Fosi Audio Box X5 Phono Preamp Review

[lini]

(...) Nothing is wrong with the AC adapter either. (...)

Hmmm - do we know that for sure?

Shall mean, given that in this case we're talking about a conventional, transformer-based AC/AC power supply, there should be at least two different models (one for ~ 115 V / 60 Hz, another for ~ 230 V / 50 Hz) - and possibly even some more, if those two don't happen to sport swappable mains plugs (or mains cables) for different countries/regions. And as quite a few ASR users don't mention their location in their user profiles, we might as well not be talking about one and the same power supply model.

Greetings from Munich!

Manfred / lini

 

[antcollinet]

Hmmm - do we know that for sure?

Shall mean, given that in this case we're talking about a conventional, transformer-based AC/AC power supply, there should be at least two different models (one for ~ 115 V / 60 Hz, another for ~ 230 V / 50 Hz) - and possibly even some more, if those two don't happen to sport swappable mains plugs (or mains cables) for different countries/regions. And as quite a few ASR users don't mention their location in their user profiles, we might as well not be talking about one and the same power supply model.

Greetings from Munich!

Manfred / lini

Its a transformer. How do you suppose it is going to generate hiss?

 

[Labjr]

How would an AC transformer have DC offset? All this wild speculation.

 

[lini]

Its a transformer. How do you suppose it is going to generate hiss?

I foremost had the audible buzzing of the power supply itself, that Hamrin has mentioned, in mind with my comment. I don't deem that likely to be responsible for the hiss from the phono stage output, though.

Greetings from Munich!

Manfred / lini

P.S.: Just btw, I'm wondering a bit about the dimensioning of the power supply. I mean, does that little thingy really need 16 W?

 

[antcollinet]

I foremost had the audible buzzing of the power supply itself,

Well that can be caused by DC on the supply. But then that is a problem of the supply - not the transformer.

 

[Heinrich]

Well that can be caused by DC on the supply. But then that is a problem of the supply - not the transformer.

There are transformer types less perceptive to DC on the mains supply line. But sure, that‘s something to be solved elsewhere.

How would an AC transformer have DC offset? All this wild speculation.

As said above, sometime other consumers down your street generate a little bit of an DC offset on the mains, which makes even very good transformers buzz. I had a JBL pro amp one with that problem.

From the TI OPA161x datasheet:

View attachment 422028

Input capacitance is negligible …

I was referring to valves back in their day. Today the input C is nothing to be minimized per se, but optimized for RFI rejection. I wonder if vinyl playback-at-home optimizers understand the back and forth of decision making in detail fully. For best reason there is still myth and belief. We need that to make us trust the message transmitted via the record.

Anyway, seems I‘m out. I‘ll sell my trusty MC, replace by new basic MM, amplify via USB interface‘s microphone input, and equalize on the digital side, SINAD expected well above of what vinyl‘s mechanics is capable of. There‘s a handfull of records I’m not willing to miss in my life—as what they are, disks.

 

[JimFarrell29]

Very Impressive - even more so, for just around 100 notes. If I hadn't already got my waxwing, I'd be buying this right now.

Ah, the waxwing. I'm in love with that thing. I can't understand why everyone with a half decent turntable hasn't bought one.
Having said that, I also have a little Douk Audio phono stage with some fun valves and adjustable impedance matching. I use it with tables I am working on and it's pretty decent sounding. Spoiled for choice these days.

 

[Jimi Floyd]

There are transformer types less perceptive to DC on the mains supply line. But sure, that‘s something to be solved elsewhere.


As said above, sometime other consumers down your street generate a little bit of an DC offset on the mains, which makes even very good transformers buzz. I had a JBL pro amp one with that problem.


I was referring to valves back in their day. Today the input C is nothing to be minimized per se, but optimized for RFI rejection. I wonder if vinyl playback-at-home optimizers understand the back and forth of decision making in detail fully. For best reason there is still myth and belief. We need that to make us trust the message transmitted via the record.

Anyway, seems I‘m out. I‘ll sell my trusty MC, replace by new basic MM, amplify via USB interface‘s microphone input, and equalize on the digital side, SINAD expected well above of what vinyl‘s mechanics is capable of. There‘s a handfull of records I’m not willing to miss in my life—as what they are, disks.

Either you don't know or you want to act as you don't understand the problem. For MM cartridges the phono stage input capacitance, summed with the one of the connecting cables, must fit the one needed by the cartridge to have the flattest possible frequency response. Not knowing the phono stage input capacitance leaves the user without a key variable needed to set that equation straight for his setup.

 

[Heinrich]

Either you don't know or you want to act as you don't understand the problem. For MM cartridges the phono stage input capacitance, summed with the one of the connecting cables, must fit the one needed by the cartridge to have the flattest possible frequency response. Not knowing the phono stage input capacitance leaves the user without a key variable needed to set that equation straight for his setup.

You may want to re-read my post(s). I‘m pretty much aware of the C‘s contribution, but I‘m pointing to additional variables. If for the moment the C of input is considered crucial, it could be evaluated or chosen via personal preference. It should be added to the cable‘s capacitance, giving expectedly a plus of 10% or so, shifting resonance by about 5%. And so forth considering damping by changing the resistive load also. The needle mass resonates against the compliance of the vinyl material, depending on composition and temperature.

Let alone cutting head differences. Followed by wear and tear of the master while pressing a finite number (which?) of individual copies. Metal master (copper?) was the last big thing before CD took over and so forth.

 

[KSTR]

However, there is usually a parallel capacitor added to ensure stability and/or block RF. Is that present? If so, what's that cap's value? Is there a ferrite bead on the input?

The input shunt capacitor can readily identifed from the PCB photo. Value is unknown of course (and a close-up wouldn't help, as ceramic SMT caps never have a printing) but I would assume a value in the 100pF to 220pF range.
No ferrite bead.

Note the very low input impedance for differential input, 20k ohms.

Keep in mind that both inputs of an opamp basically always move as a pair in unison, only a very small error voltage differential is present. Thus, the differential input impedance does not actually represent a load.

 

[Jimi Floyd]

You may want to re-read my post(s). I‘m pretty much aware of the C‘s contribution, but I‘m pointing to additional variables. If for the moment the C of input is considered crucial, it could be evaluated or chosen via personal preference. It should be added to the cable‘s capacitance, giving expectedly a plus of 10% or so, shifting resonance by about 5%. And so forth considering damping by changing the resistive load also. The needle mass resonates against the compliance of the vinyl material, depending on composition and temperature.

Let alone cutting head differences. Followed by wear and tear of the master while pressing a finite number (which?) of individual copies. Metal master (copper?) was the last big thing before CD took over and so forth.

Please don't bring so many variables into the discussion as to make it murky. We have an excellent thread on this site about frequency response (and crosstalk, and distortion) measurement of cartridges. The loading capacitance is supplied for each measurement, making users comfortable with their setup if the input C of the phono preamp is known, and this is a figure builders must supply

 

[Labjr]

IMO, the only thing vinyl is good for is material that's unavailable in a digital format. It's so much easier and less expensive to get great sound from a DAC. And the chain of equipment is much shorter.

 

[KSTR]

As for the transformer hum.... the few classic transformers that are still produced today are typically underdimensioned in terms of inductance and thus already are on the edge of saturation at nominal mains voltage, let alone higher than nominal. Add a little DC offset on the mains and they saturate heavily, draw lots of peak current and often hum mechanically. Low load make things actually worse, and that little preamp will not dissipate 16 Watts.

 

[Jimi Floyd]

IMO, the only thing vinyl is good for is material that's unavailable in a digital format. It's so much easier and less expensive to get great sound from a DAC. And the chain of equipment is much shorter.

You are posting in the wrong thread. There are several ones on this site discussing preferences between vinyl and digital. This one thread is about the performances and characteristics of the Fosi Audio Box X5 Phono Preamp.

 

[Hamrin]

Its a transformer. How do you suppose it is going to generate hiss?

It does... Just as "broken pink panther" electronics exist this happens with cheap bundled stuff too...

Two Box 5 here, two hissing transformers.

 

[guy48065]

Impossible, but whatever.

 

[Heinrich]

Please don't bring so many variables into the discussion as to make it murky. We have an excellent thread on this site about frequency response (and crosstalk, and distortion) measurement of cartridges. The loading capacitance is supplied for each measurement, making users comfortable with their setup if the input C of the phono preamp is known, and this is a figure builders must supply

As I said, we need myths and beliefs to make the performance of any audio channel trustworthy

But also, to see a problem in all its bandwidth is something I understood early in my technical education. In case you idealize vinyl in not taking degradation into account when pressing „n“ copies from the same master, to only mention one issue, you may miss out on the technology as a personal challenge. The C is just one factor.

‍As always, follow your preference.

CU

 

[mackat]

There is definitely some background hiss with my X5, most noticeable when using MM cartridges.

As far as I understand, this may be caused by using op-amps better suited to MC cartridges.

I have a Sutherland KC Vibe (another great sounding phono stage, and the MK2 version was tested here with favorable SINAD).

It also has noticeable background hiss when used with MM cartridges.

I once asked Ron Sutherland about this, and he explained that it was designed to have lowest noise with MC cartridges.

The more expensive 20/20 model I owned at one point had low background hiss with both MM and MC.

Note that this does not appear to correlate (directly, at least) with SINAD.

My iFi Zen Phono has almost no audible background hiss with either MM or MC cartridges, but its SINAD was measured to be comparatively poor.

I do wonder if the electrical “buzz” I hear with MC cartridges at the X5’s highest amplification level (separate issue) could potentially be related to the power supply.

 

[Hamrin]

My iFi Zen Phono has almost no audible background hiss with either MM or MC cartridges, but its SINAD was measured to be comparatively poor.

Same experience here... There are too many variables when dealing with these projects.
Real-world usage scenarios can differ from test bench measurements.

I own the Zen Phono and the MX Vynl, both ranked by ASR as somehow "worse" than the Fosi Box 5... For sure they seem to be, judging by the measurement results.

Anyway in the real usage the british stages here are silent even at the highest gain and their power adapters are not affected by any kind of mechanical hissing or buzzing.
The electrical system they’re connected to is the same, and so is the room...

Also, you raised an interesting point, and I regret not having tested with low-output cartridges.

I also own a ZA3 and no issues of any sort there, so reading through many conflicting comments, it seems plausible that the quality control for these early product batches isn’t yet top-notch, and the performance of individual units might vary.

 

[KSTR]

I do wonder if the electrical “buzz” I hear with MC cartridges at the X5’s highest amplification level (separate issue) could potentially be related to the power supply.

Given the tremendous gain of ~80dB at low frequencies it does not take much interference to show up as audible hum.
This is a thing one can test with shorting plugs at the input. If the input is silent then, the hum comes from the cartridge itself and/or cabling. The external power brick must be placed as far away as possible from the preamp, the turntable and the input cabling, this also applies to transformers in other devices.