I have just finished a mod job for the D-290. here are a few notes:
- The selector is a motorized type, means it does not put too much mechanical resistance against its rotating motor, which is a low-torque one. I have seen similar selectors in other UK made amps like Creek etc. The results are poor contact within the selector. The way around it is to spray it with the Caig type of contact cleaner (the oily one), rotate the selector back and force 10-20 times and then blow away the remains using air blower (much safer than air pressure).
- Main caps are not brilliant - I changed them for 15,000 uF Mundorf caps. When changing caps, note that the PCB is a double sided one, so make sure to leave enough solder on the component side where the caps fit in, otherwise you end up disconnecting the right channel from the power rail
- The amp output section has Zener diodes before the Mosfets. I originally thought these are regulators of sorts and was tempted to add parallel caps - big mistake!!! the zeners are used as limiters, sort of protecting the Mosfets, no need to add anything...
- The linestage is rubbish, its a simple op-amp buffer stage, using TL072. Better replace it with something better (I used a spare OPA2604) and improve its regulator (based on 317/337) - or replace it with TeddyRegs.
It is also necessary to replace the coupling caps for something better.
Given all this, the D290 will start shining
Yair
