The Logitech Z-2300 is a 200 watt THX®-certified 2.1 speaker system with a 8-inch long-throw subwoofer. I’m not going to tell you about how good or bad the system is because this is not a review, there are plenty of good reviews out there, just google for one. My Z-2300 worked perfectly for about 2 years but during the thirds year or so I started noticing a small hum coming out of the subwoofer no matter if it was a low or high volume, input connected or disconnected. It bothered me for quite some time but then I got used to it, until recently when I felt that the hum had increased its intensity and I couldn’t stand it anymore.

In the past few weeks I was constantly thinking that I need to fix it someday but I was thinking that I’m going to need to replace some capacitors that’s going to need some de-soldering, getting the right replacement soldering back together, this proved to be a wrong assumption as the fixing was much easier.

First of all you should start by removing the front grill. I used some small flat screwdrivers inserted between the grill and the plastic ring, first lfet-right, next top-bottom. I think the grill was glued a bit and took some force to get it to move. I managed to take mine out without any visible scratches or dents. There’s also a video on youtube, the guy recommends a hair drier:

Logitech Z-2300 Subwoofer

Next you have to remove the 8 screws holding the woofer in place, after those are out slowly take out the woofer, hold it strongly cause the big magnet on the back might jump&stick to the toroidal transformers on the bottom of the subwoofer case. Remove the connectors and take the woofer out, this will allow us to pull the PCB on the back further out so we can work on it. If the zip ties holding the cable secured to the box are too tight you can cut them, but be careful not to cut any cable, and make sure you have replacements cause you don’t want the cable to be moving around synchronized with the bass 🙂

Logitech Z-2300 Subwoofer

Next move on to the back of the subwoofer. Here you’ll have to take out all of the screws(22 of them) surrounding the metal plate. Now the backplate is kind off glued and stuck if you never opened it before so you’re gonna have to grab the heatsink firmly and give it a good twist as well as pulling on it, but be careful cause all the wires are attached to it and you can only pull it back about ~4 inches. After it pops out, look for the wires that are keeping you from pulling it further back. I had the woofer wires (black+red), I had to cut some more zip-ties to release them, and I could finally take a look at the board.

Logitech Z-2300 Subwoofer

Although its hard to spot in the picture above, I spotted a potential problem. It’s circled in red in the photo. It should help you understand whether your problem is the same as what I have experienced, it’s one of those crimping connectors used to secure 2 cables together.The black cable (ground) originally comes from the toroidal transformer placed on the other side of the box. Then when it comes close to the PCB I don’t why the guys from Logitech decided to split it, and have another small piece of black wire going to the PCB. I really don’t understand, couldn’t they’ve just used a whole piece of cable? Anyway as I was talking to a friend of mine, this seems to be a very common cause for getting noises in amplifiers, broken ground circuit.In my case the crimping connector wasn’t holding the cables tight anymore so there was an imperfect ground connection from the transformer to the PCB.

Logitech Z-2300 Subwoofer

In the above pictures you can see how I removed the crimping connector and I soldered the two ground wires together. Next some heat shrink tubing to protect the connection and the noise was gone. Put everything back together and now I can even  pump up the volume to the max with the input disconnected and there is very little noise coming out of the speakers. No wonder the z-2300 has SNR >100 dB and they’re  THX®-certified. I hope this helps you if you have the same problem.

DIY Mp3 Player Based On PIC16F877

This pocket sized mp3 player is based on Microchip PIC16F877 and comes with both C and Assembly source code but the C code version has more features and stability. The mp3 player was designed to work with compact flash cards up to 100 gigabytes. For decoding it uses the VS1001K chip and for conversion it uses the built in DAC. The principle of operation is not very complicated, the PIC reads the CF card and once it finds a file it clocks the card 512 times per sector sending all the information one byte at a time to the decoder chip. The decoder gets a valid stream of data and sound comes out of the built in DAC. The project doesn’t have a display or a fancy menu, it’s just a plain simple mp3 player.

DIY Mp3 Player Based On PIC16F877: [link]

September 14th, 2009

Infinite Baffle Loudspeaker

Infinite baffle speaker

Since I started being interested in audio, I’ve seen all kinds of speaker designs, weird arrangements and weird geometries. From all those speakers, in terms of extremely low frequency reproduction the best ones where the infinite baffle subwoofers. Those setups go easily down to frequencies like 10Hz. You may say these figures are useless with a musical program and normally i would agree but if we are in a quest for perfection i would say it’s mandatory. Even if our music doesn’t have much information below 27Hz (lowest note on a grand piano, though pipe organs go even lower) it is important to have the roll off region in frequency response at least an octave lower.

The reason for this is that the speaker and the cabinet box form a high pass filter and like with all filters it will add lots of delay in the slope region which may affect the quality of the reproduction. For Home Theater applications response down to teen frequencies becomes a necessity. If you look at the spectrogram of a .50 Barret rifle shooting sound you will see the most information is in the 10 to 20 Hz area. You may not hear the 10Hz but you will certainly feel it, much like if you would be standing next to the rifle.

The principle of IB (Infinite Baffle) is to install the woofers on a panel that is wide enough so that the waves coming from the back of the woofer never meet the waves coming from the front of the woofer. Looking at the wavelength of a 10Hz sine you will see you need a very big panel. However IB can also be done if you put the woofer in a box big enough so that it has zero damping. Custom HT rooms have the woofers mounted on a sealing or floor and have the attic or basement act as that big cabinet box.

In this project I’m presenting the author build a speaker on a panel to fit a door way and have an entire room to isolate the back waves from the woofers. He is referring to the Hoffman’s Iron Law that says: having efficiency, low frequency response and box volume one must sacrifice one of the three to have the other two. IB of course sacrifices box volume. There are some who argue this Law, because it actually holds true if you place the subwoofer in an open environment. Closed spaces have gain that will  your low frequencies even if your speaker loses efficiency, and here by speaker i mean the woofer plus cabinet. Woofer’s efficiency is constant.

Another thing is nowadays Hoffman’s Iron Law can easily be defeated with powerful woofers and equalizers. There are woofers that can take tons of power and have huge excursion and can go really low in small enough boxes. Returning to the IB setups you will also need high excursion woofers and high pass filter on your amplifier with a corner frequency between 5 and 10Hz, sometimes higher depending on the woofer your using. You will need high excursion because the woofer won’t be damped at all so it will be free to move. At high powers and low frequencies it will move allot.

In this project the author didn’t built a subwoofer but a full-range infinite baffle speaker. I don’t see the point of this expect for a center channel. He used 8 x 12″ woofers for the low frequency part. If the woofers aren’t such quality it’s better to use many of them, this way the stress will be divided between them. When i first saw the baffle i thought it is too thin to hold the eight woofers. But then i saw the bracing on the back, and that will make it more rigid for sure.

The tweeters are piezo which in my opinion are not that great. Also the crossover i think could use more work. I always liked higher orders crossovers because they give you allot more dynamic range. The whole system reaches 96dB/W/m, which is very nice. Is a nice and fun build, and even if it won’t live up to your expectations at least you will have a sonic weapon.

Infinite Baffle Loudspeaker: [Link][Via]

Miniature tube headphone amp

I’ve always thought certain sound pressure levels need to be achieved in order to be engulfed in music. This effect is most noticeable when music comes from loudspeakers and that is because when sound is played at low levels, the perception is affected by ambient noise. Even late at night when things are quiet and you don’t want to disturb people around you, there is still noise. A clock on the wall, a pet, you computer, a cooling fan, some kind of noise will disturb your listening experience. Things are not the same with headphones though. You put it on your ears and outside world is gone.

There are plenty of good headphones on the market, giving good level of detail, good frequency response, and good sound-stage. But there are some drawbacks to using headphones. You will not feel the same impact and if you don’t chose your headphone carefully you will feel fatigue after long listening time. Another thing to consider is that with speakers you can move them around the room to get the response that most suites your tastes, something that you can’t do with headphones. This is way the amplifier that drives them plays a huge role in a headphone setup.

Everyone who has a passion for audio knows about the qualities of tube amplifiers. The problems with these amps is that they are big and heavy, pretty hard to build and operating at dangerous high voltages. This usually discourages most Do-It-Yourselfers. However Mark Houston built a headphone amplifier that is battery powered and it’s small enough to fit in a pocket.

Mark used Raytheon JAN6418 Tubes in his project. These miniature tubes are pentodes made in USA and you can find them in a kit sold by Oatley Electronics. The amplifiers uses one tube per channel in common cathode configuration followed by a buffer to be able to drive lower impedance headphones. The buffer is a low distortion IC PT2308, a class AB CMOS headphone driver.  This IC has an impressive SNR of 110dB so it’s well suited for this application. The output impedance of tubes in common cathode is high so higher value resistors in the driver’s feedback loop are needed. The 6418 tubes need 1.2V to heat their filament. A 5V regulator chip heats the two filaments connected in series through a 270 ohm resistor.

This amplifier can also be used as a preamp. Mark did some modifications to component quality, replacing the PT2308 with a OPA2134 IC for example. There are also some scope traces he shows in his article measured with a load of 47k. I would’ve been curious to see how it performs at much lower loads. All being said, Mark is pleased with the sound, and with tubes you can not possibly go wrong, can you?

Miniature tube headphone amplifier: [Link]

August 28th, 2009

yPod MP3 Player

yPod MP3 Player

There are countless MP3 players projects out there, and building your own is not the most difficult task a portable music player enthusiast can undertake. What’s different about this project right here though is the fact that it’s designer claims it’s faster and cheaper than all the others. That may or may not be true, but it’s worth taking a closer look.

The yPod is based on a microcontroller from Atmel’s ARM7 processor family. The player has a 1.6″ color LCD and a 5-way switch for user control and is powered by a 650 mAh Li-Ion battery that is charged using the USB port. This is also used for firmware updates and music uploading. The player’s memory consists of a Micro SD card and the headphones connect to a 3.5mm jack. The board has a 4-layer PCB design. In terms of software, the player makes use of the VLSI VS1033 MPEG3 codec and supports MP3, WMA, AAC and WAV formats. The yPod is pretty small, having 65 x 45 x 14mm dimensions and weighing only 65g, so it fits and any pocket.

The original project was designed by Jesper Hansen and he provides a lot of additional information, schematics and source code on his homepage. The project presented here is based on Hansen’s work and makes some hardware modifications, having a DS1337 RTC chip and a crystal added, that provide a clock feature with time and date. Two firmware versions are available for download, one for each implementation, and are both released under GNU General Public License, free for use.

yPod MP3 Player: [Link]

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