Hornby Skewes Bass Boost

The Hornby Skewes Bass Boost is a rare British pedal that boosts bass frequencies instead of treble, the mirror image of the treble booster style its maker was known for. The Guitar FX Layouts blog, which documented the circuit in 2017, describes it as "super rare, so rare in fact I can't even find a video for it," and sums up its character plainly: "I guess it works like clean boost with more bass in it as described."¹

What it does

The circuit sits in the same family as a treble booster, but tilts the opposite way: "Similar to the treble booster, but boosts the bass frequencies instead of the treble."¹ In practice that reads as a clean boost carrying extra low end, which is why bass players have taken an interest in the layout.

A builder who rebuilt the circuit on breadboard with the correct pinout for the 2N3702 transistor reported¹:

The two versions

The published layouts come in two forms, matching how the original circuit was built with PNP germanium-era parts and how players might build it today with NPN parts¹:

Building it: what matters

The layouts are stripboard (vero) designs, and the blog's comments carry a few practical points for anyone building one:

• The 1k resistor to ground at position 8F forms the output filter network. Leaving it out "takes out the filter network at the output, and makes the 100nF go nowhere."¹
• Builders substitute 10k for that 1k resistor to get higher volume.¹
• The 2N3702 pinout must be corrected when substituting a modern transistor; the builder who did so found the circuit "works great with bass" with good gain even with the 1k resistor in place.¹

For more low end, one builder suggested a modification: "If you change input cap to 1u and output cap to 10u and increase 1k resistor to 3k3 it will boost 82Hz 2x."¹

Questions