DACport development blog

Ahh, it was good to relax over the long Holiday weekend. Best Holiday Vibes to all!

We have sent out the first batch of pre-ordered units and initial comments are showing up on the web. I especially like this comment from head-fi.org:

“Without a doubt, the DACport is more resolving, dynamic, and extended on both frequency extremes.”

Meantime, we are busy updating the DACport website. The current version has a “introduction” feel to it, or simply too much hype. We will be changing that shortly, updating with newly taken pictures, explanations and features. Stay tuned for that.

Meantime, we are preparing to take a number of units to CES and NAMM to demo and show around. It’s nice to be back after a holiday break.

Chicago is covered with freezing snow and temperatures are heading down to 14F (-10C) for tomorrow, so going out for cappuccinos is not fun right now. Acknowledging that we are stuck in the office we decided to publish some measurements instead of loading up on lattes…

DACport continues to amaze our whole crew. Aside from the fact that familiar recordings come to life in a totally new way (you could hear new instruments, recording mistakes and other nuances, which previously escaped your ear) DACport also measures extremely well. I guess, there should be a correllation, after all. If it measures well, it sounds excellent, and vise versa.

THD+N remains well below 95dB, but we need to measure up a lot of units before we get a good statistical value. Frequency linearity is simply astounding… How often do you come across a piece of audio equipment with linearity over the entire espectrum within only .1dB! DACport’s frequency responce  is flat 10Hz to 40kHz. This temporary graph only goes to 20kHz — we will publish the performance at 40kHz soon. Even 10Hz..20kHz, what a performer! Click the image to see the entire plot.

I don’t own a TV, but I still saw how much time was devoted recently to promoting “Our Choice”, the new book by Al Gore… Global warming is a serious concern, and here at CEntrance, we support the green cause. We want our customers to save energy and that’s why we pay special attention to power issues. Let’s talk about DACport’s power consumption.

DACport does not require any batteries or chargers. It takes its power entirely from the USB jack on your desktop, laptop or netbook computer. And DACport is very smart about the power current, to save power and make that battery last longer.

Let’s start by saying that when you first plug it in, DACport starts in “low power” mode and takes only about 60 mA of current on the 5V supply. In this startup mode it performs initial USB handshaking and then requests additional power. That’s the “polite way” of establishing a USB communication, according to the USB standard, and we follow the standard to the “T”. This negotiation is instantaneous – it takes a fraction of a second and ensures proper configuration and no data loss.

Having performed initial USB handshaking, DACport requests full power, which is granted by the OS. That starts up the main switch-mode power supply that ramps up the 5V to +/-9V for the audio circuitry, +3.3V for the digital circuitry and clean +5V for the converter circuitry. In total, DACport has 5 (five) separate internal power supplies! That’s how we ensure that clean power is supplied to all circuitry to maintain the ultra-low distortion.

When designing the DACport we took a close look at the amount of power available from the USB jack. Typically it’s 5V x 500 mA, which results in 2.5 Watts of power. Not all of it is available for Audio however – in fact about 1 W is taken up by the digital and converter circuitry, so 1.5 Watts is the real Audio output power.  In most cases, that’s plenty, since even the low-impedance headphones are very loud at 500 mW.  DACport makes 1.5W available for audio.

When no music is playing, DACport goes into low-power mode to save the battery. But when you press “Play” it immediately springs into action and turns on full power. This is the benefit of using switchmode power supplies – they react in microseconds and allow to efficiently manage power consumption on the fly.

Because DACport’s headphone amplifier is Class A, it takes a steady amount of current during normal operation, but there is some variation depending on the impedance of the connected heapdhones and loudness of your music.  DACport normally draws less than 400mA from the USB port, giving you enough power and ensuring class-compliace by a healthy margin. DACport is very careful in how it manages power – it takes only what it needs, when it needs it, which saves the battery on the computer and lets you enjoy your music for longer on the go!

The Internet is still down, and so is Internet radio, such as Shoutcast, Pandora and Last.fm… This is uncomfortable. A modern man needs to be connected.

Today was devoted to cleaning up the crystal oscillator. DACport uses a mil-spec, precision crystal oscillator that supplies the clock for all the digital chips inside.

We now have several units under extensive burn-in test. The purpose of a burn-in is to make sure that nothing in the circuit is affected by a prolonged exposure to higher temperatures. This test usually reveals the weak links in the circuit – those components that are “on the edge” and may fail sometime down the road in the field. Of course, we want the DACport to provide uninterrupted listening experience for our customers, so we are testing hard… And guess what we found – the precision crystall oscilator that features 10 ppm (parts per million stability, or .000001% frequency deviation) became unstable under a demanding temperature test. It’s actually very hard to trip it up, but our vigilant testers figured out a complicated sequence of powering/unpowering that left the crystal in the proverbial “state of shock”. It comes back to life, but you have to cycle the power again.

Well, this was definitely not good and so we immediately went for the scope and logic analyser to debug the pesky circuit looking for the culprit of instability. Turns out it was a faulty part. The part was replaced, supplier noted and a new battery of tests started… So far so good. We will be adding a new, more reliable supplier to the list.

DACport is ideal for travel as a portable, audiophile-quality sound card. Pack your favorite headphones and relax – watch blue ray movies on your laptop in an airplane, listen to hi-res music at a hotel room, or in a coffee shop. DACport has been called “the ideal coffee shop rig” because it transforms your portable listening experience, upgrading it to High Resolution Audio.

But Hi-Fi on-the-go is not the only way to use it. DACport is equally comfortable at home, as part of a permanent audio setup.

We designed DACport’s headphone amp in such a way so you can easily connect it to an external power amplifier and a set of speakers. To do that you would need a cable with a 1/4″stereo plug on one side (same plug as on pro headphones) and a pair of RCA or XLR connectors on the other side, to connect to the amplifier. Plug in the cable and DACport becomes a high-quality USB DAC, making it possible to use it as part of a home computer audio setup.

If using as a USB DAC, CEntrance recommends turning DACport’s volume knob to the max and using external amplifier’s volume control to adjust the volume (this is the best way to manage gain.) There is no danger in setting DACport’s volume level to maximum – the internal amplifier has plenty of headroom and is guaranteed to never overload, even during the loudest musical passages!

DACport’s headphone amplifier deserves a special mention.

CEntrance recently developed a brand new, direct Class A amplifier design, which is characterized by ultra-low noise floor and lowest THD. We minimized distortion by getting rid of all capacitors in the audio signal path. Capacitors can exhibit non-linear characteristics and increase distortion. Rather than experimenting with different capacitor materials to find a compromise and hoping that the selected capacitors will not deteriorate over time, we got rid of them altogether. There are zero capacitors in DACport’s signal path and the sound is cleaner for it!

DACport’s output noise is so low that we need to provide a warning. You have to be careful with your ears. With most audio products you can hear some residual noise when you turn up the volume knob. But not so on DACport – the output is equally quiet if the volume knob is at min or max settings. If you max out the volume knob while no music is playing you will not know it – the headphones will be completely quiet. So be careful to avoid accidentally blasting your ears with loud music!

This level of low-noise performance was not possible 10 years ago, but today’s circuits improved dramatically. DACport’s output amplifier features 120 dB of dynamic range, making such unbelievable performance a reality.

DACport has an internal microprocessor, which is responsible for moving digital audio over USB but also for making sure that all internal circuitry blocks, including the precision Digital to Analog converter are functioning smoothly. This week (as we wait for the correct chassis to arrive), we spent time to tune up the microprocessor code for smoother overall operation.  Such mundane operations as Start and Stop of playback, changing tracks, switching sampling frequencies and bit depths sound simple, but they take a lot of work behind the scenes. All of these functions need to happen smoothly and quietly, so that the machinery is completely transparent to the listener. All you want to hear is your music in its full 24-bit resolution glory.

So we kept working to improve the code, making sure all switching is completely silent. Today we finally arrived at a totally invisible solution. And it is truly amazing. Your humble reporter decided to listen to some of his favorite CDs - Donald Fagen, Karrin Allyson, Patricia Barber, Diana Krall and others. The results are astounding. I thought I knew these records inside out… When I listened to them over DACport I’ve discovered a lot of new material – new sounds, new instruments, even new recording imperfections.

DACport is very revealing of the tiny little details and once you try it, your music will never sound the same again. We are building the first production run off 100 units in late November. The price will be announced soon. Please submit your name here if you would like to be informed of pricing unit availability.

The reason DACport works with Windows, Mac and Linux without needing to install any custom drivers is because it supports the USB class-compliant audio standard. All major operating systems ship with built-in standard audio drivers, which is the reason that most USB headsets are plug-and-play. Typically, however, these built-in drivers only support 16-bit/44kHz soundcards.  Most 24/96 products ship with custom drivers and require the user to go through a cumbersome installation procedure.

But not DACport, a true CEntrance innovation. We spent years of intense R&D effort learning how to make a 24-bit/96kHz USB DAC compatible with the existing OS drivers. The good news is that now you can reap the benefit of that effort. DACport is true 24/96 and plug-and-play. It works works right out of the box, with any computer. How’s that for convenience.

With DACport CEntrance set out to create the smallest portable audiophile USB DAC. Not a simple USB sound card with a compromised set of parameters, but the best, yet portable headphone amp with USB input. You can’t always be near your expensive home audio setup. With DACPort, you could use it on a plane, in a coffee shop or in a hotel room to relax and listen to high quality music away from home.

A high quality DAC needs to have descrete parts for everything. It can’t use an all-in-one chip, which is typically consumer quality, but has to have separate power supply, DAC and amplifier circuits. Normally this level of miniaturization would be impossible because of physical constraints. But CEntrance also designed the MicPort and AxePort, the recording interfaces used by musicians and broadcasters all over the world. So we had some minaturization experience. We also developed dozens of pro audio products for the largest brands in the industry, such as Mackie, Alesis, Harman Pro, and Gibson. CEntrance started out as a design firm back in 2000 and since then built up our “chops” in designing miniature electronics.

Here is a picture of the two circuit boards inside the chasis, actual size (depending on your monitor, of course). We are stil counting the total number of parts, but it’s a couple of hundred, mounted on the top and bottom of both circuit boards. There is no space left – it’s a tight squeese. The first prototypes are built manually, so a steady hand, good light and magnifciation are key. You can’t assemble these if you were partying the night before…

One of the benefits of DACport’s design is the small size of its PCBs. The advantage is in the layout of the ground wiring. When ground paths are short, there is less chance for ground loops forming inside.  Fewer ground loops means less noise and higher quality sound.

But the flip side of a small space is a limited number of power supply caps, which are needed to filter out the supply ripple and create a smooth, clean power for the amplifier circuitry. The design quickly becomes a study of compromises.  How do you maintain the best audio quality while conserving USB power, and fitting everything in the smallest possible space?

Higher power supply voltage provides several benefits. Firstly, there is more power available to drive any kind of headphones. Secondly, the signal-to-noise ratio is higher. Thirdly, ClassA amplifiers running at higher supply voltages typically produce lower distortion,  so all in all more votlage is a good thing.  It’s easy to raise the supply “rails” in a wall-powered product, but how do you do that in a portable device that takes its power entirely from USB?  Well, we recently made the decision to upgrade the internal power supply to 18 V to gain the last couple of dB of THD out of the circuit. Inside of the tiny aluminum tube there is a switching power supply that makes +/-9V out of the 5 V that is provided by USB.

It took several weeks of optimization, but the end result is simply astounding—we have achieved unprecedented -97dB of THD+N at the output! This means that DACport’s distortion spec is now at the theoretical imit of its Digital to Analog converter. This is miles ahead compared to a standard CD player! We simply couldn’t improve it any further. And so, on to new challenges.