A3-Mini Stepped Attenuator
The standard A3 36-position stepped attenuator is 9 inches long, whereas this new A3 Mini is only 5.8 inches wide, but is otherwise identical. Where the resistors lay flat against the standard A3 PCB, the resistors stand perpendicular to the PCB on the new A3 Mini attenuator.
A stepped attenuator is an attempt to overcome the liabilities of the conventional potentiometer-based volume control. Even the best potentiometer compromises the quality of the signal that flows through it. The thin film of resistive paint and metal scraper that make up the average potentiometer seem to damage the signal almost as much as they attenuate it. Furthermore, finding a stereo potentiometer that follows a logarithmic 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 carbon 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 A3 Mini Attenuator is an interesting design: a hybrid attenuator that uses both series and ladder attenuators to yield the best compromise between flexibility, performance, and cost. The A3 Mini uses three 6-position rotary switches to yield a total of 36 positions of attenuation in -1dB (or -2db) resolution.
The leftmost and rightmost switches define two mono attenuators that offer six positions for each channel, each flanking switch is configured as ladder attenuator, with only two resistors switched in at a time, attenuating up to -5dB (or -10dB) per channel. The center switch, on the other hand, cascades from the two flanking switches and it defines a stereo series attenuator with 6 resistors in series per channel, with -6dB (or -12dB) decrements, establishing a maximum of -30dB (or -60dB) of attenuation.
Adding the ladder and series stepped attenuators attenuation together gives a maximum attenuation of -35dB (or -70dB). Thus the overlap of five 1dB (or 2dB) decrements by the flanking switches allows adjusting the balance between the channels. In other words, The attenuator holds its own balance control of sorts. The center knob controls the volume for both channels, and offers 6 coarse -6dB decrements; the flanking knobs offer six fine -2dB (or -1dB) decrements for each channel, creating a volume control and balance control in one easy-to-use stepped attenuator. Nonetheless, all three switches should be used to set the desired sound level. Far too many imagine that the flanking ladder stepped attenuators are only to be used when the source material is out of balance. Wrong.
PCBs are 1.4 inches tall and 5.8 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, open-frame, rotary switches and one USA-made extra-thick, high-quality PCB, with 2oz copper traces and solder mask and silkscreen.