Here: Lavry Engineering
I see in the features list of the DA11 it lists "High power discrete headphone output".
Can someone more technically minded than myself explain exactly what that means?
By "discrete" I assume that means it's a discrete audio circuit and not an IC?
By "High power" I guess that means it will easily drive headphones from anywhere between say, 30 and 700 Ohms?
But keeping the wave shape identical is where the similarity may end. One can “keep the wave shape” and do so at different voltage levels, current levels and power levels.
Devices that need to regenerate sound (convert electrical signals to air motion) require more power then devices that simply receive and process audio. Passive speakers are real power hungry devices. Headphones are second in line. The input ports of power amp, mixers, AD’s, EQ, reverb and similar gear do not require much power.
The impedance range of headphones is very wide, but all have much lower impedance then a line level and pro gear device, thus they calls for more current drive then an ordinary OP amp can supply. They also typically operate at lower voltages then most other audio devices.
A typical OPamp device is a higher voltage and lower current device, thus not suitable for headphones. There are “specialty” semiconductor devices that can drive lower voltage and higher current, but I did not find one that is good enough, so I made my own from discrete parts.
For low power applications, there is nothing inherently wrong with OP amp, and there is nothing fundamentally advantageous about discrete. The difference is mostly about packaging. But when making higher power circuits, semiconductor solution cause very high temperatures (a lot of localized heat), and discrete circuits spread the heat over many devices. Spreading heat over larger area and many devices lowers the temperature very significantly. High temperature is not a good thing for best performance and for reliability.
But the main reason I made my own circuit is the headphone itself:
Most audio loads are resistive. When a driver is “looking at” a load that behaves like a simple resistor (or nearly so), the wave shape of the voltage and the wave shape of the current are nearly identical for any audio signal.
But headphones (and passive speaker) are anything but a resistive load. That makes the designer’s life much more complicated. The relationship between the voltage wave shape and the current wave shape is complex. The load (headphone) is not resistive, it complex, it “varies with the music”. The driver circuit must be able to supply the required voltage wave shape while accommodating some other current waveform. That poses additional requirements not normally encountered in transmission of analog audio signals.
I wish I could find a “good enough ready made device”. Instead I ended up with some 2-3 dozen parts. It sure takes some doing to drive a truck, as if it were a race car, but it was real fun circuit to design.