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Fosi V3 Monos - Gain Settings ?

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Posted on September 11, 2024 at 10:46:58
AbeCollins
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Location: Maidenhead Grid Square DM79
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February 2, 2002
I read somewhere that the Fosi manual describes internal gain settings for their V3 monos.

Is this true?

How are the settings made? Jumpers? Switch?

Is there an online manual for the V3 monos?

P.S. I also read this:

"For V3 MONO units purchased on or after August 2nd, 2024: The output polarity of V3 MONO has been revised. You can connect your speaker terminals normally without reversing the polarity."


 

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Apparently, posted on September 11, 2024 at 13:12:13
E-Stat
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the Fosi manual describes internal gain settings for their V3 monos.

for single ended input only.



 

Thanks! I was able to find gain via XLR which is, posted on September 13, 2024 at 08:55:14
AbeCollins
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...only 20dB but much better for me in my setup vs very high gain beyond about 28dB.

Why is this important in my setup? You can call it gain matching and the details are as follows.

If the amp gain is too high, I have insufficient signal from my preamp to fully drive the powered subs. Why?

I use the balanced XLR from my preamp to drive the power amp but I additionally use the RCA outputs from the preamp to drive the subs. If the amp has a high amount of gain that means the preamp volume control is turned way down.... which also means the signal from the RCA outputs is lowered significantly to the point that the subs aren't getting quite enough signal (even if the subs are turned way up).




 

You're welcome!, posted on September 13, 2024 at 09:18:50
E-Stat
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Agree about models having too much gain and output these days. Some brands game the distortion results with models producing 5.2V output! What kind of amplifier needs that?

In my case, the line stage provides 14 db. Which is plenty given that using balanced connections, the DAC alone could easily overdrive the power amps. Like others, however, I have discovered that having an active preamp (paradoxically) really does provide a better overall experience. For reasons that engineers like Charles Hansen and reviewers like John Atkinson cannot reconcile, having reserves of low impedance drive(?) can work wonders. While still not requiring any *correction* for low distortion output with my unit.

Since I occasionally enjoy listening to my vinyl collection, I like the fact that the phono stage offers 58 db of gain which allows the preamp as a whole to easily drive a mid output MC cartridge.

In the HT system using a pair of powered subs, the output comes from a separate LFE channel that can be individually adjusted for output. I attenuate at the sub itself for linear output.


FWIW, it has only taken me ten years to finally test out the headphone output. :)

I ordered a 1/4 phone plug to 3.5mm stereo adapter from Azon (to be delivered tomorrow) for my Shure SE535s. The pre "bolts on" LME49720 secondary unity gain buffers to further lower output Z to front panel jack.

edit: Just did my first listen. The Shures are waaaay too efficient and noise level is high. Full gain is at about 26 on the volume scale where normal operation is more like 80 or slightly higher.

 

Hey, Abe, if you decide to get these..., posted on September 15, 2024 at 10:44:12
AudioDwebe
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Posts: 1924
Location: Pacific Northwest
Joined: November 12, 2001
I'd highly recommend getting the Sparkos opamps (two are required for each mono if using XLR). The opamps made a rather significant improvement IMO.

I've had a pair for a few months now with the lower power bricks (one for each mono) and while I thought they sounded pretty good stock, once I swapped the opamps, I felt these tiny amps truly excelled.

With them in place, I noticed a few subtleties in a few of my test tracks that I've been using for many years. Hearing these differences really blew my mind, to say the least.

I'm using them in balanced mode only, so the cost of the opamps brought the price to sub $600, which isn't exactly inexpensive but in the audiophile community that sum is really damn near dirt-cheap.




"Man, that mouse is Awesome." - Kaemon (referring to Jerry, of Tom and Jerry fame)

 

I've played with passives, posted on September 15, 2024 at 12:10:36
AbeCollins
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It's interesting that many of the FirstWatt amps from Nelson Pass are fairly low gain designs requiring much more drive from the preamp which means these amps are not very well suited for use with passive preamps.

I have observed the same thing as you. A passive is often the one trick pony "King of Transparency". But a passive will often suffer in other areas sometimes sounding a little thin but most notably not as "alive" as a good active. In most systems a good active preamp will sound better overall with better dynamics.

I had one excellent sounding system using a passive preamp but the other components in the system were critical - all the stars had to align just right or a passive based system will fall apart in the areas described above. So one doesn't just wake up one day and say, "I think I'll swap out my active preamp and try a passive".

I have a very nice sounding older Schiit headphone amp and a couple good headphones. I just can't seem to enjoy them preferring instead to sit in front of my speakers about 12-ft away.



 

Thanks for the tip...., posted on September 15, 2024 at 12:17:08
AbeCollins
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I'm curious about the Fosi V3 monos as others have praised them as excellent 'bang for the buck' amps. Good to know that the Sparkos op-amps improved their performance. Like you, I would need two op-amps per V3 mono as I prefer running balanced interconnects.



 

Me too, posted on September 15, 2024 at 12:22:17
E-Stat
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I just can't seem to enjoy them preferring instead to sit in front of my speakers about 12-ft away.

My IEMs are really for mobile use. I typically use AirPod Pros while on the lawn tractor but the last time I tried, one bud was not charged. I somehow screwed up. No problem. Attached my wired SE535s and minimized potential cable snarl by routing it down through my shirt into pants pocket where phone was located.

Provided better isolation than "active noise cancellation" with custom sleeves where you twist them into your ear canal. Eliminates inherent Apple mid bass hump as well. Still like convenient BT based solution in some cases.

Back in the day I had headphones like the classic Koss Pro4AA and Stax electrets. Never did much for me in home setting.

 

Let us know your thoughts if you get them., posted on September 17, 2024 at 21:00:36
AudioDwebe
Audiophile

Posts: 1924
Location: Pacific Northwest
Joined: November 12, 2001
There's a review by virtualHIFI on youtube that is excellent, if you haven't already seen it.

I don't know how to link it here, unfortunately.







"Man, that mouse is Awesome." - Kaemon (referring to Jerry, of Tom and Jerry fame)

 

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