The Amtec LLI-5A is a 500-style analogue module that allows for easy
interfacing of low-level guitar effects into the line-level studio environment.

It consists of two paths that share a common control knob which works both
as a variable attenuator for the SEND path and a variable boost control for
the RETURN path, so the net gain of the whole system is unity.

The range of the SEND loss/RETURN boost control is from -6dB to -30dB
ref. line level, but it can be additionally shifted down by 20dB using a push
button on the front panel.

Amtec LLI-5A User Manual
Some guitar effects are not designed to be in-phase, so when using such an
effect via the LLI-5A and doing parallel processing some phase cancellation
may occur. To overcome that issue a phase polarity switch is included in the
send path of the LLI-5A.
The SEND path, which also includes a ground-lift switch, can be used as a
"re-amping" tool. The RETURN path can be used as a clean DI.

The operation of the LLI-5A module comes down to connecting effects in
loop, choosing the proper phase and setting the right operation level. Too
high an operation level results in excessive distortion from the effects in
the loop, whereas too low level results in excessive noise.

The LLI-5A is extremely easy to use and features very short signal path
ensuring high sound quality.