I built this B1 into a garage sale Onkyo cassette case.
I bypassed the selector switch on the B1 in order to simplify the signal path. I used a Goldpoint stepped attenuator. The power supply is from a long gone Panasonic cordless phone charger which provides a dead on, dead steady, ripple free 18V. This B1 equals or betters everything else that has ever been plugged into this system.