Fosi Audio Box X5 Phono Preamp Review

[Laika2]

Anybody getting issues with channel imbalance? My left channel is much louder than the right with my unit. Tried different line level inputs on my amp (Sansui AU-8500) and, while operating the "Mode" toggle, the imbalance follows from "Stereo" to "Reverse."

Isolated it to the unit and not the cartridge, TT, or amp.

I re-read the manual. Am I psyching myself out? This thing's got higher gain than a regular preamp? So should this unit be used even with a line level input on my preamp?

There are cases on Amazon where one channel goes out. That may be the start of it. I would try the two lowest setting for MM and the two highest for MC. I would use a new rca cable on inputs, still a issue, try it out on the outputs making sure all RCAs on both ends. If that fixes the issue you might want to buy a phono cable with a ground or if the RCA cable works well just run a independent ground wire, about any wire will do.
This has happened to me over the years with RCAs, either bad cable or one end is not barely seated and when pulled out takes no real pull where seated ones take a good tug
Good luck

Yea, line level to anything other than the a recivers phono inputs DVD, CD or whatever is what you want, sounds like your gain may be too high,

 

[avantbored]

There are cases on Amazon where one channel goes out. That may be the start of it. I would try the two lowest setting for MM and the two highest for MC. I would use a new rca cable on inputs, still a issue, try it out on the outputs making sure all RCAs on both ends. If that fixes the issue you might want to buy a phono cable with a ground or if the RCA cable works well just run a independent ground wire, about any wire will do.
This has happened to me over the years with RCAs, either bad cable or one end is not barely seated and when pulled out takes no real pull where seated ones take a good tug
Good luck

Yea, line level to anything other than the a recivers phono inputs DVD, CD or whatever is what you want, sounds like your gain may be too high,

Thanks for the reply. I don't know if i can try all pf your suggestions as my phono cable on the TT is hardwired.
Swapped a bunch of components today (Fosi into different pre; fosi into AU8500 but different power amp) and magically the stereo image is centered on the original configuration; if the problem is intermittent like this, i wonder what the explanation is.

 

[Laika2]

Thanks for the reply. I don't know if i can try all pf your suggestions as my phono cable on the TT is hardwired.
Swapped a bunch of components today (Fosi into different pre; fosi into AU8500 but different power amp) and magically the stereo image is centered on the original configuration; if the problem is intermittent like this, i wonder what the explanation is.

Still sounds like a cable, many times cables get broken wires mainly close to the RCA jack, but they still work if you simply move them just a bit where they plug in, not really a fix, more of a process to figure out what cable needs to meet Mr trash can.

The TT hardwired RCAs can easily and cheaply be resoldered even if you need someone else to do it but If it's working now and you are happy no sense looking for a answer unless it happens again. Some issues just go away.

I gave up pondering and getting back to the fun unless the issue came back long ago

Happy Listening

 

[abrcdbra]

It is very strange for me that no one paid attention to the catastrophically low level of permissible overload at high frequencies. This is clearly audible even on non-overloaded recordings. The sound becomes hard, uneven, and unpleasant to listen to for a long time. For me, I listen on Michell Mycro, Rega RB300, AT VM540ML, Topping A70PRO and Kali Audio IN-5.

Maybe there is already a solution to this serious problem? If not, then I have to open the device and figure out what the problem is. Because it really spoils the sound. So as not to regret the money spent.

 

[antcollinet]

It is very strange for me that no one paid attention to the catastrophically low level of permissible overload at high frequencies.

Because it isn't

Given that the 15kHz clipping point is only about 9dB lower than that at 1Khz, yet the level in music is going to be of the order of 40dB lower. 20khz clipping point only drops a further 3dB, but musical content might be down another 10 or 20dB

Similarly the clipping point at 10kHz is only 6db lower than at 1kHz, but content in music is going to be down around 30dB

I'm also failing to pay attention to the issue. Even factoring in Riia, the higher frequencies are all more than 10dB further away from problems than 1kHz. (Typical music spectral power density)

I'm not sure what it is you are hearing but I don't think it is input overload at high frequencies.

 

[Balle Clorin]

A simple measurement of the Box X5 input capacitance using an LCR meter. Each was set to an average of 128 times.
Also, photos, THD vs. input level, and output impedance.

Does the DUT have to be ON during measurment of capacitance? I tried to use a simple LCR meter but got jut crazy values...nowhere near any spec. I wonder hat I am doing wrong

 

[KSTR]

Does the DUT have to be ON during measurment of capacitance? I tried to use a simple LCR meter but got jut crazy values...nowhere near any spec. I wonder hat I am doing wrong

DUT powered, test frequency 100kHz, test level <= 10mV.
Simple LCR meters? ... forget it

 

[KSTR]

Given that the 15kHz clipping point is only about 9dB lower than that at 1Khz, yet the level in music is going to be of the order of 40dB lower.

That's long-term RMS levels. But peak levels are almost the same regardless of frequency range (easily verified with band pass filters followed by peak levels meters).

 

[abrcdbra]

Because it isn't

Given that the 15kHz clipping point is only about 9dB lower than that at 1Khz, yet the level in music is going to be of the order of 40dB lower. 20khz clipping point only drops a further 3dB, but musical content might be down another 10 or 20dB

Similarly the clipping point at 10kHz is only 6db lower than at 1kHz, but content in music is going to be down around 30dB

I'm also failing to pay attention to the issue. Even factoring in Riia, the higher frequencies are all more than 10dB further away from problems than 1kHz. (Typical music spectral power density)

I'm not sure what it is you are hearing but I don't think it is input overload at high frequencies.

What could it be if not overload? I am a professional aerospace electronics designer and a long-time audiophile, so I can't think of any other explanation. Moreover, I saw Amir's measurements - the overload at 20 kHz is catastrophically low - about 35 mV.My cartridge at 1 kHz is 4 mV RMS, at 20 kHz about 40 mV. I think I need scheme X5. The problem is here.

 

[abrcdbra]

Because it isn't

Given that the 15kHz clipping point is only about 9dB lower than that at 1Khz, yet the level in music is going to be of the order of 40dB lower. 20khz clipping point only drops a further 3dB, but musical content might be down another 10 or 20dB

Similarly the clipping point at 10kHz is only 6db lower than at 1kHz, but content in music is going to be down around 30dB

I'm also failing to pay attention to the issue. Even factoring in Riia, the higher frequencies are all more than 10dB further away from problems than 1kHz. (Typical music spectral power density)

I'm not sure what it is you are hearing but I don't think it is input overload at high frequencies.

These are real measurements of the peak levels of gramophone records. So I think I'm right. The problem is with the device.

 

[StevenSGT98]

These are real measurements of the peak levels of gramophone records. So I think I'm right. The problem is with the device.

Looking at the graph, it is in cm/sec. You’re relating voltages, not velocities. I’m unclear on how the 2 correlate.

 

[StevenSGT98]

It is very strange for me that no one paid attention to the catastrophically low level of permissible overload at high frequencies. This is clearly audible even on non-overloaded recordings. The sound becomes hard, uneven, and unpleasant to listen to for a long time. For me, I listen on Michell Mycro, Rega RB300, AT VM540ML, Topping A70PRO and Kali Audio IN-5.

Maybe there is already a solution to this serious problem? If not, then I have to open the device and figure out what the problem is. Because it really spoils the sound. So as not to regret the money spent.

I heard this and attributed it to 2 different issues.
1. My overhang was off.
2. The record itself is bright.

By readjusting my setup a little and playing multiple different records, the issue resolved. The preamp will make it work for you, but the results will be rewarding.

 

[Balle Clorin]

Looking at the graph, it is in cm/sec. You’re relating voltages, not velocities. I’m unclear on how the 2 correlate.

A cartridge output in volt is in proportion to the velocity. so it is the same thing.... the RIAA eq and record mastering makes things more complicated

https://hifisonix.com/wp-content/uploads/2018/01/Disc-Recording-Equalization-Demystified.pdf

'

Measured Output of Phono Cartridges

I wanted to make a separate thread for this so this doesn't get buried in a thread that is really about something else. I'd imagine this is only going...

forums.stevehoffman.tv

Note:

a as groove amplitude= peak movement of tip''

 

[antcollinet]

That's long-term RMS levels. But peak levels are almost the same regardless of frequency range (easily verified with band pass filters followed by peak levels meters).

A cartridge output in volt is in proportion to the velocity. so it is the same thing.

I stand corrected - apologies. Though it is worth saying that according to that digram, and your cartridge rating of 4mv/5cm/s - then 40mV is at the extreme limit of what will be output. I doubt much music is doing that much of the time.

 

[lini]

(...) Though it is worth saying that according to that digram, and your cartridge rating of 4mv/5cm/s - then 40mV is at the extreme limit of what will be output. I doubt much music is doing that much of the time.

Might happen more often than one would think, if one considers the RIAA curve, i.e. the required boost at cutting (for example ca. +13.7 dB @ 10 kHz and +19.6 dB @ 20 kHz).

Greetings from Munich!

Manfred / lini

 

[StevenSGT98]

Might happen more often than one would think, if one considers the RIAA curve, i.e. the required boost at cutting (for example ca. +13.7 dB @ 10 kHz and +19.6 dB @ 20 kHz).

Greetings from Munich!

Manfred / lini

But, in normal music, it naturally rolls off in amplitude in the higher octave. So, just like with magnetic tape media, it’s usually not an issue.

 

[abrcdbra]

We, audiophiles, do not engage in psychoacoustics, covering up the blunders of manufacturers.) Amir's measurements at 20 kHz are a disaster for this device. How could the developers allow this? They apparently did not control how the result of their work sounds.I'll find time on the weekend and take a photo of what they did there)

 

[Balle Clorin]

Have you read post 1?

 

[antcollinet]

Might happen more often than one would think, if one considers the RIAA curve, i.e. the required boost at cutting (for example ca. +13.7 dB @ 10 kHz and +19.6 dB @ 20 kHz).

Greetings from Munich!

Manfred / lini

That chart already includes the RIIA curve - it is velocity encoded on the record - which already has RIIA applied.

 

[StevenSGT98]

A cartridge output in volt is in proportion to the velocity. so it is the same thing.... the RIAA eq and record mastering makes things more complicated

https://hifisonix.com/wp-content/uploads/2018/01/Disc-Recording-Equalization-Demystified.pdf

'

Measured Output of Phono Cartridges

I wanted to make a separate thread for this so this doesn't get buried in a thread that is really about something else. I'd imagine this is only going...

forums.stevehoffman.tv

Note:
View attachment 441549
a as groove amplitude= peak movement of tip''

View attachment 441550

Far less than 50 cm/sec. and most of that not in the upper octave.