Sjöström Audio

QSX Mark II - The extreme phono (RIAA) amplifier

 

Click on the picture to get a larger view. The front view of the original QSX Amplifier from 1986.

Click on the picture to get a larger view. The top view of the QSX Amplifier pcb. High resolution picture HERE.

Click on the picture to get a larger view. This QSXM2 Amplifier built by a customer. The power supply is of an another brand. A good job, indeed and on top of, it he became very satisfied .

Click on the picture to get a larger view. This QSXM2 Amplifier built by an another customer. The power supply is QSXPS. Also here a very good job, indeed and this person became also very satisfied.


The project has been very successful because everyone have succeeded. That is amazing if you take into account the huge amount of parts.

Interesting features

In order to get an extremely linear and extremely low distortion design I have taken a couple of measures:

  1. Symmetrical design
  2. No capacitors in the signal paths
  3. Cascodes in the input stage and in the high gain stage
  4. Buffered cascodes with emitter followers
  5. Possibility to use ultra low noise transistors
  6. High speed output stage
  7. Advanced input bias servo with chopper stabilized or conventional opamp
  8. Totally DC-coupled together with DC-servos and input bias current servo
  9. Many decoupling capacitors and EMI-filters
  10. Professional quality printed circuit board with groundplane
  11. The pcb has lot's of possibilities when it comes to tweaking. You could use JFET's as input transistors for instance.
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