Dunlop Cry Baby GCB-95

The Dunlop Cry Baby GCB-95 is a wah pedal: an analog bandpass filter that boosts a resonant frequency around 750 Hz while attenuating harmonics above and below it, and you sweep that peak up and down with your foot¹. Dunlop calls it the Cry Baby Standard Wah, "a modern interpretation of the original 1966 Cry Baby Wah sound"². It was introduced in 1982 as Dunlop's first Cry Baby, and a circuit analysis describes it as maybe the most sold guitar pedal of all time¹³.

The effect is simple to use but distinctive. Rocking your foot back and forth on the pedal changes the effect on your tone instantaneously, moving the resonant peak from about 450 Hz in the heel-down position to 1.6 kHz at toe down, with selected frequencies boosted by up to 18 dB¹⁴.

What it does to your sound

The GCB-95 is a bandpass filter with a resonant peak centered at 750 Hz when the rocker is at its mid position, sweeping from 450 Hz to 1.6 kHz across the pedal's travel¹. The manual gives the underlying filter ranges as a low pass of 350 Hz to 450 Hz and a high pass of 1.5 kHz to 2.5 kHz⁴. Maximum gain is +19.5 dB heel down and +19 dB toe down, with a maximum output level of +10 dBV⁴.

Dunlop describes the result as a focused high end and an aggressive wah sound², and Guitar.com notes that, compared to the original, the GCB95 has a more focused high-end and more aggressive wah characteristics⁸. In MusicRadar's buying guide, Michael Astley-Brown wrote that "the GCB95's aggressive sweep makes it one of the best wahs for cutting through swathes of distortion"⁹.

How the circuit works

The design uses three cascaded transistor stages with a handful of passive components and an inductor, which keeps power consumption below 1mA¹. The transistors are an MPSA13 for the input buffer and MPSA18s for the two following stages¹.

The stages in order:

1. Input buffer: an emitter follower (common collector NPN amplifier) with unity voltage gain, high input impedance and low output impedance. A 0.01µF input capacitor isolates the guitar from the pedal's DC potential and removes hum¹.
2. Active filter: a common-emitter amplifier with a voltage shunt feedback network made up of R6 (470KΩ) and R8 (82KΩ). Its calculated gain of 56.4 (35 dB) is reduced in practice to 19 dB by the feedback network¹.
3. Output stage: another emitter follower acting as a low output impedance buffer with approximately unity gain, buffering the signal from the VR1 wiper¹.

The wah action itself comes from a capacitance trick. The apparent capacitance of C2 depends on the gain of the first stage, which is set by the VR1 position; combined with the inductor L1 (500mH), this forms a resonant circuit tuned by that apparent capacitance¹. One practical detail: the output jack is taken before VR1, so the pedal's position does not affect output volume level¹.

The rocker and the 100K potentiometer

The foot pedal drives a 100KΩ potentiometer, which Dunlop brands the Hot Potz. The output of the second transistor stage feeds this VR1 voltage divider, and the rocking action shifts the resonant frequency up and down while regulating the active filter stage's voltage gain from 19 dB down to 1 dB¹. MusicRadar's buying guide notes that "a 100k ohm Hot Potz potentiometer makes for some of the smoothest wah-ing in the biz"⁹.

Power and connections

Setup is straightforward: run a shielded instrument cable from your guitar into the GCB95's input jack, then another from the Amplifier jack into your amplifier input⁴.

Power options from the manual⁴:

• One 9 volt battery, accessed via the bottom of the pedal
• A Dunlop ECB003 AC adapter (ECB003E in Europe)
• A Dunlop DCB10 DC Brick power supply

Dunlop's product page also lists the DC Brick, Iso-Brick and Mini Iso-Brick supplies as compatible². Current draw is 900µA⁴. On the power line, a ZL9M3 9.1V zener diode regulates the supply, protecting against voltage peaks over 9.1V and reverse polarity connections, while capacitors C6 and C7 remove noise¹. A 2016 MusicRadar review noted that the power jack is standardized for PSU use¹⁰.

History: from the Vox V847 to the GCB-95

The pedal that would eventually become the Cry Baby was first created in 1966 by engineers at the Thomas Organ Company¹¹. The GCB-95 itself is a copy of the original VOX model made by VOX/Thomas Organ Co in 1970¹, and Dunlop introduced the GCB95 Cry Baby Wah, its first, in 1982³.

The circuit is very close to a Vox V847. As IvIark at Guitar FX Layouts put it¹¹¹:

The real difference is that input buffer. Dunlop added it to raise the input impedance from 69.5KΩ to 1MΩ, preserving the guitar's original tone; the trade-off is that the buffer filters part of the bass content, so the Cry Baby has slightly less bass than the V847¹. The manual lists input impedance as 800 kΩ and output impedance as 10 kΩ⁴.

The design evolved over the years: before 1990 the jacks were wired to the board; from around mid-1990 they were mounted directly on the PCB; from mid-1991 a buffer circuit was added before the wah circuit (present if the PCB says "Rev F" or higher); and the current revision is much like models since mid-1992¹. In 2004 Dunlop replaced its original custom inductor with the classic red Fasel Inductor in the GCB95³.

Versions and the GCB-95F Classic

Dunlop makes many other Cry Baby wahs, including the GCB95F Cry Baby Classic¹². Released in 2003, the GCB95F was built around the famous red Fasel Inductor for a lush, vocal sound, the same inductor later added to the GCB95³. MusicRadar's review of the Classic highlighted its "vocal sweep and lush harmonics" and noted that it "scores big-time by enabling either the use of batteries or Dunlop's ECB03 AC adaptor"¹³. The GCB95F runs on 9 volts DC¹⁴.

The GCB95 circuit also lives on in signature models. The TBM95 Tom Morello Signature Cry Baby houses an identical circuit to Tom Morello's early-'80s GCB95, with the same 100K ohm Hot Potz potentiometer¹⁵. The GCB95 lists at $99.99²⁶; MusicRadar noted in 2024 that you can pick one up for $99¹⁶.

Common mods

The GCB-95 is one of the most modded pedals around, and Griffin Effects' mod service covers GCB-95 all revisions, GCB-100, ZW-45, JH-1 and JC95¹⁷. Common modifications from the circuit analysis¹:

What reviewers said

MusicRadar's review of the Jim Dunlop Cry Baby GCB-95 summed it up as "some welcome tweaks for this classic wah"¹⁰. On That Pedal Show, comparing five classic wah pedals, the presenters came to a realization about the modern version:

That bypass question is where sources disagree: the circuit analysis describes a true bypass switch¹, That Pedal Show found the modern GCB95 seems to be true bypass¹², while Gearnews describes the GCB95 as having a hardwire bypass that keeps your tone clean when switched off⁷. Older revisions were certainly not true bypass, which is why the 3PDT mod remains popular.

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