It turns out that, like tea and biscuits, treble boosters are a distinctly British affair. Also in typical British fashion, the treble booster as an effect started out as a workaround born of financial necessity.
By the mid-60s, UK guitarists had cocked an ear to the treble heavy sounds on records from the US, sounds that they were finding hard to replicate on their typically dark amps. There were two options - one, buy an imported Fender amp (which was beyond the means of most), or use a simple device to boost brighten up that AC30 (bingo!).
Many of the manufacturers of the day stepped up to meet demand for treble boosters, including Hornby Skewes, amp makers Vox and Orange, and (drum roll, please) Dallas Arbiter with their iconic Rangemaster.
As the 60s wore on into the 70s, the treble booster became something of a secret weapon in manys a Brit rock poodle's arsenal. Fast-forward another couple of decades and guitarists were again after a sound that they wanted to cop, only this time it was the UK of the 60s and 70s they were looking to rather than the USA. By this time the treble booster had faded from view almost entirely and it took a select few boutique builders to unearth the Rangemaster's magic and put that hot sound back in the hands of modern guitarists.
Taking the Rangemaster as a starting point, The 404 uses a prime cut 2N404 (see what we did there?) germanium transistor and drops it into a nice convenient modern package with true bypass, status LED and Boss-type DC jack (wired negative ground, so you CAN daisy chain with other pedals).
The 404 is the key to a world of vintage-voiced tones from Gallagher blooze to fat Iommi doom.
The 3-way toggle switch to give you 3 ranges of boost, and a single knob to control the amount of boost. In the middle it's as the stock Rangemaster - bright, soft sholdered clipping with a hint of a resonant peak around 440Hz (a little like the ‘honk’ of a cocked wah, but y'know... subtle...). The up position takes brightness down a touch - great for rhythm work. Flip the switch down and it gets you into proper Sabbs doomsville should wish to go there.
In all three settings it's wonderfully touch-sensitive and highly responsive to picking dynamics (it really digs in when you do). Being germanium it also cleans up without going all thin and wimpy when you roll back the guitar volume.
Best used with a valve amp set near or at breakup (using a Laney LC15 here). Take it away...