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Amateur Review: Fosi Audio 300w desktop sub amp


pioneerisloud
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Hello everyone and welcome to another video.  Don't forget to hit that like and subscribe button.  Oh wait, I'm not a youtuber!!! 🙃  Seriously, I'm not.  I don't care about those silly metrics.  What we're here for today is this Fosi Audio 300w desktop monoblock amplifier I bought the other day on ebay.

 

Well, let's start off with some unboxing shall we?

 

Here we have their product box.  I do like that its simple.  Box has some basic ink printed on it, but its just a box.

20220216_202614.thumb.jpg.9b183c8a0ba30ee711762f80711ce537.jpg

 

And when we open up the box, this is what we see:

20220216_202623.thumb.jpg.671574a1a6d1e4a67432485c0fab66f0.jpg

 

Everything in the box unpacked on my desk.  We have the amplifier itself and a 32v / 5a power brick.  Fosi Audio states that to get FULL POWER out of it, you need to upgrade to a 32v / 10a power brick.  I'm using a 6.5" 100w subwoofer, so I don't need to do this.  The stock power brick is fine for my uses, and they claim 150w capable with the stock brick.  Let's see if that's true.

20220216_202652.thumb.jpg.94859d10fe2cebd13e9dad1ff04ca88d.jpg

 

20220216_202702.thumb.jpg.99d0c1cf46ab91f2c73b475e70111b05.jpg

 

As far as controls and inputs on the unit, let's take a look at that.  On the front of the amp, we have from left to right, a power switch, subwoofer or full range switch, crossover frequency knob when set to subwoofer mode, and the gain knob to match the inputs to the outputs.

20220217_162155.thumb.jpg.ba77c260f3137ef1a1ee5bbb8816821d.jpg

 

On the back of the unit, we have very basic ports to use.  Again, left to right, we have the R/L RCA inputs from your source (or from a powered subwoofer RCA out), a powered subwoofer out if you wanted to daisy chain another sub in the system, the mono speaker output, and the DC power jack.

20220217_162204.thumb.jpg.9396313866e06b3d5d7aa6d015085b3a.jpg

 

 

 

Testing:

 

So for testing, I decided to go ahead and use the old tried and true DMM method with a test tone.  For those not familiar with that method, I've made a video (below).  Basically, you crank up your speaker amp to highest level with no distortion, and then you slowly turn up your sub amp and see what kind of voltage you get out of it on AC-V.  The tone that I used today was 40Hz due to it being a subwoofer amp that I was testing.  If I were testing a speaker amp it'd be somewhere in the realm of 80-100Hz.

 

So when I started off, I noticed that my SMSL AD18 speaker amp is kind of interesting.  It starts distorting around volume 40 / 60.  So volume 40 is where I stuck it at for the subwoofer amp testing.  Disconnected my speakers from it (so I don't cook them or tick off my neighbors).  What I found was that the Fosi Audio mono amp was capable of around 28vAC coming out of the leads.  At a 4ohm load, this equates to around 196w.  196!!!  That's pretty impressive for a claim of 150w on their ad.  I also noticed that it stops putting out (more) power around the halfway mark on the gain on the sub amp.  This is pretty normal for a subwoofer amp.  I was not expecting to see similar out of my AD18, however I'm not surprised as both amps are Class D amps.

 

Now, I do want to make note that testing with a DMM and test tone is a VERY BASIC test.  It doesn't show anything except those numbers I just went over.  I cannot comment on distortion at that level since my sub can't handle that type of power anyway clean or not.  I also lack the proper equipment to actually test those things.  So what we have here is a basic test anybody can do at home with a $4.99 Harbor Freight DMM.

 

Testing the amp with my DMM and 40Hz test tone:

 

 

Now, how does this little amp sound and does it do what Fosi Audio claims it does for the low price of $79 on ebay?  Well, to start off with the crossover function for subwoofers does in fact work.  I'd have to get really serious about testing the frequencies but it DOES appear to be variable between about 40Hz - 250Hz according to my ear.  It could be off a tad, but my ears won't notice nor care (yours probably won't either).  The switch to change the amp into a full range mono amp ALSO does work.  Unfortunately I only had a subwoofer hooked up, with a subwoofer signal going into the amplifier, so I couldn't actually test (in this amount of time) with a full range speaker.  But you COULD in theory use two of these to power speakers.  I wouldn't personally, but you could.  Again, keep in mind this amplifier is MONO.

 

After the testing, I tried listening to some regular music on it.  Off camera since copyrights and all that jazz.  I found for my listening, in my setup, I was very happy with the crossover set to 40Hz and the gain set to 1/2.  My Micca's extend down to right around 60Hz or so themselves, so I just needed a little oomph below that.  My "new" subwoofer setup gets down to about 37Hz successfully now, and blends down from that 60Hz range very smoothly.  There's definitely a peak at the tuning frequency of the sub at 40Hz, which I expected.  However its not anywhere NEAR as boomy as it was before running a car amp to it with a fixed 80Hz crossover.  Now, instead of being boomy at 50-60Hz, it just kind of smoothly transitions from the speakers down to the sub.  Perfect!

 

Personally, I really like this little amp and I don't say that a whole heck of a lot about a subwoofer amp.  It absolutely met my expectations and actually exceeded them for what it is.  Will this amp power a monster 15 or 18" sub capable of 500w RMS or better?  No, absolutely not.  Will it power a basic passive subwoofer of any size in the 100w range?  Oh absolutely it will with ease!  I will also make note one more time that Fosi Audio does recommend a 32v / 10a power supply for this amplifier to get its full power capabilities out of it.  So its possible with a bigger PSU it might be capable of double the power that I saw today.

 

Testing with music:

 

With all of the above said, I hope you guys enjoyed it.  Please leave a like, comment, subscribe if you weren't already, and I'll see you in the next one.  Oh wait.....I did it again, I've been WATCHING too many youtube videos I guess!!! :lachen:  Seriously though, this review was made of my own will.  It was NOT sponsored by Fosi Audio at all.  I did send them an offer of a lower price, and told them in the offer I'd write a review.  They did not ask, I just proactively offered to do so because I thought it'd be fun.  But it was not sponsored, I bought and paid for this amp.

Edited by pioneerisloud
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  • pioneerisloud changed the title to Amateur Review: Fosi Audio 300w desktop sub amp

Okay, all edits are done.  Review finalized.  Hope you guys enjoy.  If anybody is looking for how to test power output, or if they're looking to build / buy a passive subwoofer.  This review might come in handy. 🙂 

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GPU: Ref Powercolor RX 5700XT @ 2050 / 1800
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I think this site should have a section for amateur reviews. Maybe there would be a barrier to be able to post reviews, like a certain amount of rep. I like seeing this kind of user made content here. It's fun to make and read through. 

 

Nice review.👍

Edited by UltraMega
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2 hours ago, UltraMega said:

I think this site should have a section for amateur reviews. Maybe there would be a barrier to be able to post reviews, like a certain amount of rep. I like seeing this kind of user made content here. It's fun to make and read through. 

 

Nice review.👍

I think that's a wonderful idea!

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GPU: Ref Powercolor RX 5700XT @ 2050 / 1800
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A great read ! Thanks for sharing. As for an amateur review section on the site. I have no issue with that, sounds like its something that could work out. 

 

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15 minutes ago, pioneerisloud said:

I think that's a wonderful idea!

If me and Pioneer agree on anything, that means something. 😅😆

Edited by UltraMega
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16 minutes ago, ENTERPRISE said:

A great read ! Thanks for sharing. As for an amateur review section on the site. I have no issue with that, sounds like its something that could work out. 

 

Agree totally. Have seen some good content coming out of our user base. Would be more than happy to help moderate that section if it is created. 

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9 hours ago, UltraMega said:

If me and Pioneer agree on anything, that means something. 😅😆

:lachen:

 

We just have vastly different view points on some things, and that's perfectly okay!  We are products of our environments afterall.  Amateur review section is a fantastic idea, and I will gladly agree and back you up with that motion.  Like I always said when we had our scuffles off the site, we can always agree to disagree and move on. 🙂

Believe it or not UltraMega, I do value your input.  Even if it doesn't seem like it sometimes.

 

9 hours ago, ENTERPRISE said:

A great read ! Thanks for sharing. As for an amateur review section on the site. I have no issue with that, sounds like its something that could work out. 

 

Thanks E!  I had a lot of fun writing it.  If we had an amateur review section dedicated for these kind of things, I'd happily write more of them for other products I might buy.  Of course I wouldn't review the junk I buy, but anything I buy brand new, I'd review on the site if it was tech related. 🙂 

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GPU: Ref Powercolor RX 5700XT @ 2050 / 1800
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CPU: Ryzen 5800x
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PSU: Seasonic Focus GX Gold 1000w
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Moved to the new Amateurs Review section 🙂

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