Soundbox Workshop

Class-A 'Japan' Driver


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Class A 'Japan' Driver

The Class-A ‘Japan’ driver is our tip of the hat to some classic Japanese overdrive designs.

This is an all-discrete circuit full of fat tasty FETs and super quiet BJTs. Yep, we just made a tribute to Japanese overdrives and didn’t use a JRC4558. The FET circuit just seemed fatter and richer - and the LED-Si clipping circuit delivers plenty of crunch.

We threw a class-A FET booster at the start of the circuit just to push the FETs in our discrete op-amp configuration a little harder. This gives us a similar effect to throwing a FET booster or a gentle compressor in front of one of your old green Japanese friends. The detail is enhanced and the signal is fattened up before the ‘drive’ stage.

I suppose we should mention that there is no traditional tone circuit. Instead, we’ve used a three-position switch to let you adjust the frequency profile of the gain circuit. Position one gives you a classic mid-high frequency gain profile for a focused tone with the drive ramped up. The middle position pushes a bit more bottom end through the drive circuit - perfect for chunky riffs. The last position adds some extra top end to the sound as well, widening the gain profile which works great at low gain settings.

We've added a super transparent low noise output stage to keep the driver's output impedance constant to a minimum (under 1k!). This lets you plug the output into pretty much anything (even with the level knob dialed really low) without having your tone sucked dry.