Casio MT-18

(photo taken from eBay, showing my specimen)

 
This brown keyboard is simply the midsize version of Casio PT-80. Thus the main voice is still monophonic despite bigger keys. The specimen I bought even came with the same ROM-Pack RO-551.

different main features:

  • 32 midsize keys
  • better speaker (without disturbing resonance)
  • different CPU= "HD61703A01, 5B 33" (80 pin SMD)

notes:

Very unusual is that the MT-18 contains a different CPU despite the behaviour is identical with the PT-80. Thus I guess that the same CPU core was only re- released in a different package or manufacturing process for technical reasons, while the internal circuit stayed the same. Also the PCB layout and material looks very different. Despite it worked well, I found in my Casio MT-18 an exploded electrolytic capacitor (which I replaced).


Casio PT-20

(photo from eBay, showing my specimen)

This tiny instrument seems to be just a downsized Casio PT-30 and sounds very similar. (I haven't examined the hardware yet.) Unlike the latter it is missing the LCD, the cartridge slot, some of the sequencer buttons, the transpose buttons and 2 high note keys (thus also the "arp. 6" rhythm). Instead of separate rhythm and chord volume sliders it has only a combined slider. Its small case resembles the Casio PT-1. The original German retail price in a German Conrad catalogue from 1986 was 199DM (about 100€).

The likely most advanced member of this hardware family was the ultra- rare keyboard boombox Casio KX-101 (37 mini keys, chord button pad, complex sequencer that saves data on audio cassettes), which was even 4 note polyphonic.