This remains now a hobby, but I used to do: Handmade clones of Guitar & Bass Effect Pedals / Effect modding / Rewiring and Guitar Setups+levelling+refrets / Amplifier Repairs / General Audio Repairs
Swapped the NJM4558 IC-s in every monitor with OPA1602 IC-s and also removed the limiter circuit.
Now, they don't push exaggerated mids that much, and are a little flatter. A little better for accurate mixing and monitoring.