I am the lucky owner of Io with volume. Getting the volume right is a major factor for the sound. Here is some more info, hopefully helpful for others also.
The controls are big rotary knobs, that run through 45 hard-wired steps. These rotate like the hour arm on a clock. They go from a 7:00 position (zero volume), to a middle 12:00 position, and up to 18:00 (max volume). (This is European time, in US time they go from 7:00 AM to 6:00 PM).
I have a little marker on the front of each knob, so it is easier to see its exact position. The faceplate have four long and four short markings around each knob, also helping the «navigation». Like compass markings. When you turn the volume to max, it is pointing fully downwards, due south (18 o’clock = 6 PM). The starting point (no sound) however is a bit to the «southwest" at 7 o’clock.
There are 45 steps in the volume control, to ensure a smooth gradient, and each of them are hard-wired for an optimal connection.
Here are some numbers. At zero, gain position 1 of 45 steps, gain is 0. At position 2 the gain is 14,8, and at position 3 it is 21,1 – and so on upwards, according to the «Aesthetix_Io_GainbyVolume.pdf». The gain on the middle / 12 o’clock / due north position of the volume knob is 48,8.
The gain in the first usable position, 9 o’clock, is 31,7 according to this table. The next marker, ca 10:30, is 15 steps up from zero, 40,8 gain. The next big middle marker 12 o clock is 21 steps up, 48,8 gain, and the next smaller marker ca 13:30 marker is 27 steps up, 55,3 gain. The 15 o’clock big markere i 60.9 gain. Max gain is 82,5. I never go up that far. (Correct me if some numbers are wrong)
Now to the meat of the matter. I prefer the Io with the volume between 14 and 15 o’clock, the gain is ca 55-60, with the Lyra Clavis 0,56 mv signal.
Sometimes, I like to turn the Io up, even to up to 15:30, ca 68 gain. Not often, though. If I had the Io without volume, I might set it ca 55, and go on from there.
The main rule: the Io volume is part of a mix, even if you have it direct to the amp or through a preamp. Get it optimal.
Next main rule: unless other things apply, «more power to the Io» - meaning, it drives a larger proportion of the total gain chain in the system – often applies (it does in my case).
I like a preamp between the Io and the amps, but I note better sound when the Io takes over most of the gain. Up to a point (15:30 / 3:30 pm) often, in my system. This volume mix factor - honors to Aesthetix - seems partly independent of whether the signal is sent direct of thru the preamp.
