A stepped attenuator overcomes the liabilities of the conventional potentiometer-based volume control. Liabilities, what liabilities? The the potentiometer's thin film of resistive paint and metal scraper seem to damage the signal almost as much as they attenuate it. Furthermore, finding a stereo potentiometer that truly follows an audio taper and that can track from one channel to the other is tough.
With the stepped attenuator, on the other hand, high-quality fixed resistors replace the thin resistive track and, likewise, high quality switch contacts replace the metal scraper. Because tight-tolerance resistors are readily available, there is no problem in following the logarithmic taper accurately and consistently.
The new Atttn-1 is similar to the A3 attenuator in that it, too, hold three rotary switches with 3-inch spacing, but differs in that the sealed switches in the Attn-1 hold gold contacts and offer 12 positions, not 6.
The new Attn-1 stepped attenuator uses both series and ladder attenuators, with three rotary switches to yield a total of 120 possible decrements of attenuation in 0.6dB steps, which means we can step down to -60dB in -0.6dB decrements. The leftmost and rightmost switches hold eleven positions and are mono ladder attenuators for the left and right channels, with only two resistors switched in at a time, attenuating up to -6dB per channel, with a mute in the final position. The center switch cascades from the two flanking switches and it defines a stereo series attenuator with 12 resistors in series per channel, with -6dB decrements, establishing a maximum of -60dB of attenuation, with a hard mute in the final position.
PCBs are 1.8 inches tall and 9 inches long and will fit within a 1U rack-mount enclosure. Each resistor position holds a redundant set of pads, so that radial and axial resistors can be used.
The kit includes instructions and three high-quality, Grayhill gold-contact rotary 12-position switches and one extra-thick, high-quality PCB, with 2oz copper traces and solder mask and silkscreen.