Available as an assembled Module and as a DIY project.
This Module is currently available.
barton bmc032 blended bandpass, euro
This is a manually controlled bandpass filter module. In addition to the normal controls for frequency and resonance, there is a control for blending the filter's output back in with it's input to give a finer degree of control over the sound. This is combined with a phase reversal switch for the filter's output which allows for notch-like outputs when combined with the blend control
https://synthcube.com/cart/makers/michael-barton/barton-bmc032-blended-bandpass-euro?limit=100
These merchants probably sell this module. Huh?