Savel brain dump in English!

Maybe you noticed, that new home cinema systems, LCD/Plasma screens, receivers have very small amplifiers. Physically small. But the power output is quite big. And there is no big, heavy heatsinks on these devices. And no big transformers. At a first glance I thought that all this output power is represented in “Chinese wats”. But in this case, the wats are real. And these devices are using “digital” D-class amplifiers.

What a hell is D-Class amplifier? It is old-new invention- digital amplifier. “Digital” means only one bit The analog output is made using pulse width modulation (PWM) output. Some sound is converted to digital form using CPU ar special chips and this PWM sygnal is fed to powerfull MOSFETS. Real DAC conversion is made on small inductors near the output.

Here is image of one such amp:

I removed small heatsink from the top of chips. There is no need for big heatsinks as efficiency of such amp is about 90% (acording datasheet).

Here is closeup of the PCB. Note the size of SMD resistors and compare to the size of the chips. Chip is TAS5111 and TAS5112 made by Texas Instruments.

TAS5111 is buwoofer driver. Output of the chip is 70W RMS (@ 0,2% THD+N), 95dB dynamic range. And all this for single polarity 30V PSU (3.3V for logic). Other chip, TAS5112 is stereo amp (two channels) 2 x 50W (@ 0,2% THD+N).

The principle of operation is very simple. PWM sygnal from sound processor is fed to the chip. The chip is driving output mosfets in H-Bridge connection. As there are two PWM channels, the output is connected in full bridge. The chip is full of various protection circuits. All DAC is made on quite small 10uH coils (blue cylinders on PCB).

All amp is 6+1. Total 370W RMS from board sized like a CD box. Heat sink need to sink only 40W of heat during max load!

This particular board is damaged, I didn’t examined what is bad is this PCB, I picked up this PCB for weblog ilustration only.

This weblog entry is more interesting for Lithuanian readers. It is about our biggest internet provider and the problems related to DSL connection.

Nice title?

I am using cheapest DSL service at home. It is working only on evenings and weekdays. And speed is very slow- limited to 256kbits. But the cost is very low (check TEO webpages for rates).

My telephone line is quite old, and cable from crossbox somewhere in the begining of the street (about 1km from my home) is damaged. There is so called “semigrounded” pair. Sometimes I can hear AM radio in my phone… But I don’t use my phone for voice calls, I use it for my DSL connection. Few times I asked telephone company to repair, but due to private property problems they didn’t managed to swith pairs in the cable to select better wires.

So I didn’t cared about bad insternet connection. I blamed bad, old cable. Until one morning. I started my computer and noticed, that there is internet (in the morning). But must not have any internet at this time. I checked the internet by downloading some bigger file from rapidshare… wow! The speed was incredible and now lags and no “web page not found, no DNS” errors!

After some time I’ve made this screenshot, the speed increased upto 347 kilobytes per second (2.8 Mbit).

I started all internet leaching software I have. Bittorent and eMule speed was about 90…100 kilobytes per second. (Bittorent log show 1120 kB/s maximum working with eMule at same time). I started these, connection hungry, programs just to test if there is some session limitation. Normaly, bittorent and emule opened too many sesions and DLS connected freezed. Now, no problems at all!

And DNS server is working without any problems. In regular way, sometimes it lost packets and didn’t replay to DNS requests…

So I’ve made decision, that speed limitation software used in ISP TEO.LT is buggy. Also, that I have limitations in session number and this limitation is not stated in my contract!

Same effect I can achieve if I select very expensive “full speed” option in my DSL settings. I receive up to 5Mbit/s speed and no lags!
And don’t blame bad cable.

WRT54G or WRT54GL is well known Linksys/Cisco Systems wireless router. It is famous for its third party firmware. But be aware, new model sold in shop are neutered, the ROM and RAM size are reduced. Look for version with “L” index. It is rumours, that original router with new firmware became to good and was working better that “professional” models for Cisco company. So they neutered and removed some ROM and RAM chips. All these talks, that they reduced manufacture cost using smaller chips is nonsense. In our days, the price difference between 8 and 2Mbyte chips are very small. And I think is hard to get smaller chips

If you decided to get this router, it is worth to look for “L” version, unless you want to do tricks with firmware or you want to use your solder iron. If you select “L” version, more advanced options will be installed in “basic” router.

There is problem with some of these routers. Some time they hang up. One client was using “G” model with third party firmware, but he needed to reboot device from time to time. I offered him to test my personal router with “L” index, but it hang up too. At my home, this router was working fine. After more detailed investigation, I decided, that there is some problems in power supply and it’s filters. So I opened both devices and checked PCB.

Internal power suply is clasic step-down pulsed PSU. I was surprised, that manufacturer used very small and very suspicious capacitors- all caps were 25V x 220uF. Even in CPU core circuit (1.8V) and 3.3V power lines. I didn’t measured ESR, but I think the result could be very ugly.
So I decided to change this caps to bigger ones, from spare computer mainboards and VGA cards.

Here is WRT54G PCB before repair:

There is spare place for 5V regulator?

After:

Input cap is 25V x 470uF, output caps all 6.3V x 1500uF. One additional cap is soldered to empty PCB place. I detected 3.3V in that hole.

Two PCB boards for comarison: WRT54G (upper) and WRT54GL (lower). GL has 5V regulator and bigger memory (Flash ROM and RAM). I replaced all caps.

After this repair, both routers are working fine and no freezes.

Both model use third party, linux based, firmware.

In one company I was forced to install several copies of Norton Antivirus 2008. This was retail version of software in nice boxes, and I needed to enter all registration-configuration data in every computer. At a first glance, everything is very simple, just place CD, push few buttons… And I forgot that it IS Norton Antivirus. First, there were older versions of NAV in computers. Norton antivurus requested to reboot each computer twice for upgrade. And all this reboots require to enter administrator passwords…

Here is the story: go to computer, open nice box, take the CD and CD-key printed on envelope. Place CD into computer and wait for automagic install. No way! Place CD and wait for few minutes (tens of minutes- depending on the state of the computer) and then you receive message, that there is some problems with older version of NAV in this computer and need to uninstall software. Press fix-it. You jump to old version of NAV control panel- and there is RED warning that I need to dowload and install some update to remove that damn software. I killed that process and tried to uninstall software from add-remove-programs. No way, there are other users loged to this computer. And installer exited. I rebooted computer to eliminated logged users, hanguped software and other unknows reasons “not to install NAV”.
After reboot, install process continues. Then I need to register to some NAV-Symantec oline service. I don’t want, but until I didn’t register, I can’t continue configuring antivirus… But if you press “Next” ignoring red messages about invalid entries, this “registration” is skipped. After this, antivirus is loaded, and it began to worry that antvirus database is out of date. Dowloading of databases and updated took very logn time (it is not internet connection speed problem). And then… we need to restart windows.

Compared to old (7.x) version of AVG, NAV 2008 is ugly slow, time comsuming, CPU eating, silly designed and bad working software.

It took 50 minutes to install NAV2008 to old Celeron (1.6Ghz, 512Mb RAM) computer!

It is not worth such money…