after 10 years of using the pioneer A10k which has a self shutdown feature, I sometimes forget to power down the V3. where I live the cost of electricity is about 0.30euros/Kwh so idle power is a concern for me.
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Fosi Audio V3 Mono Amplifier Review
- Thread starter amirm
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I don't think either of these statements are correct. Assuming all thermal losses are extracted via the case (rather than internal airflow via vents), then for a fixed thermal loss (say the power draw at idle) the case temperature is also going to be fixed (all the heat reaches the case, case temperature then depends on thermal resistance from case to ambient air. All heat loss must flow (like a current) through thermal resistances to ambient air.
The internal thermal resistances will cause internal heat generating components to be hotter than the case by an amount based on that resistance. Higher resistance will result in higher internal component temperature - not lower case temperatures.
A lower case temperature coming from a lower case to ambient resistance will result in all those internal temperatures reducing.
The equivalent electrical situation is a current source (representing a thermal heat flow (power)) flowing connected via various resistances to ground (ambient air)
So heat generation in the power chip having the resistances : Silcon to chip case - chip case to heatsink/spreader (if used) - Heatsink/spreader to case - case to ambient air.
The temperatures are equivalent to the voltages in the electrical circuit. If you reduce the last resistor in the chain, then the "case" voltage will reduce - and all the other voltages reduce by the same amount.
TurtlePaul
Major Contributor
How much it warms up your room is determined by idle power, not skin temperature.
Is this the one?
Recommended Power: 100 to 250W @8 Ohms
Sensitivity: 86dB @2.83V/1 Meter/500Hz
Impedance: 4 Ohms
If that's the one then of course the V3 mono is an acceptable amp for them. Sensitivity is only 86 dB/2.83 V, if you sit 12 ft from them, they should play loud enough but don't expect reference level, but that's would be the case even if you go with much more powerful amps as the limit would be the speakers, not the amp.
Before I bought the fosi thought about
the potential heat. I was hoping to lower the heat with three actions.
1. Attach three aluminum heat sinks using thermal adhesive tape. (Set of 4 aluminum heat sinks on Amazon: 15–18 euros; 4–5 euros each.)
2. Install them vertically so that air can rise through the cooling vents.
3. Attach the FOSI or cooling fins to the TV stand (steel) for even better heat dissipation.
It works very well; I’ve measured it multiple times with an infrared thermometer. It doesn’t exceed 36–40 degrees even at maximum volume. Both front speakers are powered by the FOSI V3 mono.
the potential heat. I was hoping to lower the heat with three actions.
1. Attach three aluminum heat sinks using thermal adhesive tape. (Set of 4 aluminum heat sinks on Amazon: 15–18 euros; 4–5 euros each.)
2. Install them vertically so that air can rise through the cooling vents.
3. Attach the FOSI or cooling fins to the TV stand (steel) for even better heat dissipation.
It works very well; I’ve measured it multiple times with an infrared thermometer. It doesn’t exceed 36–40 degrees even at maximum volume. Both front speakers are powered by the FOSI V3 mono.
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Good solutions, but between the V3 Mono, I would just pay a little more to get the 3 e Audio that supposedly uses the same chips but run much cooler (I have both so I know..).
I bought the fosi first for the fronts (preamp mode in x4700).
Now going full preamp mode with
1x 3eaudio a7 mono center (167 bucks primeday with 48V5A)
3eaudio PAM158 for surrounds and heights
keep the fosi because they have a great sound and are already here. no further fosis for me. the v4 and v5 mono prices are a bad joke in my opinion. And thanks to amirs measurements the 3eaudio A5 (basement for PAM15x) and even the A7 mono is not far away from the great hypex amps.
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Well you are all set with better current capability than the Denon AVR amps, to me the Fosi V3, even the stereo models, and the A7 Mono sounds identical. the 3e Audio ones just run cooler that's all, but the Fosi Mono looks better/prettier, to me anyway.
It’s all behind the rack so I go 100% for audio quality / per Euro and it can look ugly as s*** (like my good working construction). If the new V4 and V5 monos would cost below 200/300, well ….Well you are all set with better current capability than the Denon AVR amps, to me the Fosi V3, even the stereo models, and the A7 Mono sounds identical. the 3e Audio ones just run cooler that's all, but the Fosi Mono looks better/prettier, to me anyway.
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Thanks for this. I just bought a pair of the Fosi. I may sell all my legacy amps if this works out.
Keep in mind the new Fosi V3 Mono amps have lower gain so if you have to turn your preamp volume up a few clicks that's not because the amps are not powerful enough ,they just need a little more help from the preamp that's all.
that’s an important advice for not being frustrated with the fosis.
“all little more help” is funny. I had to set my ADC/DAC to +4dBU (1.3 Volt) to get the fosis to life when using xlr in. With denon 60/80 Mastervolume and -10dBV in and -10dBV (ADC/DAC) out it was dead silence.
I might have been the person who "introduced" this concept that better heat transfer means a hotter amplifier case. It is not strictly true as there are some (important) nuances to it that need explanation.
If you have two devices of equal size and shape and generate the same amount of heat, at steady state, the average chassis temperature will have to be roughly the same. The reason is: At steady state, heat generated = heat dissipated.
Heat transfer to the surrounding is governed by the difference between the chassis surface temperature and the ambient air temperature. If the amounts of heat dissipated to the surrounding are the same, with amp chassis of similar similar dimensions, their surface temperatures must also be similar (when averaged over the chassis surfaces), regardless of how well or poor the heat conduction paths from the heat sources to the amp chassis are.
What a poor thermal conduction path will affect is the time response, i.e. how quickly the chassis temperature will rise. To demonstrate I'll show simulation results of both cases (good and poor thermal conduction paths to the chassis).
Only a quarter of the geometry needs to be modeled due to symmetry. The heat released by the amp chip is transferred to a heat spreader (or heat sink). The heat spreader is mounted to the chassis, with thermal interface materials (TIM) applied to fill the gaps between mating surfaces of the heat spreader and the chassis. The chassis is cooled by convection (convection heat transfer coefficent of 7.2 W/m²·°C and 25 °C ambient temperature). We'll look at the differences between effectively applied TIM and poorly applied or no TIM (50x higher thermal resistance).
In the first scenario, the amp chip released 22 W of heat for 300 seconds and then the heating stopped. Below is an animation of the 2 temperature charts. When thermal conduction was poor, we can see that the amp chip temperature rose quickly and to a level much higher than when conduction is good. However, the chassis temperature rose slower and the peak temperatures didn't reach as high as with the good heat conduction case. Therefore, in this scenario, the amp with the poorer heat conduction will have a cooler amp chassis.
In the second scenario, we kept the heat generation on continuously. We can see that for this scenario the eventual steady state chassis temperatures are the same for poor and good thermal conduction. It just took the poor conduction case longer to reach the same temperature. Notice that with poor conduction the amp chip temperature went off the chart. That means the amp would probably shut itself down or destroy itself.
Therefore, the more accurate statement is that for a system with high thermal conduction to the chassis (or heat sink), the chassis will heat up faster than one with poor heat conduction. If you have enough patience and keep the test running for a long time, the one with poor heat conduction will eventually catch up. But you may need to keep the test on for half an hour or longer.
Below are the temperature profiles with heating on for 300 seconds.
A simpler POV is that if the case-as-heatsink design is actually faulty, then a fan is required.
Or turned around, feel free to add an ultra-quiet little Noctua fan as many do, and you too can get a much cooler case.
It just won't change the amp performance short term - but maybe help longevity?
Or turned around, feel free to add an ultra-quiet little Noctua fan as many do, and you too can get a much cooler case.
It just won't change the amp performance short term - but maybe help longevity?
Agreed - but what matters is the steady state condition - because this is the point at which all temperatures have reached the maximum. As you state in your "faulty* 50x thermal resistance condition the amp will likely shut down or self destruct.
My simple electrical model of current source with resistances only models the steady state - to model the time response capacitance would need to be added across each of the resistors to model the thermal capacity of the various components.
But we're not normally comparing a good/faulty scenario in any case. We are normally comparing two functional amps - one of which gets hotter than the other.
RandomEar
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I tend to agree with @antcollinet here, because the common case I've seen people discussing in this thread is the amp getting hot while essentially in idle and often with hours of runtime being mentioned or implied. So the long term outcome seems more relevant to me.
The analysis @NTK shows is absolutely correct though and so are the arguments brought forward about non-steady state behavior and bad thermal contact. Intuitively, you want your heatsink to have good thermal contact to the thing it's supposed to cool
The analysis @NTK shows is absolutely correct though and so are the arguments brought forward about non-steady state behavior and bad thermal contact. Intuitively, you want your heatsink to have good thermal contact to the thing it's supposed to cool
TurtlePaul
Major Contributor
But the design isn't faulty and if you make this claim it is up to you to support your extended longevity assertion.
Most people do not have the necessary setup to run an amplifier test at high output to its eventual steady state condition. Thermal systems are usually slow and can take a long time to reach steady state. You'll need a well cooled dummy load for the test and which most people don't have.
If the test consists of playing loud music for as long as one can tolerate (often not more than several minutes) and senses the temperature rise with one's bare hands, one may easily come to the conclusion that an amp with good thermal conduction "generates more heat" because the amp chassis heats up faster. Those are mostly the type of situations I was referring to.
Regarding a 50x difference in thermal conduction, the difference may not be as ridiculous as it first appears. Below pictures are from Archimago's review of the Fosi V3 Mono. It has a thermal design similar to what I modeled in my post #4854.
Many of the older generation TPA3255 amplifiers have the chip mounted facing up. The heat sink has no solid connection to the chassis for heat dissipation, and rely mostly on the air inside the chassis to transport the heat to the chassis and then to the outside. The amp chip heat management largely depends on the thermal inertia of the heat sink, and the amp running at a low enough duty cycle so a slow heat removal is adequate. Below is a picture of the Aiyima A07. A 50x higher thermal resistance compared to the Fosi design is probably not an exaggeration.
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