AM8107 SH07 HP and LP Filters

Overview This module is replica of the filters from the legendary Roland SH-7 released in 1978. The Low Pass Filter is a typical 1970’s Roland 4-pole OTA design, with an additional single pole High Pass Filter. The original low pass filter uses 3080 OTA chips, and precision polystyrene capacitors, which we have retained along with the 2SK30 FET’s and 2SC1000GR transistors.  The high pass filter is a simple 1 pole design based around a single JFET and polypropylene capacitor. The original filter has a LED monitoring the peak input level which we have also retained.

Euro Rack Module: 16HP wide
User Manual: 

Detailed Description 
This module is an accurate re-production of the SH-7 low pass voltage controlled filter, using the original CA3080 OTA chips in the filter core and precision 1% polystyrene capacitors. The design includes  buffering Op Amps to interface to modular systems. It delivers a very warm and smooth sound.

There are front panel controls for adjusting the Cutoff Frequency and Resonance as well as the level of 2x control voltages and 2x audio signal inputs. Resonance is smooth and controllable into self-oscillation. There is a LED slide potentiometer that controls the High Pass filter cutoff frequency and a red LED monitors input level. The filter uses traditional skirted aluminum control knobs

There are five 3.5 mm jack sockets on the base of the front panel:

  • 2x Audio inputs
  • 2x Frequency control voltages
  • Audio output

Outcome & Availability The prototype filter works well, except the HPF cutoff control, which needs a more aggressive D taper than the standard A taper. The filter only cuts off at the very  top of the slider. D taper potentiometers are difficult to source, so I either use a PIC to map the Pot to a D shape taper or I use a more complex high pass filter with cutoff that is more linear in nature. The AM8107 remains a prototype module and is not in production.

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