No info about availability.
AC/DC Mixer
Low noise three input mixer in 4HE only (based on low noise IC NE5532).
Can be used for audio or CV mixing. Every channel has internal jumper for DC or AC coupling.
For CV mixing (DC coupled) simply set jumpers.
For audio mixing you can left jumpers set (DC coupled) or removed (AC coupled inputs=removes DC offsets).
Max amplification is two (2) at max. positions. So if any input signal is 2V p-p, it can be amplified to 4V p-p.
Output is strong enough to drive headphones.