The 517 from Rupert Neve is a 500 Series module based on the company's Portico 5017 Mobile Pre, and provides a transformer-coupled microphone preamp, opto-coupler compressor and DI input. As with the original, the unit includes Vari-Phase, Silk processing, and DI/microphone blending capabilities. The microphone preamp includes 66dB of gain and also incorporates a polarity-reverse switch and phantom power. The separate instrument amplifier includes 30dB of gain, a ground-lift switch, variable phase, and an instrument Thru connection.
As a single-channel device for instruments, the 517 can be used to phase align, combine and compress direct and amplified signals by using the Hi-Z input for an instrument's direct signal, and the microphone preamp for the speaker cabinet signal. A Blend control can mix the direct and amplified signals to achieve the desired tonal blend between the sources, and the Vari-Phase is used to minimize or extenuate phase cancellations between the two signals. This technique could also be used to create a single, mixed output of a guitar and vocals.
The opto-coupler compressor is based around a LDR (Light Dependent Resister) design that has been simplified to a single threshold control with auto make up gain. The compressor is set to a fixed 2:1 ratio with fixed attack and release. To set the compressor, dial the threshold control down until the desired amount of compression is achieved. An LED light indicates when the compressor is active.