I've a very long background in computer audio and this release harks back to the hours and hours I spent listening to the fantastic AY music on the Sinclair ZX Spectrum in the early 90's!

The ZXTT is an add-on module for Ed Brindley's YM / AY soundcard for the RC2014 DIY computer (and compatibles) and 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 Ed's soundcard, as his 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 wrong frequency can also affect the envelope effects.

My ZXTT module replaces one of the chips on the YM/AY interface and feeds the soundchip the exact 1.7734MHz clock speed so 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 of the YM/AY Soundcard boards (the version currently sold as a kit by RFC2795 Ltd here on Tindie - see their listing for YM2149 Sound Card for the RC2014) and Revision 6.1 boards (gerbers/schematics for both 5 and 6.1 are available from Ed himself on Github -> electrified/rc2014-ym2149)