Your browser is out-of-date!

Update your browser to view this website correctly. Update my browser now


Aphex Model 1100 Tube Microphone Preamplifier

Aphex Systems Ltd., now more than 25 years old, has continued to release inspiring audio products as the years pass. The company's first product (back in 1975) was the Aural Exciter. Initially it was not available for sale, being exclusively a rental product at the rate of $30 per minute of recorded time. Aphex continues to remain on the edge and the recent release of the Aphex 1100 proves no exception.

Aphex Systems Ltd., now more than 25 years old, has continued to release inspiring audio products as the years pass. The company’s first product (back in 1975) was the Aural Exciter. Initially it was not available for sale, being exclusively a rental product at the rate of $30 per minute of recorded time. Aphex continues to remain on the edge and the recent release of the Aphex 1100 proves no exception.
Product PointsApplications: Recording studio

Key Features: Dual Class A mic preamps; 24-bit/96 kHz converters; variable high-pass filters; built-in limiters

Price: $2,495

Contact: Aphex at 818-767-2929;


+ Great sound

+ Built-in 24-bit converters

+ Built-in limiting (that sounds good)

+ Extremely flexible low-cut filter


– No instrument input

The Score: For this price, the performance of the Aphex Thermionics Model 1100 preamp simply can’t be beat.
The Aphex 1100 Class A Discrete Tube Microphone Preamplifier ($2,495) with 24-bit/96 kHz A/D converter is part of the company’s Thermionics Division (its initial product was the renowned Model 107 Thermionic mic preamplifier). The products in the Thermionic line implement reflected plate amplifiers (RPA) in their design.

The patent for the RPA design was issued to Donn Werrbach and assigned to Aphex Systems Ltd. on September 12, 1995. This is a “method” patent, which means that it can be applied to a wide variety of applications and circuit variations. We can look forward to new products taking advantage of this technology to be introduced on a regular basis.


The 8.2 lb. single-rack-space Model 1100 is both audibly and visually stunning. The shiny chrome-plated rack ears offset the deep blue faceplate, which is covered with clearly labeled knobs and buttons. The 1100 boasts a maximum output level of +27 dBu unloaded with 65 dB gain and an equivalent input noise (EIN) of -135 dBu. Additional headroom (up to 20 dB) is available by using the microphone limiter (MicLim) circuit.

The MicLim circuitry, unique to Aphex, deserves a close look. It features an exclusive optical attenuator operating directly on the microphone input line. The MicLim circuit smoothly attentuates the microphone output signal prior to the preamplification by up to 20 dB. The peak limit detector is located after the preamplifier input stage and feeds a control current back to the attenuator so that the input signal remains below clipping. The MicLim has no effect whatsoever on the input signal until the preamplifier’s output approaches clipping.

The front panel’s nearly identical controls for the 1100’s two channels each feature two knobs, seven buttons and a recessed line output calibration pot. The knobs are brushed aluminum and easy to grip with just the right amount of resistance. My only complaint is that in low lighting situations it is difficult to see where they are set. The 12-position gain knob adjusts gain in 4 dB increments from 21 dB to 65 dB. The 12-position low cut knob sets the frequency for low-cut filter. The first position is off, followed by frequency selections from 30 Hz to 195 Hz.

The low cut circuit contains a second order modified Butterworth response. This optimizes the sonic effectiveness of the filter. It is the best sounding and most flexible low cut filter I have encountered on a preamplifier.

The row of seven buttons is in a recessed section of the front panel, preventing accidental button pushing. The pad button activates a 20 dB pad. A light above the button indicates if the pad is on. The polarity button reverses the signal polarity. The tone button activates a -20 dB, 700 Hz reference tone. To prevent accidental test tone activation, Aphex designed the function so the tone button must be held down continuously for at least one second before the tone is activated.

The phantom button activates 48 V phantom power. The 48 V source ramps up and down over five seconds to avoid thumps. The mute button activates a soft switch that silences both the digital and analog outputs. The MicLim button activates the Aphex-proprietary limiting module. This circuit limits the peak level to completely prevent clipping for input levels up to approximately 20 dB beyond the normal clipping level.

The clock source button is the seventh button on the first channel; it selects the A/D converter’s clock source as either internal or external. If external is selected, the clock information is taken from the rear panel BNC clock input jack.

There is an LED that lights when the clock is present and locked. The internal rate button is the seventh button on the second channel; it selects the A/D converter’s sample rate when the clock is set to internal. The choices are 44.1 kHz, 48 kHz and 96 kHz. When the clock is set to external, the sample rate is set automatically.

Both channels include 20-segment LED meters that indicate the output signal’s peak level below the point of clipping. They also include a recessed potentiometer that attenuates the analog line output stage gain from 0 to รถ12 dB, allowing the preamp’s gain to be matched with other equipment.

Power to the Aphex 1100 is via an IEC connector on the rear panel. Voltage can be changed from 100/120VAC to 220/240VAC by simply reversing the voltage card and switching the fuse. The power on/off switch is mounted on the front panel.

The rear panel of the 1100 has a male XLR connector for AES/EBU digital audio output. Two BNC jacks (word clock in and word clock out) are mounted on the rear panel to permit multiple 1100s to be daisy-chained together from a master clock source. Two more female XLR connectors provide for microphone input and two male XLR connectors for line level output.

Two 1/4″ TRS jacks offer parallel output. Both channels have nominal output reference switches that insert a 12 dB pad into the output line when activated. This allows the 1100 to interface more effectively with semi-pro equipment. Each channel is equipped with a 1/4″ mute jack. Plugging a switch into this jack allows the preamp to be remotely muted (both the analog and digital output).

In use

I have been using the Model 1100 on everything I have recorded for the past three weeks and I can honestly say I love it. I’ve been doing a lot of recording to Pro Tools lately and being able to use the converters in the 1100 has been fantastic.

The analog outputs of the 1100 also sound wonderful. The preamps are extremely quiet and the tubes add nice warmth but never loose their definition or punch. I was able to use the Aphex SB100 A/B box to accurately compare the 1100 to my staple microphone preamps. This was extremely useful and I have concluded that the Aphex Model 1100 is perhaps the finest sounding preamp I’ve ever used on vocals.

I had fantastic results using the 1100 on guitars (both electric and acoustic), violin, percussion and keyboards. The preamp always sounds clear and full, never muffled or muddy.

My only two complaints about the Model 1100 are its lack of 1/4″ instrument inputs and the inability to use the 1100’s A/D converters without going through the mic pres. I would love to have the ability to mix to DAT through the 1100. While instrument inputs are not a feature one would traditionally expect to find on a high-quality preamplifier, so many manufacturers are including them now that I have become used to the ease of being able to simply insert an instrument cable into the front panel of a preamplifier.


The manual is well written and easy to use. It can often be tricky to properly connect digital devices, but this wasn’t the case with the 1100. The manual clearly describes both digital and analog connections in detail. The proper wiring for any adapter cables is also described (e.g., to connect the output of the 1100 to a 1/4″ input of a semipro recorder). The Model 1100 includes a one-year limited warranty.

The Aphex Thermionics Model 1100 is as close to being the perfect preamplifier as possible. It is quick and easy to set up, it is made well, it combines tube electronics with a low noise circuit, and it sounds unbelievable.