The Fulltone OCD (Obsessive Compulsive Drive) V4 is an overdrive pedal for guitar, part of the long-running Fulltone OCD family. It is built around a clipping stage that mixes transistors and diodes, it carries a two-position HP/LP voice switch, and it can run at either 9V or 18V, which changes its feel noticeably. Pedal of the Day's reviewer Ben A used it as his main drive, mainly as a light overdrive, and said "the OCD is the only pedal that has never gone off my board"1.
Power: 9V and 18V
The V4 runs at 9V or 18V, and the reviewer was blunt about the difference: "I can say the difference between this pedal at 9v and at 18v are huge"1. At 9V he found the pedal "can be a bit fizzy and dare I say it 'muddy.'" At 18V, "the added headroom is huge. It clears up the fizzle and makes it sing"1. For players finding the OCD harsh or blurry at the bottom of the gain range, the 18V option is the documented remedy.
The HP/LP switch and the circuit
The HP/LP switch stands for High Peak and Low Peak. As the reviewer describes it, "All the switch does is add a resistor parallel making more signal pass through" in HP mode1. He found "the LP can get muddy compared to the HP," so HP is the brighter, more open of the two voices1.
Two circuit details are worth knowing. First, the clipping: from the schematic and PCB, the reviewer identified "a Shakka Braddah clipping stage. Its a mixture of transistors and diodes"1, rather than the plain diode clipping common in overdrives. Second, the gain control interacts with tone: "The gain pot pared with a capacitor makes a high pass filter, so when you crank the gain, it cranks the tone"1. In practice, higher gain settings on the OCD brighten as well as distort.
On its origins, the reviewer reported: "I read that the OCD is a highly modified Voodoo labs OD"1.
What reviewers said
Ben A's verdict at Pedal of the Day was enthusiastic across the board1:
"Well I'm here to say its a killer pedal!"
He described it as versatile, touch sensitive and gainy, a great pedal all around, and closed with "I suggest you all go get one from Fulltone now!"1. His own use was as a main drive, mostly as a light overdrive1.
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Questions
What does the HP/LP switch do on the Fulltone OCD V4?
HP stands for High Peak and LP stands for Low Peak. According to Pedal of the Day's reviewer, the switch adds a resistor in parallel, which lets more signal pass through in HP mode. He found the LP setting could get muddy compared to HP, so players after a brighter, more open voice tend to leave it on HP.
Can the Fulltone OCD V4 run at 18 volts?
Yes. Pedal of the Day's reviewer confirmed the V4 operates at both 9V and 18V, and said the difference between the two is huge. Running at 18V increases headroom, which he found cleared up fizz and made the pedal sing.
What does 18V do to the OCD's sound?
More headroom. At 9V the reviewer found the OCD could be a bit fizzy and even muddy, but at 18V the added headroom clears up the fizzle and makes the pedal sing. If your OCD sounds rough at low gain settings, an 18V supply is the documented fix.
What clipping does the Fulltone OCD use?
From the schematic and PCB, Pedal of the Day's reviewer identified a Shakka Braddah clipping stage, a mixture of transistors and diodes. That sets the OCD apart from the simple diode clipping used in many overdrives.
Is the Fulltone OCD based on another pedal?
The reviewer noted he had read that the OCD is a highly modified Voodoo Lab OD. Whatever its origins, the circuit also pairs the gain pot with a capacitor to form a high pass filter, so cranking the gain brightens the tone as well.
Sources (2)
- Fulltone OCD Overdrive V4, Pedal of the Day, 2015-05-30
- Fulltone OCD Overdrive v4, Pedal of the Day, 2015-05-13
