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Aphex 107

Dual-channel Thermionic Mic Preamp By Paul White
Published April 1995

Paul White compares his console mic amps to the new Aphex Model 107 Tube Mic preamp and finds some interesting differences.

In some ways, it seems ironic that a company like Aphex, the originators of the Aural Exciter, should have introduced a tube‑based product. After all, when you look back at the Aural Exciter, what Aphex really did was to recreate some of the more audible side‑effects of an overdriven tube amplifier using solid state‑circuitry. And now they've gone full circle and returned to the old tube circuitry — or have they?

One of the problems associated with traditional tube equipment is that the tubes themselves require very high operating voltages, which in turn means expensive power supplies, limited tube life, and of course a serious threat to health if you take the lid off without unplugging the unit first! It has long been common knowledge that tubes, or valves, can be run at much lower voltages than they were designed to do, but this changes the performance of the tube quite significantly. Even so, there are many successful and good‑sounding products on the market that use under‑run tubes, including many top‑name tube compressors, equalisers and guitar preamps.

Aphex have a reputation for always trying to bring something fresh to an old idea, and in the case of the Model 107, they've taken the under‑run tube idea and then applied solid state feedback circuitry around the tube to offset the increase in plate resistance that normally occurs when a tube is run at a very low voltage. Of course, every American technical innovation has to be given a trademarked name, and in the case of the 107, the power under the hood is 'Tubessence'! Because the tube is run at a low voltage, an external wall‑wart power supply can be used in place of the large transformer and banks of capacitors necessary to supply conventional tube HT, and this in turn helps keep the cost down. A further benefit is that the tube life is greatly extended.

Unlike early tube mic amps, the 107 is a hybrid design utilising a solid‑state front end followed by a tube gain stage, the idea being to offer the best of both worlds; the solid‑state circuitry provides low noise with a good transient response, while the tube provides the 'flavouring'.

The Package

Housed in a surprisingly light 1U case, the Model 107 comprises two independent mic channels, each with independently‑switchable 48V phantom power, Phase invert, 80Hz Low Cut (12dB/octave), 20dB pad and Gain control. All the switches have status LEDs and there are two further LEDs — green for signal OK and red for Overload.

The mic inputs are conventional XLRs, thoughtfully mounted on the front panel for convenience, but the outputs (which are 'quasi‑balanced', presumably a ground‑compensated, pseudo balancing circuit) are on stereo jacks, which may displease the professional fraternity. However, for the rest of us, jacks provide a universal, cheap and generally reliable means of connection, and the Aphex output stage allows an unbalanced jack to be inserted with no loss of signal level (unbalancing some balanced outputs incurs a 6dB signal loss). Slide switches are used to select either ‑10dBV or +4dBu operating levels, further evidence that the unit is aimed at both pros and project studio owners, and additional jacks are provided so that a remote switch, such as a footswitch, can be used to mute the channel.

Constructionally, the vulnerable gain mic stage is built in close proximity to the input socket which minimises the chance of electronic 'pollution', and the overall standard of construction is up to Aphex's usual high standard with no skimping on component quality. By way of facilities, I thought that a separate line input jack would have been useful for 'tubulizing' mixes, submixes and so on, but as it is, if you want to process line‑level signals, you really need to go via a DI box.

The Acid Test

On paper, this product looks well specified, and there's no doubt that the facilities are spot‑on (bar the comment about the lack of line input jacks), but even though the Model 107 is miles cheaper than most vintage valve gear, it still costs around twice the price of a decent solid‑state mic preamp, which means that there has to be an audible improvement over a typical desk front‑end if the cost is to be justified.

As it happened, the 107 was thrown right in at the deep end during a location recording session, where it was asked not only to handle the vocal mics, but also to accommodate active DI boxes which required phantom power. It's always difficult to put your finger on what sounds different about valve gear, but the 107 definitely warms up the sound, albeit in a subtle way, while adding a kind of sonic 'glitter' to transient detail and high frequencies. It's not as obvious as, say, an exciter, but the overall effect is similar in that it makes sounds seem closer and bigger without making them any louder.

Given that the 107 comes at the affordable end of the tube processor market, it represents a very cost‑efficient way to, effectively, convert any good quality mic into a tube mic. Viewed purely as a mic preamp, and leaving aside for a moment the tube coloration, the 107 is extremely quiet, and because it has two discrete channels, it's well suited to direct‑to‑DAT location recording or to feeding mic/DI box signals direct to tape without having to pass through a mixer first. Admittedly, you could buy a well‑specified solid‑state mic amp for rather less than the 107, but I feel that it's worth paying the extra for the 107's tube tone.

Once more, Aphex have added a new twist to an old idea, and in this case, it's to make a piece of tube equipment as quiet and as reliable as its solid‑state equivalent without losing any of the tonal magic. A very nice product indeed that will, no doubt, find its way into both project and professional studios around the world.


  • Real tube tone.
  • Quiet circuitry with very long tube life.
  • Full complement of pad, phantom power, high‑pass filter and phase switches.


  • Line input jacks would have added to the flexibility of the unit.


A good example of how a combination of new and old technologies can offer the best of both worlds.