Asheville Music Tools | ACV-1 | Time Warping Chorus Vibrato

What makes the ACV-1 special?

At the heart of every chorus is a short delay whose time is modulated by a low frequency oscillator (LFO). The ACV-1 uses a 1024-stage X-Vive™ high-voltage MN3007 BBD chip for its delay line. Mixing that delay back in with the original signal produces the familiar, lush sound of chorused voices in unison.

Many choruses keep the delay time fixed, but our Time knob lets you warp through the decades of chorus. Start in the middle for a tight 70’s-style chorus. Go longer for a drippy 80’s chorus and a warm slap delay, or go shorter for flanging tones.

Another uncommon addition is our Feedback knob with phase options. This lets you deepen the chorus effect and explore more exotic metallic or vocal sounds. At high feedback settings you can use the Time knob to dial in peaks and notches for resonant sounds, like a pipe or a bell. The Tone control changes the frequency response of the feedback loop to make your chorus more shimmery, or more dark and haunting. Utilizing the phase switch you can produce hollow, deep vocal sounds akin to a talk box.

Our LFO includes multiple waveforms: triangle for classic chorus sounds, sine for gooey vibrato, and square wave for rhythmic glitches and pitch jumps. The Rate and Amount controls have a huge range from subtle dimension to complete time warping madness. Or you can zero out the LFO to explore double-tracking effects, static comb filtering, and short delay.

The Mix control has a range from fully off to 100% wet, which lets you dial in subtle sounds or go all-in for true analog pitch vibrato. These settings are great for Leslie organ sounds or tape-like warble. The Tone control is even more useful here, as a way to sculpt the overall tone of your wet signal.

Finally, the CV jack rewards more intrepid sonic explorers with an even wider range of control. Increase the feedback into self-oscillation, push the LFO beyond its limit to audio rates, or drop the delay time into a lo-fi, ring-modulated soundscape. 

With its thoroughly engineered set of features, the ACV-1 synthesizes decades of time warping modulation effects to inspire a whole new dimension of sounds.

Detailed Control Overview

Time: Delay time, adjustable from 3.1ms to 59ms. Expanded to 155ms with Expression pedal, control voltages, or LFO.

Feedback: lets you deepen the chorus effect and explore more exotic flange-like sounds. Dial in peaks and notches for resonant pipe/bell sounds, add to the wet feel of chorus sounds, or add deep vocal sounds.

Rate: LFO rate, from 0.1Hz to 14Hz (or faster with use of an Expression Pedal). Modulate your playing for even more sonic possibilities. From shimmery chorus/vibrato warbles to octave shifting and more, the LFO will take you to new sounds with real fractional delay modulation that can only be achieved by true analog delay.

Amount: LFO amount. Control the influence of the LFO on the delay, from light tone enhancing shimmers to mind-bending warbles! Unlike traditional choruses that use a linear modulation, we use an exponential modulator for smooth volt/octave time and frequency shifts that stay musical over the entire sweep range.

Mix: the blend between Wet (effected) and Dry (un-effected) signals. Capable of fully muting the dry signal, ideal for parallel effects loops or vibrato sounds.

Tone: Placed inside the feedback loop. Turn the control counterclockwise for the muted warmth or turn clockwise for a bright punchy chorus or flanging sounds

Phase: sets phase of both the feedback and mix, thus shifting the notches and producing a deep hollow tone at short time settings.

LFO toggle: sets the LFO waveform between triangle, sine or square wave. Triangle mode is perfect for classic modulated sounds, and sine works well for the smoother movement of vibratos. The square wave mode can produce musical pitch jumps or atonal chaos!

Bypass Footswitch: effect on/off. The internal switch selects between True Bypass and Buffered Bypass using a JFET buffer for a warm yet natural buffered sound.

Expression Switch: 4 position rotary switch lets you assign CV / Expression control to Time, Feedback, Rate, or Amount. Connect an external expression pedal (internal +5V supplied on ring) or a 0-5V CV input for even more range and control of your playing.

True Bypass / Buffered bypass switch: Internal slide switch. Select between true bypass (takes the ACV-1 entirely out of your signal path) or a classic JFET buffered bypass to prevent noise and signal loss in your effect chain.

The ACV-1 is 100% analog and utilizes over 350 carefully selected components including premium audio-grade op amps and high-tolerance, non-microphonic capacitors to guarantee high performance, temperature & voltage stability, low noise, and maximum headroom.

We began with a classic chorus architecture using an 1024 stage Xvive™ MN3007 reissue BBD and a step-up boost power supply for maximum headroom. We then implemented a vintage-style compandor with emphasis/de-emphasis coupled with discrete transistor, 5th-order, anti-aliasing and reconstruction filters to maximize the range of delay times without undesirable artifacts. The feedback circuit uses a synthesizer-style VCA to provide a classic, warm regeneration tone while offering an accurate method of dialing in the perfect amount of musical peaks and notches.

The input preamplifier includes a discrete, high impedance, JFET stage that can also be used as an always-on buffer. We also included some soft limiting to provide character with hot signals and prevent transients from overloading the delay section.

The clock, modulation, oscillator, and even the switch logic are all fully analog. Our clock VCO includes a temperature-compensated exponential converter for a wide, even range modulation. The clock drives the BBD at extremely high current to eliminate artifacts and provide a clear, tight sound with consistent gain. An assignable expression input increases the flexibility and control available to the user.

Power and grounding deserve special attention. The ACV-1 is designed using a multi-layer PCB with dedicated split power and ground planes for low noise and crosstalk. The power input is fully protected from reverse polarity, over-voltage conditions, and ESD spikes. Our custom-designed 9V to 15V power supply works conveniently with standard 9V pedal power supplies, and eliminates sources of noise and radio frequency interference (RFI/EMI). Its boost technology runs at MHz frequencies to eliminate artifacts usually associated with simpler charge pump or older style converters.

All together, our thorough approach to engineering ensures carefree operation in any studio or performance environment!

Electrical Specifications:

• Type: 100% Analog signal and control path

• Bypass Footswitch: effect on/off user selectable True Bypass or JFET Buffered (Accessible by removing ACV-1 Cover)

• Power: 9VDC @ <150mA. 70-90mA typical. Up to 250mA start up. Standard pedal center negative 2.1mm x 5.5mm barrel.

• Delay Time:  3.1ms - 59ms. 1.9ms - 95ms with LFO and to 155ms with external CV

• Feedback: 0 to near infinite. Capable of self-oscillation using tone or EXP/CV input coupled with knob position.

• Rate: LFO RATE, from 0.1Hz to 14Hz (28Hz with CV control)

• Amount: LFO depth control from OFF to 60% of TIME sweep

• Mix: Center 50%. Adjust from full wet to full dry

• Tone: ~740Hz center tilt filter. Center = Flat to 0.3dB

  High +5dB to -10dB, Low +4dB to -7dB.

• Phase Switch: 180° phase shift of wet signal and feedback signal.

• LFO: Selectable Triangle, Sine or slewed Square wave

• Expression Switch: 4 position rotary selects Time, Feedback, Rate or Amount external control. All controls are additive to the front panel knob adding extended range. TRS jack usable with CV or Expression pedal, (CV range is 0-5V). Ring supplied current limited 5V output. Control input on Tip.

• Input impedance: >1MΩ

• Output impedance: 1KΩ Max (5k max for buffered bypass)

• Max input level: +14.25dBµ (4.0V RMS)

• Max output level: +14dBµ (3.9V RMS)

• Noise Reduction: 2:1 broadband with 10dB HF emphasis

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: 15oz (425g)