new product – _rotary_ : cv fader module for V-4 video mixers

a new circuit has been added to the underscores catalog : _rotary_ – a voltage controlled fader module for V-4EX, V-8, and V-4 video mixers

background

a few years ago while i was visiting berlin Gilbert Sinnott (autr) and i were inspecting the cv mod that had been installed by a previous owner on my Roland V4 video mixer:

you can see the 3.5mm cv jack and a toggle select switch here on the front of the mixer. Inside can just be made out some perf board with protection diodes.

these series of mixers (Roland V8 and V4EX also) have removable T-bars – this is so the user can select whether they want to have a vertical or horizontal T-bar. it also allows for swapping the T-bar interface like for example with this offical Roland CrossFader Module:

an example of the official cross-fader swappable t-bar module

prototype iterations

We started thinking about how this CV mod with protection diodes and a select toggle switch could be integrated into a swappable t-bar module…

an early rotary prototype – only cv and fader control on front

after some testing and iterations the passive mod was upgraded to an active opamp circuit, allowing for:

cv gain control over ranges 0-1v up to 0-5v
simultaneous cv and manual fader position / cv offset

schematic of cv gain and fader position / cv offset

finally we decided to also include a simple envelope follower circuit allowing for audio reactive crossfader control – with this comes the envelope/bypass toggle switch and a shape knob:

envelope following (red) of audio (blue) on a scope

this circuit uses TLV237X opamps – these are 3-MHz rail-to-rail opamp available in dip packages (video rate is not needed since limited by the frame rate of the digital video mixers)

demo video

you can see a full install / walk-through of this circuit in the _rotary_ circuit demo video:

it is in stock now in the shop as kit or assembled unit (pcb+panels coming soon)