(This information ONLY for the people who know the power amplifier circuit.)
Quad's current dumping circuit amplifier is such a simple circuit, good sounding and powerful long lasting amplifier from the past to modern days.
In the Quad current dumping amplifier big family, only Quad 405 is using op-amp in the first input stage. When compare Quad 405 circuit to her big brother Quad 606, it's simple to modify Quad 405 to Quad 606 circuit by replacing the op-amp input stage with a single PNP transistor, change op-amp(use as DC servo control), resistor, capacitor, adding transistor and diodes on the same Quad 405 PCB.
The new component can be place on either side of the PCB according the component space needed and cut one PCB copper trace for the mod job.
I made the MOD and the result is good. Sounding is good and I like the all discrete current dumping circuit.
This MOD is not the last, we can have more MOD like adding one more pair output power transistors as the Quad 520 model which can handle better speaker loading.
Quad's current dumping circuit amplifier is such a simple circuit, good sounding and powerful long lasting amplifier from the past to modern days.
In the Quad current dumping amplifier big family, only Quad 405 is using op-amp in the first input stage. When compare Quad 405 circuit to her big brother Quad 606, it's simple to modify Quad 405 to Quad 606 circuit by replacing the op-amp input stage with a single PNP transistor, change op-amp(use as DC servo control), resistor, capacitor, adding transistor and diodes on the same Quad 405 PCB.
The new component can be place on either side of the PCB according the component space needed and cut one PCB copper trace for the mod job.
I made the MOD and the result is good. Sounding is good and I like the all discrete current dumping circuit.
This MOD is not the last, we can have more MOD like adding one more pair output power transistors as the Quad 520 model which can handle better speaker loading.
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