From the source:
The JHS Twin Twelve is the first effects pedal to go after the sound of
the short-lived but revered Silvertone 1484 Twin Twelve. Available
through the Sears catalog from 1963 – 1967, the Twin Twelve was not
regarded in its day as a premier amplifier. However, modern players
looking for a vintage sound have increasingly turned towards this
Silvertone as a primary stage and recording amp. Artists such as Beck,
Death Cab For Cutie, Vampire Weekend, The White Stripes and even
Coldplay have used the Twin Twelve amp on stage, making it the vintage
amp with the most indie-cred. With the market for original specimens
drying up and prices increasing, JHS has come to the rescue by putting
that sound in an easy-to-use pedal.
The original was a 60 watt, all-tube head with a separate 2×12 cabinet.
At the heart of its sound was a Baxandall tone circuit, powered by a
pre-amp the broke up in a way that few other amps do. It wasn’t as
glassy or snappy as a Fender Tweed, or as treble-rich as a Vox from that
period. Rather than going into harmonic crunch like a dimed Marshall,
the Silvertone 1484 would get borderline fuzzy, with a very saturated
and thick natural overdrive. Its satisfying clean-ish grit and woolly
overdrive have become a defining sound in modern indie rock.
Part of the magic is in the charge pump, which ramps up the standard 9V
power it takes to 18V, giving the Twin Twelve pedal even more headroom
and punch. The Twin Twelve then uses a series of discrete transistors
that mimic the valve stages of the original Silvertone. Bass and treble
controls remain true to the ratios of the original amp, while separate
Gain and master Volume knobs help you achieve the thick, high-gain
saturation at low volumes that was only possible by diming the amp back
in the ’60s.
