Mellotronists

Hello countryman Janne (my mother's side are Finn...):

One of my trons is an EMI 400 as well and I have had some of the same 
problems:

1)  Earth loop problem
Martin at Streetly Electronics suggested I buy a 'ground fault 
interruptor' to solve this humming problem. They are available at 
Radio Shack in N. America, but I don't know about where on earth 
you'd find 'em in Suomi.

2) Disappearing sound on your middle 'C'.
This could be an Azimuth problem with that particular tape head.  
Martin and John at Streetly can fix this if you send them your tape 
head assembly.

3) Poor fitting keyboard
Emi's are notorious for being 'out of square'. (They were not 
assembled with great care).  This is more difficult as you would have 
to have an experts like John and Martin at Streetly do an overhaul.

I hope this is of some help.

Contact the tronbros at Streetly Electronics for more detailed 
information.

Cheers!