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  1. dorke

    General questions regarding transistors in different modes.

    One of the "definitions" of transistor saturation is : The linear ratio relation that holds in the active region, IC=beta*IB no longer holds . We have infect IC<beta*IB ,thus in saturation an increase in IB no longer increases IC. In this respect we can say that the max IC possible for the...
  2. dorke

    Amp keeps going into protection mode

    Yes, We just need to find out which one;) It would be best to find the faulty component and fully repair the amp. As thing are now ,the amp is working with the output DCV protection disabled. Since you checked that there is no DCV on all outputs you can play the amp as it is(with the wire cut)...
  3. dorke

    Amp keeps going into protection mode

    Checking with the small ones is fine. We can continue tomorrow. Sleep well.
  4. dorke

    Amp keeps going into protection mode

    So, Is the amp working fine now ? High volume and clear sound? We should continue testing. Rick have you got a variable DCV power supply? Or any potentiometer on hand?
  5. dorke

    Trying to Understand Full-Duplex Intercom Circuit

    dB in voltage terms(voltage amp) 20Log 1000=60dB. The thing is the LM741 GBP (Gain Bandwidth Product) is too low to achieve 60dB closed loop gain at about 5.3Khz. It will probably have that gain at about 1Khz. Which "Intro book" do you use? About Op. Amps here is a great one from TI .
  6. dorke

    Need help with SSR Wiring

    Do you know what is the staring current ? Is your SSR (which is it?) input /output isolated?
  7. dorke

    Amp keeps going into protection mode

    Rick, you should check the presence of DCV on all speakers terminals before you connect them . Since we disabled that protection mechanism. There probably isn't any, but still do check it without the speakers.
  8. dorke

    Trying to Understand Full-Duplex Intercom Circuit

    About the analogy to relay driving. Not the best one, relay(coil) driving on/off is driving an inductive load . When driving it off a "back emf voltage" is generated creating a "relatively" high voltage (higher than the supply line) ,which can damage the driving semiconductor. The diode...
  9. dorke

    Amp keeps going into protection mode

    O.k Let's continue with cutting the wire going to pin-5. and see if the amp goes into protect as before (no speakers).
  10. dorke

    Amp keeps going into protection mode

    O.K. can you "play and move " the S1 connector and repeat the resistance test between S1-2 and the black speaker terminal. Does it change the reading?
  11. dorke

    Amp keeps going into protection mode

    What is the resistance? It doesn't agree with the: "2 reads 48.5 ohms with Amp off, ground probe on ground speaker terminal, meter set to 200 ohms." from #54 . All this points should be close to zero (2.5 in this dmm and probes you use), Can you confirm this?
  12. dorke

    Amp keeps going into protection mode

    Yes ,check resistance(continuity). "Lower" as is in the diagram,the side that should be connected to ground.
  13. dorke

    opamcircuit output

    On the contrary,using just these , and knowing nothing about feedback is the easiest and most intuitive way to solve this question.
  14. dorke

    Amp keeps going into protection mode

    That means that pin 2 is not well connected to ground as it should be. Can you please check the connection between S1-2 and the"lower side" of C9 or C13. what do you get?
  15. dorke

    Amp keeps going into protection mode

    what does the meter show when you short it's probes in 200ohm?
  16. dorke

    opamcircuit output

    So, can you show the various voltages on your circuit and why they are there. Like the guy does in the video? Show us.
  17. dorke

    Wiring a Fire Bell to a flip switch?

    Yes, no transformer just the wall-wart feeding a serial switch (large round push button?) and possibly a serial fuse to the bell.like so:
  18. dorke

    Amp keeps going into protection mode

    Yes, cut it about 2" away from the connector so it will be easy to reconnect later. Was there a zero ohm between pin-2 and the speaker black terminal?
  19. dorke

    Trying to Understand Full-Duplex Intercom Circuit

    You are doing great:) Your questions are not basic at all they have to do with fine details of the circuit. A note: Don't assume that the designer of this circuit(and any other for that mater) did everything in the best and optimal way. Sometimes things are done "just in case" or because there...
  20. dorke

    help with heat sink

    Well, Here is a guide for Heat Sink Design it may help you . The number you should use from the data sheet is 2C/W for theta junction to case. Since you need an insulator it will have about 0.5C/W.(that can be lowered to 0.1C/W with better ones). So we have 2.5C/W ,to that we need to add the...
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