Is there a threshold to the power output vs impedance curve?

[Xii-Nyth]

As far as I can tell amps just follow v2/r until it reaches a maximum power and clips. I noticed though (all be it on a manufacturers specs page) that the output power at 16 ohms was lower than at 32 on a particular amp.

Since I'm getting the Aeon Open X...
(was gonna wait for a review by amir but its on sale now and I have gotten along with subjective tests of a few reviewers before so it should apply here)
...which have an impedance of 13 ohms, and the similar aeon rt required about 700 mv to reach 96 db in amirs testing, its been brought to my attention that I should double check if my choice of they atom amp+ was the right one, since the magni heresy has much higher power output.

Assuming it does scale well down to that impedance the atom should be able to output over 2 watts at that amount, but if it swings the other way and goes down even a little bit it would be cutting it pretty close.

Thanks!

 

[NTK]

The Atom+ uses the TI LME49600 as the output device. It has a rated output current of 250 mA, which means 177 mA RMS. The current limited max power output is I^2 * R, meaning for 13 ohm it is 0.4 W.

 

[Xii-Nyth]

The Atom+ uses the TI LME49600 as the output device. It has a rated output current of 250 mA, which means 177 mA RMS. The current limited max power output is I^2 * R, meaning for 13 ohm it is 0.4 W.

Wow thanks! from my experience of texas instruments datasheets vs actual limits isn't quite to the limit but getting an extra 50% is beyond the limits of heat putting a heatsink on it and I don't think that would translate over to this type of stuff anyways.

Slightly confused you you get 400 mW though...

 

[NTK]

Max current I = 0.25 / sqrt(2) = 0.177 A rms. Power = I^2 * R = 0.177^2 * 13 = 0.4 W.

 

[Xii-Nyth]

Oh

Max current I = 0.25 / sqrt(2) = 0.177 A rms. Power = I^2 * R = 0.177^2 * 13 = 0.4 W.

Oh nvm cant even figured out what mistake I made before...
so that lines up with the 32 ohm testing where amir was able to get 1.13 watts while the calculation is exactly 1.
Ok so do you know what the schiit magni heresy uses? Gonna need a little more power hope that can do it.

 

[solderdude]

Heresy: Maximum Power, 16 ohms: 2.8W RMS per channel
0.42A = 2.3W in 13 ohm so 7.6dB higher SPL.

 

[Xii-Nyth]

Heresy: Maximum Power, 16 ohms: 2.8W RMS per channel
0.42A = 2.3W in 13 ohm so 7.6dB higher SPL.

Perfect, now all I have left to do is buy an unholy pairing of an atom dac+ with the magni heresy? Gonna have to check shipping costs to canada

Edit: its not meant to exist. Shipping too expensive.

 

[solderdude]

nothing unholy about that pairing.
Amps are agnostic about what feeds their input.

 

[Xii-Nyth]

coming back becaused I realised that said 700 mV not 700 mW, and now I'm quite confused when trying to teach someone else how the calculations work.

 

[DVDdoug]

and now I'm quite confused when trying to teach someone else how the calculations work.

First, Ohm's Law (Current = Voltage / Resistance, and the 2 algebraic variations) describes the relationship between voltage, resistance (or impedance), and current.

Then the basic power calculation is Power (Watts) = Voltage X Current.

From that and Ohm's Law you can derive:
Power = Voltage squared/Resistance
or Power = Current squared X Resistance


Most "things" are "constant voltage", so the current & power depend on the load resistance. Here in the U.S. we have 120VAC constantly available at the wall outlet. The current & power depend on the resistance of whatever is plugged in. We don't know the resistance unless we calculate it but almost everything is marked with wattage or current (Amps). If something draws too much current the circuit breaker blows and voltage drops to zero.

Solid state amplifiers are also considered constant voltage. The voltage isn't really constant because music isn't constant, but the concept is that the voltage is independent of the load. And that's pretty much the case with power amplifiers... Their voltage stays the same no matter the impedance of the load up to the amount of current it can supply. Many amplifiers will clip at a lower voltage with a lower impedance load, but as long as you're not near clipping the voltage holds-up. And of course if the impedance is too low, things overheat and "bad things" can happen.

Some headphone amplifiers have internal output-impedance* which "acts-like" a resistance in series with the headphones.** And in that case they are not "constant voltage"... You'll get lower voltage with lower impedance headphones and since headphone impedance varies over the frequency-range, this causes frequency response variations. Again if you go too-low (like connecting speakers to a headphone amp) "bad things" can happen.




* All amplifiers have output impedance but it's usually low compared to the load impedance so it's not an issue. With power amps it's called "damping factor".

** That makes a voltage divider where the "top" resistor is the internal resistance and the "bottom" resistor is the headphones.

 

[Xii-Nyth]

First, Ohm's Law (Current = Voltage / Resistance, and the 2 algebraic variations) describes the relationship between voltage, resistance (or impedance), and current.

Then the basic power calculation is Power (Watts) = Voltage X Current.

From that and Ohm's Law you can derive:
Power = Voltage squared/Resistance
or Power = Current squared X Resistance


Most "things" are "constant voltage", so the current & power depend on the load resistance. Here in the U.S. we have 120VAC constantly available at the wall outlet. The current & power depend on the resistance of whatever is plugged in. We don't know the resistance unless we calculate it but almost everything is marked with wattage or current (Amps). If something draws too much current the circuit breaker blows and voltage drops to zero.

Solid state amplifiers are also considered constant voltage. The voltage isn't really constant because music isn't constant, but the concept is that the voltage is independent of the load. And that's pretty much the case with power amplifiers... Their voltage stays the same no matter the impedance of the load up to the amount of current it can supply. Many amplifiers will clip at a lower voltage with a lower impedance load, but as long as you're not near clipping the voltage holds-up. And of course if the impedance is too low, things overheat and "bad things" can happen.

Some headphone amplifiers have internal output-impedance* which "acts-like" a resistance in series with the headphones.** And in that case they are not "constant voltage"... You'll get lower voltage with lower impedance headphones and since headphone impedance varies over the frequency-range, this causes frequency response variations. Again if you go too-low (like connecting speakers to a headphone amp) "bad things" can happen.




* All amplifiers have output impedance but it's usually low compared to the load impedance so it's not an issue. With power amps it's called "damping factor".

** That makes a voltage divider where the "top" resistor is the internal resistance and the "bottom" resistor is the headphones.

oh yeah I actually work with electronics, just confused about where the mV for spl comes from, since it seems way too low to take less then a volt, since 1 volt into 100 ohms, would be only 10 mW, yet I run my amp at 1/2-3/4 with my dac at -11 dB, (50 in windows) so my amp is at like 1.5-2.25W at that point.

 

[Xii-Nyth]

oh yeah I actually work with electronics, just confused about where the mV for spl comes from, since it seems way too low to take less then a volt, since 1 volt into 100 ohms, would be only 10 mW, yet I run my amp at 1/2-3/4 with my dac at -11 dB, (50 in windows) so my amp is at like 1.5-2.25W at that point.

sorry 0.75-1 ish forgot to compensate for being 13 ohms

idk why i switched to a theoretical example for easy numbers when comparing to what I actually have

 

[Xii-Nyth]

oh so I found out that it parely makes a difference in spl, and it turns out I have been making a mistake that cause me to get a seriosly overpowered amp. now im just running on low gain with the knob near max for sweet spot sinad, unless that makes it take more power on the amp side and run hotter, ill just touch it in an hour. Anyways I have now found out that portable amps such less than I thought!