I have a nice rule of thumb evaluating claims of "pure
class A operation":
Take the continuous idle power draw from the wall and
divide it by the total rated continuous output per channel.
If it is a mono amplifier, divide the number by 2. If it is
a stereo amplifier, divide it by 4.
Now square the number and multiply it by the rated output
per channel. This gives the most generous estimate for
"pure" Class A operation, and twice this number is the
instantaneous point at which it leaves Class A.
Example:
A stereo amplifier draws 200 watts continuously
from the wall and is rated at 100 watts per channel:
200/100 = 2
2/4 = .5
.5 squared = .25
.25 times 100 watts = 25 watts. This is the rms Class A figure.
2 times 25 watts = 50 watts. The amp leaves Class A at
the instant of 50 watts, and probably operates AB to a 200
watt peak (the peak of a 100 watt rms sine wave).
All this assumes no weird circuits, and also assumes no
other losses. In real life, the numbers will be somewhat less.
class A operation":
Take the continuous idle power draw from the wall and
divide it by the total rated continuous output per channel.
If it is a mono amplifier, divide the number by 2. If it is
a stereo amplifier, divide it by 4.
Now square the number and multiply it by the rated output
per channel. This gives the most generous estimate for
"pure" Class A operation, and twice this number is the
instantaneous point at which it leaves Class A.
Example:
A stereo amplifier draws 200 watts continuously
from the wall and is rated at 100 watts per channel:
200/100 = 2
2/4 = .5
.5 squared = .25
.25 times 100 watts = 25 watts. This is the rms Class A figure.
2 times 25 watts = 50 watts. The amp leaves Class A at
the instant of 50 watts, and probably operates AB to a 200
watt peak (the peak of a 100 watt rms sine wave).
All this assumes no weird circuits, and also assumes no
other losses. In real life, the numbers will be somewhat less.
My amp, the X 150, is rated at 150 watts per side into 8 ohms and 300 into 4 ohms. Its power consumption
is 200 watts idle, 600 watts max. Pass claims it runs Class A to 20 watts output then
switches to AB. Does the math work out, or is that not enough info? Doing Nelson's math as I
read it, I get Class A to 16.67 watts.
A friend, who owns the Llano Trinity 200 wrote this:
When I got into audio nobody told me there would be math involved, when I did the
math I got 112.5 wpc RMS and 225 wpc max class A into 8 ohms vs the claim of 200. If I
understand correctly, the power draw from the wall is the total and since the Llano draws 300wpc
at idle, the total would be 600watts. That is the first number in the equation. If that is wrong
then every step after that will be wrong.
Whereupon another aquaintance said this:
Don, your AC outlets carry 110 volts. No mater what you plug in it will always be 110. If you plug
something in with an impedance of say 100 ohms so much current will flow. If you plug in 50
ohms twice as much current will flow. Voltage remains the same. The amps power supply is
similar to your AC outlet. It supplies so much voltage in DC. Current flow now depends on load
impedance. As long as the power supply can provide the current flow it will provide what ever is
needed beyond Idle. Bias voltage remains the same regardless. How that translates into power
depends on the load.
Mike
is 200 watts idle, 600 watts max. Pass claims it runs Class A to 20 watts output then
switches to AB. Does the math work out, or is that not enough info? Doing Nelson's math as I
read it, I get Class A to 16.67 watts.
A friend, who owns the Llano Trinity 200 wrote this:
When I got into audio nobody told me there would be math involved, when I did the
math I got 112.5 wpc RMS and 225 wpc max class A into 8 ohms vs the claim of 200. If I
understand correctly, the power draw from the wall is the total and since the Llano draws 300wpc
at idle, the total would be 600watts. That is the first number in the equation. If that is wrong
then every step after that will be wrong.
Whereupon another aquaintance said this:
Don, your AC outlets carry 110 volts. No mater what you plug in it will always be 110. If you plug
something in with an impedance of say 100 ohms so much current will flow. If you plug in 50
ohms twice as much current will flow. Voltage remains the same. The amps power supply is
similar to your AC outlet. It supplies so much voltage in DC. Current flow now depends on load
impedance. As long as the power supply can provide the current flow it will provide what ever is
needed beyond Idle. Bias voltage remains the same regardless. How that translates into power
depends on the load.
Mike
I think they use a secret package with a looooow!! thermal resistance and a special coating on their heatsinks.
Back to reality : you can not get pass the thermal resistance who exists from the "die" through the package .. thermal compound .. and at last the heatsink...
High effiency MOSFET are only high effiency when shifted "on" where it is possible to use their low RDS... Like they do in Class D amps.
In a "linear" amp there is no miracle!!
Sonny
Back to reality : you can not get pass the thermal resistance who exists from the "die" through the package .. thermal compound .. and at last the heatsink...
High effiency MOSFET are only high effiency when shifted "on" where it is possible to use their low RDS... Like they do in Class D amps.
In a "linear" amp there is no miracle!!
Sonny
This is hilarious....I can't believe (well, given what some other manufacturers do, I guess I can believe.....) what this guy is saying. That's absolutely hilarious to use "high efficiency" mosfets as the reason a class A (not switching) amp doesn't dissipate very much power.
You've got to be kidding. As Sonnya just stated, this attribute of FET's only applies when they're fully on, not while they're switching.
You've got to be kidding. As Sonnya just stated, this attribute of FET's only applies when they're fully on, not while they're switching.
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