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Fosi Audio Box X5 Phono Preamp Review

Rate this phono stage:

  • 1. Poor (headless panther)

    Votes: 3 1.5%
  • 2. Not terrible (postman panther)

    Votes: 8 4.1%
  • 3. Fine (happy panther)

    Votes: 35 18.0%
  • 4. Great (golfing panther)

    Votes: 148 76.3%

  • Total voters
    194
"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.
 
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.
 
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Which cart are you using?
The Fosi sounds towards the bright side, at least with AT carts of the VM series and tends to brighten my M75 Shure too.

I think this could be due to capacitance, the lower the brighter is the sound, and I guess this box has a pretty low value.
 
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Which cart are you using?
The Fosi sounds towards the bright side, at least with AT carts of the VM series and tends to brighten my M75 Shure too.

I think this could be due to capacitance, the lower the brighter is the sound, and I guess this box has a pretty low value.
Not quite, as with subjective evaluation lowering the L versus C resonance with increasing C, damped by R, would increase the perceptibility, making the „sound“ brighter.

I was just about to write a little spread sheet for evaluating the infamous equivalent input noise current from noise output with two different input generator resistors. Not only that it was pretty useless considering the surface noise of even the best, new records. But I also wonder if there is a real desire to replace the mysteries, that keep the topic of optimizing vinyl playback alive. There‘s so much ‚character‘, from imperfections, in the vinyl technology, one has to embrace it with true love, not strangle it with cold hearted analysis. Keep on!

❤️
 
Not quite, as with subjective evaluation lowering the L versus C resonance with increasing C, damped by R, would increase the perceptibility, making the „sound“ brighter.

Not quite... :)

Here we're taliking about the contribution of the phono stage.
The cart, the tonearm, the mat, the platter, even the cable, whatever you want... All are the same.

I own the MX Vynl as said before, and this one has a switch for capacitance.

If I set the AT VM95 at 50pF sounds very close to the Fosi, towards the bright side.
If I set it at 200pF (as AT suggests) the same cart sounds fuller...

So my guess is that this Fosi has a low capacitance, for sure lower than 200pF
 
Not a general rule at all... It depends from the "starting point".
Above some values trebles are rolled off.
;-)
(and it is constantly observed and measured... )
 

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You're not answering... What are you measuring here?
Which cart?

Any cart has a different response, so where you see a peak you could find a rolloff soon after...
The curve raises and moves back toward zero...
 
yes many times...standart mesureament...
there are tons of these measures right here...

sorry...find out...
 
If you wanted to experiment with the effect of capacitance on the phono input could you use a RCA "Y" adapter and connect one of these to the 2nd leg?


Temporarily, of course...
 
If you wanted to experiment with the effect of capacitance on the phono input could you use a RCA "Y" adapter and connect one of these to the 2nd leg?


Temporarily, of course...
This approach on y and "RCA plug" was marketed in the 70s ;-)

hence the interest of a minimum on the pre-phono side...see low capacitance cable...see shortcut just to help...

 

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yes many times...standart mesureament...
there are tons of these measures right here...

sorry...find out...

Low capacitance makes sound flatter, if the cart is on the bright side of the spectrum (and it is the case of the AT)... It will sound bright.
If you go above the "turning point" could make it sound "fuller" or rolled off (depending on the point of view).
At 200pF it is spot on.

Just as I described above... :)

Read again my message...My guess is that this Fosi has a low capacitance.
Did you measure it?
 
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