Erica Synths Bullfrog

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Learn to produce and perform with the Erica Synths Bullfrog, a classic subtractive synthesizer that was cocreated with Richie Hawtin. The instrument is designed to captivate and inspire beginners and professionals alike. The instrument is accompanied by a comprehensive user manual that provides a well-rounded understanding of the functionality of the Bullfrog and sound synthesis in general. Unlock the thrill of electronic music production with a comprehensive learning experience.

Bullfrog is a classic subtractive synthesizer that consists of several modules for sound generation and sound treatment. Each module requires the use of patch cables to pass signal. There is also a Voicecard preset system, which adds additional functionality, while facilitating original patch creation for easy recall. The rear panel includes the main CV and Gate inputs as well as audio and headphone outputs. The instrument can also be controlled by MIDI via the 5-pin DIN connector or from the USB-C connector. The Bullfrog includes 10 patch cords, 10 patch notes stencils, three prepatched voice cards, three DIY voice cards, and a power supply.


Bullfrog Overview

  • The Bullfrog is a classical subtractive synthesizer—It consists of several modules for sound generation—VCO, noise generator–and treatment—VCF, VCA/delay, as well as modules that generate control and modulation signals to control them—envelope generators and sample and hold.
  • The Bullfrog will not make sound on its own unless you make patches—use patch cables to interconnect the modules, or insert voice cards that create internal connections between the modules in a specific way. This approach better helps to understand functionality of a subtractive synthesizer and the principles of sound design with instruments like these.


Voltage Controlled Oscillator (VCO)

The voltage-controlled oscillator on the Bullfrog is an audio-rate oscillator that generates sine waves and pulse waves at frequencies that cover almost the entire audible range (from 20 Hz to 10 kHz).


Noise Generator and Mixer

  • Noise Generator: Generates white noise, a sound that contains all audio frequencies at equal amplitudes mixed together
  • Mixer: Individual waveforms with adjustable amplitude are available, as well as a mixed signal where you can define how much of each waveform is sent to the Mix Out. Add external sounds to the three inputs (In 1, In 2, In 3). Inserting a cable into the input will remove the normaled connection.


Voltage Controlled Filter (VCF)

The main purpose of the filter is to alter the timbre of the sound. The Bullfrog features a classical low-pass 24 dB/oct resonant voltage-controlled filter. The module features cutoff and resonance controls. There are two CV inputs to control the filter cutoff.


Voltage Controlled Amplifier (VCA) + Delay

  • VCA: The Voltage Controlled Amplifier (VCA) is the most straightforward module in the synthesizer. Its sole purpose is to alter the amplitude of the signal that leads to changes in volume.
  • Delay: The delay circuit takes its signal post VCA and includes a dry/wet knob for controlling how much of the delay signal is mixed with the dry signal. Delay Time controls the length of the delay (30 to 340 ms), while the feedback controls the number of decaying repeats.


Control Voltage Sources (CV) - Envelope Generators + Sample & Hold

The Bullfrog features three CV sources—two envelope generators (ENV GEN 1 and ENV GEN 2) that can be used also as low-frequency oscillators and a sample-and-hold module that outputs random voltages as well as pulse-wave low-frequency oscillations. All three circuits can be controlled by the manual Gate button.



  • The Divider is a utility module that divides a frequency of the incoming signal by 2, 4, 8 and 16. Normally, such dividers work with pulse-wave signals and have various applications, including computers. But on the Bullfrog, the incoming signal can be any signal, and the divider will advance to the next step as soon as the incoming signal is higher than +3V.
  • In music technology, dividers can be used as frequency dividers (remember, a frequency divided by 2 gives you a pitch that is exactly one octave down), to control sequencers, to create drum patterns and for many other applications.


Voice Cards

Voicecards expand the functionality of the Bullfrog and make it even more versatile. Essentially, the voicecards replace patch cables—they connect the modules of the Bullfrog internally. But that’s not all about them—some voice cards have built in mixers, signal generators, and advanced electrical circuits to control the synthesizer, for example, sequencer that sends CV to control pitch and gate to start events on the synthesizer.

The Bullfrog comes with 6 voicecards:

  • ACID BASSLINE: Instantly provides you with all necessary connections to produce a punchy bassline.
  • SAMPLER-LOOPER: Emulates the functionality of a tape recorder, recording up to 10" of audio from the built-in microphone or from the Bullfrog itself and then feeds it back into the audio path of the Bullfrog for processing via the VCF, VCA, and Delay.
  • GROOVEBOX: Adds electronic drum sounds to a main synth voice as well as features two semirandom pattern sequencers—a trigger sequencer for drum sounds and a CV-gate sequencer or a bass line. Essentially, it turns the Bullfrog into a fully functional groovebox.
  • BLANK DIY VOICECARDS (x3): Allows you to create custom connections of the Bullfrog modules. The voice card mimics the connection points of the Bullfrog. In order to make connections, you need a wire and a soldering iron (and a bit of soldering skills). Use pieces of a wire to connect the points on the voice card and solder the wire. We recommend first to make connections with patch cables directly on the Bullfrog, and if you a specific patch is nice, you can make a DIY voicecard for it.

Additional Voicecards are available separately for purchase:

  • HIGHPASS VCF: Expands the sound treatment capabilities of the Bullfrog by exploring high-pass and band-pass filtering.
  • ELECTRIC ORGAN: Emulates a pipe organ, when several notes are played together. It also illustrates the principles of additive synthesis, where several simpler waveforms are mixed together to generate more complex sounds.
  • ANALOG SEQUENCER: compact CV/GATE five-step sequencer that generates up to five steps of discrete control voltages that control a pitch of the VCO and gates that trigger the envelope generators. Audio and CV connections are the same as on the Acid Bassline voicecard.
  • WIND AND STARS: Automatically emulates randomly evolving wind sounds and blinking stars are controlled by the divider. (Toddlers fall asleep better when they hear sounds like these).
  • Created by Erica Synths & Richie Hawtin
  • Educational Electronic Music Instrument
  • For Beginners and Professionals
  • Designed to Captivate and Inspire
  • Subtractive Synthesis (Modular)
  • VCO, VCF, VCA, 2 x EG, Delay,
  • Built-In MIDI to CV + MIDI and USB MIDI
  • Includes 3 Preset and 3 DIY Voice Cards
  • Includes Patch Stencils + Patch Cords
  • Includes Power Supply
What's in the box?
  • Erica Synths x Richie Hawtin Bullfrog Synthesizer
  • 12 VDC Power Supply
  • 10 x Patch Notes Stencils
  • 10 x Patch Cables
  • 3 x Preset Voice Cards
  • 3 x DIY Voice Cards
Type Analog
Polyphony Monophonic
Outer Dimensions 38.5 x 21 x 4 cm
Weight 1.8 kg

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