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icOn 4 Passive Preamplifier


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icOn 4 (AVC) Passive Preamplifier

Review by George Sallit

 

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I am fascinated by passive preamplifiers (Control Units?) and have been for a few years. One of the advantages of digital analogue convertors DACs (the only one?) is they have a healthy output of 2V. With power amplifiers giving full output from an input of 0.7-1.5V that in effect means the need for preamplifiers has gone and all that is needed is an attenuator and a switch for the different inputs. No amplification is necessary.

That opens the way for a very simple preamplifier as all it has to do is have a variable attenuator. The simplest of these passive control units can be just a variable potentiometer in a box, the infamous ‘pot in a box’. You can either make a simple one yourself or for those, with my awful soldering skills, there are hundreds of commercial ones available.  One of the first was the Creek passive preamplifier with a decent pot (Blue Alps) with a motor drive. Add the ability to switch between the two inputs using a small electronic circuit and you have a cracking ‘pot in a box’ that had a remote control. I bought one and it could not be simpler. It would be pointless measuring it as it is in effect perfect. And listening to it provided good transparency and clarity. There was no distortion added. It sounded excellent and only cost a few hundred £s and was capable of embarrassing more expensive active preamplifiers. It should have sounded perfect. But……it did roll-off some of the high frequencies and reduced the dynamic impact. Nevertheless, an excellent controller.

Well if a pot, which has a carbon track and a sweeper, was not quite there how about 2 resistors? A variant on the passive theme was to have a series of resistors that changed the values of attenuation. Enter the stepped attenuator. This neat device would have a set of volume levels given by a series of resistors but with only two connected at one time. One of the better examples was the Khozmo stepped attenuator. My version was well made and had a complex looking volume controller with 48 resistors soldered per channel. As you turned the volume control different resistors were switched in. That must have been a tedious job and a half to solder all those resistors. The Khozmo sounded superb and to be honest was much better than the cruder Alps ‘pot in a box’. But it did not have remote control?? A quick word with the maker, Arek Kallas, showed he made a much more sophisticated version with 64 steps, lots of inputs, outputs and it was a true balanced volume control. Yes, there were 4 of these resistor marvels for both the + and - XLR connections and of course you need that for both channels. I ordered my version with high-quality Takman Rex resistors and this sounded ideal with only a hint of a loss of top-end sparkle and a tiny reduction in dynamics. Impedance issues?  And of course, it came with full remote control!

However, there are another 2 ways to control the signals but using transformers. I bought a great example of a transformer control unit. The Music First uses a high-quality transformer that takes in the 2V signal from the DAC and then induces in the secondary set of windings the outputs. Using a transformer meant there were fewer issues with impedance matching that afflicts resistor-based passives. And maybe improvements in sound quality?  Yes, you bet. These small boxes worked their magic and gave resistor-based clarity and transparency without the negative impact on the dynamics. They were pseudo-balanced as well. Transformer Volume Controllers are an exceptional example of clarity and transparency and they have big dynamics. I was more than happy with the MFA as it worked its magic with all the amplifiers I had to hand. Well, all bar one and as luck would have it, it was my favourite amplifier. But I could live with it. Here was a preamplifier with excellent sound quality, well above that provided by similar priced active preamplifiers. But it did not have remote control unless you were prepared to pay another 50% of the price. All was rosy (ish).

And then. The final variant and the word from ears I trust, ‘You have to try passives that use autoformers’. OK but all I could find was the Townshend Allegri. In autoformers, there is only one coil of wire that does the lot. And instead of needing about 2kms of wire for a TVC, the autoformers use 200 metres of wire. So, I bought one. And I was home and dry. It worked a treat and had nearly everything I needed. The sound quality was exceptional and the equivalent or better than multi-thousand £ active devices. And others reported they were the best preamplifiers around. One reviewer used his Allegri so much he wore out the volume control.  Quietly people were saying they were better than £20K preamplifiers. And I could believe them. But (what a greedy devil I am)…  no remote control and the input RCAs were too close together for my favourite cables with their chunky connectors.

 

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And now I am onto what appears to be the best of the best. An autoformer using a transformer made by one of the world’s best makers of them, David Slagle. The inputs were all electronically switched (no mechnicals to wear out), it had a remote volume control, remote balance control and a few other electronic goodies. The metal box it comes in is a solid affair and looks kinda cute. The remote is an Apple and it provides all you could need.

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This Wonder pre is the icOn 4 preamplifier made by Life Changer Audio run by Pal Nagy …who migrated to the UK from his native Hungary. He had worked in the electronics industry and wanted to bring high-quality autoformer preamplifiers into the 21st Century. He uses electronic switches with lifetimes measured in hundreds of years and no not those that go ‘click, click, click’…but ones that are silent.  This preamplifier was easy enough to use and worked faultlessly from day one. It has 40 volume steps nearly 2x more than other passives.

He uses a ‘dreaded’ switch mode power supply. And I have to admit I never heard a difference when I used it. Excellent isolation.

So, what does It sound like? In a word, superb. It has all the clarity and transparency I hear from good passives but with all the dynamics and sparkle from the best actives. I listened to it play my reference test music and the clarity and drive in the bass was fast and powerful with no additional ‘extra’ weight. As you might expect it added nothing. The James Blake track Limit to Your Love was not heavy or leaden and it was easy to hear the differences in the tones in the bass. And the powerful bass from Snarky Puppy’s, Culcha Vulcha, Tarova was just right. It was their first studio recording in 8 years when it was issued in 2016. The music goes off at a cracking pace with all 17 members letting go, led by the organ, Rhodes piano, with a thrumming bass, swinging violin, and blazing horns that remind me of Muscle Shoals and the drive of this song relies on the balance between the bass and the drums. The track can sound confused when all that lot let rip but not with the IcOn 04.

Voices were clear and it was possible to hear the small details that allow you to hear the emotion the singer is communicating. Laughing Lenny’s (Leonard Cohen), You Want it Darker is a really sad song, which is communicated with impact, more so knowing that his time on earth was limited. It was possible to hear his singing skills without turning it into an audio autopsy. His vocals were not the finest but nevertheless very poignant.

And you want sparkle and air? The Icon 04 had it in spades and allowed me to hear the space that great recordings were made in and hear the differences, clearly, between a large church and a huge cathedral.  Misa Croila by Mercedes Sosa is recorded with a completely different microphone set up and environment to that of the Jose Carreras’s version. One is more closely miked and the other recorded from the middle of the church. But when listening to Rock and Roll by Led Zeppelin the introduction features Bonzo really rattling the cymbals. But it is not hapless bashing but a way of creating a wall of cymbal sounds with subtle inflexions to increase the tension as Robert Plant runs with the song. It is fast-paced rock and roll and sounds it. 

But the big question.

That is all well and good but how does it compare to the Townshend Allegri? And confession time here….Errrr…..I could not hear a difference between the IcOn 4 and the Allegri. I listened and listened and thought I could hear a difference but no when I reinstated the original preamplifier the differences disappeared. Oh dear, time to hand in my reviewer’s badge? In discussions with Martin Colloms at Bristol, he said he needed his £100K system to hear a difference and a small change in the quality of a cable would make the differences disappear. Good, I am not going mad (well I might be!). So, I am going to call it a sound quality draw.

So where does that leave things? Sound quality wise these two autoformer passive preamplifiers are the same/similar to me. The IcOn 4 however, is more flexible, it can accommodate the big RCA connectors used on Audionote silver cables. It has remote control and balance control. Oh, and is nearly £1K cheaper.

The IcOn 4 is a great sounding preamplifier, it is modern with switches that will last a lifetime, it has remote control operation and all for the princely price of £1600. It sounds better than a lot/most active preamplifiers, which makes it a barg**** in my books.  

System used

 

Melco N100 + Plixir balanced PSU

dCS Bridge streamer

Audionote DAC 4.1X, Chord Qutest

Pass Labs XP22

Pass Labs XA 30.8, Transcription Audio 211 amplifier, Nord N500 amplifier, ARC Ref 110

Audionote E Silver Signature speakers

Cut Loose silver ribbon cables.

Specifications

 

  • unbalanced inputs and outputs, 4+1 or 3+2
  • autoformer volume control with 40 volume position
  • smooth control (1.5 dB steps) even at the lowest volumes
  • broad volume range: from -54 dB to +3 dB
  • balance: +/- 7.5 dB
  • distortion: less than 0.01%
  • channel mismatch: less than 0.1 dB
  • instant mute
  • full remote control with Apple Remote
  • 7 digit LED display for volume, balance and input
  • 2 display brightness and night mode
  • AV bypass function optionally
  • non linear switching algorithm executed by hermetically sealed miniature reed relays or Vishay FET switches
  • lifetime of reed relays: 1 billion switches (approx. 500 years)
  • power: 5V/200 mA
  • size:  HxWxL 70mmx120mmx260mm
  • weight: 2 kg
  • warranty: 2 years

 

https://www.passivepreamp.com/

 

 

UPDATE

 

The owner has contacted me and told me has updated the icOn 4 to the new icOn4 PRO which has more flexibility and features with many more volums steps. A Broader range of inputs have been added and a new fully balanced model is available. Of course they all still use the excellent David Slagle AVC transformers.

icOn 4 4PRO comparison.pdf

 

 

Edited by George 47
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