Catalinbread - CB30 Overdrive

So, on the topic of "Voxy" sounding boxes here's another - the Catalinbread CB30. Most of you who read this blog regulary will know that I do like Catalinbread pedals; they always sound good and their aesthetic appeal and build quality is top notch. Unsurprisingly the CB30 is no different.

Here's the description from the Catalinbread website;

"The CB30 is designed to give you jangly, dynamic, responsive overdriven tones, just like it's British 30 watt counterpart. The tone controls work exactly the same way as the actual amp, where the more the treble and bass increase, the more scooped the mids become, making it capable of being quite hollow and jangly. The CB30 can be dialed in for that immediate attack, compressed mid range honk, finished by the shimmery high end jangle, an elusive sound for many players. Like all the foundation pedals in our line it sounds excellent on its own, or when stacked with other pedals (no really, just wait until you put a treble boost in front!)

As owners of the real deal know, the amp has an amazing touch sensitivity, with the ability to go from clear and chimey, to that unique overdrive character with just your picking dynamics. The CB30 has the same response, and cleans up extremely well with your guitar's volume control. The CB30 is true bypass, and comes in a rugged silkscreened case, has black aluminum knobs that feel great, and are easy to see on stage. If you're looking for an expressive, chimey overdrive, we think you'll enjoy the CB30 for years to come."

Here's a demo video of the Catalinbread CB30 in action;

Here's a schematic from mmolteratx;

It's similar in structure to the Catalinbread Dirty Little Secret and Formula No 5; a dual mu-amp design with a tonestack taken from the amplifier family it's looking to emulate. There are a few interesting little additions to this circuit though - C6 & R2 form a gain lowering feedback arrangement for higher frequencies and the 470pF C7 really restricts low end signal from exiting that first mu-amp stage.

Some people have complained that the CB30 lacks a little gain, I'm not sure it does but here are a few mods and suggestions which will allow you to pump up the available gain without removing too much of that Vox character;

• Reduce the value of R1 (maybe 10k),
• Increase the value of C4 (47n or higher),
• Increase the value of C7 (1n-10n),
• Remove R7 or just reduce it's value,
• Make Q5 a jfet gain stage instead of just a buffering stage.

NOTE - these modifications will alter the frequency response of the pedal somewhat, it's about tweaking it to your taste while attempting to retain that Vox character!

Another favourite modification I like to use with mu-amp type circuits is an increase in supply voltage, it nearly always has a positive impact on the tone of the circuit. Pumping up the voltage from 9 to 18v opens up more dynamic headroom and pushes the gain up just a touch. Even though when playing mu-amp circuits at 9v they feel like an amplifier the higher you go with the voltage the more convincing they get. Push the voltage up to a limit of 25v as that is the limit for 2N5457 jfet type devices, any more voltage than that and you'll cook 'em!

Here's the freestompboxes.org forum topic for reference; http://freestompboxes.org/viewtopic.php?f=7&t=13691