Fosi Audio V3 Mono Amplifier Review

[NTK]

Do u have any brand recommendations?

Monoprice makes one. I have no personal experience with it. Some people found it to be OK, some didn't like its build quality.

Amazon.com

 

[GabrielPhoto]

Monoprice makes one. I have no personal experience with it. Some people found it to be OK, some didn't like its build quality.

Amazon.com

That is one I actually tried with the Monolith 7x and Starke Fiera8 and it was not better than the RCA to RCA. In fact, I recall with the Monolith I had higher hiss with like a 1db less of output when measuring both setups which i found odd.
Since RCA to XLR does not make it balanced, and I have short runs, I dont see the value on going with such a cable but I am always interested in other opinions.

 

[NTK]

That is one I actually tried with the Monolith 7x and Starke Fiera8 and it was not better than the RCA to RCA. In fact, I recall with the Monolith I had higher hiss with like a 1db less of output when measuring both setups which i found odd.
Since RCA to XLR does not make it balanced, and I have short runs, I dont see the value on going with such a cable but I am always interested in other opinions.

View attachment 413510

The recommendation by Hypex (Bruno Putzeys) is based on sound engineering principles which are explained in the linked article.

The better but a lot more expensive way, per Rane Note 110, is to transformer isolate the unbalanced connections (see Rane Note figure 2 and below).

PI-2XX | Jensen Transformers

The design begins with a rugged flanged enclosure that comes standard with gold plated XLRs and a removable screw-down barrier strip for easy installation in NEMA enclosures. Plug and play easy to use, this passive interface does not require any power to work. Inside are two Jensen high...

www.jensen-transformers.com

or

RANE - BB22

The Rane BB22 Balance Buddy is a handy professional-grade tool used to provide isolation for and convert unbalanced -10 dBV consumer level RCA outputs up to balanced +4 dBu professional XLR inputs.

www.ranecommercial.com

 

[antcollinet]

I have tried many rca to xlr cables and never found one that was actually any better than a high quality rca to rca

This is not a huge surprise. They will only have a benefit if:

1 - you have audible ground loop noise
2 - the cable is specifically constructed as described above by @NTK with separate ground wire and 0V/negative reference wire running the length of the cable**, so three wires in total. In which case you should get in the region of 30dB reduction in the ground noise.

** many or most RCA to XLR just run two wires and connect negative terminal to ground inside the XLR cable.

 

[Owis]

** many or most RCA to XLR just run two wires and connect negative terminal to ground inside the XLR cable.

The monoprice one linked at the top of the page has three wires though yes?

 

[Down South]

I have the two monos on top of each other (the DAC on top). Yesterday, after the monos had to work for several hours while watching TV at normal room volume, both of them suddenly produced an unpleasant noise in parallel, in addition to the normal sound. First quietly and then gradually increasing to a certain level.
I touched the amplifiers and both were very warm, despite the low volume. Turning it off and on didn't help. The noise came back immediately, a little quieter than before but rose back to the previous level.
The noise is independent of the volume set on the DAC.

I use the RCA inputs at 25 dB gain and RCA outputs on the DAC.

Can someone help me with this problem. Has anyone else had this too?

not a good idea to stack the amps and then with the DAC on top. If you use all three vertically on two pieces of narrow stone or wood with the orange side pieces removed you will create a flow of air - conduction current. This will seriously lower the operating temperature and life of the components.

 

[antcollinet]

The monoprice one linked at the top of the page has three wires though yes?

Yes

 

[roog]

[Edit] However, the balanced input to the Fosi V3 Mono has only 20 dB gain (whereas the unbalanced input can be as high as 31 dB). Depending on the output level of your source, you may not be able to drive the V3 Mono to full output power.

Unless I have misunderstood, this is the issue, the signal level voltage, required to obtain full output from an XLR balanced input is double that that is normally available from unbalanced RCA. Connecting an unbalanced RCA output signal to a balanced XLR input will work but may limit the power output of the connected power amplifier.

 

[jyrg]

I just bought a set of Elac Vela 407.2 at a great price and need an amp. I have a xduoo TA-66 headphone amp which can also be used as a pre-amp. Should I just hook the speakers directly to a Fosi V3 mini or is there any advantage in getting the Monos and using them with my pre-amp?
The TA-66 does have a very nice volume control knob....

TLDR:

JDS Atom DAC --> Fosi V3 Mini (32V 5A) --> Elac Vela 407.2

OR

JDS Atom DAC --> xDuoo TA-66 --> Fosi V3 Mono (48v 5A) --> Elac Vela 407.2


Speaker specs:

Type	2 ½-Way, Bass Reflex
Woofer	2 × 150 mm Ø, AS-XR Cone
Tweeter	JET 6
Magnetic Shielding	No
Crossover Frequency	450 | 2400 Hz
Frequency Range (IEC 268-5)	30 - 50000 Hz
Sensitivity	88 dB at 2.83 V/m
Suitable for amplifiers from	4Ω - 8Ω
Recommended Amplifier Power	40 - 300 W/channel
Nominal | Peak Power Handling	130 W | 170 W
Nominal | Minimum Impedance	4Ω | 3.2Ω at 200 Hz
Finishes	Black High Gloss, White High Gloss, Walnut High Gloss
Accessories Included	Plate with Spikes and Washer
Optional Accessory	Speaker Grilles
Height x Width x Depth	1000 x 229 x 266 mm
Weight	19.1 kg

Or should I buy something totally different? I think there is no point in spending more money than what the Fosis cost?

 

[NTK]

Unless I have misunderstood, this is the issue, the signal level voltage, required to obtain full output from an XLR balanced input is double that that is normally available from unbalanced RCA. Connecting an unbalanced RCA output signal to a balanced XLR input will work but may limit the power output of the connected power amplifier.

Yep. With 20 dB gain (= 10X voltage amplification), a 2 V max input can give a maximum 50 W into 8 ohm (= 20^2/8), or 100 W into 4 ohm, etc. The recent trend of imposing low gain by amplifier manufacturers limits the usefulness of the balanced inputs.

 

[antcollinet]

Yep. With 20 dB gain (= 10X voltage amplification), a 2 V max input can give a maximum 50 W into 8 ohm (= 20^2/8), or 100 W into 4 ohm, etc. The recent trend of imposing low gain by amplifier manufacturers limits the usefulness of the balanced inputs.

Which might be a problem when driving from RCA outputs. But most balanced outputs can do 4V output (or more) which with 20dB will allow 4x the power you mention above.

 

[roog]

Well the soldering of cables has been done and a V3 is sat behind each speaker and they seem happy enough. My ATC SCM40 loudspeaker specifications state that they do 85dB @ 1W @ 1metre and they perform well. My normal amp, a 90W per ch class A/B effort lies cold!

After a couple of hours at my normal listening levels, ‘comfortable’ think loud enough to annoy the ‘mother-in-law’ the V3s are warm to touch and the 48V 5A power bricks are cold.

This is probably no surprise to you lot. :0)

 

[GabrielPhoto]

This is not a huge surprise. They will only have a benefit if:

1 - you have audible ground loop noise
2 - the cable is specifically constructed as described above by @NTK with separate ground wire and 0V/negative reference wire running the length of the cable**, so three wires in total. In which case you should get in the region of 30dB reduction in the ground noise.

** many or most RCA to XLR just run two wires and connect negative terminal to ground inside the XLR cable.

View attachment 413569
Yes

Ok thats good BUT then you replied that the monoprice cable has 3 wires and it still didnt do anything positive when I tested it, in fact the opposite. Like I actually got more hiss and less spl when I tested it with the Monolith 7x.
I am going to try that BB22 and see what I get with that.

 

[antcollinet]

Like I actually got more hiss and less spl when I tested it with the Monolith 7x.

The SPL makes sense if your monolith (as is common) has less gain on the balanced input.

Hiss could make sense if the hiss is Monolith amp hiss - and nothing to do with the cable, except that you have to turn the amp volume up to compensate for the lower gain on the balanced input.

LIke I said above. Balanced cables are only a solution to noise picked up on the cable (or generated in the cable earth as a result of ground currents). They can do nothing for other sources of noise.

 

[GabrielPhoto]

The SPL makes sense if your monolith (as is common) has less gain on the balanced input.

Hiss could make sense if the hiss is Monolith amp hiss - and nothing to do with the cable, except that you have to turn the amp volume up to compensate for the lower gain on the balanced input.

LIke I said above. Balanced cables are only a solution to noise picked up on the cable (or generated in the cable earth as a result of ground currents). They can do nothing for other sources of noise.

Ok but my point is, why I got more hiss and one db less of output with that rca to xlr monolith vs my rca to rca Blue Jeans LC-1.
That was my point. So I literally gained nothing but more hiss and less output at least with the Monolith amp. So your thought is the XLR on the Monolith has an issue?

 

[antcollinet]

Ok but my point is, why I got more hiss and one db less of output with that rca to xlr monolith vs my rca to rca Blue Jeans LC-1.
That was my point. So I literally gained nothing but more hiss and less output at least with the Monolith amp. So your thought is the XLR on the Monolith has an issue?

Not possible to say categorically in your specific case without specifically examining your gear to work out where the noise in the system is, and what the gain structure is.

I've given a couple of reasons why it MIGHT be happening.

 

[SMen]

Yep. With 20 dB gain (= 10X voltage amplification), a 2 V max input can give a maximum 50 W into 8 ohm (= 20^2/8), or 100 W into 4 ohm, etc. The recent trend of imposing low gain by amplifier manufacturers limits the usefulness of the balanced inputs.

+1 - Topping I understand have been 'canny' about gain for best measurement results - lower gain for better measurements in the amps, and then (having just been reading about their Centaurus DAC) they have switchable balanced outputs to increase a typical 4v up to 5v (or 2v to 2.5v in the case of RCA). So this seems a bit 'canny' too. I am pretty sure it was a youtube video about measurements by 'Goldensound' that he pointed out that the gain in a Topping was also optimized for the measurement equipment most often used for measuring such devices.

But then the use case of RCA to balanced is maybe not what the manufacturers need to optimize for. I might get a set of those cables just to have though - interesting about the correct wiring for noise @antcollinet .

 

[ah-ra]

If there is, I haven’t seen it. My dad listens a few hours a day with the V3 Monos I gave him, driving Maggie LRS+ to levels a good bit higher than I listen to, and has had zero issues so far.

-Ed

Does the Fosi V3 match well with the LRS+? I have the original LRS and am looking for a good amp to combine it with. At least the original LRS habe somewhat exaggerated mids, which can be annoying if the amp sounds too harsh. Yes I know some people don't believe amps can sound different, but to some extent for me they seem to do...

I remember you also had the b100 from topping which has far less power, but did you try those with the LRS as well? If so, how do they compare.

 

[EddNog]

Does the Fosi V3 match well with the LRS+? I have the original LRS and am looking for a good amp to combine it with. At least the original LRS habe somewhat exaggerated mids, which can be annoying if the amp sounds too harsh. Yes I know some people don't believe amps can sound different, but to some extent for me they seem to do...

I remember you also had the b100 from topping which has far less power, but did you try those with the LRS as well? If so, how do they compare.

The V3 Mono pair wonderfully with the LRS+!

I would not attempt to drive LRS+ with B100. Nowhere near enough power. Maybe B200…maybe.

-Ed

 

[Bleib]

I’m currently soldering the shortest speaker cables that I have ever made :0)

The only thing I might be concerned about is the big magnets on the speaker drivers. It's the only thing I can think of which could alter normal operation