Fosi Audio Box X5 Phono Preamp Review

[Laika2]

What's your audio setup like?

Check your PM's don't want to derail this thread more than I have.

 

[Heinrich]

Had my records stored safely for 30 years, went CD ... but it's like having 2 different mixes ...

Most probably that is actually the case. Let alone tayloring the signal, in the more technical dimensions, to what a vinyl disc can bear.

 

[Northa40]

What gain setting are you running at with the x5

I am using the 38db setting and to me it works fine. The AT120eb is 4mv and the 2M Blue is 5mv.

 

[StevenSGT98]

I am using the 38db setting and to me it works fine. The AT120eb is 4mv and the 2M Blue is 5mv.

I’ve settled in on 38db also with a VM95ML. I’m exploring the noise profile of this a little and am still early on. What I’ve had to compare it to so far is a built in stage in a Denon 3803 and an Art DJPre II. At first I was sensing more noise from the Fosi until I laid down a 1khz track at 5cm from a test record and used a SPL to balance output across all 3 devices. On my system the Fosi was the highest output using 38db setting. The DJ Pre ii was -4db. And the internal was also -4db or so. Once the DJ Pre ii was gain adjusted, noise loudness was getting fairly consistent. Same for the internal Denon.

The sound of the noise was different. The Fosi was “cleaner” hiss. The DJ Pre ii has more dirt in the signal as did the Denon, but it was slightly cleaner than the DJ Pre ii. The Fosi hiss seemed crisper, where the others duller or more rolled.

Long story short so far, gain differences play a major factor in subjective noise perception.

I’m still chasing down if there are ways to improve the noise profile in my system. It sounds more like a inductance than anything from the cartridge.

I’m wondering if power supply has any bearing on this. Also if the design of the Fosi compared to other preamps has any affect on cartridge noise levels and shape?

 

[Heinrich]

Also if the design of the Fosi compared to other preamps has any affect on cartridge noise levels and shape?

Yepp, it was shown that the choice of the input opamp isn't optimally suited for moving magnet systems. It's the very same opamp for both, MM and MC. It would have been better to take the NE5532 for MM duties and the other for MC, but that would ask for a different topology and so for an entirely different product.

This thread got a bit engaged, but is otherwise quite instructive, me thinks: https://www.audiosciencereview.com/...and-sinad-of-mm-phono-preamps-properly.60594/

 

[StevenSGT98]

Yepp, it was shown that the choice of the input opamp isn't optimally suited for moving magnet systems. It's the very same opamp for both, MM and MC. It would have been better to take the NE5532 for MM duties and the other for MC, but that would ask for a different topology and so for an entirely different product.

This thread got a bit engaged, but is otherwise quite instructive, me thinks: https://www.audiosciencereview.com/...and-sinad-of-mm-phono-preamps-properly.60594/

So, reading this thread fairly thoroughly, I see that the opa 1612 has a vn of 1.7pA/rt(Hz). I’m seeing bipolar opamps running 1 to 2.4. It looks as the resistance from coil loading is somewhat unpredictable as to be non linear as voltage increases, noise may increase at a higher rate.

I didn’t see any calculated noise for the opa 1612. Did I miss that somewhere? I’m just curious if what I’m hearing is what I’m gathering from my afternoon reading

 

[Heinrich]

So, reading this thread fairly thoroughly, I see that the opa 1612 has a vn of 1.7pA/rt(Hz). I’m seeing bipolar opamps running 1 to 2.4. It looks as the resistance from coil loading is somewhat unpredictable as to be non linear as voltage increases, noise may increase at a higher rate.

I didn’t see any calculated noise for the opa 1612. Did I miss that somewhere? I’m just curious if what I’m hearing is what I’m gathering from my afternoon reading

Maybe a typo, the NE5532 shows a noise current around 0,5. Thing is, the used opa1612 (?) clocks at least three times higher, and that dominates once the inductive and resistive parts of the common MM pickup, including the prescribed termination resistor of 47kOhm are considered. The OPA637 would come close to an ideal opamp for MM purposes, the NE5532 would be "good enough" for most people, but the said 1612 is a compromise leaning towards MC use. Your original question was:

"Also if the design of the Fosi compared to other preamps has any affect on cartridge noise levels and shape?".

As You see in the linked thread, its's not that easy, but I think the conclusion is imperative.

Anyway, as the surface noise of even best quality, new records is going to be much higher than that of the op1612 in combination with an MM pickup, should we really care?

 

[StevenSGT98]

Anyway, as the surface noise of even best quality, new records is going to be much higher than that of the op1612 in combination with an MM pickup, should we really care?

True. I purchased the X5 for its other attributes - the linearity, low distortion, high overhead clipping, and even selectable gain and mm mc compatibility if I ever feel like mounting one. These features alone made it a no brainer. The noise that is there is, slight and for lack of better word “clean” and only is heard when the gain is quite high - high enough I would never drop a needle at that gain setting. As was said before, the noise disappears when the needle is in the wax.

A couple future features for an upgrade could be an auto mute, switchable loading and a selectable rumble filter.

I think if anyone is hearing harshness maybe should revisit cartridge set up. I need to play with angle a bit as I’m picking up some on the outer wax but towards the inner wax, resolution clears right up, making me think it’s off a bit. This phono stage will make you work for it, because you CAN hear it. That’s what we want right? Not something to smother it.

 

[Heinrich]

... an auto mute ...

It was proposed before, and some older platters have it already. No probs with idle noise anymore.

 

[StevenSGT98]

Maybe a typo, the NE5532 shows a noise current around 0,5. Thing is, the used opa1612 (?) clocks at least three times higher, and that dominates once the inductive and resistive parts of the common MM pickup, including the prescribed termination resistor of 47kOhm are considered. The OPA637 would come close to an ideal opamp for MM purposes, the NE5532 would be "good enough" for most people, but the said 1612 is a compromise leaning towards MC use. Your original question was:

"Also if the design of the Fosi compared to other preamps has any affect on cartridge noise levels and shape?".

As You see in the linked thread, its's not that easy, but I think the conclusion is imperative.

Anyway, as the surface noise of even best quality, new records is going to be much higher than that of the op1612 in combination with an MM pickup, should we really care?

I dropped needle on a Mofi Philadelphia Orchestra Sibelius Four Legends and played the first side. My room this time of day runs about just under -42-43 db. When my Denon is at -5db gain the background hiss is just there but SPL is the same and most of the sound pollution in my room is rumble. Needle on deadwax runout is about 48-49 db (mofi uses super vinyl) OK

The lowest passages in live performance were touching deadwax quiet, perhaps a db or 2 above - maybe - around 50db and saw it tick down to 49 a bit. My loudest peak hit 98.8db so this particular record on this side measured almost 50db. Not too shabby!

Point? Even at - 70+ SINAD who is going to benefit from more? How many records go above this? That in itself is 20db of headroom.

70+ db on vinyl is enough for mere mortals.

 

[Heinrich]

I dropped needle ...

So You have 50dB of dynamic range in-room, limited by both, noise from the environment and record surface noise in roughly the same proportions, but in different frequency ranges.
Hiss from the preamp / pickup combo alone, not playing, is expected to be at -70 dB referring to peak level (+100db). Now it depends if hiss at +30dB is audible with the background of mostly rumble (+45dB) from the room, as you say. Because hiss around 7kHz appears amplified to the human ear (see weighting curve "D", or D-weigthing) I would argue it is, but barely.
Once the needle touches the surface, the record itself would rightfully attract attention to itself with not only noise but also clicks, dust and all that grind we love so much ;-)

 

[StevenSGT98]

So You have 50dB of dynamic range in-room, limited by both, noise from the environment and record surface noise in roughly the same proportions, but in different frequency ranges.
Hiss from the preamp / pickup combo alone, not playing, is expected to be at -70 dB referring to peak level (+100db). Now it depends if hiss at +30dB is audible with the background of mostly rumble (+45dB) from the room, as you say. Because hiss around 7kHz appears amplified to the human ear (see weighting curve "D", or D-weigthing) I would argue it is, but barely.
Once the needle touches the surface, the record itself would rightfully attract attention to itself with not only noise but also clicks, dust and all that grind we love so much ;-)

The other side hit 103 I should state this was at 10 feet. I believe the record to be the limiting factor. This was c weighted fast response. Specs on the table say it has a S/N of 78db, which is pretty good. So if the Fosi stage is pulling 73db, I’m leaving 5 db on the table, which in reality would never be used anyway. 0db is supposed to be RIAA, correct? Meaning the hiss is below the wax and just above rumble. Dead wax was creating 5 to 8 db of noise. Some of that could be from the table itself. So, I figure there to be about 20db of headroom I never used - if the stylus is capable of tracking it.

Hiss at this gain was almost inaudible at idle.

 

[mike70]

not only noise but also clicks, dust and all that grind we love so much ;-)

That's my grandpa turntable ... today you can clean and care records. I don't listen to pop / clicks / dust, etc.

Please, listen to a modern analog system with proper care and then tell me. Do you want samples? Many on YouTube.

 

[StevenSGT98]

That's my grandpa turntable ... today you can clean and care records. I don't listen to pop / clicks / dust, etc.

Please, listen to a modern analog system with proper care and then tell me. Do you want samples? Many on YouTube.

It varies. I’ve had new stuff scratched and warped out of the sleeve, then I’ve had some approaching cd like quietness on the silence. There is an ever so occasional tiny click.

By far, the biggest problem has been the manufacturing QC issues. I’m in search for a source of consistently good vinyl. It’s elusive. Some is good. Some is not.

 

[mike70]

It varies. I’ve had new stuff scratched and warped out of the sleeve, then I’ve had some approaching cd like quietness on the silence. There is an ever so occasional tiny click.

By far, the biggest problem has been the manufacturing QC issues. I’m in search for a source of consistently good vinyl. It’s elusive. Some is good. Some is not.

I understand, you're right about QC issues ... but, suffer with dust / click / pops isn't a problem of the manufacture. Is a proper care of the record, you don't have to get that problems (unless older and already damaged records)

 

[StevenSGT98]

I understand, you're right about QC issues ... but, suffer with dust / click / pops isn't a problem of the manufacture. Is a proper care of the record, you don't have to get that problems (unless older and already damaged records)

I have an ultrasonic and vacuum. I’ve had records from the store with clicks and pops. It’s amazing how much a good clean will help vinyl. Cleans up a lot. However, damage is damage. It has to be improper plant handling.

Until the kids start caring the plants will keep doing it.

I apologize if this went off topic.

I have no problem with the Fosi x5. All this other stuff that came up points to all the faults that vinyl has to overcome. A tiny noise is a non issue. It sounds like it should. Not there.

 

[Laika2]

I have some issues with new pressings, mostly out of ex Sovit block countries like Romania and Poland but also others, researched it, seems some plants do not remove the oil from the pressings that keep the vinyl from sticking to the press. I don't have a ultrasonic at this time. Cleaners are almost all water so they don't clean oil well. I find if I use D3 with a old discwasher 3 times, drying between each and really using the diskwasher, also cleaning with distilled watter between each D3 scrub I can get the surface noise to almost zero. I do a forth clean with just distilled watter. Four almost always does it, a few times five. This is for new pressings of course. Old ones are likely not pressing oil on the record.

 

[StevenSGT98]

I have some issues with new pressings, mostly out of ex Sovit block countries like Romania and Poland but also others, researched it, seems some plants do not remove the oil from the pressings that keep the vinyl from sticking to the press. I don't have an ultrasonic at this time. Cleaners are almost all water so they don't clean oil well. I find if I use D3 with a old discwasher 3 times, drying between each and really using the diskwasher, also cleaning with distilled watter between each D3 scrub I can get the surface noise to almost zero. I do a forth clean with just distilled watter. Four almost always does it, a few times five. This is for new pressings of course. Old ones are likely not pressing oil on the record.

I pretty much clean all new records now as a precursor. I’m using cap of Photoflo in my tank. Seems to get most of it. I’ve thought about an acid pre etching to pull any embedded metal flakes out. I haven’t gotten around to it yet.

 

[StevenSGT98]

Here’s an RTA showing the impact of the stage. This is at 10ft at -5db on my system. This produced a 103 db peak as discussed in a previous post.

So a few db of audible hiss on an open system.

 

[Kolner]

Does this thing really have 10k ohm output impedance?