Yamaha SPX-90

Yamaha SPX-90 Processor-Mod, Feedback Loop

This well known mid 80ies multieffekt-unit now has a feature that adds subtle but unique colouring to the sound. I was interested in experimenting with the „processor pitch mod“ on a effekt unit and decided to try this on my SPX-90.

Later i added a quick-dirty-feedback loop to take the sound tweaking possibilities even further.

One side of the stereo output is fed back to the input of the machine – which extendes decay and also can bring the loop into self oscillation. This relatively simple idea that is very common with analog spring reverbs. On the SPX-90 it generates endless delays, metallic room sounds and tuned self oscillations with ease.

In addition to combine the self oscillation loop with external effekts i added a simple unbuffered send & return path.


  • processor-/pitch mod
  • feedback loop with send & return path

link >>>

pdf >>>

build docs >>>