Prototype For Sale

I'm no longer in need of my original prototype, so I'm going to sell it as-is or part out the individual components. I plan to post the sale on eBay, Craigslist and some Facebook groups dedicated to audio. When I get a chance to take some photos, I might update this post. If you are interested, feel free to contact me at gregg dot plummer at gmail dot com.

This first prototype consists of a combination of amp modules and a FireWire audio interface in a utilitarian aluminum chassis. I was pretty concerned with overheating because of the 5 high powered amps so I used a fairly thick aluminum to help dissipate any heat. It's also vented at the top, just above the amps and there's a very quiet 120mm fan to blow air out the back. BTW, I worked with a mechanical engineer who did some thermal analysis on the prototype to make sure we dissipated the heat. It was probably a little overkill. My price for the prototype is $825. My cost, not including the considerable amount of time designing, building and testing were about $2,500.

The components included are:

Aluminum Chassis - this includes the 120mm fan, special mounting plates for the power supplies and mounting brackets for the audio interface. On the back is the A/C receptacle with a switch (A/C line cord included) and a 10A Bussman time delay fuse socket. On the front, there's a momentary pushbutton switch that has 2 operation modes. In one mode, the audio interface is powered on while the amps remain off. The other mode switches on the audio interface and all the amps. Not sure if anyone would be interested in this because the layout is designed specifically for the rest of the components. The price for the chassis is $295 $100.

Power supplies - At the time of this design, the only practical choice for the system were linear power supplies. I really wanted to incorporate SMPS (switch mode power supplies), but ones with the characteristics I wanted for this high-quality audio application were not available. I used different amps for the front and rear channels, so the system utilizes 2 different power supplies.

• The power supply for the rear channels includes a 400 VA (115/33 Vx2) toroidal transformer and a Hypex HG power supply. My prices are $65 for the 400VA toroid and $100 for the Hypex HG PS.
• The power supply for the front channels includes a 1000 VA (115/45 Vx2) toroidal transformer and a Hypex HG power supply. These are $100 for 1000VA toroid and $100 for the Hypex HG PS.

Amplifier modules - I used the highest quality Hypex UcD amp modules that were available at that time. This prototype only needed to provide power to 5 channels because, in a typical 5.1 home theater system, the subwoofer is self-powered (channel .1). To each amp module, I attached an aluminum plate heat sink with fancy Neutrik speaker binding posts.

• The 3 front channels - right, center, left use Hypex UcD400AD amp modules. These are each rated at 400W RMS into 4 ohms. Unfortunately, only 2 of the 3 are currently working. The one I was using for the center channel has a faulty component that causes the amp to output a terrible thumping sound. So, I'm including it for free with either of the other working modules. I think it just might need a new cap but I'm not sure and Hypex no longer services this amp. The price for the working UcD400AD modules is $85 each or $165 for the pair. 
• The 2 rear surround channels use Hypex UcD180AD amp modules. They are rated at 180W RMS into 4 ohms. My price for a UcD180AD module is $65 or $125 for the pair.

Audio interface - this is the device that your PC will use as the audio device or soundcard in your HTPC. It was the AudioFire8 and was sold by Echo Audio for something like $750. This is a high quality 8 channel FireWire audio interface typically used for audio recording and mastering. I took mine apart and reinstalled it inside my chassis. A rectangular port is cut into the front of my chassis to access the front of the AudioFire8. I also paid Echo Audio $5000 to write a custom multichannel driver so my device could output surround audio. Since my center channel amp stopped working, I used the AudioFire8's software console to reroute the center channels to the front left and right channels balanced evenly. It's now a working 4.1 system and still sounds great. I can put the AudioFire8 back in its original chassis and sell it for $175. Echo Audio still has drivers on their website that you can download for Windows 7, 8 and 8.1. They are no longer developing audio interfaces and have discontinued further updates so it may not work on Windows 10.

Misc components - A handful of components were included to complete this system. To avoid the loud click that normally happens when you turn on the amps, I added Hypex's softstart module. To connect the AudioFire8 to the amps, there are custom cables with 1/4" TRS connectors. Also included is all the hookup wire between toroids, power supplies, and amps.

UPDATE 2/14/2018: Items that have sold are indicated as such by striking the text. I've listed the remaining items on Craigslist here:

https://madison.craigslist.org/ele/d/diy-amplifier-components/6494593237.html

I've reassembled the Echo Audio AudioFire8 and reduced the price to $100:

https://madison.craigslist.org/msg/d/echo-audio-audiofire8-audio/6494579793.html

I'm also selling an M-Audio FireWire 410 for $75:

https://madison.craigslist.org/msg/d/audio-firewire-410-audio/6494554911.html

AND, I'm selling the 5.1 speaker system that I used to demo my prototype. These are awesome speakers:

https://madison.craigslist.org/ele/d/era-design-5-speaker-system/6476114140.html

New Ultraefficient Audio Amplifier Technology

Audium Semiconductor Ltd. (Bristol, England) has raised $8.5 million in a first round of funding. The company claims to have proprietary audio power amplifier technology that requires one-twentieth (1/20) of the power of competitive Class D amplifiers at "normal listening volumes."

This is written on Audium's website:

QUOTE::

Today’s audio power amplifiers only achieve optimum efficiency at full output power. Because a typical audio signal has a very high peak-to-average power ratio, amplifiers operate at less than optimum efficiency most of the time.

Audium’s amplifier technology changes all of that by dynamically adapting the DC operating conditions of the amplifier to ensure that it’s always working at peak efficiency.

Benefits include a 20X reduction in power consumption at normal listening levels*, smaller form factor and a saving on heat sinks. What’s more, the Audium advantage increases with the amplifier output power.

*Normal listening level is defined at 70dBC SPL at 1m with a speaker sensitivity of 89dBC/W/m.

::ENDQUOTE

Their technology appear to be geared mainly for portable audio, but they do have products with 100W/channel peak power output. The applications mentioned include battery powered MP3 docking station speaker systems and totally wireless speakers for home and PC audio. Obviously, both of these applications would benefit from more efficient amplifiers.

Here's my question: How do they sound?

I can't find any performance specs, other than peak power output and frequency response. No noise or distortion stats. I doubt these are really intended for high fidelity audio.

New HTPC amp

There's recently been some discussions on AVSForum about a new amplifier board that was developed by D2Audio. Actually, most of the comments have been about a new MSI 7411 motherboard that supports the D2Audio technology. Instead of using the typical on-board 7.1 HD-Audio chips like those from Realtek, they have included D2Audio's DAE-3 class-D PWM controller with this motherboard. This controller includes the standard HD-Audio interface and works with one of two add-on PCIe cards, either a 7.1 preamplifier card or a 5.1 amplifier card.

This isn't the first time someone has integrated an audio amplifier with a PC motherboard. A little over 5 years ago, Acer introduced their AOpen AX4B-533 Tube motherboard with built-in tube amps. I don't know how well it sold, but it got some attention, probably because of the novelty of the combination. Obviously, it didn't revolutionize the way other manufacturers designed motherboards because we haven't seen anyone else release a similar product until now. However, it does look like more PC manufacturers are working toward making convergent products and taking the HTPC market more seriously. This time, instead of using tubes, the D2Audio amps use class-D circuitry.

These products are exciting to AVSForum readers because they may finally have an HTPC that can replace their A/V receiver and many of the source devices. With something like this, you wouldn't have to deal with the current hassle of trying to pass HD encoded audio, like Dolby TrueHD and DTS-HD MA, via HDMI to your AVR. You can just connect your HTPC directly to your hifi speakers. I guess the next question is, how will it sound compared to a good AVR? Based on D2Audio's literature it is designed to compete head-to-head with current AVR gear. Chris Morley, President of Omaura North America has listen to it and says it sounds fantastic.

I don't doubt that it would sound as good as a low to moderate priced AVR, but after researching class-D amps for several years, I'm skeptical that this technology can sound as good as dedicated or even integrated amps. For those of you that are interested in high end sound quality, I created this chart to compare common specs of the D2Audio amp card to other class-D amp modules:

Product	Power Rating	Distortion THD+N	SNR / Dynamic Range	Power Efficiency	Peak Output Current	Frequency Response
D2Audio 5-Channel x 100W (AAIC100-5) Card	100 W Peak at 8Ω	less than 0.1%, f = 1KHz, P = 1W	more than 105 dB	93%	?	±0.5 dB (20Hz to 20KHz)
ICEpower250A	125 W at 8Ω, 210 W at 4Ω	0.005%, f = 1KHz, P = 1W	112 dB A-weighted	93 %	> 25 A	±0.3 dB (20Hz to 20KHz, all loads)
Hypex UcD180 HG Version	105 W at 8Ω, 180 W at 4Ω	0.008%, f = 20Hz to 20KHz, P = 1W	120 dB A-weighted	92 %	10 A	±0.3 dB (10Hz to 50KHz, all loads)
Huygens MHzpower-2	100 W at 8Ω, 200 W at 4Ω	0.0035%, f = 1KHz, P = 10W	123 dB	91 %	26 A	+0/-3 dB (DC to 150KHz, at 8Ω)
CAD Audio D250A	250 W at 4Ω	0.02% typical	110 dB	?	20 A	+0/-1 dB (20Hz to 20KHz)
CL3 Gemincore	250 W at 8Ω	0.002%, f = 1KHz, P = 1W	115 dB	97 %	19 A	0 to 70KHz
PowerPhysics A-108	100 W at 8Ω	less than 0.05% P = 0.1W	115 dB A-weighted	more than 90 %	?	20Hz to 20KHz

It's hard to make valid comparisons because all manufacturers don't use the same measures. My first concern with the D2Audio amp board is its power rating. To be fair, I limited the comparison to modules that were close to the AAIC100-5's power rating of 100W. D2Audio has calculated the power rating based on an 8Ω speaker load. A lot of the amp manufactures will quote power ratings based on 4Ω loads, but 200W at 4Ω is similar to 100W at 8Ω. The specs from D2Audio's website list their power rating as 100W peak at 8Ω. Most of the other manufactures will list the power rating using an rms (root-mean-squared) calculation. D2Audio may mean you can get 5 x 100W peak power for a short period of time before the PC's power supply cuts out. That's probably why they state in their literature, "the DAE-3 engine provides real-time power management to protect against power supply overload and potential Media PC shutdown from loud music or explosive sounds that occur during movies or games." So maybe if you have a large enough power supply it can provide a continuous 100W rms power. If not, if they really mean peak, then the rms power is actually 50W per channel.

The distortion figures for the AAIC100-5 are not that impressive when compared to most of the others in the chart. Not too bad when you compare it to some tube amps, but not as good as most solid state AVRs on the market. It also depends on the type of distortion. A tube amp may have a lot more distortion, but some people perceive the relatively high 2nd order harmonic distortion to be pleasing and adding "warmth" to the sound. Even though solid state amps have much lower 2nd order harmonic distortion, the other higher order harmonic distortion is not too pleasing. With most inexpensive solid state amps, the distortion increases as frequency increases making them sound bright or harsh. The THD (total harmonic distortion) for class-D amps are primarily second harmonic in nature, but there are also some higher order harmonics present. The best class-D designs use a feedback loop to compare the output to the input so they can minimize any errors in the output. With a pure digital PCM-PWM amp, you have nothing in the input to compare to, so without some pretty expensive and complicated circuitry, it is nearly impossible to get good distortion ratings. That's probably why D2Audio's digital amps don't match the THD specs of these other analog class-D designs. It's also probably why most respected class-D designers abandoned the pursuit of pure digital amps a few years ago in favor of analog class-D. I've been very impressed with Hypex's UcD amp modules and if you look at their THD figures you can see why. They are able to get very low THD over the entire frequency range (well at least from 20Hz to 20KHz). Older class-D amps without feedback circuitry had pretty poor THD at higher freqencies and this is why they were used mostly in active subwoofers and got a bad reputation for true hi-fi. I hope the high frequency performance of the D2Audio PCIe amps don't help to reinforce that reputation.

You can also see that the dynamic range of the AAIC100-5 doesn't compete with the others in the table. Considering the fact that many of the DACs in popular soundcards have SNR specs around 120 dB, the D2Audio amps might become the weakest link in the audio electronics chain of your system.

The other specs compare favorably to the others in the chart. Power efficiency and frequency response are in the same range with the other amp modules.

There are a few other audio specs that are not listed in D2Audio's literature that would be worth knowing. Since the AAIC100-5 is installed inside your HTPC and is dependent on the PC's power supply, I'd like to know the spec for power supply rejection ratio (PSRR). PSRR indicates how good a device is at rejecting noise from the power supply. The PSRR of the ICEpower and Hypex amps are about 60 and 65 dB, respectfully.

In conclusion, I think the new MSI motherboards with integrated D2Audio technology is a pretty cool thing. I'm happy to see any product that makes HTPCs more useful and popular. I'm not a big fan of digital amps, mainly because their specs, especially THD, don't measure up to good quality class-D analog amps. I also don't like the fact that these amps are totally dependent on the PC's power supply. If you've read some of my previous blog posts about HTPCs, you also know that I like my HTPCs to be pretty small. Ideally, I'd like a fully functional HTPC about the size of a Mac Mini. This would be impossible if you throw in the amps. So, unless this sort of technology makes some dramatic improvements in the future, you won't see anything like this available from Amplio.

update 3/28/08: I received a more detailed datasheet for Huygen's MHzpower-2 amp module and noticed some differences with the specs in my chart. So I updated the chart above to match their datasheet. I also noticed that the PSRR of the MHzpower-2 is 71 dB. These are pretty impressive specs. Unfortunately, I haven't had a chance to test them out. Fumac, if you read this post, please remember to email me your price sheet. I also haven't read or heard any feedback from any of Huygen's customers, but I know there are a few European amplifier manufactures that are using the Huygen modules in their expensive amps.

More Hypex Announcements

Hypex, the Dutch electronics company known for their high quality class D amplifier technology, sent out a newsletter yesterday announcing a couple new products.

First, they announced a new line of switch mode power supplies designed for use with audio amplifiers, especially Hypex's own OEM series of class D amplifier modules. The first one, the SMPS180, will be available some time this summer ('08).

The second announcement was for their new 2500W (yes, this was not a typo, it is 2500W not 250W) class D module, called the UCD2kW. It will also be available coming up this summer ('08).

Web Anonymity Bites Back

One of the class D amp / SMPS module manufacturers I've been watching is the Spanish company, Coldamp. The owner/designer's name is Sergio Sanchez Moreno. Coldamp is one of the few companies that offer both an audio grade switching power supply (SMPS) and class D amplifier modules. The advantage to the SMPS, especially with a multichannel product, is the decreased weight and size. The challenge is to get them to sound as good as a linear supply. Sergio claimed Coldamp's SMPS sounded better than linear supplies and several DIY'ers from the diyAudio forum supported this claim. They also claimed the Coldamp class D amps were comparable to Hypex's highly regarded UCD amps. I don't think anyone was suggesting that they were better. Just different, but in a positive way. Several DIY'ers were satisfied with using a combination of the Hypex UCD amps with Coldamp's SMPS.

Anyhow, we are following the progress that all designers are making with both class D amps and SMPS development. Probably the most respected designer, Hypex's Bruno Putzey, was just written up in IEEE Spectrum magazine. You can read the online version of the article here.

I have also noticed that our blog regularly gets several hits from people doing a Google search for Coldamp. So obviously there is some interest in their products that seem to direct traffic to our blog. Since we have a few posts announcing Coldamp's products (see: Coldamp Plans to Offer 750W Class-D Amp Module), I felt obligated to update our readers with some disappointing news. The moderators of diyAudio have confirmed that Sergio was also signing on with another alias, named Pierre, claiming to be a happy Coldamp customer. It appears Sergio was using this alias on other websites as well. Most of the time, he was posting as just a very satisfied Coldamp user, sharing his experience with others looking for advice. As misleading as this may be, sometimes Pierre's posts were basic design and engineering questions directed to the experienced engineer's on the forum. These experienced engineers are particularly upset with this deception since they may have helped a potential competitor. They are also shocked that many of Pierre's questions were so basic that it demonstrated a fairly elementary level of expertise with the technology. One experienced designer/engineer named JohnW, stated, "Reading back though the "Questions" posted as Pierre; some are at such a basic fundamental level that they should never have been asked by a competent designer already SELLING SMPS!" Another diyAudio forum member, Eva responds, "The main problem is not how a designer gathers the knowledge, it's the fact that it's completely unfair to advertise and sell your very first prototypes as if they were state-of-the-art class D and SMPS, when they are full of hidden pitfalls that you don't know how to solve or don't know about at all because you still have a lot to learn."

Since this discovery, Sergio and his alias, Pierre have been banned from diyAudio's forums. I've also noticed that Coldamp's website is now down. So it appears they might be out of business. I think this is extremely unfortunate. Hopefully, Sergio and Coldamp can come straight and avoid a total collapse. Some of Coldamp's customers have posted in the diyAudio thread that they are happy with their purchases and felt the service and support from Coldamp has been very good. They work and apparently many people say they sound great. The problem is with how they learned to build class D and SMPS products, and are they really going to be safe and reliable over the long term?

Here's the diyAudio thread, in case you want to read more comments and judge for yourselves.

Go Green with Class D Amps

Here's an article from Electronic Design that talks about the advantages of running a Class D amp when compared to other amplifier designs with regard to power efficiency.

They explain that an amplifier works by applying a voltage of alternating polarity to a loudspeaker, driving it back and forth to move the air that produces the sound. The amp basically has 2 power rails for the + and - polarity voltages.

With a Class A amp, both switches are on simultaneously to create the required voltage, so they're only about 15% efficient. This means that only 15% of the power is used to drive the speakers. The other 85% is lost as heat. That's why the higher power (over 100W) Class A amps are usually pretty large and include massive heat sinks. With Class B amps, only one switch is on at a time, resulting in efficiencies of around 75%. Unfortunately the trade off is poorer sound quality. Class AB is a combination or compromise between A and B with both switches on simultaneously, but the non-load carrying rail was only minimally on. This improved the sound, but only resulted in efficiencies of about 30% due to switching losses. The Class D amp does this by switching these voltages on and off. With the Class D amps, the switching losses are very low resulting in an overall efficiency of more than 90% with very good sound quality.

Read the article if you are interested in more of the details.

Coldamp Plans to Offer 750W Class-D Amp Module

I also came across an announcement from another potential supplier of amplifier modules.

Coldamp, another Class-D amplifier module manufacturer, recently announced they are developing a bigger amp module. Here's what owner Sergio posted in the diyAudio forums:

Now that you ask... the module you are referring to is to be launched at the end of March, we are making the production boards after having tested the prototypes throughly.

We are really very proud of it: it can produce >750W at 4ohm with no problem (more with lower loads) and it does it happily, with more than 30A peak current capability (electronically limited). Some features...

• Needs only a symmetrical supply. No need for input voltages, driver voltages, etc. It has a small switching DC/DC converter inside so power dissipation is extremely low (around 8W at +/-85V rails with no signal). So it is even more efficient than BP4078 but with more power.
• It has a header for what we call "input plug-in boards": small PCBs (10x20mm) that implement high pass filter, low pass filters, etc. and that very very cheap and easy to install. Making a triamp application is extremely simple by simply installing the suitable plug-in board in each amplifier.
• Small sized (80x95mm) rugged flat-base chassis, allowing top mounting on heatsinks (similar to VICOR half-brick dc/dc converters) and also the usual inserts for bottom mounting on a chassis, like in the BP4078.

...All this with the extremely good sound and abundant features of the successful BP4078: clipping indicator, on/off control, sync capability, lossless overcurrent, undervoltage and overvoltage protections, etc.

We have also designed a special version of our most powerful switching power supply, SPS80HV, to feed one of this modules at full power, with +/-85V rails.

Best regards,
Sergio

It would really be great if there were standard physical sizes for these amp modules. Similar to what we have for hard drives, like half-height, full-height, etc. There would be a standard size for 100W modules, 200W, 400W, up to 800W. Then they could fit into a standardized cartridge or some kind of enclosure. So if someone were to buy one of our systems, the chassis could work with several configurations. If a newer, better amp module is developed (like the ones from Coldamp or Hypex) the customer can upgrade their system by swapping out the older amp modules. So far, none of these manufacturers have shown any interest in this sort of thing, but we'll keep pursuing this.

Hypex has a 700W module as well, but I doubt we will ever use these in our multichannel products unless there is a lot of demand.

More Information on the new UcD Amplifiers

Jan-Peter responded to more diyAudio inquiries with the following information:

We have taken our time to review a lot of different brands of capacitors, the caps we have chosen perform extremely nice. To be honest we are very happy to find such a good performing capacitor.

The complete list of changes are:

• Audiophile version of the UcD Modulator (small PCB).
• using Mini Melf resistors and NP0 capacitors on critical places in the Modulator and around the buffer op amp.
• Audiophile decoupling capacitor, 220uF/100V. (with own printing)
• PSRR improved of the local power supply regulator for buffer stage.
• Audiophile AC coupling capacitor in input stage.
• THD further reduced.
• improved temperature stability.
• all potentiometers are Sealed Bourns 3362 P.
• optional a soon-to-be-released extra 12V full discrete regulator with extremely good specs.
• and we will use the LM4562...we love this op amp...

UcD180HG extra updated:

• better power FET, lower gate charge for faster switching/lower THD.
• the same type of output coil as the UcD400ST/AD/HG

In about 3~4 weeks we will have them available.

Exciting News from Hypex

We are using Hypex amp modules in our current prototype. So far, they are the best Class-D modules we've found and are the leading candidates for our commercial products. According to a recent post in the diyAudio Class D forum by Jan-Peter van Amerongen, Hypex's Founder and General Manager, their next generation 180W and 400W amplifier modules will receive the following upgrades:

• Audiophile version of the UcD Modulator (small PCB).
• Audiophile decoupling capacitor, 220uF/100V. (with own printing)
• PSRR improved of the local power supply regulator for buffer stage.
• Audiophile AC coupling capacitor in input stage.
• THD further reduced.
• improved temperature stability.
• optional a soon-to-be-released extra 12V full discrete regulater with extreem good specs.
• and we will use the LM4562...we love this op amp...

"It will be our state of the art product.... "

We've been very happy with the performance of the first generation, especially after a few tweeks. I can't wait to hear these. Now, I wonder when they'll finish their SMPS...

Audio DesignLine: Class D Audio Amplifiers

The Audio DesignLine website has posted a series of Class D Audio Amplifier articles. These were written by Eric Gaalaas of Analog Devices and are based on his original article which was published in EE Times magazine. Some of the data used to show the performance of Class D amplifiers in these articles is based on technology from Analog Devices, like the AD1994 Class D amplifier. The 25W AD1994 doesn't necessarily meet the performance specifications of a high end home theater system, like the Class D amplifier modules from Hypex, ICEpower or ColdAmp, because it is designed primarily for applications like automotive audio, or integration with flat panel televisions. However, this series of articles does provide a fairly good overview of the technology.

The first article, Class D Audio Amplifiers: What, Why, and How, describes the different topologies of Class A, B and A/B linear amplifiers and their power dissipation characteristics. The main point here is the Class A amps dissipate a lot of power in the form of heat (in fact, more power is dissipated than is sent to the loudspeakers), but the sound quality is very good; Class B amps don't dissipate as much power, but the sound quality isn't very good; and, Class A/B, which is a hybrid of the two, dissipate less power than Class A and a little more than Class B, but also sounds much better than Class B.

The second installment, Class D Audio Amplifiers: What, Why, and How - Part 2, describes the basic architecture of a Class D amplifier and explains how they are much more efficient with regards to power dissipation. They mention how the output efficiency effects system design and that products with less efficient amplifier topologies sometimes use large, heavy heat sinks or fans to avoid over heating the components.

In the third article, Class D Audio Amplifiers: What, Why, and How - Part 3, the author talks about Class D amplifier terminology and compares single ended to differential designs.

The fourth article, Class D Audio Amplifiers: What, Why, and How - Part 4, describes some of the challenges with Class D technology and discusses techniques for improving sound quality by using feedback circuits.

In the fifth installment, Class D Audio Amplifiers: What, Why, and How - Part 5, he discusses the modulation techniques used to convert the analog signal into pulses. The most common method used is pulse-width modulation (PWM), which is why you may find Class D amplifiers sometimes referred to as PWM amplifiers. The PWM modulators may have problems with distortion in some implementations and can generate EMI (electromagnetic interference). The author also explains that with PWM, pulse widths become very small near full modulation, and because of the limited drive capability of the output-stage gate-driver, which cannot switch fast enough to produce the very short pulses, it is almost impossible to get full modulation. This means you cannot achieve full theoretical power. Alternatives to PWM include pulse-density modulation or PDM, which has an advantage when it comes to EMI, but has limited power efficiency. Another alternative, uses a self oscillating technique instead of the fixed frequency modulator used with PWM. This is the method used with the Hypex amplifers that we included in our prototype system. The self oscillating amplifier avoids some of the problems associated with PWM.

The sixth article, Class D Audio Amplifiers: What, Why, and How - Part 6, mentions that the high-frequency components of a Class D amplifier can generate a lot of EMI, which can interfere with the operation of other nearby equipment. The author then discusses several techniques used to minimize EMI.

The seventh and final article in the series, Class D Audio Amplifiers: What, Why, and How - Part 7, talks about the cost savings associated with audio systems that use Class D amplifiers. These costs savings are due to the higher efficiency of the Class D amplifers. Since they don't generate nearly as much heat, the systems don't need the large expensive heat sinks and chassis. However, the advanced circuitry for feedback loops and filtering adds to the expense. So in reality, using Class D amplifiers doesn't necessarily mean they will be less expensive than a system that uses Class A/B amplifiers.

Open Architecture

In previous posts I've mentioned that we'd really like to design a product that has the modularity and flexibility of the personal computer. Not the closed or proprietary architecture of the Mac, but the open architecture of the PC. Then people could choose the amp modules, power supplies, case, audio interface (soundcard), etc., that would meet their needs for number of channels, sound quality and budget.

From Wikipedia:

"Open architecture is a type of computer architecture that allows users to upgrade their hardware in all of the computer hardware & components (for example the IBM PC had an open architecture). This is the opposite of a closed architecture, where the hardware manufacturer chooses the components, and they are not generally upgradable (for example the Amiga 500 home computer had a closed architecture).

Open architecture allows potential users to see inside all or parts of the architecture without any proprietary constraints. Typically, an open architecture publishes all or parts of its architecture that the developer or integrator wants to share. The open business processes involved with an open architecture may require some license agreements between entities sharing the architecture information."

I'm not sure if we will ever be able to do this, but it is something I am interested in achieving. I think there is great potential here. It may even turn part of the consumer electronics industry upside down or inside out. Of course, this may not appeal to the ultra expensive, high end, "audiophile" producers and consumers, but I think it would really be great for the rest of us.

What do you think? As a consumer, would you like to purchase a system that could be expanded from 2 channels to 8 channels? Or upgrade the DACs or amplifier modules when a new generation is released? Be able to choose from a variety of case manufacturers to have one that best fits your style?

If there are any reps from manufacturers of amplifier modules, power supplies (the best technology for this would be switching power supplies or SMPS), or sound cards reading this, I'd love to hear what you think about this idea? Do you think it would expand your market, or not? Do you think the technical hurdles for designing your components to meet a specific form factor and use of standard connectors would be too limiting? Maybe someone like Creative would offer a version of their X-Fi that would be compatible -- and like the "Intel Inside" promo, they could have "X-Fi" inside. Of course, we could also have "UCD powered", etc.

So, When Will It Ship?

I've been asked several times about the ship date for our product. I don't have an answer for that, but I can tell you about the changes or improvements we need to make to the current prototype before we are ready to ship a commercial product. In this post, I'll give a general overview of improvements needed for each of these subsystems:

1. the chassis
   
2. power supplies
   
3. amplifier modules
   
4. soundcard section
   a. computer interface
   b. drivers/software
   c. digital/analog section - DACs, ADC, etc.
   

I will provide more detailed information about each of these sections in future posts.

As you can see from the prototype photos, the current chassis is not something many people would want in their living or family rooms, unless they're really into the industrial design style. They actually might look kind of cool in an a loft space or something, but that is sooo 90's :). So we need to come up with a more aesthetically pleasing design. We would also like to minimize the size and weight, and allow for optimal heat dissipation. Fortunately, the internal components are relatively small and don't generate too much heat so we should be able to create a chassis that isn't a monster. We'd also really like to design a chassis that would let do-it-yourself (DIY) people build or upgrade their own systems. Much like you can do with PC today. This means the inside of the chassis would include the framing to mount things like power supplies, the printed circuit boards and amp modules. Ideally, the amp modules would simply slide into slots in the back of the chassis.

The main changes we plan to make with the power supplies for our commercial product will be to replace the linear power supplies with switch mode power supplies (SMPS). The latest SMPS technology designed for audio applications is very promising. Compared to general purpose SMPS, the SMPS designed for audio applications usually have much larger capacitors to provide a larger energy reserve for the faster and deeper current demands. General purpose SMPSs are typically designed for fairly constant loads, so they don't usually have large enough capacitance at the outputs for audio applications and adding capacitance to a general purpose SMPS wouldn't work very well because the feedback circuit doesn't take into account this additional capacitance and the added phase shift and oscillation would make it unstable. The main benefit with using the SMPS instead of the linear supplies is since they operate at a much higher frequency, they can be much smaller and lighter than the equivalently powered linear supplies we were using. Since a SMPS recharges its capacitors about 1000 times faster than the rate of a linear power supply, which needs a fairly large transformer and big capacitors to keep up with the current demand, the SMPS can get by with smaller capacitors.

We are pretty pleased with the amplifier modules in the conceptual prototype. The amp modules we've tested are from Hypex Electronics, a Dutch amplifier manufacturer who has developed a very good reputation for high quality products. There are a few things that can be done to optimize these for our application, which will be done if we decide to use their UcD amps in our commercial products. Since we started this business, we have discovered a few other class-D amplifier modules from other manufacturers worth considering. And there is also the possibility of developing our own class-D amp, but unlikely considering the development costs and time. To accommodate our modular chassis design, we would really like to find an amp module that will fit into a small enclosure. This enclosure would be similar to the case of a hard disk drive. It would protect the circuit components, dissipate heat and would allow for an easy method to insert the amp into the back panel of the chassis. If the sizes were standardized, you could upgrade or replace amp modules when newer, better designs were available by simply unplugging the old amp and replacing with the new. We would also be happy to support more than one amplifier manufacturer. Some of the class-D amp modules have a reputation for being very accurate and transparent to the source. These amps sound great, but if the source material isn't very good, like a poor recording, the flaws are pretty noticeable. Other class-D amp modules might be a little more forgiving of these types of recordings. I guess it all depends on your listening preferences. I think it would be nice to have a choice. Now, if only we can find a few manufacturers to work with us on a design for these standard amp cartridges. Wouldn't it be great to have the options of different amp modules just like you currently have with hard drives or video graphics cards?

The soundcard section is where we have the most work ahead of us. The current unit in our conceptual prototype was designed primarily for pro-audio applications - recording and mixing. There are quite a few components that aren't needed in a music playback or home theater system. For example, we don't need 8 balanced inputs if the audio source is the PC. The analog outputs of the pro-audio soundcards are good and usually sound better than your average A/V receiver, but they may not sound quite as good as the high-end dedicated preamp/processors. Their outputs are designed to be good enough for an audio engineer to monitor a mix, but might not meet the needs of someone that is really into critical listening. Our goal is to design a soundcard that sounds as good as some of the high-end dedicated prepros, but at a much lower cost. We've also got a lot of work to do on the software - both the drivers and the control panel applets for controlling things like volume, channel mixing, etc.

Like I said, we'll cover each of these areas in a little more detail in future posts. Please let me know what topics you would like to learn about first.