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  1. autir

    bjt / jfet / mosfet as input in audio amplifier

    Hello all. I am trying to design a low power guitar amplifier using only BJTs. Since the output impedance of a guitar is high, I was thinking of using a jfet instead of a bjt as the first stage. The problem is, I have no experience with fets and I do not know what to use. I have read in several...
  2. autir

    LM317 Variable power supply

    Hi is the circuit of this guy http://casemods.pointofnoreturn.org/vregtut/tutorial-full.html a good example of star topology? any ideas on how to connect the LM317K (TO3 package), mounted on a huge heatsink? also I have comprehended the problem with the resistance between the 317's output pin...
  3. autir

    555 with unconnected trigger

    Hello all. I have built a simple circuit with a 555 as a monostable multivibrator on my breadboard. The circuit is the one documented in TI's 555 datasheet. The output goes to a 0-999 counter (three 7447s and three 7490s ICs). The 0-999 counter is a seperate circuit built on stripboard and works...
  4. autir

    logic family selection

    Hello all. Recently I discovered that the TTL ICs praised in my books are in reality power hungry, ancient technologies - even the LS variant I have used to make some simple circuits. I would like you to propose an alternate logic family. I would like the following characteristics: DIP package...
  5. autir

    NiMH Charging

    Thank you for your reply :) One final question: If we have some rechargable cells and we are not certain if they are all of the same charge level, can't we just connect them in parallel? So the full ones will charge the empty ones and everyone will be ok. (I suppose that if the cells would...
  6. autir

    NiMH Charging

    Are your two examples referring to devices that were always charging when not in use? 2500mAh batteries in a 100mA charger require 25 hours to charge fully. Taking the typical 66% efficiency in consideration, we have 25*1.5=37.5 hours. If this slight overcharging you have mentioned takes place...
  7. autir

    NiMH Charging

    I have read a few articles regarding recharging methods for Ni-based rechargeable batteries (NiCd, NiMH). I have a few questions about the simple constant current method, that is without timers, dV/dt or dT/dt detectors, or anything else. 1) What do you think of the figures given here...
  8. autir

    7447, 7448 decoders

    Thank you for your reply  :D So: If I connect the anode of the segment to Vcc=+5V, I will need a voltage drop of 3V across the resistance (I assume that the voltage drop across the led will be 2V, like in a typical "lamp" led?). R=V/I =3/0.01 <=> R=300 Ohms, we will select 330 Ohms for...
  9. autir

    7447, 7448 decoders

    Hi all. I have downloaded TI's datasheet about the 7446-7449 family of BCD to 7-segment display decoders. (http://focus.ti.com/docs/prod/folders/print/sn7447a.html) 1) The '46 and '47 decoders claim to "drive indicators directly", while the '48 decoder claims that "internal pull-ups eliminate...
  10. autir

    BJT biasing formulas

    @Walid: I don't believe that there is anything wrong with my circuit apart from the wrong application of the Thevenin theorem (that is, regarding calculations. The choice of
  11. autir

    BJT biasing formulas

    Alun thank you for translating the .doc file. Feel free to call me Autir  ;D You are absolutely right. I have verified it by running simulations having used several values for R1 and R2. I use Thevenin in a wrong way. In the past you, among others, have advised me to stick with the BC546-550...
  12. autir

    Circuit Simulation and Layout Software Comparision

    Electronics Workbench? Orcad?
  13. autir

    suitable fuse for digital multimeter

    Hello all. I have blown the fuses of my two "el cheapo" digital multimeters. What should I replace them with? Slow-blow or fast-blow?
  14. autir

    BJT biasing formulas

    I have designed a class A preamp from scratch and written the procedure in a Word document. I would feel very obliged to all that can read it and point out any mistakes/ misconceptions etc. class_A_preamp_v.0.1.zip
  15. autir

    BJT biasing formulas

    Ehmmm.... guys?!?  ;D
  16. autir

    BJT biasing formulas

    Because the electronics I have learnt is that of the computer scientist, that is very few and almost all of it digital. Plus my theory books were meant for physicists and electrical engineers. They are too complicated. Regarding electronics I am a hobbyist, not a professional. ;) @walid: Thank...
  17. autir

    BJT biasing formulas

    As always, many  ;D The circuit without the emitter resistor is indeed a bad design, as it is dependent upon the hfe of each transistor and the shifts of the hfe value caused by temperature etc. change. I included it just to see how the formulas change with the transition from the simple (no...
  18. autir

    Good book for beginners?

    Electronic Principles, Albert P. Malvino The Art of Electronics, Paul Horowitz and Winfield Hill
  19. autir

    BJT biasing formulas

    Hello all. For the past few months (ok, it was not my sole occupation
  20. autir

    Volt regulator & Battery

    Then the LM317 is unsuitable for you. Pay attention on the choice of your voltage regulator IC.
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