Hmmmm...
I'm starting to be very doubtful about this range of class D amps. So this 120wpc amp would be much less powerful than my class AB of 80wpc (Sansui AU 9500)?!
It's very annoying...
-
WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!
Fosi Audio V3 Mono Amplifier Review
- Thread starter amirm
- Start date
I'm starting to be very doubtful about this range of class D amps. So this 120wpc amp would be much less powerful than my class AB of 80wpc (Sansui AU 9500)?!
It's very annoying...
First of all, the % display on the DAC has no relationship to the % power out of the DAC. In fact are you sure it is % at all. Could it be dB?. The DAC display will relate to the voltage output from the DAC. That gets converted to power by the gain in the amp, and the impedance of your speakers.
Your DAC will output about 5V max - but that is only at full volume AND with a full scale (0dB FS) input. Music will typically average around -12 to -15dB FS to allow space for the peaks to get close to 0dB FS without clipping. Some music lower, and some higher of course depending on the mix.
Your amp has a gain of 20dB or x10. Which means the output VOLTAGE is 10x the input voltage. I'll assume your speakers are 8 ohm.
So say your music is at -12dB FS, that will be around 1/4 of the maximum output volts = 1.2V. Now you have that turned down to 80% (or is it -20dB - there is a huge difference), that will be less than 1V output. So less than 10V out of the amp. With 8 ohm speakers that will be 11.8W - nowhere near 100W.
With your 86dB speakers, that should be around 96dBa SPL - which should be pretty loud depending on listening distance. Also depending on the level of your program material etc etc.
But all this depends on what 80 on your display actually means. If it is %, what is it a % of? is it a linear %? Or is it a dB scale - in which case all the calculations above are nonsense and we'd have to look again.
No, they don't, they just have different gain, don't confuse power and gain
Sokel
Master Contributor
- Joined
- Sep 8, 2021
- Messages
- 8,785
- Likes
- 9,299
Imagine if you had to try this new Topping 122dB SINAD amp with it's 10dB gain (at low setting) and it's 12.5V input sensitivity
Also bear in mind that 120W is only 1.76dB above 80W. So if you are expecting a big volume increase compared with your Sansui you are not going to get it.
For a perceived doubling in volume, you need around +10dB power. This 1.76dB will result in a (very approximate) 17% increase in perceived volume.
@Keauval Just to clarify what is meant here.Imagine if you had to try this new Topping 122dB SINAD amp with it's 10dB gain (at low setting) and it's 12.5V input sensitivity
Your sansui has an input sensitivity of 100mV (0.1V). Meaning only 0.1V input is needed to drive the amp to full power. This is typical of older gear from when sources output much lower voltages.
Your FOSI amp has an input sensitivity (8ohm) of 3.1V (31 times higher) meaning you need to drive it to 3.1V on the input to deliver 120W into 8ohms. This higher needed sensitivity is typical of more modern amps which expect to be driven by modern DACS which can output 2 or 4V (RCA or XLR) or more.
Your DAC can output 5.2V which is more than enough to drive full power from this amp, so you have no worries. But because of the lower gain, you will need the volume control at a higher level than you are used to to get there.
Last edited:
It has the power it is specified to have.
Sokel
Master Contributor
- Joined
- Sep 8, 2021
- Messages
- 8,785
- Likes
- 9,299
Though quoting you it was, as you pointed out directed towards @Keauval . Sorry, I thought that was clear based on the message. Should have made it explicit though. I've added an @
Do you know the output voltage from your DAC XLR outputs? Is it perhaps just putting out RCA voltages on the XLR pins?
If the above is the case it isn't ideal but you won't have to worry about having the volume high as you won't be putting any more power through the speakers than you would with a proper XLR input and lower volume settings.
edit: sorry, posted this before reading the subsequent messages. apparently your XLR output voltage is fine
Last edited:
Just leave it on Auto? I don't turn things off at the wall plug, leaving them sleeping. The pre-amp is the same. The only sounds I get are the relays switching power on the monos'. They consume pretty much nothing and only warm up when working. The in-rush thermistor is the component I care about, the less action this sees the longer things work.
JeremyFife
Major Contributor
That's a great looking system btw - and room. Amazing to think that you have bit-perfect streaming, 10 band PEQ and plenty of clean power in that tiny package.
Certainly, if you don't plan to turn off V3 Mono's power and there is no power noise issue in your setup, simply leave them in Auto mode.
Many many thanks for this answer about input sensitivity I'm understanding much more, it s really clear and I understand much better why my volume is at 15% on my old Sansui
Last edited:
This, which apparently seems like a limit or a lack of power, is actually a system that allows you to manage the volume in a very gradual and fine manner but, if necessary, use all the power that the fosi are capable of, just increase the volume a little more without worrying about the discrepancy between the DAC's volume level and the perceived volume compared to your old amplifier.Many many thanks for this answer about input sensitivity I'm understanding much more, it s really clear and I understand much better why my volume is at 15% on my old Sansui
Basically, get used to it like this.
Sokel
Master Contributor
- Joined
- Sep 8, 2021
- Messages
- 8,785
- Likes
- 9,299
The problem is that gain structure may contain other caveats too,apart from low-level recordings,etc.
Room EQ for example may lower the whole chain by a considerable amount.This must be taken into account for power needs too.
Room EQ for example may lower the whole chain by a considerable amount.This must be taken into account for power needs too.
Down South
Active Member
- Joined
- Jul 20, 2022
- Messages
- 201
- Likes
- 97
I used to live behind the Sierra Nevada mountains in Andaluz and normal summer temps. were 38-40C and the last 7 weeks in 2009 were @ 1500 hours 45/6c. I had to stop using my KT88 power amp, it just got too hot.
I bought a Bada hybrid power amp I had a slate box made - no top or back panel, removed the base plate, raised the o/put tx off the top plate which allowed the mosfets and power resistors heat to escape, because conveniently there were slots cut into the top plate right over the mosfets. Using an adjustable computer fan placed underneath dramatically lowered the operating temperature. As I lined the box with car sound dampening material the fan was silent.
I like the look of your fan enclosures - where did you get them and how much did they cost? Fosi could have done a much better job at heat dissipation, it's always an after thought if at all. By designing enclosures to encourage a 'convection current' to be created in operation. These enclosures are so small they could have been made vertical with weighted bases.
Similar threads
