Interview with Thorsten Loesch of iFi - AMR about iFi iPhono

iPhono. A phono budget statement

I highly appreciated what Thorsten Loesch is you trying to do. Bringing down best sound for the people at large with product like iPhono. He gets my highest respect for that. This is best times to be an audiophile. Even on low budget.

I have on my hands phono preamps from 100-30.000k and iFi iPhono fella kick some serious butts!

In the world where mobile phones and computers get miniaturized by days it’s great to finally see some audio company really pushing the boundaries. Once I'v seen the back plate of iPhono there was no turning back. I was hooked even before my ears were involved.

Here are few questions that keeps mind occupied in contemplations:
Matej Isak: How its possible to bring down noise floor so much in so small device and keep headroom of bigger preamps? How it’s possible to bring so many functions into such miniature device? How it can perform at such level that rival phono preamps costing quite few times more? It basically cannot be even remotely simple with such performance and choices on hand to design and manufacture such device?

MI: How it all started with Iphono?
TL: Actually, the history of the iPhono goes back to the early days of the internet and the dark days when we all thought Vinyl was dead...

I was in one UK focused On-Line discussion group called Analogue Addicts. And everyone was bitching that no modern gear had Phonostages and that there were no affordable phono stages that were any good.

So I designed one, simple, easy to build, which sounded surprisingly good.

Over the years I have occasionally refreshed the design a bit. While in terms of the exact circuit and parts the iPhono has little to do with this "Analogue Addicts" Phono, it is conceptually the same.

MI: Major phono preamplifiers lacks the proper headroom. Only few seems to being mastering that?
Back when I designed the Analogue Addicts Phono I addressed specifically this issue... Headroom is simply a design choice. You can arrange EQ circuits in many ways. One that has often found favour in Japan is called there CR-EQ.

It has the advantage of 14 - 34dB more headroom, using the same active parts and power supplies, as the so called "passive EQ" the Americans especially are so fond of. Shindo and the later versions of Kondo's M7 (Phono) Pre's also used CR-EQ.

The second thing I do, many designers just use the "Chip du jour" with passive EQ and some big power supplies. You can get pretty decent sound this way, for sure and you can just find the circuit in textbooks and application notes, voila, anoth cookie cutter Phono Stage is born.

Yet using Op-Amp's is a bit of a skill. With normal passive EQ the Op-Amp has linear gain. Now an Op-Amp is a feedback circuit. Feedback as such is neither good nor bad, it just must be understood. Normal feedback amplifiers tend to have a bandwidth open loop of at best a few 100Hz, chip Op-Amp's have a bandwidth without feedback that is at best something like 50Hz. So, using Op-Amp means as frequency rises we have less feedback and thus the amplifier progressively distorts more as frequency rises.

If we combine this feature with passive EQ, the results can be disastrous. With Passive EQ you also need to use two Op-Amp's, so you have the same problem twice. I only use passive EQ with Tubes, as these have a massive surplus of headroom and distort the same no matter what the (Audio) frequency.

Using CR-EQ instead linear gain block and passive actually means that gain of the circuit with feedback looks a lot like the gain of the circuit open loop and nearly the same amount of feedback at all frequencies and so distortion at high frequencies is reduced much, in fact, we come close to the Tube ideal of (same distortion at all frequencies).

Of course, CR EQ and Op-Amp implementation is not always easy. There are many pitfalls. In the iPhono we do not use any of the common "Audio" Op-Amp's, as they do not have the right parameter set. We selected one from a Japanese maker that offers unusual parts for Niche markets.

This Op-Amp has low enough noise to use it for MC Cartridges and has very low distortion. But if used with CR-EQ it becomes very sensitive to power supply noise and it has a very weak output stage. It makes it very difficult to apply using generic circuitry from Textbooks using a cookie cutter approach.

In the iPhono discrete circuitry is added to address these shortcomings and to create a resulting circuit with very low noise and excellent headroom in both current and voltage domain (voltage headroom is worth diddly squat if you do not have the current to back up that voltage).

One other key part is that the iPhono directly couples the cartridge, no coupling capacitor between Phono and MM Cartridge. It needs a very special Op-Amp to do that, common 5532/5534 have a lot of DC current on the input which causes trouble if it flows in the cartridge coil.

So farwe have really only talked about the MM part of the Phono stage.

Since the days of the original AA Phono I have preferred to use a separate headamp. While some IC's exist that can take a MC Pickup direct and use CR-EQ and sound good, most have been discontinued and the remaining ones are not the best. Using a dedicated discrete headamp gives the designer full control over all and any parameters, compared to using just any old low noise Op-Amp or Microphone Preamp, which seems the way many do at lower price end.

I love J-Fets because they are quite resistant to RFI and they have no input current. But few parts exist with very low noise. Sadly, the super low noise Toshiba J-Fet I used for the Headamp in the AA Phono is long discontinued and impossible to get, so I had to design something else.

The new Headamp is based on a pair of complementary bipolar transistors. Complementary transistors are used to cancel the base current bipolar transistors have - this current would flow in the cartridge coil (not good) so we would need a coupling capacitor. I like to use as few coupling capacitors as possible and thus to eliminate the coupling capacitor to the cartridge and to the MM Phono stage.

This bipolar circuit does require a lot of care in implementation, as it is crazy sensitive to noise on power supplies and needs protection against RFI, without increasing the otherwise low noise, so we cannot simply insert an RF filter in series with the signal. In return however it repays us with very low noise.

It is incidentally not based on the common base MC PrePre's pioneered by John Curl (Mark Levinson), Marshall Leach (University of Georgia), David Reid (Classe), Jean Hiraga (lÁudiophile) and Nelson Pass (Threshold), all these circuits load the MC Pickup in unpredictable ways, which is on main reason why they fell out of favour. Our Headamp has a high input impedance and cartridge loading is explicit, using individual resistors switched in parallel with the cartridge.

Some final tricks were used. The kind of Headamp I have always favoured inverts polarity, until the iPhono I never managed to come up with a simple and pure way of avoiding this, a price I was willing to pay for simplicity and sound quality (one can just swap the cartridge leads of MC cartridges to get the correct polarity back).

In the iPhono the whole Phono Stage is non-inverting for both MM and MC and additionally, the switching between the inputs is done using shunt switches, instead of the common switch in line with the (MM) signal, which was the way the AA Phono did it and many still do.

This means the unused input is switched (muted) to ground - so no switch is in series with the low level cartridge signal. The signal is coupled directly (MM) or just through the Headamp (MC), absent any coupling capacitors or switches. I feel this is a major contributor to the sound quality attained.

The final part of the recipe is the selection of passive Parts. In our work at AMR we constantly evaluate new parts and test them both objectively and by listening. As a result we have found that most surface mount resistors and capacitors are of very poor quality. However, we also found parts that do offer levels of quality that exceed conventional components with leads on them and make good on the promise of SMD to eliminate wiring, reduce parasitic capacitance and inductance and so on.

All sonically critical position in iFi gear use these parts exclusively. You do not find them in normal catalogues of the big electronic supplies, these come directly from the factory (mostly from Japan) and one must buy very large quantities to be able to buy them.

MI: MM vs MC... We've seen the rise of modern MM in performance, but a lot of companies still stick to MC. What is you take?
TL: There are good MM's, there are good MC's and there are "oddballs" be they high out MC, the Grado Moving Iron ones, Decca London Cartridges and even the optical cells from the ELP Laser turntable.

Personally I am partial to good MC's, I really like the Denon DL-103 in the right Arm (series I SME or Ortofon), there is a rightness to the sound of this that few other cartridges have, though of course there are many cartridges that exceed the 103 in some aspects, they often lack the coherence and musicality the 103 Offers.

MI: Another point is the flexibility of iPhono. It seems you wanted to cover as much of possible timelines of different EQ's?
TL: This EQ thing is a bit of a religious question. There are different groups who subscribe to different views on this. Based on listening I feel that there is more difference than I like to live without being able to compensate the EQ used during cutting, but then, my collection is rich in Decca LP's from 60's and many other European ones.

I can see however how people who own mainly later US pressings and modern Re-issues may sneer at the concept of different EQ's. In the iPhono the challenge was how to implement these EQ's in a low cost product without compromising Sound Quality or adding much to cost. I’ll leave the religious debates if EQ’s should be selectable or not to others.

MI: Its mind boggling actually. Having high end performance phono preamp in such a compact box... I guess this would be impossible to made few years back?
TL: Actually SMD components have existed for several decades. Audio Designers have always had a healthy distrust of them, as our testing bore out. Yet the less common ones we use also existed a long time. It is just a question to go looking.

In principle, the “wire-less” construction of SMD components and their small size means they can perform better than traditional components, the best available make good on this promise.

Also, nowadays SMD components are placed automatically by “robots” on the circuit boards. The circuit boards undergo a solder process called reflow (they are effectively “baked” in a special industrial oven that liquefies the solder all at once on all solder joins of the whole board. This has an incredible level of quality and consistency, human error is minimised, so using SMD as much as possible has a lot of attraction.

The compact size is only a side benefit. I do remember small Phono stages even in the days of big components, but to pack so many loading options, EQ options and others into so small a case needs SMD.

MI: We already established that you pushed boundaries to the max. How close Iphono comes to AMR phono preamp? (btw on DL-103... i agreed best open secret cartage... I know people with 50k tt rig that refuse to use anything else.. I'm swron to it also)

TL: I personally do not feel that there is much point comparing the iPhono and PH-77. They are very different products. The PH-77 is a much more accomplished Phono Stage in all areas.

Yet it is a bit like with the (very cheap) Denon DL-103 cartridge. I could live with the DL-103 & iPhono very happily, even knowing what a Top of the Range Lyra Cartridge with a PH-77 sounds like. Then again, if I am free to choose, PH-77 and Lyra Kleos please.

MI: How would you compare the sound outake and performance of iphono and iDac?
TL: I do not think one can compare a DAC to a Phono Stage. There are too many variables. The aim with all iFi Products was and is to have a sound quality that is "very good" combined with what I would call "right sound" as much as possible. Right sound is just that, it is "right".
Matej Isak. Mono and Stereo ultra high end audio magazine. All rights reserved. 2006-2013. ..:: None of the original text, pictures, that were taken by me, links or my original files can be re-printed or used in any way without prior permission! ::..