The M1 stepped attenuator combines both series and ladder stepped attenuators into a single functional attenuator. The ladder attenuator's job is to provide six fine steps of attenuation, each step being -1dB; the series attenuator, eleven coarse steps of attenuation, each step being -6dB. The result is that 66 attenuation settings are possible. In other words, we can set the attenuation to any value from 0dB to -65dB in -1dB decrements. The genius of the design is that it only requires two inexpensive rotary switches, instead of one 66-position, insanely expensive rotary switch, assuming that a 66-position rotary switch is even made. In Addition, the GlassWare M1 mono stepped attenuator only uses 21 resistors, not the 66 resistors that a series attenuator would require or the 130 resistors demanded by the ladder attenuator.
The ladder attenuator portion of the M1 takes account of the series attenuator's load impedance, so the M1 always presents a fixed load impedance to the signal source. Because the M1 mono stepped attenuator offers such small volume adjustments (1dB), two of these mono attenuators effectively create a balance control, as each channel can be tweaked in 1dB steps to restore balance.
The extra-thick, 2oz copper PCB is 1.4 by 5.8 inches big and the rotary switch spacing is 3 inches. The PCB are made in the USA. M1 mono stepped attenuators include user guide with assembly instructions and a resistor-value table.