Fosi Audio Box X5 Phono Preamp Review

[KSTR]

Two Box 5 here, two hissing transformers.

Hiss is normally used when a constant but random noise appears that is similar to wind in a forest or waves on the ocean shore etc. Cambridge dictionary writes "to make a noise like a long s sound".
As others have said, hiss is very unlikely to be produced by a mains transformer.

Maybe what you are hearing would be better called hum&buzz where you can basically hear a pattern or pitch.

 

[morillon]

if in the audible a capture comes a small app like spectroid etc can be very explicit... ;-)

 

[restorer-john]

The socketed 5532 DIP is sort of a dummy opamp, actually not needed (other than for part of switchable gains maybe) but designed in to appeal to the opamp-rollers, IMHO.

I like the idea of a dummy socket to fool opamp-rollers. Ones not even in circuit. LOL.

This discrete opamp thing is out of control.

https://www.aliexpress.com/w/wholesale-discrete-opamp.html?spm=a2g0o.home.search.0

This one has multiple tubes, triodes and even low-error surface mount triodes...

 

[Heinrich]

Hiss is normally used when a constant but random noise appears that is similar to wind in a forest …

I like the idea of a dummy socket to fool opamp-rollers. Ones not even in circuit. LOL.

This discrete opamp thing is out of control.

Yeah, people like such „make-believe“ things. But I wonder what we are talking about. Hiss as a term needs to be explained, the use of an socketed opamp is speculated to be nil, no use?! I would say that close to everything attributed to the X5 is not even an educated guess. People should learn to measure things themselves, example given the input C, the noise‘s spectral distribution. It has become so easy and cheap to gain relevant information for oneself, if only the proficiency was established.

 

[restorer-john]

The 500mH + 1350 Ohms is representative of a typical MM cartridge and should cause no issues as a measurement standard.

If you are to pick a standard, the V15 at 1350R is an outlier and not the one to pick for a "measurement standard".

It is no longer made for a start. It's ancient and if you can find two V15 (II, III or IV etc) that have even remotely matched coil DCR/Ind from L to R, I'll eat them. The quality of Shure's internal construction is a joke, no precision at all. No consistency. It was bad enough before they moved to Mexico.

The world's largest selling cartridges by a clear margin is Audio Technica. They sell more in a year than all the other brands added up. They have been manufacturing the the AT-91 for at ~40 years and it is used in millions of turntables today, and the 3600L. I sold them back in the 1980s and 1990s as they were the same price as a replacement generic stylus. Not the best cartridge, but well made and more than good enough for most people. I wouldn't know how many tens of millions have been sold. It would be scary. The coil DCR/Inductance are very consistent for the stuff coming out of the Chinese AT factory. The new and 40 year old cartridges are pretty darn close, with the new Chinese ones being much more accurate channel to channel.

It has ~400mH and ~400R DCR.

 

[Verig]

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.

My Zen Fono (last gen, not the new one) is absolutely silent. And it's nice it can be driven by 5V usb sources if needed, tried a cellphone charger battery pack, works well.
I wouldn't write any audible hiss to sinad. Even if Zen measures a bit worse it's still better than my TT and records. And "buzz" is electrical interference anyway, not related to performance per se. Some kind of grounding/psu problem I'd say.

 

[Verig]

The world's largest selling cartridges by a clear margin is Audio Technica. They sell more in a year than all the other brands added up.

And some brands are re-branded AT so there sure are a lot of them around.
Mostly cheaper ones but for example Linn Koil and AT-OC9XSL look, ahem, quite similar. Linn is some 50% more expensive though.

 

[KSTR]

if in the audible a capture comes a small app like spectroid etc can be very explicit... ;-)

Yeah, Spectroid is killer, I use it all the time for a quick picture of what's going on.

 

[Heinrich]

My Zen Fono (last gen, not the new one) is absolutely silent. And it's nice it can be driven by 5V usb sources if needed, tried a cellphone charger battery pack, works well.
I wouldn't write any audible hiss to sinad. Even if Zen measures a bit worse it's still better than my TT and records. And "buzz" is electrical interference anyway, not related to performance per se. Some kind of grounding/psu problem I'd say.

Today‘s ether is full of stuff, especially in close vicinity to a laptop. I personally fried my tweeter when once accidentially picking up all that nasty RFI/sideband noise. (Education didn‘t help 8-(

Could anyone reporting on „hiss“ take a spectrogram, using for instance free REW software? It‘s easy, and would clarify a lot. Thank you!

 

[KSTR]

the use of an socketed opamp is speculated to be nil, no use?!

I didn't say no use, but it is not there to perform any core function, just used for a little gain and as output driver.
But the decision to use a socketed DIP8 for sure is marketing driven, which is fine by me of course.

BTW, I speculate a reason for the dubious output impedance spec of 10k could be bleeder resistors after the last DC blocker caps (but before the output relay), where 10k would be a typical value to use, to create a charging path for the capacitors so that the output settles at 0V quickly.

 

[KSTR]

If you are to pick a standard, the V15 at 1350R is an outlier and not the one to pick for a "measurement standard".

I did a quick sim with an OPA1602 (2.5nV/rtHz, 1.8 pA/rtHz @1kHz) RIAA stage, looking at the 20...20kHz output noise.
- Shorted input : 28uV
- AT3600L : 120uV
- Shure V15 : 145uV

Cart inductance has a bigger influence than resistance: stepping the inductance for the AT 300mH, 400mH and 500mH gives 100uV, 120uV and 140uV, resp.
A larger inductance degenerates the shorting effect of the cart resistance earlier in frequency.

 

[Hamrin]

Hiss is normally used when a constant but random noise appears that is similar to wind in a forest or waves on the ocean shore etc. Cambridge dictionary writes "to make a noise like a long s sound".
As others have said, hiss is very unlikely to be produced by a mains transformer.

Maybe what you are hearing would be better called hum&buzz where you can basically hear a pattern or pitch.

Alright, I’ll rephrase using your definitions.
The two Fosi Box 5 I had here showed:

- hissing coming from the speakers at normal listening levels, perceivable from a 2m far listening point (only for +48dB and above).

- persistent buzzing coming from the AC adapters bundled, perceivable from any point of the room, without music playing.

 

[Heinrich]

Alright, I’ll rephrase using your definitions.
The two Fosi Box 5 I had here showed:

- hissing coming from the speakers at normal listening levels, perceivable from a 2m far listening point (only for +48dB and above).

- persistent buzzing coming from the AC adapters bundled, perceivable from any point of the room, without music playing.

A starting point. Buzzing is more often than not an effect of DC offset on the mains. DC offset is unavoidable, tolerances vary. Some transformers are susceptible, others less so. Switching power supplies are, to my knowledge, immune. DC offset can be measured, but that needs extended technical awareness. I cannot recommend to DIY—at least with European 230Volts one may risk life, literally.

On hiss, if normal listening level is 90phon peak, then noise with a silent MC is expected at around 30phon (average) and up, -60dB as told by the sinad. In a quiet room that may be perceivable. But not as hiss of more trebly quality. Due to the RIAA it should be colored neutral or darker.
In case you provide a spectrum of that noise we could speculate further on the origin. It may be RFI picked up, and possibly demodulating at the input‘s diode-like nonlinearity (before feedback can chime in). Without spectrum, it would be very hard to understand the problem. Alas, I don‘t have the X5 at hand, and logically cannot reproduce the issue, but others may do.

 

[cfwotzka]

Alright, I’ll rephrase using your definitions.
The two Fosi Box 5 I had here showed:

- hissing coming from the speakers at normal listening levels, perceivable from a 2m far listening point (only for +48dB and above).

- persistent buzzing coming from the AC adapters bundled, perceivable from any point of the room, without music playing.

talkin hiss: perhaps I missed information but do you hear the hiss with open input's or turntable/cartridge connected? I've got the Fosi and can perhaps simulate your situation. my is dead quiet as well as the AC adapter is

 

[joqueval]

I don't have any noises either in the transformer or in the signal.
My area is 220 V. 50 Hz.
In the first few songs I recorded some video and everything was ok, the sound on YouTube is terrible, it even sounds better on my cell phone.
Regards

 

[morillon]

I don't have any noises either in the transformer or in the signal.
My area is 220 V. 50 Hz.
In the first few songs I recorded some video and everything was ok, the sound on YouTube is terrible, it even sounds better on my cell phone.
Regards

it's for sure..the signal is full of noise!!

 

[Skeeter]

"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."

This is exactly what I'd expect if you measure SINAD by shorting the input. SINAD measured with the input shorted is no predictor of performance with an MM cart attached because the biggest noise contributor - input noise current - is not present.

 

[Borko]

"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."

This is exactly what I'd expect if you measure SINAD by shorting the input. SINAD measured with the input shorted is no predictor of performance with an MM cart attached because the biggest noise contributor - input noise current - is not present.

Could you please clarify, how is SINAD actually measured ? With input shorted or with an MM attached ? According to reply you quoted the iFi Zen Phono has less noise with MM cartridge. However, the opposite is expected due to presence of input noise current ?

 

[Heinrich]

"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."

This is exactly what I'd expect if you measure SINAD by shorting the input. SINAD measured with the input shorted is no predictor of performance with an MM cart attached because the biggest noise contributor - input noise current - is not present.

The comment lives in between two worlds. For one it refers to objectively measured data in a well controlled environment, second it refers to subjective experience under utterly uncontrolled circumstances. Third you just speculate on something not measured, the current noise, which effect again depends on unspecified, widely varying properties.

If you like current noise to be specified, I support the inquiry.

 

[Hamrin]

I don't have any noises either in the transformer or in the signal.
My area is 220 V. 50 Hz.
In the first few songs I recorded some video and everything was ok, the sound on YouTube is terrible, it even sounds better on my cell phone.
Regards

The issues I experienced were not in sound reproduction, I'm glad you've found a fine unit.
You're using a Concorde-like DJ cart as far as I can see. Usually these should be above 6mV.
I'm pretty sure you're at the base gain.
The hissing appears at +48dB in my case.

Anyway, this video strengthens my belief that the quality control for these early product batches isn’t yet top-notch, and the performance of individual units might vary.