icOn4 AVC (Autoformer) Passive Preamplifier
This simple passive auto-transformer line control unit may not
quite best Martin
Colloms' Reference choice, but he has to admit it gets very close.
Andrew Harrison recently reviewed two passive preamplifier/control units, namely the earlier series Life-Changer Audio icOn2 earlier this year (HIFICRITIC Vol 13 No1) and also the Bespoke Audio Company Pre-amplifier in (Vol 13 No2). Now a new and even more interesting version of the icOn series from that irrepressible designer and manufacturer Pál Nagy. He is full of enthusiasm for his subject and a burst of imagination allied to the versatility of the Arduino micro-computer module he incorporates, has allowed him to take the project further. He is striving for the ultimate performance, inching incrementally towards full transparency with each design iteration.
While there are alternative implementations of this line control genre, for example using double winding transformers, or a resistor ladder, enthusiasts including Pal and myself have homed in on the single winding multi-tapped autotransformer. Here audio signals enter at the high impedance start of the winding and leave at a series of low impedance volume stepped taps, selected by some form of switch. Aside from that single switch contact there is nothing else to interrupt or corrupt fidelity in the signal path.
The icOn4 has some user selectable, programmed facilities, and some at additional cost, but the key matter is the move to the autotransformer mode, here adopting mu-metal core single winding autotransformers, from US specialist Bruce Slagle, in place of the previous SAC Super Permalloy transformers). As before that convenient and effective Apple remote control handset is used for control of the top model, but also to access and set the several user options.
You also get a two-year warranty, while the service life for the Vishay complementary FET switches used is essentially unlimited.
Those options include an online hardware upgrade possibility, for example, through a Bluetooth app to 40 steps instead of 24, along with automatic input level matching and other facilities such as app control from anywhere in the house, and the inclusion of a high quality optical encoder with variable sensitivity for fine volume control, manually operated. The display is now intrinsically noise free, non-multiplexed, while improved switching timing offers smooth control without audible glitches.
The base price model may readily be reconfigured depending on the price paid, and has 24 steps: -49.5 dB, -45, -40.5, -37.5,- 34.5, then 13 very usable 1.5dB steps of 19.5dB to -15dB and finally five 3 dB steps to 0 dB. When purchased in 40 step mode, all steps are 1.5dB. Surprisingly there is also a useful +/-7.5 dB control of channel balance in 1.5dB steps. '0' on the display denotes full muting.
Midrange was essentially top class for neutrality and detail, while the deep transparent imaging was really good. At high frequencies, also rated close to excellent, shaded by a hint of grain and blur, this was hard to describe, this more like a interconnect cable difference. I have to rate the icOn4 as excellent, even if it is a little behind the Townshend Allegri plus. I reckon that in many systems they could not be differentiated.