Fosi Audio Box X5 Phono Preamp Review

[pl4w]

Why is this thread so long?

Why shouldn't it be?

Bought one and really happy with it, it replaces my Cambridge Alva Duo.

 

[grotesque]

Why shouldn't it be?

Bought one and really happy with it, it replaces my Cambridge Alva Duo.

Out of curiosity, why did you make that switch? I'm asking as the Alva Duo measures excellently, has a lower input capacitance of 100pF, integrated power supply rather than a brick and a subsonic filter so seems like a superior offering.

I am looking at changing from the Fosi X5 specifically because of the slightly high 150pF input capacitance. Considering the popularity of Audio Technica cartridges with a 100-200pF recommended capacitance I find it strange many manufacturers would build with 150pF as a default. Assuming optimistically about 30pF turntable wiring + 70pF RCA cable + 150pF phono stage you'll always be out of spec. If they targeted 100pF as default you'd cover Audio Technica (100-200pF) and Ortofon (150-300pF) cartridges but maybe I'm missing something. Preamps like the Schitt Skoll/Mani offering a wide range from 50pF (47pF for Mani...), 100pF, 150pF, 200pF seem like a more logical design.

For the gain options, both seem to have a slightly high 'low gain' setting of 38/39dB as well. If you have a 5.5mV output Ortofon Blue then the recommended starting point gain (as per the KAB Calculator) would be 35dB. Is this calculator off? And do people generally use the equation below? (Apologies for the Excel style notation..)

Gain = 20*LOG(1/(Output Voltage/1000))

 

[Laika2]

Out of curiosity, why did you make that switch? I'm asking as the Alva Duo measures excellently, has a lower input capacitance of 100pF, integrated power supply rather than a brick and a subsonic filter so seems like a superior offering.

I am looking at changing from the Fosi X5 specifically because of the slightly high 150pF input capacitance. Considering the popularity of Audio Technica cartridges with a 100-200pF recommended capacitance I find it strange many manufacturers would build with 150pF as a default. Assuming optimistically about 30pF turntable wiring + 70pF RCA cable + 150pF phono stage you'll always be out of spec. If they targeted 100pF as default you'd cover Audio Technica (100-200pF) and Ortofon (150-300pF) cartridges but maybe I'm missing something. Preamps like the Schitt Skoll/Mani offering a wide range from 50pF (47pF for Mani...), 100pF, 150pF, 200pF seem like a more logical design.

For the gain options, both seem to have a slightly high 'low gain' setting of 38/39dB as well. If you have a 5.5mV output Ortofon Blue then the recommended starting point gain (as per the KAB Calculator) would be 35dB. Is this calculator off? And do people generally use the equation below? (Apologies for the Excel style notation..)

Gain = 20*LOG(1/(Output Voltage/1000))

I went from a FOSI on lowest gain to the Cambridge running a Ortofon Black LVB 250. I can't comment on the math but the Cambridge had what I would call a lower audio noise floor, the FOSI had a noticeable hiss at high volumes, no big deal, only in quiet spots and easy to ignore but it was there. Tried the Cambridge and it's dead silent cranked, it was nice to have the hiss gone and worth it to me but to many it may be a non issue considering the price difference, takes good silent vinyl records to notice.

 

[mike70]

Considering the popularity of Audio Technica cartridges with a 100-200pF recommended capacitance

The brand new AT vm500 line have higher capacitance.

 

[grotesque]

The brand new AT vm500 line have higher capacitance.

Do you mean the brand new AT-VMx line? e.g. AT-VM745xML which are 150-250pF. I think if your phono preamp had 100pF input capacitance then combined with turntable wiring/RCA cable (probably at least another 100pF) you'd still be in the sweet spot for this new cartridge line wouldn't you?

The VM500 line (e.g. VM540ML) and VM700 (e.g. VM740ML) are 100-200pF.

 

[mike70]

Do you mean the brand new AT-VMx line? e.g. AT-VM745xML which are 150-250pF. I think if your phono preamp had 100pF input capacitance then combined with turntable wiring/RCA cable (probably at least another 100pF) you'd still be in the sweet spot for this new cartridge line wouldn't you?

The VM500 line (e.g. VM540ML) and VM700 (e.g. VM740ML) are 100-200pF.

I use a short RCA cable (2ft) with 50pF the meter (3 ft) and then I don't get complicated with any AT cartridge.
I mean, you can use a convenient cable and that's all.

 

[dst]

Trying to create a setup where I wouldn't have to manually turn on my Fosi X5 every time I start listening to LPs. There's no trigger input, and apparently the device starts up in powered off mode–I have it hooked up to a smart plug, but that's not enough by itself. Any ideas?

 

[EJ3]

Let's simply consider that Fosi engineers, able to develop that kind of quality proven phono amp, have more than carefully selected the OPAMP that fit's best to their design.

Why? (this is what I would do, because I am lazy and tend to agree. However, if others want to play with them, that is their prerogative). It is POSSIBLE (maybe not PROBABLE but POSSIBLE) to find something that had either been tried by their engineers & computer systems and said to not be a good match or try a combination that was not thought of & for it to work better.
So why discourage it?
It doesn't affect those that do not do it in any way.

 

[renaudrenaud]

Trying to create a setup where I wouldn't have to manually turn on my Fosi X5 every time I start listening to LPs. There's no trigger input, and apparently the device starts up in powered off mode–I have it hooked up to a smart plug, but that's not enough by itself. Any ideas?

Some dev with an esp32 or raspberry pi zero and a web interface available via your smartphone. At this time you need to have something else running all the time. A bit of complexity and consumption in a side instead of moving to the Fois to push a button.

 

[Sublimity of Analog]

Thanks Amir for you great detailed knowledgeable analysis and measurements.

I hope you review vincent pho-300 or pho-500.
Thanks again

 

[davmol]

I have the buzzing power supply. It doesn't come through the speakers or get in the way of music but I can hear it buzzing in the room and it's annoying. I read the comments about it likely being DC on the AC supply. Is this a scenario where a power conditioner would actually do some good, and if not is there any other solution, other than to ditch it and go for a DC powered phone stage?

 

[Laika2]

Trying to create a setup where I wouldn't have to manually turn on my Fosi X5 every time I start listening to LPs. There's no trigger input, and apparently the device starts up in powered off mode–I have it hooked up to a smart plug, but that's not enough by itself. Any ideas?

I am big into remotes, 24 devices controlled by a harmony so I don't have to get off the couch. Just wanted to ask, you need to get up and put a lp on, why not turn the Fosi on then. To me auto turn on does not matter if I am right there with a lp a foot away from the box, it will still auto turn off. Is your fosi hidden or far from the turntable? Or do you leave a album on the table all the timeand can start play with a remote? Just wondering, remote freak like me or a real need to make things much easier.

 

[dst]

I am big into remotes, 24 devices controlled by a harmony so I don't have to get off the couch. Just wanted to ask, you need to get up and put a lp on, why not turn the Fosi on then. To me auto turn on does not matter if I am right there with a lp a foot away from the box, it will still auto turn off. Is your fosi hidden or far from the turntable? Or do you leave a album on the table all the timeand can start play with a remote? Just wondering, remote freak like me or a real need to make things much easier.

That's an excellent point! I mean I do have to turn on the turntable anyway, so I don't know why powering on the Fosi box has become such a hangup for me. Maybe because I've a somewhat extensive Home Assistant setup and the previous phono preamp did turn on when I selected the appropriate input on my AVR…

 

[Laika2]

That's an excellent point! I mean I do have to turn on the turntable anyway, so I don't know why powering on the Fosi box has become such a hangup for me. Maybe because I've a somewhat extensive Home Assistant setup and the previous phono preamp did turn on when I selected the appropriate input on my AVR…

OH, I get it my friend. Actually tried to do the same a year ago and ask myself the same question. Why am I doing this. Bought a phono preamp with a 12v trigger and though maybe, till it hit me it's going to be on about 6 hours a day for movies, TV and flac files. Only a album or two a week will get spun and I'm killing it's life turning it on and off with a 12v trigger for no reason.

 

[Vince3]

The X5's price/performance ratio has me wondering what the catch is. Maybe it's a loss leader. As tempting as the X5 is, I'll stick with my trusty and satisfying Pro-Ject Phono Box MM until I'm ready to splurge on a Michael Fidler Spartan 15. For a dedicated MM user like me, the Spartan 15's reputed build quality and performance leave me with little doubt that it should be my destination phono preamp.

If I were on the market for a phono preamp at this price, I'd head straight for the X5 based on this review and others.

 

[Lux Maldini]

I read that the input resistance is 47k for MM and 100Ω for MC, but without any information on the MM loading capacitance it is not possible to take into consideration the possibility of buying a phono preamp. @Fosi Audio you must supply the input capacitance figure. If it is very low it is OK even if not adjustable, one can always add some externally, and modern MM all require a very low one anyway, but is it? Also, I think @amirm should think about getting the equipment needed to perform the input capacitance measurement.

Hello, I would like to ask you, if our MM impedance is set at 47K Ω and the capacitor can be set to 3 levels, what would be the most suitable setting?

 

[Jimi Floyd]

Hello, I would like to ask you, if our MM impedance is set at 47K Ω and the capacitor can be set to 3 levels, what would be the most suitable setting?

Thanks for your interesting question,

1) first level: the lower you can. Due to unavoidable wiring parassite capacitance this would be at least 25pF. BUT, possible RF problems could arise with a vey very low input capacitance, so just in case bring the first level C to 40-50 pF. Mated with a low-C turntable cable one can obtain all the low-C values needed by many today's MM cartridges. Being able to start from the lowest input capacitance available is a must. More capacitance, by the use of normal-C cables or C plugs, is always easier to obtain than a lower one, which should be given by the first level Phono-pre input.

2) second level = first level + 50pF. This is fine tuning for most cartridges around depending on the RCA TT-to-phono cables capacitance

3) third level = first level + 150 pF. This would be close to 200pF total. It is a vintage setting. 70s or 80s receivers and amplifiers had a standard input capacitance around 220pF, thus suited for many vintage cartridges like Shure, ADC, Stanton etc. Thanks to modern replacement styli producers like e.g. Jico in Japan, a lot of people is using vintage cartridge bodies from the vinyl golden era which love some higher capacitive load.

 

[Lux Maldini]

Thanks for your interesting question,

1) first level: the lower you can. Due to unavoidable wiring parassite capacitance this would be at least 25pF. BUT, possible RF problems could arise with a vey very low input capacitance, so just in case bring the first level C to 40-50 pF. Mated with a low-C turntable cable one can obtain all the low-C values needed by many today's MM cartridges. Being able to start from the lowest input capacitance available is a must. More capacitance, by the use of normal-C cables or C plugs, is always easier to obtain than a lower one, which should be given by the first level Phono-pre input.

2) second level = first level + 50pF. This is fine tuning for most cartridges around depending on the RCA TT-to-phono cables capacitance

3) third level = first level + 150 pF. This would be close to 200pF total. It is a vintage setting. 70s or 80s receivers and amplifiers had a standard input capacitance around 220pF, thus suited for many vintage cartridges like Shure, ADC, Stanton etc. Thanks to modern replacement styli producers like e.g. Jico in Japan, a lot of people is using vintage cartridge bodies from the vinyl golden era which love some higher capacitive load.

If we default the capacitance to 0pF and have 4 levels of adjustment, with the first level being+50, the second level being+50, the third level being+50, and the fourth level being+50, then you can get five levels of adjustment: 0/50/100/150/200pF. What do you think?
Will 0pF cause any problems?

 

[Jimi Floyd]

If we default the capacitance to 0pF and have 4 levels of adjustment, with the first level being+50, the second level being+50, the third level being+50, and the fourth level being+50, then you can get five levels of adjustment: 0/50/100/150/200pF. What do you think?
Will 0pF cause any problems?

0/50/100/150/200 pF is an optimal choice. Anyway as I understand it, 0pF for you would mean no capacitor added at the input. This is not the same thing than having actually 0pF as input capacitance because of the parasite capacitance from cabling etc. which usually amounts to 10-30pF

 

[Lux Maldini]

0/50/100/150/200 pF is an optimal choice. Anyway as I understand it, 0pF for you would mean no capacitor added at the input. This is not the same thing than having actually 0pF as input capacitance because of the parasite capacitance from cabling etc. which usually amounts to 10-30pF

Yes, that's why we set a 0-pF level, mainly for capacitors attached to cables and plugs. Thank you very much for your suggestion! If anyone else has other suggestions, please feel free to raise them.