It is possible to alter the range of the mid control on the 1228, (as long as the version is Version 2, which is most likely).On the channel circuit board near IC4 there are two capacitors, C14 and C15. The original value is 6n8 (6.8 nanofarads). If you change these capacitors to say 15n, that will reduce the operating frequency of the mid control and should not affect anything else. 