Updates: November 2017
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Roland GR-33B Bass Guitar Synthesizer

Roland GR-33B Analog Bass Guitar Synthesizer

Features and Specifications:

  • 4-voice polyphony
  • 2 oscillators per voice
  • VCOs (voltage controlled oscillator) are directly harmonically locked to each string, but can be tuned separately
  • VCF (voltage controlled filter, low pass), 2 modes, -12 dB or -24 dB per octave, with envelope modulation (attack and decay)
  • Low Frequency Oscillator with lag (delay) generator
  • Built-in foot switch controls the VCF or VCA modulation
  • Built-in foot switches control the VCO harmonize pitch (detuning of the VCO's)
  • Built-in foot switch selects envelope presets A or B
  • Pedal control input for the VCF
  • The GR-33B can output either the guitar, the synth, or a mix of the two
  • Synchronized, flashing LED status indicators
  • Dimensions: 15.75" (W) 11.125" (D) 4" (H)
  • Power Requirements: 20 watts
  • Response Time: 13.00 ms
Roland GR-BB Set
Roland G-88, G-33 and GR-33B

Introduction to the Roland GR-33B:

The Roland GR-33B is the bass guitar version of the GR-300. Some changes were made to meet the specific needs of bass players. Also, there is no hex fuzz circuit.

The GR-33B also has two selectable envelopes, and a choice of VCF and/or VCA modulation. While the GR-300 has a -24 dB per octave filter, and the GR-100 has a -12 dB per octave filter, the GR-33B actually has both, with a switch to select -12 dB or -24 dB operation.

There is no pitch sweep like on the GR-300. The GR-33B has a very cool variable LFO delay. This delay follows the envelope generator. This means you can play a note and hear the LFO quickly or slowly swell in. Playing notes rapidly means that you will not hear the vibrato effect. It is very expressive, and makes sense for the bass player that may not want constant vibrato. If you check out the Frankenstein demo, you will hear vibrato swelling in on the main line. I did not use the touch pads to activate the vibrato each time I played the phrase, but instead set a short delay so the vibrato would swell in on the longer quarter notes in the melody.

Early GR-300/GR-33B Brocure
From the Roland 1982 Brochure

The GR-33B sounds very much like the GR-300. If you compare the block diagram for both synths, you will see that they are basically the same. Likewise, the synth response time for the GR-33B is very fast, like the GR-300. I did a few timing checks when recording demos for the GR-33B, and the delay was in the range of 2 - 4 milliseconds. This is the kind of speed that a digital synth could only dream of.

I would like to mention that I really wish the GR-33B provided access to the square wave output. Like the GR-300, the main output is an unusual ramp waveform. When the duet mode is engaged, you can hear a square wave and the ramp wave. The problem is the aggressiveness of the ramp wave. It is much more like a brass wave, than the buttery smooth sound of a classic Minimoog bass patch. You can filter the ramp wave to eliminate the aggressiveness, but the waveform becomes very dark with few harmonics. You can hear this sound in the VCF and VCA modulation demos below. The Frankenstein demo also shows off the aggressive sound of the GR-33B.

Finally, the response of the GR-33B system has some uneven areas compared to the GR-300, which has flawless tracking. In particular, playing the low E and low A strings can confuse the synth tracking system. The problem does not seem noticeable with the D and G string. I spent an entire weekend testing my system before concluding that the GR-33B is pushing the limits of guitar synth technology with the low notes. Mark Smart, a serious musician and guitar synth genius reported to me that his main problems with tracking came from the lowest notes. And I was able to exchange emails with Pablo Leocata, another serious GR-33B user who reported similar playability. Depending on how you play, this could be unnoticeable, or an annoying inconvenience. My theory that this issue has to due with the different quality in sound from the open strings to the fretted strings.

Links to more information:


Roland GR-33B Roland GR-33B Roland GR-33B
Roland GR-33B Roland GR-33B Roland GR-33B
Roland GR-33B Roland GR-33B Roland GR-33B
Roland GR-33B Roland GR-33B Roland GR-33B
Roland GR-33B Roland GR-33B Roland GR-33B
Roland GR-33B Roland GR-33B Roland GR-33B
Click on any image for larger view.


YouTube Playlist: Roland GR-33B Analog Bass Synthesizer - 10 Video Clips

Schematics - Repairs - Service Bulletins:

There are no know service bulletins from Roland addressing any GR-33B problems. As a safety precaution, I strongly recommend replacing the orignal blue tantalum capacitors. These capacitors, while very popular in the late seventies, are known to fail.


GR-33B Case
GR-33B Case Interior
CB-300 Carrying Case

Page six of the 1984 Roland GR series brochure lists several options and accessories for the GR-100, GR-300, GR-33B and GR-700.

FS-1 footswitch: The FS-1 footswitch is a nice vintage footswitch to use for string select.

FV-200 volume pedal: The FV-200 volume pedal could be used to control the filter cutoff on all the vintage Roland synths, GR-100, GR-300, GR-33B and the GR-700. The FV-200 could also be used as a pitch pedal with the Roland GR-700. The both the Roland GR-100 and GR-300 owner's manual list the FV-20 volume pedal for use with the GR-300.

CB-300 case: The rarest of all vintage accessories, Roland made a leatherette case for the Roland GR-100, GR-300 and GR-33B.

And page five lists the Roland US-2 Unit Selector and the C-24D connecting cable.

Most of these accessories are impossible to find now, but there are modern equivalents that you can use to expand the playing experience with the vintage Roland GR-33B.

Roland FS-1 Roland FS-1 Roland FS-1
Roland FS-1 Footswitch
GR-33B Rear Filter Pedal and String Select Inpjuts
GR-33B Guitar and Synth Outpus

The GR-33B has two control inputs on the back: filter pedal sweep, and "string select." With "string select" strings can be individually turned on and off, so you can choose to have the synth sound on only the bottom two strings, for example. By plugging a basic on/off switch into the "string select" input, you can turn this feature on or off. With the "string select" on, strings can be individually turned on or off, and with "string select" off, all the strings are active.

Filter Pedal Input: