Fosi Audio Box X5 Phono Preamp Review

[lini]

If we default the capacitance to 0pF and have 4 levels of adjustment, with the first level being+50, the second level being+50, the third level being+50, and the fourth level being+50, then you can get five levels of adjustment: 0/50/100/150/200pF. What do you think?

Actually, if you'd you'd like to implement switchable input capacitance, a smart way would be to use for example a 4x DIP switch and four capacitors per channel in parallel configuration, with the capacitor values doubling from one value to the next. That way you can go in lowest cap value steps from from zero extra capacitance to the highest sum value (= all four caps active in parallel). For example, if you'd choose 25 pF, 50 pF, 100 pF and 200 pF, you could go in 25 pF steps from 0 pF to 375 pF - or in case of 50 pF, 100 pF, 200 pF and 400 pF in 50 pF steps from 0 pF to 750 pF.

Greetings from Munich!

Manfred / lini

 

[Deepinton]

Sorry if this is covered elsewhere, but has anyone tried using the US adapter that says 110v with a 220v supply? Some of these adapters can handle multiple voltages and I am kinda hoping that Fosi just failed to put that on their adapter

 

[Deepinton]

Well, I emailed Fosi tech support and got a response back within 2 minutes. Yes, it does work with 110 or 240v.

 

[LTig]

Well, I emailed Fosi tech support and got a response back within 2 minutes. Yes, it does work with 110 or 240v.

That should be stated on the adapter! I'd be careful before using it at 220V - connect on its own and measure the output voltage with a simple multimeter, just to make sure it's not to high.

 

[Deepinton]

That should be stated on the adapter! I'd be careful before using it at 220V - connect on its own and measure the output voltage with a simple multimeter, just to make sure it's not to high.

The adapter states 110v only. I would presume the Fosi tech support folks know their stuff. But yes, a voltage test is a simple enough procedure to be absolutely sure.

 

[tiagosv]

Is there a thread or an official way to request a review on a phono stage?
I'd love to see how the built-in Technics SL1500C's phono stage performs. A few people's subjective opinion is that it performs admirably well and is quiet enough to be on par with a lot of budget phono stages but it would be very interesting to see objective data to see if this is actually the case and how much you'd need to spend on a separate phono stage to have a significantly better performance.

 

[Laika2]

Is there a thread or an official way to request a review on a phono stage?
I'd love to see how the built-in Technics SL1500C's phono stage performs. A few people's subjective opinion is that it performs admirably well and is quiet enough to be on par with a lot of budget phono stages but it would be very interesting to see objective data to see if this is actually the case and how much you'd need to spend on a separate phono stage to have a significantly better performance.

Most of the time members submit equipment for review.

 

[lini]

Well, I emailed Fosi tech support and got a response back within 2 minutes. Yes, it does work with 110 or 240v.

You'd better not believe that. Shall mean, as the back side of the X5 clearly says "AC 16 V", it's most likely, that it'll definitely require incoming AC to internally create a symmetrical supply voltage (like for example +/- 15 V, i.e. one +15 V and one -15 V rail relative to ground) via two voltage regulator ICs - which in turn makes it most likely, that the external power supply is a very simple, conventional, transformer-based model, which most likely contains nothing but a transformer plus thermal fuse. And unlike modern switched-mode DC power supplies such simple, conventional AC power supply models typically aren't multi-range. So unless you'd find a switch on the thingy for switching between ~ 115 V(AC) and ~ 230 V(AC) operation, I'd strongly suggest you not to try a model for ~ 115V(AC) at ~ 230 V(AC).

Greetings from Munich!

Manfred / lini

 

[nagster]

I measured the output voltage of the AC/AC adaptor that comes with the Fosi Box X5. No load.

Input 　: 　Output
096.0V : 14.99V
108.1V : 16.86V
120.1V : 18.72V
132.1V : 20.57V


Edited and added images:
It seems there was no need to measure. There was a screw on the back of the adapter.

 

[LTig]

My advice then: never ever connect this power supply to more than 120V mains. It will fry the amp. @lini was right on the spot.

 

[penguin]

Worked fine with a MM cartridge, but when I use a MC cartridge it seems something inside of it has broken. It now produces a hum. 230V.

When I switch gain, the humming stops, then a click, a little pause and another click, and then humming starts.

 

[Huey2001]

Hi, I noticed a 16V ac power supply specially for the X5 on the fosiaudio shop. As my supplied (220V) power adapter hums a bit, I have ordered one to see whether this one is quiet.
Hope it is. Adds to the the cost, which is a pity… Guess new orders are still delivered with the same humming adapter, or would they start including this one?

Shipping takes awhile, so I have to be patient to find out the result…

 

[Roland68]

That should be stated on the adapter! I'd be careful before using it at 220V - connect on its own and measure the output voltage with a simple multimeter, just to make sure it's not to high.

The adapter states 110v only. I would presume the Fosi tech support folks know their stuff. But yes, a voltage test is a simple enough procedure to be absolutely sure.

You'd better not believe that. Shall mean, as the back side of the X5 clearly says "AC 16 V", it's most likely, that it'll definitely require incoming AC to internally create a symmetrical supply voltage (like for example +/- 15 V, i.e. one +15 V and one -15 V rail relative to ground) via two voltage regulator ICs - which in turn makes it most likely, that the external power supply is a very simple, conventional, transformer-based model, which most likely contains nothing but a transformer plus thermal fuse. And unlike modern switched-mode DC power supplies such simple, conventional AC power supply models typically aren't multi-range. So unless you'd find a switch on the thingy for switching between ~ 115 V(AC) and ~ 230 V(AC) operation, I'd strongly suggest you not to try a model for ~ 115V(AC) at ~ 230 V(AC).

Greetings from Munich!

Manfred / lini

I measured the output voltage of the AC/AC adaptor that comes with the Fosi Box X5. No load.

Input 　: 　Output
096.0V : 14.99V
108.1V : 16.86V
120.1V : 18.72V
132.1V : 20.57V


Edited and added images:
It seems there was no need to measure. There was a screw on the back of the adapter.

My advice then: never ever connect this power supply to more than 120V mains. It will fry the amp. @lini was right on the spot.

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.

Hi, I noticed a 16V ac power supply specially for the X5 on the fosiaudio shop. As my supplied (220V) power adapter hums a bit, I have ordered one to see whether this one is quiet.
Hope it is. Adds to the the cost, which is a pity… Guess new orders are still delivered with the same humming adapter, or would they start including this one?

Shipping takes awhile, so I have to be patient to find out the result…

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.

 

[davmol]

Well, I emailed Fosi tech support and got a response back within 2 minutes. Yes, it does work with 110 or 240v.

That is quite a dangerous mistake for Fosi support to make!
Here is my UK supply - stating 230v - so they do provide different supplies for different input voltages / different regions.

 

[mackat]

Some anecdotal info: I used a (presumably higher quality) JDS Labs power supply of identical power specification with my X5 and did not notice any hum reduction. It was still very much there.

 

[JeyElDee]

Hi, I noticed a 16V ac power supply specially for the X5 on the fosiaudio shop. As my supplied (220V) power adapter hums a bit, I have ordered one to see whether this one is quiet.
Hope it is. Adds to the the cost, which is a pity… Guess new orders are still delivered with the same humming adapter, or would they start including this one?

Shipping takes awhile, so I have to be patient to find out the result…

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.

 

[Roland68]

Some anecdotal info: I used a (presumably higher quality) JDS Labs power supply of identical power specification with my X5 and did not notice any hum reduction. It was still very much there.

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.

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.

 

[guy48065]

I'm amazed nobody has modified their X5 to use a DC linear power supply.
The low cost/ excellent sonics of the unit would make it an ideal candidate for simple upgrades.

I bought mine intending to make PS and ctg. loading mods but then life intruded. I moved and decided I'm done with analog.
The X5 and my turntables are in boxes.

 

[antcollinet]

I'm amazed nobody has modified their X5 to use a DC linear power supply.
The low cost/ excellent sonics of the unit would make it an ideal candidate for simple upgrades.

I bought mine intending to make PS and ctg. loading mods but then life intruded. I moved and decided I'm done with analog.
The X5 and my turntables are in boxes.

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.

 

[Roland68]

I'm amazed nobody has modified their X5 to use a DC linear power supply.
The low cost/ excellent sonics of the unit would make it an ideal candidate for simple upgrades.

I bought mine intending to make PS and ctg. loading mods but then life intruded. I moved and decided I'm done with analog.
The X5 and my turntables are in boxes.

To do that, you'd have to modify the device, because you can't connect a DC power supply to the Box X5. This is technically impossible due to the half-wave rectification.

It wouldn't offer any advantage anyway, since the Box X5 has two dedicated voltage regulators on its circuit board, so further modifications would be necessary.
Basically, it already uses a very good linear power supply, similar to all the well-reviewed headphone amps with AC power supplies.