The 788T introduces a new microphone preamp and analog-to-digital topology to Sound Devices. This new circuit improves the dynamic range of the microphone inputs beyond the performance of the class-leading 702, 702T, 722 and 744T recorders.
The preamps in the two and four-channel 7-Series (702, 702T, 722, and 744T) use discrete transistors (high-quality, old-school, high-current op-amps). These are great sounding preamps connected to a quality, low-noise analog-to-digital converter chipset. Performance versus power consumption broke new ground when these products were introduced, and have yet to be bested in their class in real-world measurements...until the 788T.
The preamps in the 788T were designed in 2008 with the latest topologies and electronic parts. The 788T mic preamps outperform the preamps on the two and four channel recorders, while drawing less power. The 788T has improved dynamic range, resulting largely from an analog-to-digital converter with several dB more dynamic range. While this A/D chip draws slightly more power than those in the two/four channel 7-Series, the preamp circuitry draws less than the earlier recorders. Additionally, these new preamps are fully digitally controlled. There is no analog audio running through a pot like in the old designs. This gives several benefits, including precise gain matching between channels, more control over the limiter, and a much more dB-linear gain curve. It also provides for hooks to control levels electronically, if required in the future.
Because the 788T has eight microphone preamps, its inputs can draw more overall power than the inputs on the two and four channel recorders. When not using inputs the front-panel gain control can be used to turn individual microphone preamps and A/D circuits off, increasing battery runtime.
No, the 702, 702T, 722, and 744T cannot be upgraded. The 788T is a clean-sheet design with an entirely new analog architecture that is not retrofittable to the smaller recorders.