For best results, any active device with the exception of the output transistors operating in class A. This is to avoid bias to saturate or block the entrance to all the clipping level, should be selected. This raises some difficulties for a BJT amplifier, where (to stay in Class A) driver stage collector currents, the base of BJT output current at maximum output current (ie in our case some of 10A) No is not exceeded. Therefore, the overall bias regime redesigned to allow space for the swing base BJT output current.
Even in these circumstances, the power dissipation in the driver’s relevant and it is doubtful if a heat sink on board (as in our design side MOSFET included) help, if maximum performance is desired 200W into 4 ohms. It is therefore assumed that the power BJT design based on our application can not be more than one goal and 100W/4ohm 50W/8ohm. Of course, for such relatively modest achievements, it is not necessary to install three pairs of output devices, a pair of (ex) MJL4281/MJL4302 or equivalent work will be done.
Adjusting the balance Hawks Word is a double potentiometer (minimum of ten rounds) with more than 0.5% of correspondence between the sections. We replaced R20 and R81 with a 2K potentiometer Bourns 10 turns and adjusted for minimum distortion 20kHz Open Loop. You will find that the minimum is strongly dependent on the frequency, always adapting to at least the higher frequency in the audible range. At low frequencies, the feedback loop gain in reducing DHT levels to help you. Measured values ??and replace the potentiometer with fixed resistors.
The minimum is usually very close, if you need 0.5% or better precision resistors. The aim should be to bring the open-loop THD-20 below 0.01% to 10 Vrms input level. We built four previous CE FPO advice and got the last open-loop THD-20-values ??at 0.0065% 0.0075% 0.0090% and 0.012% (the latter, we can not source of precision resistors required values).
The network output Zobel is the stability amps together. For the same reasons, shoud not be 2UH air core output inductor.
The error amplifier frequency compensation C17 is the signal ground of the amplifier that takes full power to the ground. It is for reasons of stability and provide a grounding shield for feedback (output port).