The Z12 amplifier was introduced in January 1966, and replaced the X-10 which had been something of a disaster for Sinclair as the boards had been produced mirrored, which caused a significant delay for customers. Even after this was rectified, the amp did not perform nearly as well as Sinclair claimed in the advertising.

The Z12 was built in Thetford, Norfolk in a chapel building formerly operated by Cathodeon as part of the employment policy of Pye to bring employment to the wider Cambridge and East Anglia area.

Things were only slightly better with the Z12. It was only capable of 3 watts of power, despite claims it could handle 12, which is why it is named the Z12. There were also reliability problems, if the unit was run at full power, it would fail within hours, mainly due to cheap components which were not considered good enough for other manufacturers.

Despite the problems, the unit was cheap and therefore sold reasonably, and was in production for around two years. Other products were added to the range such as power supply units, and the Stereo 25, which gave volume and tone controls to the Z12.

The Z12 eventually became part of a wider range of hi-fi products comprising the PZ3 and PZ5 power supply units, plus the Stereo 25, a control unit providing volume balance and tone controls for the Z12.