Spice Simulation – Rane MA6

Spice – Rane MA6

Fig 1 is the DC analysis of the Rane MA6 circuit. As I mentioned before, the circuit resembles the Peavey CS800 vintage of 1976. There are a few changes though, most notably is the 1.3k emitter resistor in the first transistor. 

Fig 1 – DC Analysis

The DC analysis ran smoothly with the resistor values in Rane’s schematic. The first transistor with a collector load of 1k has 1.3mA running through it. In the next stage, the VAS standing current is 12.19mA. This is quite an ideal figure. Finally, I’m able to bias the power transistors to 25.81mA.

Fig 2 – Transient Analysis

The Transient analysis in Fig 2 shows an output of approximately 38V with an input signal of 1V. This correlates with the gain of 34x in the amplifier.

Summary

It is not often that I see a 1.3k resistor in the emitter of a transistor. Normally, it’s about 100Ω for emitter degeneration. Some of the advantages of having such a high resistor value is an improvement in stability and a higher bandwidth. The trade-off is less gain.

In the Rane MA6, because of the high emitter resistor resulting in less gain, the op-amp will now have to swing more to compensate for it. This is not an issue. In fact, an op-amp like the 5534 is more than capable. She not only can provide the voltage but the current as well.

Compared to the vintage CS800, this MA6 simulates much better. This means I will have less problems when I prototype this circuit.