Spice Simulation – Phase Linear 300 Series 2

Spice – Phase Linear 300 Series 2

The previous Ampeg SVT-4 Pro resembles the Phase Linear 300 Series 2. Some resistor values were changed but the overall typology essentially remains the same.

Historically, the Phase Linear 300 Series 2 was manufactured in 1979, whereas the SVT-4 Pro made her appearance in 1997. That is almost 20 years later. The main difference is the latter adopted IRFP240/9240 mosfets for the power transistors.

Fig 1 – DC Analysis

Fig 1 is the DC analysis of the Phase Linear 300 Series 2. Her DC operating points are quite ideal. There’s 1.94mA flowing through the first set of transistors. In the VAS, the standing current is 17.03mA. This is a nice and beefy amount for this stage. After that are the drivers and finally the power transistors.

The DC at the output of the op-amp is 5.42mV. The amplifier’s DC at the output is -3mV. Essentially, no DC offset of any kind is required.

Fig 2 – Transient Analysis

Fig 2 is the Transient analysis of the Phase Linear 300 Series 2. With an 8Ω resistive load, she’s able to swing to full power. Though the amplifier’s internal gain is at 44x, her sensitivity is at 1.5V. That’s due to the reduction of the in-coming signal at the op-amp inverting input (10k + 39k to ground).

Summary

The power transistors in this Phase Linear 300 Series 2 are no longer in production, hence a lot of vintage power amplifiers are left to rot because of this.

However, it is possible to revive her using new outputs. Transistors like the Toshiba 2SC5200/2SA1943 and the Sanken 2SC2922/2SA1216 are good candidates. When I prototype this amplifier, I will test them out to evaluate their sonic performance.