APH-12 12-Stage Phaser

This isn’t your father’s monster, wood-sided phaser.

Instead of simply updating a lost 12-stage phaser of the past, we rolled our own from the ground up.

At the start of the APH-12 Phaser project, we spent much time deciding how to bring something special to the table with our unique Asheville Music Tools touch. We knew it had to go beyond the usual expectations of phasers to achieve new sounds coupled with cross-generational appeal. It couldn’t just recreate what Hawker or others had done in the past. Furthermore, it needed to be in a guitar and pedalboard-friendly format that balanced size, features and sound quality to keep it approachable.

At its core, the APH-12 nails that classic 12 and 6-stage phaser sound with warm overdrive on tap. From there, we went a little wild. We exploded the low stage counts and out of phase odd stages to create vocal and filter sounds that are rarely heard in phasers. We know of no other phaser that has done this. Did you know that a 1 stage phaser is a high pass filter and makes for a great tremolo sound? Or that a 2-stage phaser is a notch filter? Or that 3 stages (with envelope control) can challenge any auto-wah out there?

From there we created a uniquely sculpted regeneration circuit that sums the feedback at a different part of the loop than most phasers. This accentuates the notches of the comb filter and gives more pronounced resonance, for an attention-grabbing intensity without uncomfortable sibilance.

Next we knew we had to add the envelope follower, based on our AFG-1 flanger circuit, to the APH-12 as well. This feature adds funky, expressive capabilities to your playing dynamics in a way that typical asynchronous modulation just can’t touch. If our beta testers are any indication, you will get lost in it!

Then there are all of the signature AMpT touches you have come to expect, including our new saturation circuit with drive, our smooth and natural sine wave, exponential (rather than linear) LFO modulation, a two-speed LFO switch, and a calibrated mix switch to give you three distinct phaser sounds from subtle to deep phasing and vibrato. And of course, we added external expression or control voltage capabilities for those adventurous enough to go beyond the front panel controls.

Developing the APH-12 was a fascinating learning experience: with all the excitement of a 12-stage phaser (and of course, there is nothing quite like a 12-stage phaser with a 2 minute sweep) we were surprised to learn how much we loved the under-explored character of the out-of-phase 3 and 5 stage modes, or the utilitarian tremolo-like sounds of 1 and 2 stage modes. Add on top of that the power of envelope followed modulation, and we knew we had something special. Far from a simple phase shifter, this is a versatile modulation toolkit for discerning guitarists and bold sound designers alike.

Start hearing purple all the time.

The APH-12 is built from the ground up combining vintage audio processing techniques with advanced, high-tech electronics using over 400 high-quality components. At its core is an all-pass filter network with a selectable number of stages from 1 to 12, with odd stages out of phase, and three calibrated mix settings.

The filters are based on an OTA style filter IC from legendary designer Dave Rossum. From there we built out our signature control voltage processing infrastructure, with an LFO spanning from glacially psychedelic to audio rate ring-mod and a responsive, funky, full wave envelope follower. The all-pass frequency may be modulated by a sinusoidal, exponential LFO or a dynamic envelope detector. A JFET input driver and a new colorful JFET based saturation stage provide level matching, tone shaping, and harmonic enhancement. In addition, we have implemented a tuned approach to regenerative feedback summing and filtering for our own signature sound. And of course, we included an assignable expression/CV input for even more versatility. We used modern low noise and high headroom op amps, matched transistor pairs, precision voltage-controlled amplifiers, and stable, precise, C0G capacitors. Our design is rounded out with temperature stabilized circuitry, an emphasis/de-emphasis circuit, and a high voltage bi-polar double regulated power supply. All together this means the APH-12 can provide high headroom, low noise, and carefree operation in any stage or studio setting. 

Electrical Specifications

• Type: 100% Analog signal, modulation and control path

• Power: 9VDC @ <125mA. 70-100mA typical. Up to 200mA start up. Standard pedal center negative 2.1mm x 5.5mm barrel.

• Input impedance: >1MΩ

• Output impedance: 1KΩ Max

• Maximum input signal: -10dBµ / 0.25VRMS = 1% THD, +1dBµ / 0.87VRMS = 10% THD

• Maximum output signal: -0.9dBµ / 0.7VRMS

• Noise Reduction: 12.5dB HF emphasis 3dB = 1.4kHz

• Stage options: 8 Total, 1-12 stages: 1-6, 9, 12. Odd # = out of phase.

• Sweep Range: Center 25Hz to 10kHz typical. 3Hz to <50kHz with use of LFO, Envelope or external Control Voltage.

• Resonance: Off to self-oscillation using EXP input coupled with knob position.

• Rate: LFO RATE, Type: Sine Wave. Slow <0.01Hz to 2.3Hz (3.3Hz with CV control). Fast <0.3Hz to 78Hz (~115Hz with CV control)

• Envelope: Positive SWEEP control of modulation. Fast Attack, medium release.

• Amount: LFO depth control from OFF to ~60% of SWEEP.

• Drive: Up to 30dB of boost with increasing saturation and mid emphasis as gain is increased.

• MIX Switch: 3 Position; Mix: FX/Mostly dry, 50/50, VIB/100% wet.

• MOD Switch: LFO Selector: Fast, Slow, Envelope

• Expression / CV: 4-way switch: Sweep, Regeneration, Rate or Amount external control additive to front panel knob, extending range. TRS jack usable with CV or Expression pedal, (CV range 0-5V). Ring supplied current limited ~5V output. Control input on Tip.

• Bypass Footswitch: effect on/off. True Bypass: LED indicates LFO rate or Envelope pre-amount signal.

Physical Specifications

• Genuine Hammond™ die-cast aluminum enclosure

• Dimensions: D=4.95” (12.5 cm), W=3.75” (9.4 cm), H=2.25” (5.8 cm)

• Weight: 14oz (425g)

Note: All specifications subject to change at the whim of our overlords

Check out our manual for a deeper explanation of the controls.

Phase Module

• Sweep: Filter center frequency. Manually adjusts the All-Pass filter’s frequency from about 25Hz to 10KHz. When modulated this becomes the center frequency for the LFO or the start frequency for the envelope control.

• Resonance: Affects how much signal is fed back into the filters to adjust the intensity of the effect. Increases both the peaks and valleys of the comb filters. Extreme settings will produce self-oscillation, providing drone tones that are tuned by the SWEEP knob.

Mix Switch:

• FX Mode: Favors the dry signal, tames intense settings.

• Phase Mode: Balanced mix, calibrated for deep phasing.

• Vibrato Mode:100% wet signal for true vibrato tones.

Drive and Control Module:

• Drive: Controls a JFET-powered preamplifier with 2nd JFET saturation circuit for up to 30dB of boost with increasing saturation and mid emphasis as gain is increased. Use for level matching or to add harmonics to the filters.

• Stages: 8 position switch giving you the choice of 1-6, 9, or 12 stages of all pass filtering. Odd number stages are out of phase for a unique expressive tone. Lower stage counts act as tremolo or a notch filter.

LFO, Envelope and Modulation

• Rate: Adjusts the sine wave modulation from imperceptibly slow to audio rate modulation depending on the Modulation switch setting.

• Amount: Adjust the amount of bi-directional LFO modulation in LFO mode or the start of modulation in Envelope mode.

Modulation Switch:

• Up: Slow LFO from <.01Hz to about 2.3Hz for classic slow phasing.

• Middle: Fast LFO from <=0.1Hz to about 78Hz for faster phasing, vibrato, and ring mod sounds.

• Down: Envelope-followed modulation, post drive control, that follows your playing dynamics.

Footswitch: True bypass with a mechanical footswitch.

LED: LED tracks LFO rate or Envelope signal depending on mod switch setting.

CV/Expression Control: Expression or CV control with +5V ring source and active tip. Adds control and extended range to any of the top knob controls. Assign using EXP rotary switch.