Fanless version of Overdrive now available as an option
Overdrive® USB DAC/Pre
USB digital to analog converter, Pre and Head amp
The Overdrive DAC is a breakthrough audio product. It incorporates our excellent low-jitter 192 asynchronous USB interface technology* and breaks new ground for D/A converter technology. It it not just a USB DAC. It also has S/PDIF coax input and I2S input. The Overdrive design philosophy is “less is more”, with one of the simplest analog paths ever devised. The Overdrive provides innovative solutions for the three most important aspects of digital sources:
- Jitter
- D/A noise/distortion
- Volume control noise/distortion
This high-performance triple solution is unprecedented and delivers a totally new sound quality level.
“...regardless of how I employed the Overdrive DAC I was aware that I was listening to the best USB DAC I had ever reviewed.”
Steven Stone, The Absolute Sound, Feb. 2010
The Overdrive DAC has received The Absolute Sound ‘Golden Ear’ Award 2010
The Overdrive 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 Off-Ramp 4 or Pace-Car USB reclocker. The I2S interface allows the master clock to be closer to the D/A chip inside the Overdrive DAC, reducing clock jitter even more.
The Overdrive must be powered from the included Substation chassis. The DAC has a multi-pin high-current DC input connector only, so it requires a separate umbilical cable and supply chassis, the Substation. The Substation stores a LOT of energy for the DAC, as well as providing power sequencing and protections.
The Substation has 3 DC power inputs, +12V, +18V and –18V. The +12V powers the digital sections and the +/- 18V powers the analog sections. Each of these power inputs has a separate high-current AC adapter to drive it. These AC adapters were chosen not due to cost, but to improve performance. These adapters are much faster reacting than linear supplies, and eliminate the distortion caused by AC power cords and line transformers. It is much easier to filter-out the high-frequency switching noise of these power supplies than the 50/60 Hz noise of typical linear power supplies. 50/60Hz is in the audio range after all. Just look at JA’s distortion measurements in Stereophile of any AC-driven product. There are always 50/60Hz noise spikes. There is also a BIG advantage in cabling DC over a 6-foot flexible cable rather than AC over the same distance. The distortion effects of the typical AC cable are not present once you have DC.
The +12VDC AC adapter can be replaced with our Monolith LI Battery Supply to improve audio quality. The separate supplies are preferably plugged directly into wall outlets, avoiding AC power cords, conditioners and large low frequency transformers. These affect dynamics and sound quality and have large variances in performance, so it is best to avoid them. The internal voltage regulation and filtering of the Overdrive effectively removes any RF from the AC adapters, and there is no 50/60Hz hum. The outputs are dead-quiet, as if it is powered off
Overdrive Technology
The performance of the Overdrive DAC is a result of several innovative design breakthroughs
- Low jitter Clocks
- Low jitter 192 Async USB interface module
- Ultra-Simple pure Class-A analog Path
- D/A Volume Control
- Ultra-Linear Output Stage
- Fully Balanced Analog Path
- A large number of Black-Gate electrolytic capacitors
- Point-to-Point silver wiring for the analog output stages — Signature version
- High quality output coupling caps — V-Caps and Sonicap Platinums
Low jitter/Upgrade Clocks
The Overdrive requires 2 clocks in the USB module section because of the asynchronous USB protocol. The other inputs (S/PDIF and I2S) are clocked by the incoming stream. The two clocks provide for the two sample rate ranges on USB: 44.1/88.2/176.4 and 48/96/192. The standard clocks used in the Overdrive are upgraded monolithic clocks with very low jitter. We also off the dual Turboclock, which is an extremely low jitter upgrade clock with 2 Hynes voltage regulators. The Turboclock takes the Overdrive to a new level. Feedback from customers indicates that this clock enables the Overdrive to beat good vinyl systems: http://www.audiocircle.com/index.php?topic=95464.msg960567#msg960567
Low jitter 192 Async USB interface module
This USB module is the same device that we use in our outstanding Off-Ramp 4 USB converter. This is a 4th generation USB converter and rates number one against all other converters on the market.
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. There are no switches in the signal path, but there are output relays for muting.
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 changed by adjusting the reference voltage of the D/A. 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. This technique is unique in the industry. Unlike other volume control methods it has the characteristic of reducing the S/N ratio as the volume is decreased - an ideal situation.
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 improved performance by eliminating crossover 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.
Hynes Regulator Upgrades
Three Voltage Regulator upgrades are available: for the USB module, the D/A chip and the analog output section. Voltage regulators are the part of the power supply that provide fixed unvarying voltages to the circuits to minimize signal noise and prevent the devices from behaving badly. The better the regulator, the better it rejects input noise and the tighter the regulation of the voltage.
Paul Hynes is internationally known for his ultra-fast regulator designs that reject input noise. Each of the 3 regulator upgrades adds more dynamics, clarity and makes it more analog-like. If we had to recommend one, it would be the D/A regulator, which improves detail and dynamics. Next in line would be the analog regulator upgrade, which makes it very analog-like as well as providing a more 3-D image.
The USB module and D/A chip regulators are more complicated and more expensive because they require other board mods. The 8 regulators for the analog output section are drop-in replacements. Except for the USB regulator upgrade, the regulators are custom designs done for Empirical Audio, however, even the USB regulator is customized.
Specifications
Download User Manual
Measurements (Measured at 24/96):
- THD+N (1kHz @ 0dBFS): -100dB
- THD+N (1kHz @ -20dBFS): -105dB
- Crosstalk (typical @0dBFS): -118dB
- Crosstalk (@ 20kHz 0dBFS): -110dB
- Frequency Response (-10Hz to 20kHz): -0.6dB
- IMD (with 100K ohm load): -106dB
- Dynamic Range (A-weighted 1kHz): 106dB
- RCA Output Level: 1VRMS or 2.3VRMS
- XLR Output Level: 2VRMS or 4.5VRMS
These links show the impulse response of the Overdrive DAC at 24/96 and 24/192. Hardly any pre-ring and the pulse gets almost to 1.5V (the input level). Pulse on the 24/96 reaches 1.233V. Other DACs have more pre-ring and never get anywhere near the amplitude of the input signal. This demonstrates the fast slew-rate of this DAC and the grip that it has on transients.
Inputs:
- USB 2.0, Mac or PC, up to 5 meter USB cable – up to 24/192 supported
- S/PDIF coax – RCA, BNC or WBT NextGen ** – 44.1, 88.2, 96 and 192 supported at 16 and 24-bits
- I2S (Empirical standard RJ-45) – 44.1, 88.2, 96 and 192 supported at 16 and 24-bits
- DC power (+12VDC, -18VDC, +18VDC) from included Substation
Outputs:
- RCA left and right channels
- XLR left and right channels
Controls:
- Input Select
- De-emphasis Select
- Digital Filter Select – High, Medium, Low
- Line/Volume Select – recessed
- High/Low gain Select – recessed
- Volume knob
- Internal jumpers for 3 volume ranges
Included:
- Overdrive DAC
- Substation DC power supply – over 60,000uFd of energy storage
- DC power supply umbilical cable
- 5 meter USB cable
- AC power supplies
- CDROM with PC/Mac installation software
- RCA to Phone-jack Headphone adapter – only high-impedance headphones supported
Download Drivers
- Windows 7 / Vista
- Windows XP / 2003
- Mac OSX 10.6 Snow Leopard
- Mac OSX 10.5 Leopard
- Mac OSX 10.4 Tiger
Configure Your Overdrive
*USB Software/Firmware licensed from M2Tech
**NextGen is a trademark of WBT