Aphex 661 Expressor

Tube Compressor / Limiter

Aphex 661 Expressor Tube Compressor / Limiter

Review by George Shilling

A friend of mine has a theory that any audio equipment is guaranteed to be good if it is American and has an 'X' in its name. Well, Lexicon, dbx and MXR all satisfy the criteria, but perhaps less common in recording studios are units by Aphex.

Many major studios have an old Aural Exciter somewhere in the rack, but that technology is no longer the buzzword it once was. Today, Aphex is more popular with Broadcast folk. In the recording studio, valve or tube gear is what most aspire to. It is no surprise then that Aphex, always an innovator, have pitched in with a valve design with a difference.

This unit is essentially a mono compressor, although there are some special features not found on other units. Build quality is high: a 1U case bears a smart metallic finish and pleasantly damped black knobs. Legending is small yet neat, switches are of the very tiny plastic variety, and there are plenty of LEDs to tell you what is happening.

The front panel includes a Bypass switch and a rocker Power Switch. Connections are on TRS jacks and XLRs with a switch for +4/-10dB operation. Additionally there are unbalanced jacks for Send and Return and a Link socket for connecting two 661s, configurable from the front panel.

The manual is very slickly put together with plenty of smart graphics and a lot of what could be unkindly described as good ol' American bull! Firstly, there is a Message From The President (of Aphex, that is). Then, before I'd read that, a leaflet fell out promoting merchandise - you really can buy the T-shirt, sweatshirt, leather jacket, etc.!

The manual, whilst very helpful, is full of boastful explanations of why all the Registered Trademark features are so good.

The most proudly proclaimed feature is of course the valve circuit, its registered name being Tubessence. This is genuinely different from other tube designs, utilising a 12AT7 dual triode using an unusually low plate supply voltage with a Reflected Plate Amplifier circuit. This overcomes several 'problems' associated with tube circuits, such as 'Miller Effect' (high frequency attenuation), high power dissipation, microphonics, etc. It is certainly the coolest running valve equipment I have ever encountered.

Next, Easyrider mode apparently "eliminates the nasty artifacts that are the by-product of nearly all other compressors". Well, excuse me, but I rather like some other compressors and their 'artifacts'! I can only presume that the Aphex designers and manual writers are just overly proud of their products, and this is no bad thing, even if perhaps they have sometimes missed the point slightly.

In reality, Easyrider is very smooth auto attack/release compression. In this mode you simply set Input and Output levels and Threshold for transparent compression using Aphex's patented "No-Knee" circuitry. The Fast setting is more suited to percussive sounds, whereas the Slow mode is intended for use on vocals. This is much like older Aphex designs that aimed to compress without the compression being audible ("Express, don't Compress"!). It works well, but often, I like to hear my compression. So when Easyrider mode is defeated, Manual mode gives you control additionally over Ratio, Attack and Release and enables a Soft/Hard Knee switch.

These controls give a wide range of compression characteristics, including Peak and Program Limiting, which will be popular with broadcasters. Additionally there is a switchable Sidechain Low Cut filter, for use perhaps with two linked 661s when wanting to compress bass or bass-drum heavy mixes without pronounced pumping.

Two rows of large LEDs provide an In/Out Level meter and a very good visual indication of compression. Interactive with the compression circuitry is the patented HFX circuitry which is high-frequency expansion that only works when the compression threshold is passed. This is a smooth, pleasant effect designed to eliminate compression 'dulling', and is controlled by Ratio and Frequency knobs giving up to 6dB of treble lift or 'decompression'.

Yet another patented feature is the Spectral Phase Refractor (SPR) switch. This effectively delays mid and high frequencies to bring forward low frequencies in the signal, with a huge list of promised benefits according to the manual. This is a subtle psycho-acoustic effect such as those of the Aural Exciter or BBE Sonic Maximiser, and can be used on individual instruments or the whole mix (with two 661s). As a confirmed sceptic and one who is underwhelmed by the BBE effect, this took me by surprise. It immediately pulled together the bass and bass drum of a mix and allowed them to punch through with a coherent warmth that was previously absent. On individual sources however, the effect was often unnoticeable.

Overall this is a very useable compressor, the Tubessence circuit works so well, and the limiter is so fast, that you could almost believe this is a completely solid state design. However, there is a definite hint of valve to its character. This is something different from the norm, and certainly much thought has gone into the design. The only downside is that if you want one of these, then you undoubtedly want two to make a stereo pair.

Reproduced with kind permission from Copyright ©1997

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