Download the Filter-Buffer Schematic
Download Filter Buffer Schematic
The circuit uses 4 quad op-amps, three of the op-amps are used for the filtering circuit, and the last op-amp is used for the buffer. To simplify the design and for quality control 1 uF capacitors are used for all filters, with the values of the resistors changing to set the filter cutoff points.
You will notice that the circuit also includes a +5 volt voltage regulator. This added a +5 volt output to the circuit, which could be used to control the volume of the attached Roland guitar synth. A few acoustic players wanted to be able to control the volume of their synth with a foot pedal, rather than using the GK S-Volume control.
All the parts for building the Filter-Buffer should be readily available, though you may have to purchase from a large distributor such as Mouser Electronics to get the exact value of the resistors required.
Introduction to the Filter/Buffer 13-pin Roland Guitar Synthesizer Processor:
The Filter/Buffer does three things: first, the six subsonic filters remove nonmusical and mechanical noise from the output of a 13-pin Roland guitar synth controller to improve synthesizer tracking and COSM modeling.
Second, the Filter/Buffer provides two buffered auxiliary inputs to enable non-GK equipped guitars or any audio source to access COSM amp modeling and effects in a Roland guitar synthesizer like the GR-55.
Finally, the Filter/Buffer adds a master effects loop for both the two auxiliary inputs, and the normal guitar output from the Roland 13-pin guitar synth controller.
"Finally had a break in the weather and hooked up the filter buffer and gr55. Fantastic! No ghost notes at all, except when I get sloppy. The better I played, the better it sounded. Didn't have to touch the sensitivity adjustment at all. Perfect out of the box. Definitely worth the money. Thanks so much for providing a permanent fix for this problem. - Gus"
History and Development:
The basic idea of the Filter/Buffer is not new, for years Roland included subsonic filtering as a part of the circuit design of the Roland VG-8 and VG-88.
Previous Roland synths like the VG-88 included subsonic filtering.
But when the VG-99 shipped in 2007, players with piezo systems like the Godin guitars with the RMC pickups, or the Graphtech Ghost system, immediately noticed that patches that worked so well with the VG-88 were muddy and indistinct on the VG-99. Even after a Roland software update, the problem remained.
Richard McClish, founder of RMC Pickup company, developed a replacement electronics board specifically for the VG-99, the V9SF. The V9SF contained six, Butterworth subsonic filters that restored the subsonic filtering to the VG-99 and solved the problems piezo guitar players were having. Similarly, when the GR-55 shipped in 2011, Richard McClish developed an electronics board for the GR-55, the RMC OPT-01 tracking optimizer.
Now, the Filter/Buffer is the first product of its kind offered as an inline device. Meaning that it can be used with the GR-55 or VG-99. Placing the Filter/Buffer before a Roland US-20, or UX-20 clone, means that both attached synthesizers get the benefit of the filtered guitar signal.
The Butterworth Filter design was selected for the flat response in the passband range.
The Filter/Buffer follows Richard McClish’s published specifications, using 6, 4-pole, -24 DB per octave Butterworth subsonic filters, operating at 50, 75 and 100 hz.
The Butterworth design was chosen for its flat frequency response in the passband range. The filter points were selected to keep musical information, but eliminate mechanical noise that can effect both synthesizer tracking, and COSM modeling.
The Filter/Buffer even benefits Roland GK-3 equipped guitars that may be using a tremolo system, or players that experience problems with palm muting, as this can also add unwanted mechanical noise to the divided hex pickup output.
Auxiliary Inputs and Master Effects Loop - Use Non-GK Guitars to Access COSM Modeling Amp and Effects:
In addition to the benefits of subsonic filtering, the Filter/Buffer has two auxiliary inputs, designed to accommodate the impedance of conventional guitar pickups, but any audio source can be used.
Filter/Buffer diagram. Click on image to enlarge.
Auxiliary input signals one and two are mixed together, using an active mixing system, and combined with the conventional guitar output from the 13-pin guitar.
Before these blended signals are sent to the attached Roland synthesizer, they also pass through a master effects loop.
The master effects loop enables a chain of effects pedal to be used with both the 13-pin Roland guitar synth controller, and with the auxiliary inputs.
In the video clips shown below, both a bass and keyboard are used with the FIlter/Buffer, and a Roland EV-5 is used in the effects loop as a master volume control.
Links to more information: