Hi, Can I use a speaker on my Sony CD walkman d-EJ361 If yes, which one are recommended?

YES YOU CAN. SEE MY COMMENT FOR INSTRUCTIONS.

Yes!!! Check the voltage size, get a docking station 30 pin adapter, which has the same output and input voltage size. and thats gonna solve it for you ok.

It could be that the lens needs cleaning. Try a CD Lens Cleaner like this. They can be found at most major grocery stores and supermarkets.

hi,
check the out put voltage of that adapter may be its out put is higher than 4.5V dc.
thats why the Walkman displays HI dc IN. do one thing purchase a 4.5V 1amps SMPS adapter (connector with same polarity). it will give a constant output of 4.5v (110v t0 240v input)
ok

Hi try www.sony.com

Yes, alternate AC adapter should supply same voltage.

Well, try to record something onto your mobile and check if the recorded track echos at different instances...If yes, have your mobile speaker checked withthe vendor.. If not, clean up the vicinity of the speaker... 

Hello,
Go to Sony Support and check downloads area where you can get driver and SonicStage for your MZ-N505 Sony walkman.

I assume you've tried batteries, cleaned the laser, etc. If so, then the laser might be knackered!

it means the power supply it's not the original one and/or it doesn't have the right voltage or amperage, maybe you are using an aftermarket one or one with the wrong polarity at the tip.