Category: audio


A couple of years ago I decided to build myself some class-d amps based on the Hypex NC400 modules.  I had also designed some custom billet aluminum cases but I knew they were going to take a while so I put them in temporary enclosures.  I had noticed during the summer months when the weather was warmer, one channel would click off.  I finally figured out it was thermal shutdown and so I turned the case over and put some metal objects on top to act as heat sinks.

Fast forward to a couple weeks ago, I needed to turn my equipment off to make some changes to the setup.  It took me overnight to make all of the changes and when I went to plug the amps in the next day, neither would turn on.  No signs of life at all.  No clicks, no lights, nothing.  I was a little confused that both could die at the same time.  They are in separate cases on opposite sides of the room but when I popped them open, I reached for my cap wizard and started testing out some of the caps in the power supply.  Turned out several were cooked.  Some did not even move the needle on the cap wizard.  To my suprise, even one of the largest caps, a 820uf @ 200v, had drifted far out of spec.

I decided I would just replace all of the caps on the power supply boards because I wanted to make sure they were perfectly matched and I figured they all probably have a shortened life span from the heat they incurred.  My first task was to remove and map out all of the caps.  To get to the 2 largest caps on the board, the large heatsink HS1 needed to be removed.  In order to remove that large heat sink, R2 needed to first be removed to access the screw holding D43 to the heat sink.  After I got that out of the way, then I could  remove and catalog the caps.  This board is not particularly easy to work with.  The holes are drilled with very small tolerances compared to most.  This means you really need to get all of the solder out of the holes or the new components won’t go in easily.

4x 820uf 200v (C1, C15)
16x 220uf 35v (C3, C4, C5, C6, C7, C8, C13, C14)
4x 22uf 63v (C22,C26)
2x 470uf 50v (C9)
12x 100uf 100v (C10, C11, C12, C19, C20, C21)

After that, I ordered the caps for about $40 shipped and replaced them when they showed up.  So far so good.  Everything seems to be working again.  Lesson learned.  Even though these amps use a very small amount of power and run very cool for their power outputs, cooling is still super important.  I would suggest having plenty of cross-ventilation in your cases.  Make sure you leave adequate distance between the amp and power supply.  Also make sure your NC400 module is attached to a larger and thicker piece of metal to properly cool it.  Apparently a smallish piece of light gauge aluminum is not adequate when in an enclosed space.  If you need to replace your caps, ONLY use 105 degree varieties and use the ones rated for the most amount of hours at that temperature.

NC400 & SMPS600

This may seem like an obvious thing to some folks but it might be a mystery to others so I’m writing up a short post.

I have been recently working on sweepers for the ISD Podcast and Rick sent me a garage band file with a few audio clips that I didn’t have in my collection.  I wanted to extract these clips so I could cut them up and rework them with a tool such as Audacity.

From the finder, I simply right-clicked on the garage band file and clicked “show package contents”.  From there, I looked in the “media” folder that showed up and all the audio clips I needed were right there so I copied them out so I could work on them.

Airtunes and the emu 0404

I’ve had my stereo system since 1994. For electronics that is getting old but I bought good stuff to begin with so I’ll continue to use it for many more years. It’s a Marantz system with the MA500 monoblocks that they made for years and years. It has a single cd player since that was the best I could afford as a teenager and I don’t mind changing the disc manually. All in all, it still sounds good but I was shopping in Canada with my wife’s uncle who is a real audio nut. We were at a store and I kept seeing these Sonos boxes everywhere so I asked for a demo. The salesman was really excited about it and I could see why. It basically allows you to stream audio from Napster, your pc or hundreds of Internet radio stations. The quality was entirely dependent on the bit rate of the source recording.

Needless to say I was very impressed with this setup. Of course the fact they had it hooked to a $2,000 Bryston DAC didn’t hurt I’m sure. After coming back home I did some research to figure out how I could set up something similar at home.

I hadn’t ripped my music collection yet so I had the opportunity to chose a format. I decided to go with Apple lossless. There are a couple of reasons for this. First off, it’s lossless. This means when it’s decompressed, it is bit-perfect when compared with the original wavform. The second reason is because of the transport mechanism I chose which is the Apple Airport Express. When the audio is sent across the network for playback, it is converted from whatever native format into Apple lossless anyways so I thought it would be prudent to save a step.

My “transport” the Airport Express looks just like the AC adapter for my Macbook Pro only without the cord. It has a network jack for setup and for certain uses and also has a 1/8″ audio jack that has analog and digital optical output. This is the key to my setup. With that digital output, I was able to feed the input on my new Emu 0404 USB DAC.

Is the DAC worth the extra $185 it added to my setup? YES! It made the sound noticeably clearer and crisper. Listening without the DAC, it sounds like hooking up an iPod direct to your stereo. It decent, not as bad as tape but definitely not as good as a CD. With the DAC the audio actually sounds better than my CD player. To be fair, my CD player is over 15 years old so it’s to be expected that DAC technology has come a long way since then.

The last piece of the puzzle is the interface. For this, I purchased a used iPod touch off Craigslist. There is a remote app in the iTunes store that allows you to browse your collection and playlists. It also allows you to turn on and off your speakers. This is cool because you can have several Airport Expresses in the house but choose which ones are playing at any given time. It also allows you to turn off the speakers on your computer if you desire.

There are a couple of caveats to my setup. First off, my Macbook has to be turned on, in the house and iTunes has to be open. Next, don’t try to hook anything else to the DAC. The inputs are not isolated even though it looks as if they should be. Lastly, wifi and wired networks are not perfect. I have not had many glitches and almost all have been when I’ve been downloading Linux ISO’s or something similar. Not a big deal but something to be aware of.

Overall, I’m totally satisfied with this setup. I’m confident it would sound good on a far more expensive setup than mine even. Furthermore, there is no reason someone couldn’t feed a $2,000 Bryston DAC with the Airport Express and theoretically have an even better system. I thought about it for a minute but then remembered that my wife would probably leave my if I spent $2,000 on something like that. The emu 0404 is a secret gem in the audiophiles community. It is not well respected because it look like pro audio gear instead of audiophile gear but don’t let that put you off. I’ve people spend way more for less true benefit. Cable stands and hospital grade power cords anyone?

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