grandPa Expander


Spa is an expander for the granular sampler module grandPa. It adds CV inputs for nearly all parameters and a clock input to trigger the grain shift. It doesn’t work without the grandPa Eurorack module.

More CV inputs and a clock input to trigger grain shift

The voltage on the CV inputs is relatively added to the grandPa settings on both channels A and B. All CV inputs react only to positive voltages. The update rate of these CV inputs is 20 Hz. Communication between SPA and Grandpa can introduce audible artifacts to some samples while tweaking the SPA knobs.

Four CV inputs have attenuator knobs. These CV inputs are normalized to 5V, so the knobs act as a signal source when nothing is connected to the CV input.


  • independent CV inputs for most parameters of the grandPa module
  • CV inputs with attenuators are normalized to 5V, so the attenuators work as direct controls of the parameters for both channels A and B of the grandPa
  • CV inputs react only to positive voltages from 0-12V
  • grain size and shift speed CV inputs with attenuators
  • switch to select whether the other two CV inputs with attenuators control Start/End or Attack/Release parameters
  • crush cv input
  • grain sync input to trigger grain shift
  • front panel from aluminium or oak wood with custom knobs
  • handmade locally by Bastl Instruments in Brno, Czech Republic

Technical details

  • 5HP
  • PTC fuse and diode protected 10pin power connector
  • 50 mm deep
  • connects to grandPa with a ribbon cable on the back side
  • power consumption +12V: < 25 mA
  • pdf user manual download

DIY kit

Go through the complete assembly guide below and make sure that you understand all the steps. The assembly guide includes a BOM.

GrandPA / SPA firmware upgrade

Did you know that all grandPAs from 2015 and earlier can be easily upgraded to current firmware v1.1 offering more features? You can find all the information here. You can get the update pack either from our shop or from your local dealer and watch this video