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elix

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Posts posted by elix

  1. :D even though it works perfectly in the sim i have to make something of my own creation, else i'm not learning so i'm going to try it now with a active current sink since i can use the gate voltage swing to my advantage.

    you've won this round *shakes fist*


    ;D

  2. i'll try and figure out a way to lower the impendance. some heat wasted is ok, i only need 1 watt from each channel and the mosfet bias will come from the op-amp.

    question:

    to lower the impendance don't i have to raise the current or can it be done a simple circuit, i'm trying to keep a class a single ended mosfet. (gotta learn  :P)

  3. i am starting over  ;D



    btw that current source was working right then i pulled a resistor live and now i have two holes in my breadboard and two cracked fets  :-[  good thing i have more  :)

  4. your right, i have it hooked up right on the board but wrong in the schematic, funny thing it works fine in the sim then when i put it right i got a jagged wave!!! so i got rid of the 317 and put a more flexable current regulator in, tell me what you think.



    still have to build this one but i must go to bed.



  5. here are the node voltages, i have a vom hooked up to the bottom of r8 and the voltage is hardly moving but something is giving me crazy bass from this regge song, sounds great! 6 ohm load, r1 is 4 ohms, have on a small lead acid battery. i had it as shown and worked great. clean sine waves to 5Mhz, no artifacts to 15Mhz which is the max i can test to.


    the more current i have the less voltage swing i need?
  6. "Your OP37A opamp has a voltage gain of 19k/10k= 1.9 with a low impedance source, and a voltage gain of 19k/(4.7k + 10k)= 1.3 without an input. But the OP37A opamp is de-compensated and is unstable with a voltage gain of less than 5. It will oscillate."

    does it matter since i'm not using a split supply?

  7. i've made some changes again, the amp did oscillate but because the mosfet was actting as an anttena in the low Mhz. new mosfet, some changes. so far no problems from the op-amp, will look at the data sheet.

  8. using split supplys if i keep the gate at 4 volts above drain it saturates, when gate equals 0~4 volts above drain it stays in linear mode (corresponds to Vgs for irfz44, which is what i'm testing). Id=2k[{(Vgs-Vt)Vds-Vds^2}/2] is how you calculate drain current in linear mode but here's my questions:

    Vt should be what?
    is Vds the drop between drain and source? it shows up as one diode drop if so.
    how do you figure out what k is?

  9. ok i have 3 points

    gate voltage  current gain  Vd

    4.6                  2ma              1.8
    5.2                  13ma            2.2
    5.6                  25ma            2.45





  10. ok, i think i understand mosfets when they are in saturation mode but i'm having trouble figuring how to calculate gate voltage (Vgs) to drain current (Id) using G(transconductance ratio). in the schematic i just left generic values, i have a led in the place of r2 and i'm making a plot, but for now this is good enough, bed time  ;)
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