AM Audio A-4 Stereo Pre-Amplifier

One more out of an exceptional breed

Product: AM Audio A-4 Line Pre-Amplifier
Manufacturer: AM Audio - Italy
Approx. cost: 2600 €
Reviewer: Giorgio Pozzoli - TNT Italy
Reviewed: March, 2004

Introduction

All readers of TNT are probably already acquainted with AM Audio. Hence, in inviting you to browse through the previous reviews of AM Audio products here on TNT, I just add a very brief presentation of this atypical company.

AM Audio was born quite a few years ago; throughout all these years they have been producing very high quality audio gear, building up a reputation in the Italian market and abroad, despite the fact the products are almost impossible to find in the shops, due to the choice of avoiding, as far as possible, any intermediation between producer and customer (direct sales only).

AM Audio catalogue includes a wide range of pre- and power amplifiers, as well as loudspeakers and tweaked Teac CD players.

The look

The A-4 looks like all the other AM Audio pre-amps: a low, solid, fully-black block, 6.7cm (2.6") high and 44cm (17") wide. The front panel, with a glossy black finish, is made of an abnormally (12mm=1/2") thick plate, utterly reinforced in the center section by a protruding panel of the same thickness, which groups the two only knobs and the central blue power-on light with the AM Audio golden logo.

The panel edges and the knobs are rounded, so that for me the global feeling is really strange: it always gives me the impression that such a slab with such a finish can only be wood, and instead is solid metal.

The inscriptions on the panel, of a light blue, are correctly scarcely intrusive, even though someone more interested in reading than in listening could also say they are small and difficult to read. As a matter of fact, the simple controls make the inscriptions almost useless: there is for sure no risk of confusion...

A little hard to see is instead the reference line on the knobs, these too from solid metal: unbelievably, this happens because the line is too deep, and if it is not under directly light the light blue at the bottom remains in the shadow! This too in any case helps in keeping the design so clean.

The feet are composite, metal and felt; the front left foot includes also the remote control receiver, that in this way does not pollute the very straight and simple panel.

As said, on the front panel there are only two knobs, an input selector, with 6 positions, and a volume. No power switch, as it is on the back panel, near the IEC power cord socket. The position suggests that it is better to leave the unit always on, but as a matter of fact, the differences in its sound just powered up and after a couple of hours are really difficult to perceive, if any.

The back panel seems to compensate for the simplicity of the front one: there is a total of 18 RCA pins. The RCA pins are arranged in two separate groups, one for each channel. From the right you find: the power switch, the IEC socket, two power supply output sockets (to power the external AM Audio phono stages, even though separate PSUs for them are also available), the five left channel input pins on an horizontal line, two left channel tape out pins and two left channel pre-amp output pins, followed by the same 9 pins arrangement for the right channel.

Please note the doubled output pins, that make it possible to drive two different amps, so that it is very easy to set-up a multiamping configuration, which is supported by AM Audio (as a matter of fact I auditioned such a system in AM Audio atelier in Vigevano, near Milan).

The remote control unit, small and smart, even though not comparable with the pre-amp armour, is clearly a standard component, given the fact it displays the Philips logo in full evidence. Here simplicity rules, as the remote can only control the volume level.

The unit makes use of a few "microprocessor" tricks: at power up the output is disconnected, the volume is zeroed (really disconcerting, up to the time you get used and understand how useful this feature is) and only after a few seconds the unit gets operative.

This prevents any power up transient to be sent to the output. AM Audio amps, with their very extended frequency response at the low end of the audio renge are rather sensitive to this transient problem, that causes their protection circuit to be activated: hence the builder suggests in the very complete manual to switch on first the sources, then the pre-amp and finally the power amp, and to follow the inverse sequence in switching the system off.

Technical information

We have already been talking of the ultra professional internal component layout, immediately evident to everyone (look at the photo above...). The technical aspects are anyway as much interesting.

First of all, the unit is completely dual mono, that is it contains two completely separate and independent pre-amplification channels. As a matter of fact, the only evident common point from the electrical perspective is the power input IEC socket, the power switch and the services (essentially the remote control receiver and elaboration unit).

The IEC socket, on the back panel, is integrated with a couple of fuses and a power supply filter, to keep any power line disturb out of the unit.

This costs money, but it should be mandatory, based on current regulations, and makes, as in my experience, the unit very scarcely sensible to the substitution of the power cord. This is a very positive factor, in my view, as is a very good measure of the independence of the behaviour from what happens outside in the power system, and testifies for a stable and constant behaviour in any condition. And also it allows you to avoid spending a huge amount of money in a very special AC cords...

The power switch is placed on the back panel, not so easy to reach, but this avoids having power cords running through the unit. This is my favourite solution too.

From this point, every single component is duplicated, as is possible to see in the photo above. The two amplifiers are distributed in two parallel blocks running through the main board from left to right.

First from the left there are two rather large (declared 25VA, but from the size you would say at least 30...) toroidal power transformers, one for each channel, enclosed in metal boxes.

Then there are the rectifier diodes. The discrete components bridges are preceded by resistors and each diode has a small (yellow, very visible in the photo at the left) capacitor in parallel, both to reduce any disturb possibly irradiated by the diodes while switching. A precaution rather rare, but very important.

The power supply rectification capacitors, that level out the pulsed DC voltage produced by the diodes are next: the major ones are 4 x 2200uF.

Here we meet one of the characteristics of AM Audio: the combination of different high quality capacitors, electrolytic (for low frequencies) and film (for higher ones) in parallel to minimize the impedance at any frequency, from the lower to the highest. Obviously, this does not help to reduce costs...

After these, there are rather complicated voltage regulation units, that definitely level out any disturb or ripple filtered through the passive filters. Note the large metal case transistors (MJ15022/MJ15025) and their heatsinks; other active devices are placed nearby. The whole circuit seems definitely oversized... It is in any case necessary to take into account the possibility of connection of two other external unit for power supply.

Before the audio circuit, there are still other RC filters, again with paralleled capacitors and high power vetrified resistors.

The audio circuit is rather simple. It is composed by a differential stage, followed by a class A complementary symmetry Mosfet output stage with individual heatsinks.

The first stage is implemented with a dual Fet, while the second with MOSFETS.

Input output feedback is completely absent, while a certain degree of local feedback is required to keep distortion (of the order of 0.2% up to 5V output signal) resonably low.

Everywhere in the audio circuits are used polypropilene capacitors, including the two huge red ones which take care of output de-coupling, while MKT (polyester) are used in the power supply units.

The potentiometer is an Alps Black Series (R27), a very high quality component.

The back panel has another small vertical card, with the input switching relays (the orange small boxes: the front panel rotary control just pilots the relais). The thickness and quality of the boards used is here evident: the beautiful blue mother board, that groups 90% of components, is really a masterpiece.

Other points to be noted, the aluminum, and hence amagnetic, box. And the surprise you get when you unscrew the top panel: it is a 2.5mm(1/10") thick slab of aluminum, totally non resonant.

And there is more than meets the eye: for example the strict component selection and matching, and the care the ground lines have been designed.

The Sound

AM Audio sound is rather typical. Smooth, imposing, assertive, resolute, and at the same time gentle and correct.

The A-4 does not drive significantly apart from this family sound. It is a little more gentle and round than other AM Audio pre-amps, but it has been designed for this, because AM Audio pre-amps are not differentiated on price, and have therefore to present different characters to match different tastes.

Compared with the reference, the colour is just a little dark.

Deep bass is present and detailed enough, just a little less controlled than the reference (which is exceptionally, I would dare say exceedingly, tight and controlled in this area).

Mid bass is sumptuous, warm, round, sometime slightly covering the deep bass so that it tends to appear less tight than it really is.

Medium frequencies presentation is beautiful, marvellously warm, pleasant. This band is slightly pre-eminent with respect to the other bands, so that voices are a little more in evidence than what I am used to. Both male and female voice acquire a very realistic body and shape, without loosing anything in detail. The character is beautifully conveyed to the listener; the singer inflexion and attitude are very clear and evident.

High frequencies are sweet, soft, smooth. Female voices are beautifully carved, they are always smooth and sweet but they keep any hint of aggressiveness the singer has in fact put in the performance, with a care that really seems to extract any nuance from the support.

The sound stage is rather detailed and precise, with a huge width and a very good depth. The presentation is a little more upfront then the one I am used to, but many audiophiles would consider my one too laid back and distant.

The speed is not as high as in some other pre-amps, but for sure I cannot say that it is slow at all: it simply never hurries after the music, does not dramatize speed for the sake of it, it just keeps the pace of the music. Really natural and relaxing.

But now, I am just realizing that the dissection of this pre-amp qualities is missing the major point. And it is necessarily so, because the beautiful musicality of this unit pervades all aspects of its presentation of sounds and all frequency bands, and blends all the different characteristics in a strong, fully expressed and extremely involving character.

The musical event is not dissected, analyzed, but re-presented as a whole, through beautifully placed, colourful brush strokes that go directly to the heart of the matter, to the deep meaning of the music, like in an impressionist painting, much more than (iper)realistic and precise in any detail as in a Bellotto or a Flamish painting.

This, as anything else in the world, has obviously some trade offs: some loosing of precision in the top high frequencies and in positioning of the instruments, and a kind of very thin, musical vapour, of ether that pervades all of the soundstage. But I must make it clear that all details are apparently present, even though perhaps less evident, and that in the end this ether is just a beautiful way to convey the ambience and more in general the live happening information to the listener.

Issues

This is one of those cases when the reviewer is really in trouble: too little negative to report, it is not realistic... So, let's think hard for something wrong.

OK, then: the small aluminum panel with the AM Audio logo on the remote does not match at all the other lines of the system; probably a lucid acrylic black panel would have been more adequate. But taken by itself, the remote is a really nice thing, of the right size to be easily used and with a gloss finish on most of its body perfectly matching the front panel.

The number of pins crowding up the back panel leaves so little room that in some cases to extract or insert a connector can be a problem. A big one for a reviewer, but for sure a minor one for a less pathological user...

Oh, well, yes, there is something I really hate in this pre-amp. I really detest the way this sneaky beast secretly reduces the volume to zero after power on, leaving me standing there like (yes I know, the word "as" would be more appropriate...) an idiot waiting for any sound coming out of the loudspeakers...

Obviously it is a feature, a wise one, and not a fault: it is clearly the best way to eliminate the risk of full volume explosions at midnight, for having simply forgot the volume too high.... Not a problem of mine, indeed: my wife is familiar with any sonic experience at any time in the night, and my neighbours are mostly old persons, appreciably deaf (great luck, for an audio reviewer...). The only doubt is ...for how long will resist my other, younger, next door neighbours, before shooting or suing me...

In any case, this feature can be disabled setting an internal microswitch. Firmly not suggested, IMHO.

Conclusions

The A-4 is a very good unit, with a pleasant sound and a nice look.

It is not a low price unit, but still a bargain: the sonic performance is already good, as a minimum aligned with the best competition for the same price, but if you add the finish, the 5 years warranty, the direct access to the producer and the care in the building and in the design, the full package is really something very few, if any, companies can afford at these prices.

Can this preamp be suggested as a best buy for everyone? I am not completely sure. It has a very defined character, very similar for some aspects to many tube designs, even though it also has the strength and power of solid state.

So, there is no shortcut: before buying it, you must carefully evaluate if this character matches with your tastes, and possibly listen very carefully to it, and make out a decision by yourself.

Take also into account that AM Audio has others pre-amps with price tags in the same segment, with the same overall quality and different characters. So, even in case you might find this is not your ideal unit, it is probable that in the AM Audio range there is the one that exactly matches your very personal tastes.

So, a visit to Vigevano will hardly end up with a lost of time. But in case you cannot go there, it is always possible for AM Audio to come and visit you...