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  1. Shahriar

    Choosing PA for my 3-way active Cross over circuit

    Hi I want to build this Active 3-way cross-over circuit. But I do Not kow how to choose Power amplifiers. Here the problems: 1- If I choose a 15W subwoofer and a 15W STK power Amplier (STK4121) for it then what kind of Midrange and tweeter will be needed? Does it mean I have to choose a 15w...
  2. Shahriar

    Pc Resets after a while. Where to look for the Probelm?

    Hi I am trying to repair Some ATX power Supplies.but some of them do not have ordinary faults. Most of them are in these two categories. 1- The computer assembler told me that with this bad PS, computer is working well but after a while (i.e. 10 Minutes or more) it will resets. but when they...
  3. Shahriar

    How this regulator works?

    Hi Look at the this OLD ATX power supply. Can somebody explain how the 3.3V regulatosr built around TL431 IC works. It looks like a Shunt regulator but very strange. I know How TL431 works but can't understand this circuit. i.e. if Q13 Current changes, how does this affect 3.3V rail. (look at...
  4. Shahriar

    85C Cap ESR vs 105C Cap ESR!

    Hi I can remind some times ago some one has written that it is better to replace 85'C Caps with 105C caps in old devices. (I think it was audioguru) Today, I was reading an article about SMPS troubleshooting. Look what a repair man has said: "(From: Jeroen H. Stessen...
  5. Shahriar

    50Hz when you touch Oscilloscope probe

    why when you touch Oscilloscope probe a 50Hz signal will appear? I think it should be related somehow to  Earth connecttion. ThanX Shahriar
  6. Shahriar

    What si that series resistor with Diode in and Inductor Switch circuit?

    Hi When an inductor is to be switched by a transistor, Usually a Diode is placed in parrarell with inductor to Protect Transitor from High voltage created with Inductor when Switch turns off. (I have forgotten the English name of this diode) But sth. a Resistor is placed in series with this...
  7. Shahriar

    Does the Magnet with a Staurated Core get stronger if we Increase Current?

    Hi I want to know If I have an Electromagnet connected to a DC Voltage with a saturated Core, Can I pick up More heavy masses If I increase Current? or because the Core is saturated no difference will be? If I can, Then what is the difference between a Non-Saturated Core with a saturated core...
  8. Shahriar

    How UPS recognize a voltage fault in Line!

    Hi Does anybody know the standard solution for detecting a fault in Lines to turn on a UPS before PCs reset. ThanX Shahriar
  9. Shahriar

    How to use the ratiometric Hall effect sensor(UGN3503) in a levitron

    Hi I want to build a levitron by using a PWM IC (UC3843). I explain the PWM Controller behavior as below very simple to explain my problem. PWM=1 if VFB < 2.5V (Controller Vref) PWM=0 if VFB > 2.5V In most of Levitrons on the web, The sensor is placed near the ElectroMagnet. the...
  10. Shahriar

    Noise Measuring Unit Meaning!

    Hi I was reading an article about a Regulator and it was witten as below: "" Figure 1 combines low noise components and extra filtering to achieve an output noise floor of only 6 nV/Sqr(Hz).  " Can Anybody tell me what does "nV/Sqr(Hz)" Mean! Of course the electronic Meaning, I know the...
  11. Shahriar

    Download Elektor Journal Here...

    Hi One of my friends has uploaded this Journal in the link Below. I Put it here. Maybe others like it. http://www.4shared.com/file/1212367/9d46f8df/elektor_january_2006.html PASSWORD = vampire ُShahriar
  12. Shahriar

    How to add a mute system to an OpAmp

    Hi I have an OpAMp (NE5532) which is driving a Headphone. I want to add a Mute System to this circuit. How is it possible whether it has a Dual Supply or single Supply. (If it differs) ThanX in advance Sahriar
  13. Shahriar

    Data Transferrinf Over a 25 Meter Wire.

    Hi I am designing a new Language laboratory System. I want to send serial data via a Common bus to all Stations (Students devices). The length of this bus is around 20-25 meters. Which method is the best for transferring Data. I mean FSK, RJ485 (if I wrote it right), SPI (that I don't think it...
  14. Shahriar

    Why Sink current is higher than Source current?

    Hi Can anybody tell that why Sink Current in most of Integrated circuits are higher than Source current. i.e. a TTL Gate can sink around 20mA while it can not source more than 10mA. (The Numbers I said are not very sharp.) ThanX Shahriar
  15. Shahriar

    You can download OpAmp hand bokk here!

    Hi Follow the links below. when you downloaded all 13 links, then extract number one to creat a PDF. This book is in 877 pages and one of my friends has uploaded it. http://www.4shared.com/file/811501/4b4cfb69/OpAmpApplicationsHandbook__2005_part01.html...
  16. Shahriar

    Video Multiplexing system!

    Hi I want to build a Video Multiplexing device, Which can show a single video picture on a big screen which has been consist of 4 or 16 or more single screens (CRT or LCD). I have tried to show what I mean in the attached picture. This project is just like those in TV SHows that show the...
  17. Shahriar

    Library Aid Device

    Hi Have you ever gone to a Library, and when you are reading a book, you need to take some notes of the book. You have probably found it disgusting! The Problem is worse, when there is a picture in that section. If there was a device which you could take it to library, and when you need to...
  18. Shahriar

    433 MHz RF Amplifier!

    Hi I have a 433MHz TX and RX module which you should connect it to a 50ohm Antenna and enjoy! I plan to use a i.e. 1W RF amplifier to increase the output power. Does any body have a Schematic for this Power amplifier ThanX Shahriar
  19. Shahriar

    How To calculate the feedback resistors in an OpAmp Amplifier?

    Hi Imagine that you want to build an Inverting OpAmp Amplifier with the Gain of 30. What is the difference if I choose two resistor as (Rf=100K, R1=3.3K) or  (Rf=10K, R1=330R). In both cases the Gain is 30, but In what conditions, does it make difference? and what about a Non-Inverting One...
  20. Shahriar

    What kind of Electronic related devices are good to work as a job?

    Hi One of my friends (who has enough money) and I want to start a new job. we have disscused very much about what kind of bussiness we begin. At last we agreed to find a factory or company in another city or country(litttle bit difficulat) and tell them that we can sell their products and give...
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