The original blue-stripe models were replaced by the black-face "C" model,the 1176LN (LN stands for low noise), which employed low-noise circuitry encased within an epoxy module (presumably so it couldn't be reverse-engineered by other companies). The next ,model D integrated these improvements into the main circuit board. The model E, introduced in the ealy 1970s, was the first to accommodate European 220V mains power with a voltage selector on the rear panel.