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New Fosi MC351 amp/DAC received and hooked up

Brian Hall

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Received an email from Fosi yesterday about the MC351 being released. Ordered it from Amazon and received it today.

My intention is to use this to simplify my office setup and move the Fosi ZA3 and other components to another room.

Setup: MC351 output to Sony SSCS5 speakers. Inputs: CD player to coax. Wiim Pro Plus to RCA inputs. PC, Chromebox and Xbox Series X to optical (HDMI audio extractor).

First impression, very clean and clear. Much louder output than the ZA3 at the same clock position. 12:00 is loud. The MC351 has bass and treble controls. I added just a touch of bass. I love the VU meter. Not a digital display, an actual old fashioned moving needle.

First test, Sony 4k Blu-ray player using the coax input playing a CD to try out the DAC in the MC351. It sounds great. Not a blind test, but I don't hear any differences between this and the Eversolo DAC-Z8 I was using previously.

The speakers are totally silent with the CD paused. No hiss with the volume at max.

Second test, my Galaxy S23 ultra connected to the USB input, using the UPnP player Pro to play flacs (44.1/16 bit CD rips) from my server. Again using the DAC in the MC351. Played metal, country and classical tracks. All sounded perfect as expected.

Third test, Galaxy S23 ultra connected with Bluetooth. Played Spotify, Youtube Music and Tidal. All sounded great.

Fourth test, Hiby R6 Gen 3 DAP connected to USB. Played flac files (44.1/16 CD rips) stored on the DAP. Sounded great.

Fifth test, PC running Linux connected with optical. Played flac files from my server, Spotify, Youtube Music and Amazon. Sounded great.

Sixth test, Wiim Pro Plus connected to RCA jacks (using the Wiim's DAC). Played Tidal. Had to turn it down. Tidal always plays louder than any other service. Sounded great.

I like the MC351 so far. Great sound and seems to have a good DAC. More power than the ZA3.

Now I need to figure out what to do for a headphone amp. The MC351 has a preamp out (3.5mm). I hooked that up to my Schiit Midgard using a 3.5mm stereo to RCA connection. The pre out volume is controlled by the volume control. The headphone amp worked, but still had output going to the speakers which won't do. Any suggestions for this?

Fosi, if you are listening, this would have been the perfect DAC/amp if you had just included headphone amp functionality or a switch to cut off the speaker output.
 
Can you confirm if it has an adjustable crossover (low pass and high pass) for the speaker outputs?
Thank you

Sorry, I have no idea. The pre out sounds like full range going to my headphone amp and headphones based on a quick listen with the speakers unplugged.
 
Can you confirm if it has an adjustable crossover (low pass and high pass) for the speaker outputs?
Thank you
From what I can tell, there's nothing on the MC351 to adjust a crossover with. No knob, toggle switch, etc.

Furthermore, nothing on the MC351's website suggests that it is capable of high-passing the Mains.

My guess is that the Main out is full-range and the Sub out has a fixed LPF.
 
The DAC inside is speced at 90dB Sinad, but we'll, seems that good enough.
 
Size comparison of the MC351 to the ZA3:

49734.jpeg
 
according to the manual the BT is only sbc/aac

coax opt = 24/192

usb = 24/96

so i'm guessing they are not using a current DAC nor are they using a current USB input processor
 
I wonder how @Fosi Audio intends a user to match the level of their passive subwoofer to their passive mains.

With an active sub plugged in via RCA Sub out, one can just use the volume knob on the back of the sub to match levels.

But with a passive sub, there is no such volume control.

Is that not a major design fail?

Basically, either you win the lottery by having a sub and main speakers with identical sensitivity, or you just live with whatever unbalanced sub<->mains sound comes out of the MC351?

Seems like an incredible oversight to me..
 
What DAC chip is used in the MC351?
Where can we see the specifications for the USB input?

I haven't been able to find anything about which DAC chip is used.

The manual says:

Sampling rate:

USB 24bit/96khz
Opt/Coax 32bit/192khz
 
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What DAC chip is used in the MC351?
Where can we see the specifications for the USB input?
From this teardow:
SSS 1700: USB bridge maybe USB DAC as well (has DAC and i2s output as well). This is the most limited and worst performer of the bunch.
MS8412: probably spdif DAC
ATS2853: bluetooth
all of them ballpark 75-90 dB THD+N

 
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From what I can tell, there's nothing on the MC351 to adjust a crossover with. No knob, toggle switch, etc.

Furthermore, nothing on the MC351's website suggests that it is capable of high-passing the Mains.

My guess is that the Main out is full-range and the Sub out has a fixed LPF.
That would be a major miss...in my opinion a full and adjustable crossover would be the minimum for a 3 channel amp (SMSL's 3 channel amp does have that for 89 USD....)
 
I've been playing The Eagles - Hotel California from Qobuz through the Wiim App. Says it is 24/192. Using the Wiim Pro Plus dac (RCA out to the MC351) vs the MC351 dac (Coax out to the MC351).

Not a blind test. Just switching outputs in the Wiim app and inputs on the front panel of the MC351.

As expected, I don't hear any differences between the dacs other than volume. The Wiim RCA output is louder than the coax output. Whatever dac is in the MC351 is good enough for me.
 
I have this on my cart but I can't pull the trigger to buy it.

On the back of my mind....
What am gonna do with that passive sub output?
What is the DAC chip?
Why no option in buying the unit only?
I don't have a passive subwoofer, I have a few idle dac units from smsl and topping, I have extra PSUs from ZA3s and other brands....
 
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Another piece of work from Fosi, this time with BAD DESIGN on different levels.
Hard to believe that this is from the same team that designed the V3, ZA3 and V3 PFFB.
 
Another piece of work from Fosi, this time with BAD DESIGN on different levels.
Hard to believe that this is from the same team that designed the V3, ZA3 and V3 PFFB.

It was close to being great. I noticed a slight manufacturing defect. There is some type of glue on the front below the VU meter.

It isn't going to let me simplify my office setup like I was hoping. I've decided to return it and go back to the ZA3. I will say it sounded good and could go louder than the ZA3.

Fosi: To make the next version great, I recommend the following changes:

1. XLR inputs
2. The VU meter looks great, but there should be two for left/right
3. Include a 1/4" headphone jack and cut off the speaker output when a headphone is connected
4. Make the case bigger, the same footprint as an Eversolo DMP-A6 and include some vents like the ZA3. It gets pretty hot.
5. Lose the passive sub woofer output and replace it with a coax output for active subs
6. Add a remote control for volume and input selection
7. Easier to read indicators for the selected input. Instead of a light next to the tiny letters for the selection, put the light behind the selection so it is readable
8. Add an additional optical or coax input
9. Add a couple of mid range knobs in addition to the bass and treble, something like the Schiit Loki
10. The dac chip sounded fine to me, but others seem to be objecting to the one you used

The current version is priced at about $185. Make the changes listed above and I would be glad to pay quite a bit more.
 
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