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Amtec Model 099

Fairchild-inspired Valve Limiter
Published August 2017
By Hannes Bieger

Amtec 099Photo: Hannes Bieger

Bringing the 099 to market took 15 years of ingenuity and application — and the result offers far more than a typical Fairchild clone.

When I saw the first photos of the Amtec 099, they really conveyed the sense that this unit is a genuine child of the 1950s — only upon closer inspection did some details reveal the more contemporary nature of its hardware and circuitry. It’s not often that I’ve found pictures of a newly made unit that are so intriguing, and it’s even rarer that the gear has fulfilled all the promise of that first impression. The Amtec 099 does that: it oozes quality and elegance in a way that’s rare even in the highest echelon of outboard processors. So let’s delve in a bit deeper and find out just why I think this such a brilliant and extraordinary bit of kit.

Overview

Amtec mastermind Lukasz Piotrowski from Gdynia, Poland, allowed himself an unusually long time to develop and refine his original concept — he spent 15 years to bring this project to fruition — so he had plenty of opportunity to think, rethink and ‘overthink’ aspects of the design! Accordingly, the 099 boasts a sense of refinement and sophistication that I’ve not often seen, either as a producer/engineer or equipment reviewer.

The broad idea behind Piotrowski’s design was to attain the character of the original, while turning the Fairchild theme upside down — both figuratively and literally, in fact: if you flip the limiter’s product number, 099, it reads ‘660’! His approach centred on a decision to replace the original set of 6386 remote cut-off valves of the Fairchild with fewer, more readily available types. He then set about combining these ‘standard’ valves in a clever way to provide the characteristic curve of the Fairchild’s gain reduction. It was the fine-tuning of this unusual concept that meant he took so long to arrive at the final product.

Piotrowski’s own description gives a sense of how challenging this simple concept turned out to be in practice: “The tubes used are two ECC81 and one ECC82. [The] ECC81 has more gain, but cuts off earlier than the ECC82. So [the] ECC81 provides most of the gain with no gain reduction, when the amplification is large, but when the control voltage goes toward negative it gently cuts off, leaving the amplification duties to the low-gain ECC82 tube, which also starts to lose its gain when the CV goes even more negative. Actually there is another ECC81 tube that works, sort of, [with the others] to make the composite characteristics exactly like those of a 6386. It was one of the two most challenging parts in developing the 099. It took months and months and hundreds of tests to divide the currents between tubes through the whole range of control bias to achieve the perfect composite transconductance and anode impedance characteristics at every point.“

In other, simpler words, he reverse-engineered the Fairchild, seeking to recreate its behaviour rather than to copy its circuitry exactly, and he was able, through countless listening tests, to reach his goal by employing standard valves. A benefit of this approach is that, should you ever need replacement valves in a hurry, they could be obtained, as he puts it, “on a Friday night”. It’s a very different approach from the rest of the current crop of Fairchild clones, most of whose circuitry has a much more direct relationship with that of the original. Freed from the shackles of such slavish authenticity, the Amtec unit is also able to add a number of bells and whistles that make it a far more versatile and more useful tool in today’s studio environment.

On a typical Fairchild-type unit we’d expect to see controls for Input Gain, Threshold and Time Constants — and these are laid out in the traditional scheme on the Amtec, too. The 099 offers 18dB of gain to be switched in 1dB steps and a continuously variable threshold potentiometer. The time constant switch is labelled with the familiar settings 1 to 6, each of which offers the typical attack and release values.

One of the special treats of the original Fairchilds is the combination of fairly fast attack and relatively slow release times. The original attack values are never slower than 0.8ms, and most settings offer a very fast 0.2ms, whereas the fastest release on the vintage design starts at 300ms. This was considered ideal for unobtrusive limiting, at a time when the Fairchild was employed to safeguard cutting styli or broadcast transmitter valves, but it soon became clear that this behaviour was useful for music production as well; the stellar results a Fairchild can deliver for vocals have been well-known since the early days of the Beatles.

However, for today’s bus-compression duties, a Fairchild-type limiter may act rather too quickly on the attack at times, and too slowly on the release. I’ve seen countless vintage Fairchilds in various studios all over the world, and most are switched to the time constant setting 1. This usually proves to be the most useful setting for today’s requirements. So the distinct attack/release combinations can also be viewed as the Achilles’ heel of the 660/670 (and they’re known to ‘eat’ the precious 6386 valves at a fast pace, too!).

Although the control set looks reassuringly familiar, the Amtec 099 adds versatility, with five time-constant options added to those of the original Fairchild.Although the control set looks reassuringly familiar, the Amtec 099 adds versatility, with five time-constant options added to those of the original Fairchild.

Consequently, the 099 adds five new time-constant presets (F, P, S, E and D) to the menu, and these greatly enhance the scope of the original. Preset F is a faster version of setting 1, offering a 0.15ms attack and 150ms release. P combines a medium 3ms attack with a fairly fast 300ms release, similar to the fastest setting on the EMI TG limiter. Preset S is a slightly slower version of the former, offering 6 and 800 ms for the two time constants, and it was inspired by the EMI RS-124. Preset E is a medium-fast setting with a 1.5ms attack and 500ms release, whereas D stands for drums, with this setting boasting a slow, punchy-sounding 20ms attack and a fast 300ms release. The last one, in particular, is a combination that I sorely miss when using the vintage Fairchild or one of its direct clones.

But that’s not the end of the story by any means. The three-position bypass switch also allows for the stereo-coupling of two units. And while the Fairchild can only operate as a classic feedback limiter, the Amtec can also be configured for feed-forward compression. There’s an external side-chain input, and the built-in side-chain filter can help to refine the results. The latter gives you the option of four corner frequencies between 60 and 250 Hz, and there’s a de-essing mode too. The 099 also sports a front-panel slope/ratio switch, a control that was available on the original but only in the form of an internal trim pot (labelled ‘DC threshold’).

One of the most characteristic features of the Fairchild is the absence of a dedicated output stage, which has both beneficial and awkward consequences. On the plus side, it means there’s a very short signal path: the signal runs only through the input/output transformers and a single push/pull valve stage, thus helping to maintain signal integrity. But adjusting the levels is a bit tricky, since there’s no dedicated output-gain control, and changing the input gain inevitably alters the amount of gain reduction that’s applied. The Amtec unit instead employs a three-way output attenuator, which is placed after the output transformer, with 0, -5 and -10 dB settings, for both 600Ω and high-impedance destinations. This is still too coarse for precise gain adjustments post-compression, but with the switch engaged the valve stage can drive the output transformer harder, resulting in a more ‘colourful’ timbre.

Finally, the face plate boasts a large VU meter, displaying gain reduction, a small removable panel covering the calibration controls, the power switch, a status light, and a standby switch. The last are more usually found on larger power amplifiers, but Lukasz Piotrowski found it useful because, he says, “Cold tubes can be fairly unbalanced, which would magnetise the output transformer, resulting in a worse low-frequency response.“ This switch is an effective cure for this.

A clean interior: the Amtec 099 has been manufactured to the highest of standards.A clean interior: the Amtec 099 has been manufactured to the highest of standards.

Speaking of transformers, Piotrowski tells me that developing these was the second most challenging stage of his design work. The output transformer in particular proved difficult, as it had to be scaled up in comparison to the original (because the Amtec’s tube stage is a bit more powerful than the Fairchild’s). Also, the triode stages of the 099 exhibit a slightly variable frequency range and distortion characteristics, which depend on the amount of gain reduction being applied, and the transformer had to be fine-tuned to the Amtec’s valve stage to provide the same character as the Fairchild — this process apparently took several months and countless prototypes, and resulted in proprietary specifications for the coil and core construction. Hence the transformers employed in the 099 are bespoke designs, manufactured in Poland.

Amtec 099Originally, the 099 was conceived as a limited-edition production run with a cost-no-object approach but, thankfully, Amtec have abandoned that idea — the 099 will be available in unlimited quantities, yet built to the same exacting standards. The 3RU device has been designed, like the units of the ’50s, to outlast us all, with a very solid chassis. In contrast to the vintage unit, though, it relies on a solid-state PSU and side-chain circuitry; these help to reduce size, weight, production effort and, ultimately, end-user prices. All three valves are mounted on the rear panel behind a protective cover, next to the connectors for audio I/O, side-chain input and stereo linking, and they’re easily accessible.

Getting Hands On

Working with the 099 is a joy because, physically, it’s as sturdy as such a unit can be, and the control layout poses no awkward questions — as with the Fairchild that inspired it, operation is extremely intuitive. Manipulating the controls is fun too, especially the chunky time-constant switch, which feels good. It’s worth noting that while the controls themselves are largely self-explanatory, a glance at the manual is probably still required, as this will help you gain a greater understanding of that time-constant switch; settings 1-6 will be familiar to anyone who’s used a Fairchild (real or emulated), but the extra settings provide so many more useful options.

Because the Fairchild is so well known as a wonderful vocal processor, I started my 099 exploration here, and found that it really delivers the goods! By employing the standard time constants, it’s possible to achieve a thick, vibrant sound, imbuing the signal with presence and authority. Most pure vocal recordings need one form of processing or another, and within the typical Fairchild realm the results can be fine-tuned to taste. However, a big plus is that the 099 can go a lot further due to those additional time constants. The F (fast) setting proves extremely useful to achieve that extra squeeze that we sometimes need, and my secret weapon for vocal compression has become the E setting, which offers medium-fast attack and release, and this means that transients and consonants don’t get choked too much but still seem easily reined in. The effect is, again, a thick and heavy vocal that somehow still retains a lot of ‘life’.

As with most units, stronger gain reduction seems to thin out the bottom end a little — the compressor simply reacts more strongly to the more energetic lower frequencies. This can be to our advantage, as the slightly tightened-up material can seem to cut through the mix a bit better, but where this action is not desirable it can be tamed with a flick of the side-chain filter switch; I usually found the 180Hz setting a good compromise that kept all that desirable warmth intact even when the unit was pushed harder. A little more colour is available via the output attenuator switch. The gain reserves of the 099, albeit larger than those of the vintage unit, aren’t stellar, but they’re certainly enough for most vocal applications, even with the -10dB setting on the output. This brings out the inherent colour of the unit to larger degrees — thick, velvety, smooth timbres with just the right touch of air.

The mains and output transformers and the audio connectors are located on the rear. So too are the valves, which are protected by a  neatly designed cover.The mains and output transformers and the audio connectors are located on the rear. So too are the valves, which are protected by a neatly designed cover.The fast attack values guarantee loud results. The compressed signal not only sounds stronger and more powerful, but the outcome can also be seen on a meter, or when looking at the recorded waveform display. So the 099 excels in one of the key competencies of a great vocal limiter: it lets the signal jump out of the speakers both audibly and measurably.

I’ve prepared some audio examples to accompany this review (http://sosm.ag/amtec-099), and these show that good to great results can be achieved on other types of signals, too. For instance, it can tighten up bass lines, bringing them forward in the mix, or it can make them punchier, at the expense of average level but with the added focus on the initial transient infusing life into flat-sounding parts. And again, the timbre may be shaped via different gain staging options and the very effective side-chain filter.

A Fairchild isn’t typically the best choice for drum compression, as that unit’s time-constant options can be too fast on the attack and rather too ‘swampy’ on the release — very often you need the polar opposite of this to make drums stand out. While the 099 doesn’t offer the variability of, say, an API 2500 in this regard (we’re comparing apples with oranges, but the API is a great drum processor), it greatly expands on the options offered by the Fairchild. The results on drums range from thundering room explosions to pretty smacky transients, and there’s a broad range in between these effects. I didn’t expect a Fairchild-type limiter to be so useful on drums, but when I tried it, the 099 displayed some serious muscle, adding, (depending on the setting), weight and punch alongside its sense of cultivated elegance. Importantly, even when pushed harder, the results remained good; I never experienced any unwanted harshness or aggression.

Conclusion

This may read more like a rhapsody than a review, but I mean every single word of it. Yes, the Amtec 099 sports an enticing look. Yes, it comes with impeccable build quality. And yes, it was made using great parts. But this is no clone — it’s much more than that. It’s an expanded, modernised version of it, without becoming some feature-laden Frankenstein’s monster. The 099 shows just what sort of results are possible when a great creative mind spends 15 years refining an already-wonderful concept.

As with all high-quality all-valve units of this nature, there are expensive parts and lots of labour involved in the manufacture and testing (not to mention the ridiculous hours of research and development), and so this type of kit is never cheap. But taking all the qualities of the Amtec 099 into account, and the lofty asking price of original Fairchilds and the clones I’ve discussed in the Alternatives box, the price is more than just fair — at a fraction of their cost, the 099 competes with the very best.

Audio Examples

Follow the link to download the Audio Example:

Download | 51 MB

Alternatives

There are quite a few units currently in production that follow the original Fairchild design more or less closely. The Undertone Audio Unfairchild 670M II, the ADL 660 Tube Limiter or 670 Stereo Tube Limiter, and the Analoguetube AT-1 (mono) and AT-101 (stereo) all fetch premium prices, and follow the original circuitry in uncompromising fashion, while the EAR 660 Tube Compressor and the Mercury 66 MkIII are single-channel designs, like the Amtec.

Published August 2017