Agreed. However, the coil is much more efficient in preserving the amp from being overloaded with highly capacitive load.
During one of the experiments with no inductor at the output, 1.1uF capacitor's lead (copper) have melted (20V p-p square wave).
This does not happen if the coil is in place - it just does not allow the currents being that high.
The inductor does not work by limiting the current, but by removing the cause of the current: oscillation.
A capacitive load draws huge currents on the edges and the output inductor decreases that dramatically.
Even a stable amplifier (with global negative feedback loop), loaded with highly capacitive load, will always experience ringing at the tops of the square wave half-periods. This ringing results in the short term currents, especially high at the edges of those half-periods. Much higher than normal. The amp is working on practically zero ohm load in the beginning os each half-cycle.
Inductor decreases the higher order spectrum components of those currents, decreasing the load at high frequencies.
What would you consider a high frequency? If it is over anything audible, why not just filter anything over 20k and not worry about it? Also if the inductor pretty much right at the output, with not much after it and in some cases nothing really after it, the choke can be placed prior to the driver for the same results no?
Because it is the interaction of the output transistor with the speaker that causes the high freq. oscillation that the 14 turn coil parallel 10 ohm resistor is supposed to damp out. The that gadget is not for interaction of the output transistor with the driver transistor. That gadget appears between output transistor emitter and speaker terminal of nearly all amps - except my 1966 design amp that was infamous for melting output transistors (for more than one reason).
Read about RLC oscillators, and imagine the output transistor as the C and the speaker as the L. The mechanical analog they teach in physics 200 class, the L is a spring and the C is a weight. Boing boing. R is friction. Power transistors do have significant output capacitance after all. The MJ15015, the successor to the venerable 2n3055, has max output capacitance of 600 pf.
Read about RLC oscillators, and imagine the output transistor as the C and the speaker as the L. The mechanical analog they teach in physics 200 class, the L is a spring and the C is a weight. Boing boing. R is friction. Power transistors do have significant output capacitance after all. The MJ15015, the successor to the venerable 2n3055, has max output capacitance of 600 pf.
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