What is the input and output impedances of the icOn 4PRO?
– the input impedance of icOn is depending on the power amp input impedance and the actual position of the volume, it’s different for every volume. Smaller the volume – higher the input impedance. For normal listening volumes it is higher than 1 MOhm. At 0 dB volume the input impedance of the icOn is equals with the input impedance of the power amps. For +1, +2, +3 dB it’s a bit smaller, than the power amp input impedance.
– the same is true for the output impedance, but with the opposite correlation. Smaller the volume – smaller the output impedance. With normal listening volumes (-20 dB) it’s only 1/100th of the output impedance of the source + the copper resistance of the Slagle autoformer, which is approx. 70 Ohm.
The good news is that the impedance matching is automatic with an AVC (or TVC) and they produce the best possible impedances both for the sources and the power amp. This is the huge difference comparing to the resistive stepped attenuators and the explanation why the autoformers are a much better choice.
Why does the icOn 4PRO use Autoformers for the volume control?
From 2016 till 2019 I used TVC transformers from SAC Thailand. http://www.sacthailand.com/Transformer_Attenuator.html They were good but not the best. Currently the best magnetic attenuators are the autoformers from Mr. Dave Slagle. They produce much better, more transparent sound and without any colouration. I use the customised Dave Slagle autoformers only. He builds these autoformers only for me based on my specification.