The tranny is a very exotic volume control, it has a hidden part, which is called an auto former
An auto-former is like a choke and a transformer:
She is the best of both worlds and the auto-former is built on a seductive HY Nickle Core
Like a choke, the auto former has a single winding, but the auto-former has several taps to attenuate the signal in 32 steps. Like a transformer, the auto-former has a core, but it doesn’t pass the signal through the core from the primary to the secondary.
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Some consider the Auto Former superior to resistor based volume controls or attenuators because they don’t attenuate the signal through heat loss.
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If u are wondering which is better a transformer volume control or auto former volume control just read this thread
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same dynamics to be heard at all levels - it is so utterly
transparent
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The middle switch is a three input selector switch
Rather than using a single switch, two discrete switches are used to control the level. The switch on the left has 12 positions that are in 3.75dB increments. The switches in the middle have 3 positions allowing +1.25dB, 0dB and -1.25dB modification of the overall level. By using this dual switch arrangement 1.25dB steps are possible. The total attenuation range goes from +1.25dB to -41.25 dB in 32 steps. The nature of the device skips the -3.75dB tap so the steps are +1.25, 0, -1.25, -2.5, -5, -6.25, -7.5. 1.25db steps to -41.25 and off.
This is the only manually controlled auto former based volume control being currently produced