Sorry if this has been covered before, but has anyone measured external case temperature while idle for any TPA3255 amps at different voltages and amperages? I have TPA3255 amps from Fosi, Aiyima, Douk, Nourus and all run at least warm at idle. Lots of people recommend running lower voltages to limit heat, but I would love to see some quantitative measurements of idle heat versus input voltage (not sure amperage makes any difference). I have many power supplies including a fan cooled 10A variable voltage power supply that can output 24V-55V. It would seem pretty easy to measure case temperature at a variety of input voltages while the amp is idle. Has anyone done this? I think having some quantitative idea how idle case temperature relates to input voltage might help some of us decide on the right power supply for our TPA3255 amps. It would also be great to measure temperature at various power output levels versus voltage, but that is obviously a lot more complicated.
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Idle heat for TPA3255 amplifiers measured at different voltages and amperages?
- Thread starter Mr_RGB
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Roland68
Major Contributor
Unfortunately, the idle case temperature doesn't say anything about the idle temperature of the TPA325X, since a large portion of the heat dissipation comes from the 12-volt voltage regulator/regulator. Sometimes these are even mounted on the same heatsink.
This heat dissipation is, of course, also related to the input voltage.
DVDdoug
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The current depends on the load. I don't know if that amplifier will ever "draw" 10A. It will draw more current a higher power and with lower impedance speakers. In other words, you can ignore the power supply's current rating as long as it can supply the required current when needed. i.e. The battery in your car can supply hundreds of amps but car stereo is only using a couple of amps (unless you have a "killer" sound system. 
)
There may be a difference with different voltages at idle, or there may not be.
Under normal operating conditions I wouldn't expect much difference UNLESS you "take advantage" of the additional voltage by turning-up the volume for more wattage into your speakers.
Some basic electronic math:
Current (Amps) = Voltage / Resistance. That's Ohm's Law. It defines the relationship between voltage, resistance, and current and it's the 1st thing you lean when you study electronics.. We don't know the effective resistance of the amplifier, and we usually don't care, and it depends on the conditions. The more power the amplifier is putting-out, the more current it draws so that means lower resistance. You could calculate the effective resistance at idle if you know (or measure) the voltage and you measure the current... But the real question is usually the current anyway.
Power (wattage) = Voltage x Current. When you turn-up the volume, more voltage goes to the speakers and the speakers draw proportionally more current,
From Ohms Law, you can derive Power = Voltage Squared/Resistance. or Voltage Squared / Impedance. As you may know, impedance is also Ohms but unlike pure resistance it can be different at different frequencies.
With a single-ended supply and a "normal" single-ended amplifier, the power supply limits the maximum peak-to-peak voltage. RMS voltage (which determines the power with AC) is about 0.354 times peak-to-peak. So about 17V RMS from a 48V power supply. That's a theoretical maximum of 72W ingo 4-Ohms (unrealistically) assuming no voltage-loss through the amplifier. With a bridge amplifier you can get double the peak-to-peak and RMS voltage for 4 times the power.
)There may be a difference with different voltages at idle, or there may not be.
Under normal operating conditions I wouldn't expect much difference UNLESS you "take advantage" of the additional voltage by turning-up the volume for more wattage into your speakers.
Some basic electronic math:
Current (Amps) = Voltage / Resistance. That's Ohm's Law. It defines the relationship between voltage, resistance, and current and it's the 1st thing you lean when you study electronics.. We don't know the effective resistance of the amplifier, and we usually don't care, and it depends on the conditions. The more power the amplifier is putting-out, the more current it draws so that means lower resistance. You could calculate the effective resistance at idle if you know (or measure) the voltage and you measure the current... But the real question is usually the current anyway.
Power (wattage) = Voltage x Current. When you turn-up the volume, more voltage goes to the speakers and the speakers draw proportionally more current,
From Ohms Law, you can derive Power = Voltage Squared/Resistance. or Voltage Squared / Impedance. As you may know, impedance is also Ohms but unlike pure resistance it can be different at different frequencies.
With a single-ended supply and a "normal" single-ended amplifier, the power supply limits the maximum peak-to-peak voltage. RMS voltage (which determines the power with AC) is about 0.354 times peak-to-peak. So about 17V RMS from a 48V power supply. That's a theoretical maximum of 72W ingo 4-Ohms (unrealistically) assuming no voltage-loss through the amplifier. With a bridge amplifier you can get double the peak-to-peak and RMS voltage for 4 times the power.
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- Thread Starter
- #5
The only reason I'm asking about measuring external case temperature is because it's easy compared to measuring the actual temperature of chips within the amp. I see lots of people opting for the lowest possible voltage power supply that supplies the output power they need. My impression is this is mostly prompted by perceived heat issues. What I don't see is any quantitative process for deciding the optimal heat versus power/headroom compromise in limiting voltage. I'm sure there is some direct relationship between heat dissipated and input voltage I just don't see any methodology, formulas, or rules of thumb to help decide on an optimal input voltage that will potentially reduce heat stress on the amplifier components.
Roland68
Major Contributor
As I said in my post above, there is a connection, especially with the voltage used (32-51 volts), to the required 12 volt voltage.
I know of two TPA3255 projects in which the required 12 volt voltage for the TPA3255 and the voltage for the small-signal range come from external power supplies. This has significantly reduced the idle temperature of the devices.
The second point is interference/noise artifacts in the input/small-signal range, which can of course directly lead to additional heating of the TPA3255 when idle.
- Thread Starter
- #7
I agree with all technical descriptions of electronics theory. What I really want to know (and this may require me to choose a specific one of my amplifiers) is what is the highest voltage that one these amps can run at that will not cause heat damage over a series of years without additional cooling methods. Again, I see lots of people opting for less than 48V without stating any quantitative reasons for choosing a particular lower voltage. Trial and error?
Roland68
Major Contributor
I've been noticing an unfounded heat hysteria here in the forum for a few years now.
There have been amplifiers, mostly AB operation, that have been operating for at least 15-30 years at heatsink temperatures of 40-50°C, sometimes even higher. Since these are mostly full-size units, the cabinets themselves usually don't feel that warm.
Is there any evidence that this is no longer the case with today's amplifiers?
As long as you can hold your hand on these amplifiers for 10 seconds, there's no reason to worry about it at all.
As for choosing the voltage, simply use the voltage the amplifier is designed for and the one you prefer.
Of course it would be overkill to use a 48 volt power supply if you turn the amplifier up to half the maximum with 36 volts.
- Thread Starter
- #9
This is exactly what I had thought, but just wanted to be open to technical reasons to go with less than 48V. I must say I have been addicted to Wattage overkill for many decades resulting in multiple large 200WPC A/B AMPs. So my $56 Douk A5 AMP may not last ten years, I can live with that.
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