The Attn-12 is a new stereo stepped series attenuator that holds 11 resistors per channel and offers twelve -6dB decrements, with a hard mute at the bottom twelfth position. The closest analogy to the series attenuator is a normal audio-taper potentiometer used as a volume control in 99.99% of audio gear. It consists of a rotary switch that holds many differently-valued resistors placed in series, creating a long chain of resistors, with each resistor connection attached to a switch contact. The rotary switch’s moving contact then selects between resistor connections, thus providing a selectable amount of fixed signal attenuation. The chain of many fixed resistors wired in series defines the total input resistance of the attenuator.
If you use a sealed switch with audio signals, it is essential that the contacts are hard gold, which the Attn-12 uses. True, silver is a better electrical conductor than gold, but it makes a poor switch contact in a sealed switch when dealing with small audio signals. On the other hand, silver makes a better contact material when you are switching higher-voltage, high-current loads—something audio stepped attenuators never do, as the line-level audio signal cannot burn off silver oxide tarnish the way 1A at 120Vac switching can. And as the switched is sealed, we cannot apply contact cleaner to the oxidized silver contacts. The Attn-12 stereo switch is made by the American Grayhill company.
The kit includes instructions and one high-quality, Grayhill gold-contact rotary 12-position switch and one extra-thick, high-quality PCB, with 2oz copper traces and solder mask and silkscreen.