if there's actually a problem.

Of course, you can get a high-quality transformer, such as potted toroidal or R-core transformers, which don't hum under normal circumstances, but please only do this if you know what you're doing.

in the overwhelming majority of cases hum in a phone chain is due to grounding issues in my experience. my Box X5 has zero hum and acceptable hiss

 

[Roland68]

in the overwhelming majority of cases hum in a phone chain is due to grounding issues in my experience. my Box X5 has zero hum and acceptable hiss

I'm talking about the mechanical hum of the transformer and DC hum, which can have both mechanical and electrical effects. This has nothing to do with hum related to grounding problems.

 

[guy48065]

When it already measures so close to state of the art - what do you expect you will achieve with non engineered (suck it and see/ trial and error) "upgrades"?

My expectation : Nothing. Or an actual reduction in performance.

The PS in its current configuration is problematic. It's not unreasonable to assume it can be improved on.
Others in this topic have commented that it's unfortunate that cartridge loading is unknown and not adjustable. The improvement seen from proper cartridge loading is easily measured. Surely you're denying this?

 

[antcollinet]

The PS in its current configuration is problematic.

How? What evidence do you have of that?

 

[Roland68]

The PS in its current configuration is problematic. It's not unreasonable to assume it can be improved on.
Others in this topic have commented that it's unfortunate that cartridge loading is unknown and not adjustable. The improvement seen from proper cartridge loading is easily measured. Surely you're denying this?

What exactly do you mean, the external Brick, or the circuitry inside the Box X5?

 

[guy48065]

What exactly do you mean, the external Brick, or the circuitry inside the Box X5?

Two complaints being discussed...
In regards to the PS I'm referring to the discussions lately of the excessive hum from the basic AC transformer. And my personal bias here is that I would prefer AC to be kept as far away from high-gain amplifiers as possible.

In regards to the lack of adjustable cartridge loading--yes that should be an *internal* feature of a phono preamp.

 

[antcollinet]

And my personal bias here is that I would prefer AC to be kept as far away from high-gain amplifiers as possible.

That is all it is - a bias. It has no particular basis in any actual benefit, as evidenced by mains noise in this case being below -90dB - even with 38dB of gain.

Whereas here is a device a good 15dB worse than that - even thought it has an external DC supply.

Which demonstrates that what is important is overall good engineering - rather than what and where the power supply is.

iFi Zen Phono 3 Preamplifier Review

This is a review and detailed measurements of the iFi Zen Phono 3 phono stage and preamp. It is on kind loan from a member and costs US $224. The desktop design of iFi products has been "agricultural" as Brits would say. It is nice to see them refine it in Phono 3, bringing some elegance. I...

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Here is another DC power supply example - whose mains noise is a good 40dB (EDIT : 20dB (it is MC only so 20dB higher gain) worse than the x5 - and costs ten times as much.

Graham Slee Reflex C Review (phono stage)

This is a review and detailed measurements of the Graham Slee Reflex C phono preamplifier. It was kindly sent to me by a member and costs US $1,240 (695 pounds in UK). This is the first moving-coil-only phono stage I have tested. Usually they are either moving magnet only or both. The case...

www.audiosciencereview.com

Oh, and the best SINAD phono pre measured here (Cambridge Audio Solo) has mains going directly into the device - which means even the mains transformer is inside the box with the electronics. Again - good engineering is key - not where the power supply (or even the transformer) is.

 

[jdjung]

I came a bit late to reading all the comments here. I don't have the Fosi X5 but was considering it as I have my phono outputs going to my RME UCX II at +13 in Total Mix. I currently have a Cambridge Audio Duo as my phono preamp and was thinking of the Fosi X5. Does anyone know the capacitance of the inputs? The Duos is 100pF and after going through some cheapy interconnects I found one with 320-340pF so the resonance peak is to Shures spec.

Oh, I have a Technics SL-M3 recapped, lubed up and fully services two years ago with a Custom Shop Jico Shure V15 III on a 192-VN35 HE needle which I believe Shure recommends between 400-500pf. Using my multimeter to measure my cable internal pf at its length measures 320-340pf plus the 100pF of the Cambridge is 420-440pf. If the X5 input capacitance is the same as my Cambridge I'm all set and I can set a low rumble filter at the UCX II. I guess I can remeasure all my RCA to match the Fosi if I have to.

Don't know if this is worth it though, I would like the higher headroom for pops and clicks if and this is an if it's comparable to how Amir tested the Duo in the past.

 

[guy48065]

What does Amir say the X5 input R & C measured?

 

[jdjung]

What does Amir say the X5 input R & C measured?

I don't think he does? I know it's important to fine tune where you want your resonance peak is going to be, and shifts the turntable sounding more warm or bright depending on this. I think it's an important figure to know so you can match your RCA's and Tonearms pf based on the cartridge used. This does make an audible, and measurable difference, but imho very difficult to really evaluate/rank a phono preamp, as it would be very time consuming and confusing to test the pf of all devices, and RCA cables pf changes by length (pf raises as you add length). Headroom at the inputs though is very good to know for those pops and clicks, the higher the better! I suppose if you used a specific cartridge and needle as a reference dummy load? But that would still vary based on the needle and cartridge used by the end user. Turntables are complicated, which is why I went with a quartz linear turntable with a service center to keep it tip top, so I don't have to mess with skid, needle weight, needle pressure being to much to the right blah, blah, blah.

Also you need to know how to measure the pF of your cables, which is easy with a multimeter, just put the red tip (I use alligator clips) to the post, and the negative to the outer ring without it being connected to anything. Dead simple. Add an additional 30-50pf from the tone arm and find the pF requirements of the cartridge you're using. If you want it brighter, then try for less pf then suggested and vice versa for a warmer tone.

 

[jdjung]

The more I think about it, a lower pF at the inputs of the phono preamp may be better, as it gives you more headroom to add pF. It's easier to add pF then take it away so a phono preamp with a very low pF would generally be better?

 

[LTig]

The more I think about it, a lower pF at the inputs of the phono preamp may be better, as it gives you more headroom to add pF. It's easier to add pF then take it away so a phono preamp with a very low pF would generally be better?

Yep.

 

[guy48065]

It's a basic measurement in any head amp review. Maybe he figured you can't change it so why report it?

 

[orangetang]

Thanks for this review. I've been trying to figure out why a cheap AT-LP60 sounds so much better (using its line out from internal phono stage), vs a much nicer table and cartridge through an Onkyo receiver.... The X5 has my old Technics sounding great. I honestly doubted a phono stage would make such a difference, but it's clear now this is about the first place to start.

 

[Huey2001]

Once you receive it, please post your idea and a picture ? Mine did vibrate enough to make it move ! They sent exactly the same one as a replacement. It also hums but less.

Grrr. Unfortunately just an exact replacement… Quite disappointing.

Will get in touch with Fosi to return it…

 

[Heinrich]

Couldn't resist the 'black friday' offer and bought the X5 for 95€ all included.
The power supply defaults to match EU standards, and so works flawlessly. It doesn't buzz at all.
When checking for performance I (again) was shocked how bad the vinyl record actually measures. Maybe the disc is already worn out, but boy! It distorts as if there were no tomorrow, channel separation is a joke, and wow/flutter, as seen in the side skirts of a single tone is hilarious with a real, only slightly warped specimen. Love my ol' collection anyway ;-) It feels grounding to mentally move past all the flaws for the sake of the musical message.

My main concern was the noise in regard to opamp choice for MM. If it were a real thing I wouldn't stand that lapse of jufgement as a crack in technical aesthetics. Don't want to resurrect previous discussions! Only that I discovered, that my Grado MM is an MI (moving iron) actually, and as such won't be affected as much by a) current noise of the opa 1612(?) and b) self noise of the generator. The alternative is a Denon DL103--you see, tech/ junky me. That made the X5 a practical choice.

I measured. I have data. Data wasn't provided in the before mentioned discussion, which I think is odd. Teaser: the well suited MI, that the Gradeo Green is, degraded, when compared to a gounded input, the SINAD by about 9dB. The comparsion to a quite standard AT pickup, an MM, is pending due to the effort. What would be a proper questionaire, leaving the muddy grounds of thrown-in anecdotal numbers? What I cannot do w/ the X5 alone is to separate the adverse effect of current noise from the inavoidable thermal selfnoise(!!) of the source. Simulation is at hand (LTSpice). We need something that convinces on first glance.

Love my musical box ;-)

 

[psemeraro]

Vinyl records often sound better because they are simply better mastered.

Yes.

It's fascinating looking at the waveforms in Pro Tools or other audio editor. The peak to average variation was typically 15dB and sometimes as much as 20dB for pop music (60s and 70s) and a bit less than that in later decades but still plenty of room to "breathe". CD versions of the exact same album would often show 6dB - 10dB of dynamics literally chopped right off, then the track would be normalized back up to digital zero to make it LOUDER. When mastering mixed content in my theme park work, to get a consistent perceived volume, everything ends up getting adjusted around the average level. Once that process was completed you could see the normal looking waveforms from vinyl vs the digital tracks with the dynamics completely missing, like they were chopped off with scissors. Not every CD of course but quite a few regular CD's showed this and nearly all of the "remastered" CDs showed the chopped waveforms. And many of the remastered CD's also had boosted lows and highs which would have to be undone as well.

To an onlooker it might have seemed crazy to capture vinyl in real time vs 20 seconds to "rip" a CD track but for more tracks than I expected it was easier to work with the original version from vinyl with the full dynamics vs trying to "undo" the CD mastering. Jazz and acoustic type artists showed less of this but anything "pop" was Pandora's box.

Cheers,
Pat

 

[guy48065]

... you could see the normal looking waveforms from vinyl vs the digital tracks with the dynamics completely missing, like they were chopped off with scissors...

Loudness Wars: High & Tight!

What a travesty!

My digital library has several dubs from vinyl. Some were not available in digital format but many just sounded better from the original vinyl. Yes there's some quiet hiss if you crank it up--but I find it easy to "hear thru" that surface noise to the magic behind it.