Fosi Audio V3 Amplifier Review

[ddaudio]

Would the impedance curves of the amp and speaker not just be added together?

It is effectively 2 resistances in series, so the signal voltage will be divided according to the value of each resistance.

For example, if you have a signal of 9 volts fed into a circuit containing 2 resistors, the first 2 ohms and the second 4 ohms, you'd get 3 volts across the first resistor and 6 volts across the second. The important thing is the ratio between the resistances.

The speaker will not see the voltage that is lost due to the amp's output impedance, which will be in proportion to this ratio, which will change at different frequencies due to the speaker's varying impedance.

Here are some measurements by member @pma of the Aiyima A07, a similar amp to the Fosi V3: The first graph shows the impedance of the test speaker load, and the second the frequency response of the amp.

 

[Lux_ury]

Ok I’ve had limited time for testing, but have tested the following:
Ed Sheeran - Bad Habits 320k mpeg Optical to D10 DAC to RCA out Bluetooth Samsung Note 20 ultra. 240v domestic to Amplifier 5v lithium battery to DAC
Aiyima A07 32v 5amps
Fosi Audio V3 48v 5amps

B&W CDM2 Special Edition Specs: 2-way configuration, Bass reflex via rear-firing port, Woven Kevlar cone midwoofer B&W ZZ11177 165mm, rubber surround, Alloy dome tweeter B&W ZZ9938 25mm, 30-120W@8Ω, 65-20000Hz ±3 dB, Sens. 87 dB, Mm 220x316x242, 7,0.KG

First the B&W’s A07 32v sounded clear bright tad harsh in upper freqs base flat.

V3 48v Bass heavy mid and highs to harder to separate and pushed back.

V3 32v 5amp sounded lively forward, balanced separation really good. Best combination with V3 with B&W’s.

Wife ran same test blind, same conclusion as her ears are better than mine. (Shame emoji) ‐-----------------------------------‐-------------------
Infinity RS7b:
SPECIFICATIONS INFINITY SYSTEMS INC.
RS 7 Reference Standard 3-Way Nominal Impedance: 4 to 8 ohms Power Rating: 20-125 watts RMS Crossover Frequencies: 500, 5,000Hz Frequency Response: 45Hz-32kHz +/-2.5dB

48v 5amps V3 yielded best lively deep base perfect synergy.

Side notes:
As stated the volume knob is natural to sound increase and very progressive in feel, better than A07.
I hear small feed back when switching off the pop! Tiny but still audible.
I think it’s due to the potentiometer having its on/off switch on the same dial.

I’m not going to stick the 48v 5amp power brick into my Aiyima as I’m waiting for a 36v 6amp to arrive at some point for testing.
Temps never reached past 38C.
Quality of power brick is key here I think? but I don’t have tools to measure noise plus AC will vary my house is 1941 build.

 

[simnick]

V3 34v Bass heavy mid and highs to harder to separate and pushed back.

Did you mean 48v for this one?

 

[Lux_ury]

Did you mean 48v for this one?

Thanks good spot corrected now.
Thumbs up emoji.
I could go into more detail, but it was subjective for misses and I.
I can only report what I prefer to hear.
I have a few more speakers to play with but It takes time lifting heavy speakers around( sad emoji )

 

[sarumbear]

I've got kind of a noob question here. If it's more appropriate in another area of the forum, I'll be glad to delete and re-post.

Anyways, I have an old Rotel RSP-1572 AV preamp/processor that was gifted to me by a friend. It's been sitting in my closet unused for about 5 years now. Its spec sheet says Preamp Output Level/Output Impedance = 1.0V/1k ohms.

I can't find any info on the V3's input sensitivity, but I think I've heard mentioned on ASR that 2V output is a "standard" of sorts for getting the most out of amps. Would using the Rotel to drive a Fosi V3 be problematic? If so, what would be the effects on the various measurements?

Thanks!

I cannot find the gain value of the amp from @amirm's test, however: I can confidently say that you will get pretty decent level by feeding a 1V nominal input using this amp. The difference between 1V and 2V is just 6dB, which directly reflects to SPL and 6dB is not that huge even though it is twice the level. Just turn the volume fully up and use your Rotel's volume control.

 

[mccririck]

Thanks good spot corrected now.
Thumbs up emoji.
I could go into more detail, but it was subjective for misses and I.
I can only report what I prefer to hear.
I have a few more speakers to play with but It takes time lifting heavy speakers around( sad emoji )

I noticed the base more with my 48V V3 than with my SMSL DA9. I think it's only natural that the mids and treble are going to be less obvious when the bass has more punch, but maybe that just the way the recordings are supposed to sound?

Or perhaps the impedance dependency is making the speakers lose a bit of treble sparkle?

 

[Lux_ury]

I noticed the base more with my 48V V3 than with my SMSL DA9. I think it's only natural that the mids and treble are going to be less obvious when the bass has more punch, but maybe that just the way the recordings are supposed to sound?

Or perhaps the impedance dependency is making the speakers lose a bit of treble sparkle?

It's really hard to say the B&W’s have always been top heavy which is why they ended up in the attic. I'm not a fan of 2 ways as I've only regularly listened to 3 ways which my RS7bs are perfect as base is plentiful and so is mids & highs.
The original capacitors in the infinity were finished I recapped and re foamed so near best I can remember what they sounded like in its day.
Everyone can say load dependencies it doesn't change the fact not all crossovers have the same pass filters (series, parallel etc)which makes it more interesting to listen. I'm not into debating science vs mind control I like to think the science is a guide to a close Artificial curve or best curve as you get towards, as not everyone can hear every frequencies nor I care if I'm not orthodox in thought and logic when it comes to music.
All I know is I'm having fun.
£80 amp B&Ws out of retirement in a bedroom for easy listening I'm happy!
I have to get the bigger toys out to remind my ears sometimes (Wink emoji)

 

[eightbald]

The 3.5mm Pre-Out can be used for both input and output by simply connecting and branching the RCA inputs in parallel.

Apologies for such a basic question - can you ELI5 how I can use the 3.5mm Pre-Out as an input? It sounds like you're saying it's more complicated than just hooking a 3.5mm from, say a phone to the Pre-out?

 

[Toku]

Apologies for such a basic question - can you ELI5 how I can use the 3.5mm Pre-Out as an input? It sounds like you're saying it's more complicated than just hooking a 3.5mm from, say a phone to the Pre-out?

Nothing is difficult. It's that simple.

Both RCA and 3.5mm are just connected in parallel.
Therefore, both can be used as input terminals. However, they cannot be used at the same time.
Also, when an input signal is connected to one side, the branched output of that input signal is obtained at the other side.
Therefore, the same signal can be used as an input signal for other devices.

 

[ddaudio]

Nothing is difficult. It's that simple.

Both RCA and 3.5mm are just connected in parallel.
Therefore, both can be used as input terminals. However, they cannot be used at the same time.
Also, when an input signal is connected to one side, the branched output of that input signal is obtained at the other side.
Therefore, the same signal can be used as an input signal for other devices.

Just be aware, if you leave it plugged in, depending on the impedance of the component at the other end of the line in/out, it may affect the signal input voltage supplied to the amp, and therefore the volume.

 

[SPD_RCR]

for those that have "rolled their own" power supply, what cabling and connector did you use?
Specifically, to "feed" DC voltage from the Power Supply to the V3?

 

[GabrielPhoto]

I wonder how 2 of these will work for Atmos...

 

[Toku]

Just be aware, if you leave it plugged in, depending on the impedance of the component at the other end of the line in/out, it may affect the signal input voltage supplied to the amp, and therefore the volum

It is a matter of course.

 

[Guddu]

I wonder how 2 of these will work for Atmos...

Probably just fine.
Tried something similar, but didn’t feel safe to leave powered ON and hate to power on/off manually every time/day.
Power ON/OFF merged with vol. makes it difficult to put it back to same calibrated vol. settings.
A power amp (no vol., but a power switch not just mute function) of similar quality/specifications would make a great used case with avr pre-out.

 

[sarumbear]

I wonder how 2 of these will work for Atmos...

Atmos base is 9 channels plus sub

 

[bbjayo]

it measures better than a07 but is this difference audible ?

I've been using an A07 for a few months and have had a day or so to play with the V3. Using a Meanwell LRS-350-48v power supply on both, limited testing so far has been AT-LP120X tt to Fosi x2 to T9 Pro and line out to A07 or V3. Volume on both amps set to full and vol controlled via T9 Pro remote. Volume noticeably louder on the AO7. Separation seems to be defined a bit better with the A07 too. V3 sounds a bit warmer but definitely has lower volume than the A07 using the same PS. Big caveat here (although some would argue it shouldn't make a difference), the A07 is fitted with 2 x Sparkos SS3602s. Not sure if I can be bothered pulling these out and popping them in the V3 but will update here if I do. Speakers are Q3030is

Might do some basic Db measuring with my phone of the weekend too.

 

[GabrielPhoto]

Atmos base is 9 channels plus sub

???

 

[JSmith]

???

He probably means 7.1.2, which has 2 height channels and 1 sub.


JSmith

 

[sarumbear]

???

I.e. you need 5 of these amps.

 

[sarumbear]

He probably means 7.1.2, which has 2 height channels and 1 sub.


JSmith

I was talking about the number of channels not how they are connected.