Fosi Audio V3 Mono Amplifier Review

[antcollinet]

I’ll be using Wiim Ultra as source which only has RCA out. Would using RCA to XLR cables into the V3 Mono’s offer any improvements? I know the signal would still be unbalanced, however wondering if using RCA to XLR cables could offer lower noise and higher dynamic range, as V3 is rated to perform better with XLR input

The answer to that is not simple.

First - if you experience no audible noise, then there will be no benefit to connecting to the XLR input.

If you are getting audible ground noise, then XLR will only help if you use an RCA to XLR cable wired as "pseudo balanced" using a 2 wire plus shield cable, with the shield and "cold" wire both connected to the ring at the RCA end, but at the XLR end they are separately connected to pin 1 (shield) and pin 3 (cold). The Hot wire is connected to pin at the RCA end and pin 2 at the XLR end.

Most RCA to XLR cables are not wired this way and it is difficult to identify those that are.

In any case you don't get a better dynamic range, because that relies on the higher voltage on an XLR output - which obviously the Ultra doesn't have.

 

[Rotel75]

I’ll be using Wiim Ultra as source which only has RCA out. Would using RCA to XLR cables into the V3 Mono’s offer any improvements? I know the signal would still be unbalanced, however wondering if using RCA to XLR cables could offer lower noise and higher dynamic range, as V3 is rated to perform better with XLR input

The volume/gain is different, XLR 20dB vs RCA 25/31dB
You can skip the RCA opamp

I think amps only need XLR inputs (see Topping B200).
Just use the appropriate cable/adapter

 

[SeaBeef]

The volume/gain is different, XLR 20dB vs RCA 25/31dB
You can skip the RCA opamp

I think amps only need XLR inputs (see Topping B200).
Just use the appropriate cable/adapter

Sorry how do I skip the RCA opamp? By using RCA to XLR cables out of the Wiim?

 

[Rotel75]

Sorry how do I skip the RCA opamp? By using RCA to XLR cables out of the Wiim?

yes, see here
I'd say, the less opamps the better

 

[SeaBeef]

yes, see here
I'd say, the less opamps the better

The signal would still be unbalanced though wouldn’t it? Even if using XLR

 

[antcollinet]

The signal would still be unbalanced though wouldn’t it? Even if using XLR

If you use the psuedo balanced cable I identified above you get most of the benefits of balanced for ground noise rejection. Based on a back of the envelope calculation I did, you get around 30dB noise rejection, compared with around 40dB for fully balanced, depending on the output impedance of the RCA device.

Note that this only works from RCA to balanced - not the other way around.

 

[SeaBeef]

If you use the psuedo balanced cable I identified above you get most of the benefits of balanced for ground noise rejection. Based on a back of the envelope calculation I did, you get around 30dB noise rejection, compared with around 40dB for fully balanced, depending on the output impedance of the RCA device.

Note that this only works from RCA to balanced - not the other way around.

I understand this, and may make some semi-balanced cables if I run into noise.

@Rotel75 was saying that if I use RCA to XLR it would bypass the RCA opamp, however according to the Fosi spec sheet, it says opamp 1 is for unbalanced to balanced conversion. Using RCA to XLR would still be unbalanced, so not sure if this would infact bypass opamp 1…

 

[antcollinet]

I understand this, and may make some semi-balanced cables if I run into noise.

@Rotel75 was saying that if I use RCA to XLR it would bypass the RCA opamp, however according to the Fosi spec sheet, it says opamp 1 is for unbalanced to balanced conversion. Using RCA to XLR would still be unbalanced, so not sure if this would infact bypass opamp 1…

It will - you just will have a balanced input with only the hot wire carrying signal. But skipping an op amp or two - the difference will be well down below the level of audibility.

The improved measurement of the XLR input comes from the increased input voltage and correspondingly reduced gain. Not from reduced op amps.


What you might get though is if the amp is fully balanced internally - ie each one of the balanced signals independently driving 1 half of the bridged amp, (and I don't know if it is or not) then when driving only one of the balanced input signals, only one half of the amp bridge will be driven, resulting in output voltage being limited to half the full value, and the amp only capable of 1/4 power.

 

[MCH]

I understand this, and may make some semi-balanced cables if I run into noise.

@Rotel75 was saying that if I use RCA to XLR it would bypass the RCA opamp, however according to the Fosi spec sheet, it says opamp 1 is for unbalanced to balanced conversion. Using RCA to XLR would still be unbalanced, so not sure if this would infact bypass opamp 1…

I am not sure how the fosi is wired internally, but be aware that if you use the cable in post 4050 you might end up using half of the 4 inputs of the amp chip. In doubt, I would stay RCA to RCA. Maybe others here can confirm.

 

[SeaBeef]

I think I’ll just stick with RCA to RCA haha

 

[antcollinet]

I think I’ll just stick with RCA to RCA haha

Good plan.

 

[somebodyelse]

I think amps only need XLR inputs (see Topping B200).
Just use the appropriate cable/adapter

I don't know about the B200, but Topping implemented the B100 as a bridged pair of single ended amps - hot drives +ve output, cold drives -ve output or vice versa. If you use an RCA to XLR cable, or an impedance balanced output with only one side driven, then you only use one of the two amps, and can't reach rated output. A high performing balanced input to drive a bridged output will need more opamps. See 'The G Word' for details.

 

[SeaBeef]

Has anyone worked out a simple way of powering the 12V Fosi fans to turn on and off automatically with amps? The Wiim Ultra has a 3.5mm mono plug trigger which I could use

Also my Elipson XLS 15 speakers are rated 6ohms but reported to drop as low as 3.2ohms. Would the V3 Mono handle this okay?

 

[Old_School_Brad]

I think I’ll just stick with RCA to RCA haha

K.I.S.S.

 

[antcollinet]

Also my Elipson XLS 15 speakers are rated 6ohms but reported to drop as low as 3.2ohms. Would the V3 Mono handle this okay?

Yep - if you look at the review (next to last test), Amir took the power cube tests down to 2ohm, and the mono aced it.

 

[Sokel]

I don't know about the B200, but Topping implemented the B100 as a bridged pair of single ended amps - hot drives +ve output, cold drives -ve output or vice versa. If you use an RCA to XLR cable, or an impedance balanced output with only one side driven, then you only use one of the two amps, and can't reach rated output. A high performing balanced input to drive a bridged output will need more opamps. See 'The G Word' for details.

Not necessarily,depends on the circuit.It can run as a loop with the right config,key is balancing the output impedance of the pre with a resistor at the cold output.
I don't know how Topping does it but that's how it looks at a bridged icepower:



Of course the output of the SE pre is usually half,so...

 

[somebodyelse]

Not necessarily,depends on the circuit.It can run as a loop with the right config,key is balancing the output impedance of the pre with a resistor at the cold output.
I don't know how Topping does it but that's how it looks at a bridged icepower:

View attachment 423223

Of course the output of the SE pre is usually half,so...

Of course plenty of amps with balanced inputs do it properly, bridged or not. I draw attention to it because the B200 was mentioned, and @pma found this specific problem with the B100 when testing long term power output. Schiit do the same with the XLR for the Vidar 2, but they at least mention it in their FAQ.

 

[Sokel]

Of course plenty of amps with balanced inputs do it properly, bridged or not. I draw attention to it because the B200 was mentioned, and @pma found this specific problem with the B100 when testing long term power output. Schiit do the same with the XLR for the Vidar 2, but they at least mention it in their FAQ.

Yes,I now remember the problem.
Strange choice though.

 

[drodgers]

Cool. Have you shared the 3D printed stand design on Thingiverse or elsewhere?

Yep, it's available here: https://www.thingiverse.com/thing:6920770

 

[telemike]

My new setup