The ZXTT Module from Quazar is an add-on module for Ed Brindley’s YM / AY soundcard for the RC2014. Its purpose is to give it the exact clock frequency to the soundchip to have the correct pitch matching the AY-3-8912 that was fitted in the ZX Spectrum 128K onwards.
The tone of the YM and AY soundcards are all derived from the clock signal it receives. The ZX Spectrum’s AY soundchip was fed with a 1.7734MHz clock, which this module matches. There isn’t much control of the clock on the soundcard, as the circuit can provide a clock from either the main system clock divided by 2 or divided by 4, or on the Rev 6.1 card a separate oscillator module. If you are using the card to play ZX Spectrum tunes and the AY is fed a clock speed lower then the pitch of the tones will be lower. Likewise if clocked higher then the pitch of the tone will be higher, so the tunes won’t sound exactly right.
The ZXTT module replaces one of the chips on the YM/AY interface and feeds the soundchip the exact 1.7734MHz clock. Therefore the tunes will be the exact same pitch as the ZX Spectrum. Essential for any serious ZX Spectrum demotune fans out there!
This module will fit both the Revision 5 and 6.1 of the YM/AY Soundcard boards
The ZXTT Module is supplied fully assembled and tested with documentation.