Here is a bump - hoping for IFI Audio to provide the promised responses to the previous questions
Cor blimey! Loads of questions...this is gonna eat into pub time….
Q#1A: I noticed your specs seem to reference 'short duration' peak power rather than continuous power.
Music has a relatively high so-called ‘crest factor’ or ratio between peaks and average power, usually 10:1 – meaning for music mainly looking at the ‘peak power’ is somewhat relevant. Sine-waves as used for equipment objective testing have a peak to average ratio of 1.414:1, meaning they stress equipment greatly and may create overheating.
Comparison of Sinewave & Music Crest Factor
The iCAN Pro omits any protection circuitry that is directly connected to the audio path, as this often causes sonic degradation. To avoid a risk of blowing out the output stage in case of overload (which may occur with sinewave testing) we have integrated current limiting circuitry into the power supply.
This circuitry allows short term unrestricted peaks, but will progressively limit available current to protect the device based on temperature and clipping of the amplifier, all the way to an eventual complete shut-down of the iCAN Pro if overload is sustained, to avoid damage to either iCAN Pro or headphone.
Q#1B: What is the actual normal use power rating? For 200ohm headphones? Is it adapting (such as by impedance matching), based on the headphone connected?
Power = Voltage X Current.
Voltage directly proportional to the input signal is what almost all amplifiers deliver (exceptions exist), current flowing is determined by the load.
Even if the amplifier is unconventional (e.g. current output types), the actual power is always dependent on the load (Headphone/Speaker) impedance. This applies to any amplifier of the ‘voltage output’ and ‘current output’ type.
In theory it would be possible to design an amplifier that delivers constant output power regardless of load impedance, but there is at this point in time no known headphone that would actually show any benefit from such a design.
Too low or too high load impedance both result in max output power allowed with that particular load lower than the absolute max capable by that amplifier.
For the iCAN Pro the power supply voltages to output stages limit the output voltage to 11.5V for single ended headphones and 23V for balanced headphones. The long term current limit for the iCAN Pro is around 1A peak per channel, which means with sinewave testing around 700mA is available, which in case of the balanced connection is shared between the signal phases.
Short term current can be much higher, the absolute maximum is certainly more than 7000mA for several milliseconds; it is not the easiest number to measure.
All this means the maximum long term sustained power with sinewaves with balanced connections will be 8,000mW into a 64 Ohm load and for single-ended connections it will be the same 8,000mW with a 16 ohm load for maximum power.
For short term peaks the main limitation is the length of the peak, we test with music that has relatively long, high level peaks at clipping to determine the equivalent sine-wave power.
For lower load impedances than those stated above the power will be limited by available current, for higher impedances it will be limited by available voltage. It should be noted that this behaviour is not unique to the iCAN Pro but applies actually to each and any amplifier under the sun.
Finally, if using 200 ohm headphones the power is limited by available voltage only (again, this happens with all amplifiers) so you would get around 660mW with a single-ended connection and around 2,640mW for balanced connection.
As most headphones tend to deliver > 100dB/mW SPL these power levels are insanely high, basically like driving a high-sensitivity horn speaker like AvantGarde with amplifiers having a kilowatt or more power!
If the 200 ohm headphone was 100dB/mW the single-ended connection would produce 128dB at full power and the balanced connection would produce 134dB at full power. These are extremely high SPLs and permanent hearing damage is a real danger at SPL levels this high.
Very few headphones will ever require even a small fraction of the power available from the iCAN Pro, having such large extra reserves allows it however to for example drive very inefficient headphones such as HiFiman HE-6 or AKG K-1000 with authority.
Carpe diem with these hungry headphones