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Fosi Audio Box X5 Phono Preamp Review

Rate this phono stage:

  • 1. Poor (headless panther)

    Votes: 4 2.0%
  • 2. Not terrible (postman panther)

    Votes: 8 4.0%
  • 3. Fine (happy panther)

    Votes: 35 17.4%
  • 4. Great (golfing panther)

    Votes: 154 76.6%

  • Total voters
    201
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?
no... perhaps if a version more complete and successful come..
(juste for fun..i have many prephono )


for you
Post in thread 'Phono Cartridge Response Measurement Script' https://audiosciencereview.com/foru...esponse-measurement-script.41148/post-1461053

etc etc etc
 
Low capacitance makes sound flatter...
Wrong terminology. Lowering the capacitance causes the output to roll-off sooner. Every cartridge presents a unique load to the phono input. The RLC of this load can be 'tuned' by changing parallel Resistor & Capacitor values. There will be some combination where the combined values yield an optimally flat response. Go BELOW that capacitance and it will sound dull. Too much and it will sound too bright (harsh, sibilant).
 
I've never seen an impact below ~1kHz from loading, and certainly nothing in the bass region. "Thin" means different things to different people. On a VM95ML at 50pF all-in you'd be about -2dB at 5.5kHz, -1dB at 10kHz, and -2dB at about 15kHz. If flat is the goal, the best compromise for that cart is about 250pF. All assume 47k Rl.
 
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.
The 1350 ohms isn't the problem. It's the 400+ inductance. The quality of construction has nothing to do with using it as a reference source.
 
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 ?
It is currently measured here and at Stereophile with a very low source impedance which for this discussion is the same as shorting the input and measuring the noise at the output. Measuring using a low source impedance means the biggest noise contributor in an MM phono amp - the input noise current - flows through ~0 ohms and thus does not develop a noise voltage, which IS what happens if you feed it with a real-world MM source. You therefore end up with the bizarre situation that opamps like an AD797 or OPA1611 are quieter than an NE5532 or OPA1642 and so get ranked more highly for noise performance when in fact they are 7-10 dB worse when you connect a cartridge. You have to select the correct type of amplifier depending on the transducer you are using. For MC, you want very low noise voltage (so use an AD797 or OPA1611/12) and for MM, you should choose something with very low or negligible noise current and low noise voltage - so use an OPA1641/2 or NE5532/4 (these latter two have higher noise voltage than either the AD797 or the OPA1611/12
 
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 want to see current noise specified. We are getting into technical details that probably most are not interested in unless they are designing low-noise analog circuits. I am suggesting that instead of measuring phono amps on this site directly out of an AP - which is a low source impedance - it is better to do it using a real-world MM source. @SIY has suggested just feeding the AP through the MM cart coils which seems a good approach to me. This will give a true reflection of the preamp noise performance when a cartridge is connected.
 
I don't want to see current noise specified. We are getting into technical details that probably most are not interested in unless they are designing low-noise analog circuits. I am suggesting that instead of measuring phono amps on this site directly out of an AP - which is a low source impedance - it is better to do it using a real-world MM source. @SIY has suggested just feeding the AP through the MM cart coils which seems a good approach to me. This will give a true reflection of the preamp noise performance when a cartridge is connected.
Alas, I feel that I‘ve fallen out of the ongoing discussion. But anyway, equivalent current input noise is measurable, easy in my book at least, and as such could be used to estimate the impact of any generator impedance. That would not be possible when measuring the phono pre with just one real cartridge, and would need further calculations when using more than one. Besides the technical stuff, I strongly suggest to just play around, because vinyl is about that to the best of it. I‘m not on an irony ticket, I mean it. I loved my platter once for a reason. Can‘t put my finger on it, there‘s something about personal involvement hard to describe.
 
Alas, I feel that I‘ve fallen out of the ongoing discussion. But anyway, equivalent current input noise is measurable, easy in my book at least, and as such could be used to estimate the impact of any generator impedance. That would not be possible when measuring the phono pre with just one real cartridge, and would need further calculations when using more than one. Besides the technical stuff, I strongly suggest to just play around, because vinyl is about that to the best of it. I‘m not on an irony ticket, I mean it. I loved my platter once for a reason. Can‘t put my finger on it, there‘s something about personal involvement hard to describe.
Agree noise current is easy to measure and the total noise contribution will depend on the cartridge used. But, the 500mH + 1350 ohms I proposed is a good compromise since the 500mH L bit is pretty consistent with most mainstream carts and in the big scheme of things the 1350 DC coil resistance is neither here nor there - it will not materially affect the real-world noise measurement with a standard 47k load.

Anyway, I concur there is a magic about T/Ts!
 
This certainly makes obsolete the measurements and classification in mm practiced here until now...but offers a clear approach for the future, using a fairly standard cartdrige, and more relevant measurements...

but does not prohibit redoing a classification in mc which would seem to be globally quite relevant....

(Perhaps the opportunity arises to re-measure those who offered very optimistic measures in mm in the same way to put things in perspective.)
 
Anyway, I concur there is a magic about T/Ts!
Sure, it is about the feel of it. Not to far in the past (digital) measurement was science fiction for most of us. Do we want to spoil the experience of personal preference in letting numerical ranking take over? Given the not always fully understood limitations, in all their variety, is measuring one or the other isolated data reasonable? There is so much not just right, all by at least one order of magnitude well objectionable (vertical tracking angle, horizontal tracking angle, degradation with the n‘th copy from a ‚mother‘, … ), hopeless and promising at the same time.

(Perhaps the opportunity arises to re-measure those who offered very optimistic measures in mm in the same way to put things in perspective.)
With the recent advent of low cost, quite stabile, low voltage noise opamps, current noise became an issue. MM data is affected, sure. With the X5‘s design one might argue that it is hard on the edge. But still it won‘t be easy to declare the data presented here misleading.

If there‘s substantial criticism, I would expect it be presented by the critics beyond vague suspicion ;-) I‘ve seen nothing so far …

Add.: Look, the 1300 something Ohm DC won‘t do anything serious with noise current, the resonance from L/C at 10kHz or so is located where the preamp is 40dB below its max amplification, and it is narrow band, or low in reactive resistance. Plus the opamp is specified to be quite well behaved up to 10kOhm anyway (complicated because the reactive part dominates).
 
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Add.: Look, the 1300 something Ohm DC won‘t do anything serious with noise current, the resonance from L/C at 10kHz or so is located where the preamp is 40dB below its max amplification, and it is narrow band, or low in reactive resistance. Plus the opamp is specified to be quite well behaved up to 10kOhm anyway (complicated because the reactive part dominates).
I experimentally showed over a 20dB difference when using a MM cartridge impedance as a source compared with a low impedance source. Noise current is an issue that can be significantly reduced with design, but Johnson noise (both of cartridge and load) can't be. A few minutes playing with the cartridge Johnson noise calculator over on my website will demonstrate the importance of that factor.

Still, although current noise can be minimized, it isn't necessarily. There's a lot of badly designed phono stages out there. Part of the issue is that devices which are optimal for MC (low base spreading resistance BJTs, for example) are not optimal for MM. And devices which are optimal for MM (JFETs, for example) are not optimal for MC. So if a phono preamp has variable gain to accommodate both, chances are that it's not optimum for at least one of them. I cringe when I see something like an AD797 (which works well for MC) ignorantly used in an MM preamp because its voltage noise is low.
 
I experimentally showed over a 20dB difference when using a MM cartridge impedance as a source ….
Maybe in a pathological educational example, but not here fore sure. You are stressing a point not in case. What else to say?***

Anyway, vinyl is about personal preference, frankly accepting limits in favor of the content, not counting numbers for obvious reasons. Loosing a few dB of SINAD to noise or distortion doesn‘t compare to hum & buzz from a bad grounding technique, or, forgive the cruel example, loosing it to the pre-owners neglect of cleaning the record before playing, using a worn needle, embossed forever and a day into that single ‚unobtainium’ rare copy you may find in all your remaining lifetime.

The X5 is transparent regarding noise and distortion in all practical use cases. If in doubt please present some real data, example given on above mentioned 20dB—which real MM was it, and what of a real pre amp?


*** you didn‘t find your time to showcase the speculated issue with the X5, using opamp xyz, using your calculator, did you?
 
Maybe in a pathological educational example, but not here fore sure.
Quite the opposite. A very standard phono preamp with a very standard MM cartridge. In this very thread (besides my original post in a different thread a couple years ago). I don't have a Fosi in house to demonstrate this, but I would expect a very similar result since it's physics driven.
 
The idea of carrying out a test with a protocol closer to reality is not surprising, right? Especially since it doesn't seem very complicated to do...
;-)
 
Yes, very easy to do. I think the SINAD ranking on MM inputs on this site would change significantly. For starters, anything using an AD797 or OPA1611/2 would drop in a SINAD test to about 63dB (my calculator result ref 5mV) and a top notch JFET (opamp or discrete) would sit about 10 dB higher.

With shorted inputs, the noise floor on an AD797/OPA1642 is at -87 to -91 dB while a JFET input stage would be about 5-6 dB worse at -84 dB, which is a completely misleading result (these figures are unweighted).
 
Yes, very easy to do. I think the SINAD ranking on MM inputs on this site would change significantly.
Come back when you can show this. Don't do math without considering RIAA equalization.
 
This is with math. RIAA will ‘improve’ the flat response noise by about 10dB due to the response shaping (the top 2 octaves in a MM pre account for near enough half the total thermal noise over 20 Hz to 20 kHz). LTspice models this very well but I also have a spread sheet that gives near enough identical results.

:)
 
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