DACport development blog

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.

If you look through our website you won’t find an explanation of our company name anywhere. Which, you may say is an omission. So for lack of a better place, let’s explain the meaning of CEntrance here.

You’ve probably guessed by now that this humble blog is authored by Michael Goodman, our cheif cook and bottle washer. Back in the day, when there were fewer dishes to wash, one could actually spend time thinking big picture thoughts. I still get to do that, but time is stretched rather thin these days, partially due to the introduction of DACport… But back to the company name.

CEntrance is the expression of my life-long passion for Consumer Electronics. CE is actually inside our company name. Twice, if you look closely.

Any great concept (if I say so myself), eventually develops a life of its own and other people  find new meanings in it, which is what happened the first time we attended a European trade show. As some of our readers will know, CE stands for Communauté Européenne, or European Union, in French. This was quickly brought to our attention. Quite flattering, thank you, although we aren’t that big just yet Others have suggested that our name should stand for Customer Entrance because we are so relentlessly customer-focused. Bring it on–we welcome all positive feedback! Probably the most obvious meaning is that of “core essence”, which is the one that’s near and dear to my heart.

A lot of people mispronounce our company name. The correct way to say it is “Sentrance”. So there you have it–an excursion into the long-forgotten year 2000 when CEntrance was originally formed as an Illinois corporation, located 20 minutes north-west of Chicago.

Incidentally, the company turns 10 years old next February. Not a small feat.

Some people have asked to see a picture of the finished product. Here is a photo of a pre-production sample.  The final product will look almost the same, except slightly lighter gray. Click the image for a larger size.

We are still deciding on the final packaging, but most likely we will start out with the same box with a transparent window, which we currently use for our other products.

Feel free to ask questions in the comments section. And yes – we will be announcing the price this week.

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!

This week I will be reporting from Los Angeles. CEntrance maintains a busy consulting practice and that means frequent travel for your humble reporter. Today LA is cold and the usual feeling of exhilaration one experiences coming from Chicago is gone. From one cold city to another — there is no fun in that! But… the strawberries on the west coast are simply delicious! Lush, firm, juicy and sweet. All organically grown, too. Well, travel must have some perks.

Meantime, DACport development continues at full speed as our engineering team keeps working back home. New samples of the chassis should be coming in next week and work continues on redesigning the PCB: We are fitting in a better crystal and getting rid of a couple of blue wires to improve manufacturability. More on this soon.

Our customers will be happy – DACport will be more robust in the result of a recent spur of R&D activity.

Stability of digital devices is key and your humble reporter got concerned last week when we discovered a bug that caused the 24.576 MHz crystal to suddenly quit oscillating when the ambient temperature increased. We mentioned previously that a burn-in test allowed us to discover this failure.

Simply replacing the part with a cross from another manufacturer just didn’t seem like a robust solution… At CEntrance we believe in “No stones unturned” engineering discipline, so we dove head-in in to the physics of ceramic oscillators, to determine the factors that could cause oscillator failure.

Our mil-spec, 10ppm crystal will provide its incredible frequency stability as long as it’s driven by an appropriate oscillator circuit. The more precise the part, the more demanding it is on the operating environment. The crucial parameter in this case was “oscillator drive”, which is a function of the chip that drives the crystal. The chip provided enough power, but with little safety margin. As temperature increased, things got out of whack and oscillation became erratic – a sure sign of things being on the edge.

We won’t name the reputable vendor that somehow omitted this important parameter from the datasheet… We ended up having to contact the manufacturer to get the low down on the internals of the circuit. Note to self: Even reputable vendors can throw a curve your way…

And you think CEntrance of anyone should know — CEntrance is the official 3-rd party design firm for Texas Instruments, Analog Devices and many other semiconductor vendors. Do things always go smoothly? No, they don’t and this blog gives you a glimpse into the daily life of the developers. We certainly don’t know everything, but we know how to get information and we learn quickly… I’m just glad that we caught this bug before DACport went to production! Testing, testing and more testing…

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.

This is a short post. Our Internet line went down yesterday and while we are waiting for it to be restored I am blogging from the iPhone. It’s amazing how dependent we are on this modern lifeline.

Meantime, we have finalized the text for the unit’s chassis. The original plan was to use silk-screened labels, but we experimented and decided against that. DACport will have laser engraved labels instead. It’s more expensive, but looks solid and professional compared to paint. We are going for color contrast with the white tube and black end caps. It will look super-sharp when we finally get those chassis finished!

Our Internet connection should be restored shortly. Until then, I’ll be taking a break and reading a book… Turns out those things are made out of wood – how entirely analog!

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.