New Products

Empirical Audio Overdrive Signature USB DAC

Updated

February 15, 2009

For a limited time, a hot-rodded version of the Overdrive DAC, the Overdrive Signature, is available. The Signature version includes:

A large number of Black-Gate electrolytic capacitors
Point-to-point perfect-crystalTM silver wiring for the analog output stages
Upgraded output coupling caps – V-Caps and Sonicap Platinums
Hand-assembly with silver-loaded solder

Once the Black Gate capacitors are gone, no more Signature versions will be available.

The Overdrive USB DAC delivers unparalleled sound quality with features including:

Non-digital volume control
Balanced and SE outputs
I2S interface
2-chassis power system
USB interface supporting 24/96
Non-upsampling with digital filter selection
Able to drive most high-imp. headphones
Optional battery supply in 2009

The Overdrive USB DAC is a breakthrough audio product. It incorporates our excellent low-jitter USB interface technology and breaks new ground for D/A converter technology. The Overdrive design philosophy is “less is more”, with one of the simplest analog paths ever devised. The Overdrive provides solutions for the three most important aspects of digital sources: Jitter, D/A noise/distortion and volume control noise/distortion. This high-performance triple solution is unprecedented and delivers a totally new sound quality level.

The Overdrive is a non-upsampling DAC (no ASRC) that has an ultra-simple analog signal path, reducing background noise and harmonic distortion to unprecedented levels. It incorporates a preamp function that has never been tried in ANY audio product before. This preamp function adds no devices whatsoever to the signal path, leaving it simple and ultra-low noise. It has selectable digital filters that allow one to tailor the sound to your personal taste. You can effectively eliminate them if you want.

The sound of the Overdrive is simply indescribable and utterly magical. The clarity is unlike anything you have heard before, particularly driving amps directly. Other DAC’s sound muddy in comparison. The bass is tight and the detail and imaging is more than first-rate, it’s breathtaking. Drums are rendered with more realism than any other DAC is capable of. The leading and trailing edges and harmonics of percussion, strings and woodwinds are delivered with true realism. Even with this level of detail and dynamics, it still gets vocals right. The Overdrive USB DAC resets the bar for the term “accuracy” in digital to analog conversion.

The Overdrive can be powered from the included Substation chassis or from a Battery Supply that we will offer in 2009. The DAC has a high-current DC input connector only, so it requires a separate supply chassis. It has three digital inputs, USB, S/PDIF Coax and I2S. It has no analog inputs. We put the I2S input on the Overdrive so that it could be driven from the I2S output on our Pace-Car 2 reclocker. The Pace-Car 2 reduces jitter for many types of devices, including computers and WiFi servers. The I2S interface allows the master clock to be closer to the D/A chip inside the Overdrive DAC, reducing clock jitter even more.

Overdrive Technology:
The performance of the Overdrive DAC is a result of several innovative design breakthroughs:

Low jitter USB interface module
Ultra-Simple pure Class-A analog Path
D/A Volume Control
Ultra-Linear Output Stage
Fully Balanced Analog Path

Low jitter USB interface module:
This USB module is the same device that we use in our popular Off-Ramp 3 USB converter. This is a 3rd generation USB converter and rates #1 against all other converters on the market. Very low jitter, no drivers or ASIO to load, and it converts 16/44.1 to 24/44.1 automatically. This enables bit-perfect playback from XP or Vista PC’s and allows for 8-bits of digital volume control without any loss in resolution. USB also handles up to 24/96.

Ultra-Simple Analog Path:
The analog path consists of an I/V stage (op-amp) driving a single output transistor through a coupling cap. All stages are run Class-A, so it gets a bit warm. There are no resistors at all in the analog signal paths, except for very small damping resistors on the output. Resistors add noise, so they are best avoided. No relays or switches are in the signal path either.

D/A Volume Control:
Volume control is accomplished without any added parts to the line-output signal path. It is not an entirely digital or entirely analog volume control. It is a little of each actually. The volume is adjusted by changing the behavior of the D/A conversion. It does NOT adjust attenuation of a resistor divider, change the gain of an amplifier stage or truncate bits in the digital data. All of these would add noise and/or distortion to the signal.

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Ultra-Linear Output Stage:
The output stage is a single transistor in Class-A mode. It is well known that this simple configuration results in some compression distortion, but also sounds most natural. In order to effectively eliminate this compression distortion, we incorporated a compensation circuit in the Overdrive. The output stage impedance is low enough and the power output high enough to drive most high-impedance headphones easily, so we provide an adapter. It can drive either normal or balanced headphones such as Sennheiser.

Fully Balanced Analog Path:
There are 4 analog paths, all identical. They connect from the D/A converter chip to the outputs. All 4 are used for the balanced outputs, 2 of the 4 are used for the Single-Ended outputs. Resistors provide some isolation, so all outputs may be used. We recommend low-capacitance interconnects if all 4 outputs are used, and shorter is better. The output drive is sufficient for all preamps and amps, and even high-impedance headphones like Sennheiser.

Design Choices:
A number of design decisions were made in order to optimize performance and sound quality over all other criteria:

Small Chassis size — This was critical to reducing both digital and analog signal path lengths. Long signal paths add distortion due to circuit-board dielectrics and also introduce more noise due to ground-plane coupling and crosstalk.

Op-Amp I/V conversion — This was necessary in order to optimize the loading of the D/A converter. Some D/A chips require certain loading and voltage on their outputs in order to guarantee best linearity and low-distortion.

AC-coupled output — This was chosen because the alternative of DC-coupling would not allow a pure Class-A operation throughout, which delivers lower distortion. The coupling capacitors available now are very close to a copper wire in performance.

AC power cords eliminated — wall-type power supplies were chosen for best sound quality. They eliminate the need to purchase a $1200-2K power cord.

Specifications:
Inputs: