I decided to create a new stereo stepped attenuator based entirely on the ladder structure. Most of my previous attenuators were, such the A3, Atten-1, Attn-2, M1, a blend of series and ladder. The closest analogy to the series attenuator is a normal audio-taper potentiometer used as a volume control in 99.9% of audio gear. A rotary switch holds many differently-valued resistors daisy-chained in series, with each connection attached to a switch contact. The rotary switch’s moving contact then selects between resistor connections, thus providing a selectable amount of signal attenuation. The many fixed resistors wired in series define the total input resistance of the attenuator. This is simple enough, but not without some problems. Where the conventional potentiometer has only three solder joints, these attenuators have as many solder joints as there are steps.
A ladder attenuator is nothing like a potentiometer. Perhaps you have seen the small fixed attenuator plugs that hold one male RCA plug and one female RCA jack and two fixed resistors inside a small barrel; these fixed attenuators are useful when bi-ampping and one of the amplifiers offers too much voltage gain. Now, imagine a bunch of these fixed attenuators and some means of selectively swapping the right one in place.
The ladder improves upon the series attenuator by setting up an array of many two-resistor voltage dividers and the means to switch to the desired pair. Now we are back to just three solder joints and just two resistors in the signal path—but at the cost of twice the switch contacts and twice the resistors used. This is the no-compromise approach to stepped attenuator design. The downside to this attenuator topology is that twice as many resistors and switch poles are needed. In other words, a comparable series attenuator will cost half as much as the equivalent ladder attenuator.
In the Atten-Ladder, two ladder attenuators cascade, one with fine decrements of volume, one with coarse steps. The result is 66 steps of possible attenuation in 1.09dB decrements, for a total of 70.9dB of maximum attenuation.
Kit includes three gold-contact USA-made switches and PCB. Resistor packs are also available. Includes user guide.