Continental Dual Mono

Built to be Epic!
When we started working on our newest generation Continental wanted to do something amazing.  We examined each element of the amplifier – 6111 tubes, Wolfson DAC, Power Supply, Volume Potentiometer, Battery, Capacitors – to find the best sounding component.  As we put them all together we ended up with The Continental Dual Mono.
Pure Power
Each stage of the CDM has its own dedicated linear voltage regulator.  This means the internal voltage of each stage is independent.  This minimizes the sharing of differing internal voltages across each stage of amplification and the digital to analog converter.
Linear voltage regulators are used because they produce a cleaner voltage rail than typical switching regulators.  Because they do not use a switching waveform, linear regulators have lower output noise.  Lower output noise is better for clean amplification.  And in high fidelity amplification it is critical.
Dedicated linear voltage regulators to each stage of amplification provides optimally clean power. Less crosstalk between the stages and better isolation of the analog and digital sections.

The Touch of Tubes

At the center of The Continental Dual Mono are a pair of New-Old Stock 6111 Vacuum Tubes.  Each tube is individually soldered to a custom PCB.  This provides mechanical isolation of each tube, insulating them from unwanted microphonics.  It also provides a quick and easy solution for tube-rolling.
Directly following the volume potentiometer, the dual 6111 vacuum tubes provide the current gain (ie tube “buffer”) to the amplification.  This provides a clean, strong and dynamic signal to the headphone output stage at a lower output impedance.

Running in Class A, the Dual Mono implementation of the vacuum tubes provides improved stereo separation and an expanded soundstage.  This is because of lower levels of crosstalk achieved between Right and Left channels.  The tubes are auto-biased so there is no need for any time consuming manual biasing.

Microphonics are a unique challenge when introducing vacuum tubes to a portable amplifier.  The design of the tube circuit in The Continental Dual Mono minimizes the inherent microphonic tendencies of the tubes.  Utilizing the tubes as a buffer, handling the current gain and not the voltage gain reduces microphonics.  Mechanical isolation of each tube and the component layout of the PCB further assist eliminating any distracting microphonics.

While the tubes are user replaceable, the vacuum tubes as implemented can easily be expected to provide 5+ years of reliable operation.

Supremely Solid (State)
The Continental Dual Mono is a “tube/SS hybrid” amplifier.  It delivers the low output impedance, tight bass and sonic precision of a solid-stage amp, but with the added midrange richness, expanded soundstage and spaciousness of a tube amp.
The Class AB solid-state output stage is designed laid out with short path lengths and a low part count.  Only the highest quality components are used in The Continental Dual Mono.  The voltage regulators, decoupling capacitors and resistors all have tight specifications.  Rated to operate at wider temperature ranges and for extended cycle life.

Digital Dynamo
The Wolfson WM8741 DAC chip occupies the heart of The Continental Dual Mono’s digital section.  We selected this chip after extensive examination of all available reference DAC chips.  The WM8741 has exceptional signal to noise ratio and extended dynamic range. It also provides low noise, low distortion and superior linearity. The Wolfson provides high resolution DSD and PCM playback and offers musically compelling digital filters.

WM8741’s minimal phase digital filter is more natural sounding because it has no ‘pre-ringing’ of its impulse response.  Just as a piano doesn’t produce sound before a key is pressed, the minimal phase filter doesn’t ‘pre-ring’ its impulse response.
The power feed to the digital section is turned OFF when the USB cable is unplugged.  When the DAC is active, the internal Li-Ion battery and linear voltage regulators provide the power.  The noisy 5V rail from the USB is not used for any part of the power. This means less grain to the sound and no digital harshness.
For lowest amounts of jitter and cleanest digital to analog conversion we used a high quality clock IC in The Continental Dual Mono.   For both PC and MAC computers, PCM 16/24 bit – with these sample rates (kHz) of 44.1, 48, 88.2, 96, 176.4, 192, as well as DSD64 are all supported.  MACs require the driver provided for DSD playback.  PCs require a driver for both PCM and DSD playback.

Mobile devices also play well with The Continental Dual Mono.  Most Android devices can pair with the DAC using a micro USB OTG cable and the ALSA driver.

Please note: Apple iDevices can in general pair with the DAC using an Apple Camera Connection Kit and micro-USB to USB-A cable.  iPads work consistently.  iPhones with iOS 9.02 appear to work well.  iPhones with iOS 9.1+ have mixed results, depending on track, music App, etc.

The front panel lights provide you with quick access to the DAC’s sample rate.  Red = 44.1 / 48kHz, Green = 88.2 / 96kHz, Blue = 176.4 / 192kHz, White = DSD64

Big Beautiful Battery
The Panasonic 18650 batteries are combined into a 3 cell pack to provide clean, reliable power to The Continental Dual Mono.  The 3-cells are in series to deliver the voltage the tubes demand.
We selected the this battery because it has a high cycle life, approximately 1000 cycles.  It also provides short circuit and overcharge protection.  It is also safely user replaceable.  So when you reach the end of the batteries life, you can swap in a new one and keep the music going.

Using a high quality battery to power The Continental Dual Mono makes the music come alive.  Beyond the low noise floor you’ll discover tight controlled bass, natural midrange and a grain-free extended top-end.  The clean power is immediately appreciable in the dynamic sound from the amplifier.

Audio Line Out
The Continental Dual Mono has a true “Line Out” on the rear panel.  This is a fixed 2Vrms analog output signal. This signal is from the output of the DAC’s analog output stage.  It is tapped before going through the volume control or headphone output stage.

We included this feature to showcase this exceptional DAC.  It is intended to drive a preamp, integrated amp, another headphone amp, such as our Studio Six headphone amplifier. Please note that the Line Out is not intended to drive headphones directly, but instead offers you flexibility in using the DAC with your other components.

Awesome by Design
Our new enclosure design is inspired by our daily use of our products.  Machined markings resist wear and the minimal icons keep you focused on the music.  The Gorilla Glass window lets the tubes shine without exposing them to the elements.  Expanded vents running along the sides of the CNC’d aluminum enclosure keep The Continental Dual Mono breathing as the tubes heat the interior.

Designed and Assembled in the USA
Each amplifier is hand assembled and tested in our Portland, Oregon workshop.  Each one is carefully inspected to assure you years of satisfied ownership.

Reviews

“It takes three seconds to tell that ALO went to great lengths to get CDM right, not just good enough. It is a damn near-perfect valve amp/DAC.”   “CDM is stable, powerful, wonderfully machined, beautifully branded, and a great match for everything from sensitive earphones to full-size headphones. Its brilliant DAC even nails native DSD decoding, adds spicy contrast, and a thoughtful low-pass filter.”

– Nathan @ Headfonia.com