Fosi Audio V3 Mono Amplifier Review

[rsqt]

Right - but now. you are connecting an antenna to an open RCA input which has high input impedance. It is not representative of real world listening, and has no bearing on what the noise of the input is like.

Short the other end of the RCA cable - and the noise will go away - that is what a low impedance output of a source looks like.

I did so and there is (no normal) noise over the complete frequency range. I have 4 Fosis and they all do this. The 3E is quiet.

 

[rsqt]

Using RCA the noise is "pulsing" a bit. Using the XLR input with XLR/RCA adapter and RCA cable it is nearly gone. Ear 20cm in front of the speaker.
Maybe this is the better way.

 

[TurtlePaul]

I did so and there is (no normal) noise over the complete frequency range. I have 4 Fosis and they all do this.

As the Fosi have no volume control, there is likely no resistor between signal and ground when the input is open. The volume pot on the A7 pulls the input down to ground when there is no source connected and hence you hear nothing. The Fosi should have less Johnson noise, although that is usually very small.

 

[rsqt]

I have the 3E Mono DIY boards without volume control.

 

[Jost Buergi]

Let's assume we have a preamp without XLR outs but it's able to deliver up to 3 Volts or more on its RCA outs (with good SINAD). Am I right that in this case V3 Mono's XLR input is a good input choice, using a RCA to XLR cable?
Because if my maths are correct it only takes around 2.7 Volts on its XLR input (20.5 dB gain) to drive the V3 Mono to its max. power output.

Bonus question: would the XLR input also yield a SINAD advantage on the amps's side (-100 dB XLR vs. -94 dB RCA acc. to Amir), or maybe in crosstalk..., or would this require a "real" balanced connection?

 

[antcollinet]

Let's assume we have a preamp without XLR outs but it's able to deliver up to 3 Volts or more on its RCA outs (with good SINAD). Am I right that in this case V3 Mono's XLR input is a good input choice, using a RCA to XLR cable?
Because if my maths are correct it only takes around 2.7 Volts on its XLR input (20.5 dB gain) to drive the V3 Mono to its max. power output.

Bonus question: would the XLR input also yield a SINAD advantage on the amps's side (-100 dB XLR vs. -94 dB RCA acc. to Amir), or maybe in crosstalk..., or would this require a "real" balanced connection?

There is no benefit to using the XLR input unless you are experience ground noise on the RCA input AND you use a properly wired "pseudo balanced" cable. Most RCA to XLR cables are not.

The sinad improvement in the measurements between RCA and XLR are almost entirely due to the higher input voltage, and hence lower gain. 6dB is directly related to doubling of the voltage.

 

[Jost Buergi]

There is no benefit to using the XLR input unless you are experience ground noise on the RCA input AND you use a properly wired "pseudo balanced" cable. Most RCA to XLR cables are not.
The sinad improvement in the measurements between RCA and XLR are almost entirely due to the higher input voltage, and hence lower gain. ...

Thank you! Sounds good because basically I do consider XLR just as a lower gain input option. So connecting RCA out to XLR in is generally nothing to be concerned about, right?

Can someone pls suggest such properly wired "pseudo balanced" cables? Don't how how to recognize them.
Sorry for my pedestrian questions. If there are resources on that topic I'll gladly read into it.

 

[mike70]

Thank you! Sounds good because basically I do consider XLR just as a lower gain input option. So connecting RCA out to XLR in is generally nothing to be concerned about, right?

Can someone pls suggest such properly wired "pseudo balanced" cables? Don't how how to recognize them.
Sorry for my pedestrian questions. If there are resources on that topic I'll gladly read into it.

A topic on that:

D

'RCA to XLR Cable ("pseudo-balanced") to buy ?'

Feb 1, 2023

just a short question here:

I want to buy (not DIY) RCA to XLR (male) cables in the ("pseudo-balanced") fashion that Hypex and others recommend (see picture below).

I want to buy ready made / 'off the shelf' cables (of several different lenght) that are of very good* "mechanical" quality,
*by this I mean good materials and well done workmanship, ("should be pleasing to my fingers and eyes") -> I do not mean any cable-woodoo silver rhodium ultra high resolution blah blah

Any quick recommendations from your experience (a link is sufficient).




drawing from Hypex Datasheet:...

• Dirk_67
• Replies: 52
• Forum: General Audio Discussions

• 

And ... you can use converters ...

https://www.amazon.com/Nobsound-Balanced-Converter-Audio-Selector/dp/B07D7P7366

 

[rsqt]

Someone here on ASR tested several cheap converters and none was really good. If they do not say anything about noise and THD......I would not buy it.

This one works well.

Non-Balanced to Balanced Preamplifier Kit, Some Funny Ideas for Those with Good Ears

Converts uncompromisingly any unbalanced signal in the audio range into balanced - 2 channels.

www.kaltecs.com

 

[mike70]

Someone here on ASR tested several cheap converters and none was really good. If they do not say anything about noise and THD......I would not buy it.

This one works well.

Non-Balanced to Balanced Preamplifier Kit, Some Funny Ideas for Those with Good Ears

Converts uncompromisingly any unbalanced signal in the audio range into balanced - 2 channels.

www.kaltecs.com

Mmm ... do you think that?
The switcher on the same line of products was spectacular.

'Little Bear MC3 XLR & RCA Switch Review'

Jun 17, 2023

This is a review and detailed measurements of the One Little Bear (Nobsound/Duok) Little Bear MC3 XLR and RCA switcher. It is on kind loan from a member and costs US $69.99.

I like the large knobs although I wished they had aligned them better. As you see, you can switch between one RCA and two XLR connections:

This is a passive device so no conversion between the types. The box is heavy enough for RCA use but my XLR cables managed to topple it backward. Still, quality is pretty good for such a low price.

Little Bear MC3 Switcher Measurements...

• amirm
• Replies: 75
• Forum: Amplifiers, Phono preamp, and Analog Audio Review

• 

 

[SoySalsaPicante]

Thank you! Sounds good because basically I do consider XLR just as a lower gain input option. So connecting RCA out to XLR in is generally nothing to be concerned about, right?

Can someone pls suggest such properly wired "pseudo balanced" cables? Don't how how to recognize them.
Sorry for my pedestrian questions. If there are resources on that topic I'll gladly read into it.

Buckeye is selling this type of cable, fully pre-fabricated:

Buckeye Amps Cables

Buckeye Amps utilizes the most advanced audio amplifier technologies available. Authorized seller for Hypex and Purifi Class D amplifiers. Based in the US. Free shipping and worldwide service!

www.buckeyeamp.com

 

[rsqt]

Mmm ... do you think that?
The switcher on the same line of products was spectacular.

'Little Bear MC3 XLR & RCA Switch Review'

Jun 17, 2023

This is a review and detailed measurements of the One Little Bear (Nobsound/Duok) Little Bear MC3 XLR and RCA switcher. It is on kind loan from a member and costs US $69.99.

I like the large knobs although I wished they had aligned them better. As you see, you can switch between one RCA and two XLR connections:

This is a passive device so no conversion between the types. The box is heavy enough for RCA use but my XLR cables managed to topple it backward. Still, quality is pretty good for such a low price.

Little Bear MC3 Switcher Measurements...

• amirm
• Replies: 75
• Forum: Amplifiers, Phono preamp, and Analog Audio Review

• 

It is only a switch, not a real converter. It is the same as in a RCA/XLR cable, only pseudo XLR.

 

[Punchy_Power_Cat]

Can the Fosi V3 Mono be run with 24V?

The TPA3255 says yes, but the writings on the DC-slot say 32V minimum.

I realized I don't need that much power, but I could run it off an isolated 90W PSU but they only come up to 24V.

 

[effj]

Can the Fosi V3 Mono be run with 24V?

The TPA3255 says yes, but the writings on the DC-slot say 32V minimum.

I realized I don't need that much power, but I could run it off an isolated 90W PSU but they only come up to 24V.

The spec sheet on their website says voltage range 32V to 48V.

 

[rsqt]

I think you need some more voltage that the small regulators are able to generate the clean voltage for the opamps which is about 32-36V.

 

[Punchy_Power_Cat]

How do you guys think a 32V suppy would alter performance in terms of SINAD compared to a 48V?

The issue at hand is that those TPA32XX chips somewhat get better THD with higher wattage output, of course up until they reach a threshold and collapse right after.
So they have a sweepspot around 75% of their capability in terms of wattage.

This means: If I use an overpowered Fosi V3 Mono with an undersized speaker that will max. out long before the THD-curve of the TPA amp gets into its sweep zone, I don't get to benefit from this chip as much as I could. So driving it from a 32V supply could -in that case- be benefitial to SINAD, because it would need to go higher/nearer to its sweep spot to drive these lower power speakers compared to the 48V. Or am I wrong?

 

[NTK]

How do you guys think a 32V suppy would alter performance in terms of SINAD compared to a 48V?

The issue at hand is that those TPA32XX chips somewhat get better THD with higher wattage output, of course up until they reach a threshold and collapse right after.
So they have a sweepspot around 75% of their capability in terms of wattage.

This means: If I use an overpowered Fosi V3 Mono with an undersized speaker that will max. out long before the THD-curve of the TPA amp gets into its sweep zone, I don't get to benefit from this chip as much as I could. So driving it from a 32V supply could -in that case- be benefitial to SINAD, because it would need to go higher/nearer to its sweep spot to drive these lower power speakers compared to the 48V. Or am I wrong?

In Amir's test of the Fosi V3 Stereo, the SINAD performance of 32 V and 48 V supplies were the same at low power. I doubt there is any benefit from using a lower supply voltage for lower power levels.

 

[BrooklynNick]

Can someone please tell me the input impedance of this amp? I can't seem to find it and I need to know for configuring an external high pass filter's dip switches.

 

[Punchy_Power_Cat]

I doubt there is any benefit from using a lower supply voltage for lower power levels.

Now that I reviewed the review I am pleased to note that the Fosi V3 Mono is even better performing in 8ohm leaving it just slightly (~-3db SINAD) behind the infamous e3 Audio A5 nearly on par with the better brother and more expensive e3 Audio A7/A7 Mono. This accounts only for 20Hz-1Khz which is perfect for my use case as an amp driving dedicated high sensitive low toners. Fantastic value from 20-1Khz. Above this I would prefer something else though, f.e. the Ayima A07 or the more expensive e3s.

 

[rsqt]

You should think more about damping your listening room than of a sinad of +-3dB to hear what an amp is able to deliver.