X-Altra Mini II Discrete Line Stage

X-Altra Mini II Discrete Line Stage

This is the line stage used in the X-Altra Mini II line level preamplifier discussed in detail elsewhere on this website. The attached presentation discusses the design and presents the measurements of just the discrete line level amplifier.

This is a paired down, simple design that nevertheless offers excellent measured performance and an intresting alternative to IC based opamp stages in line level amplifier applications. By running the VAS at a high current (c. 20mA), it is able to remain in class A up to 9V RMS into a 2K ohm load with distortion no more than 10ppm – at less output levels, its even lower – at 2V RMS out into 2k it falls below the measurement gear noise floor of about 3ppm.

Here is the BOM (updated 25th July 2022 to include TI JFE2140 option for U3 and U4)

Here are some performance measurements using the Texas Instruments JFE2140 dual JFET in place of the LSK389 originally specified. The TI device offers better device matching and slightly lower overall noise – its also readily available from Mouser

You can buy a PCB for the line stage by clicking on the button below. The price is $15 +$10 for postage and shipping.