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  1. audioguru2

    3 Channel Spectrum Analyzer - question

    A computer power supply won't hurt the circuit if you connect it with the correct polarity. The circuit is missing any kind of filtering for the supply so the output might have buzzing from the computer. Add a 100 ohm resistor from the +12V input to the positive supply to the opamps and a 470uF...
  2. audioguru2

    Led Help

    Hi Steve, Your "transformer" is an AC adapter with a DC output. It is rated at 12V with a full load. A single LED is hardly any load so its voltage is higher because it doesn't have a voltage regulator. The LED is about 3V so the 470 ohm current-limiting resistor has 12V across it. Ohm's Law...
  3. audioguru2

    The relationship of Amplifier vs Power vs Frequency

    Hi Walid, Small signal transistors like the 2N3904 and BC547 have a frequency response up to 300MHz, so stray circuit capacitance limits their high frequency response if the resistors have a high value. Power transistors like the old 2N3055 have a poor high frequency response which is extended...
  4. audioguru2

    Looking for datasheet: STK 090

    Sanyo made many STKxxxx amplifiers. But Datasheet Archive couldn't find any info about yours.
  5. audioguru2

    white led

    Hi Pier, You have an LM317 voltage regulator and a two-transistors current regulator. You don't need the voltage regulator. The LM317 can be a current regulator by adding only a single resistor (1.25V/320mA= 3.9 ohms) to it as shown in its datasheet. Two Lumileds might need a max voltage of...
  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    I think your -5.6V supply is actually +5.6V because the other two diodes are backwards.
  7. audioguru2

    pi filter

    This is a 3rd-order lowpass filter. Its slope is 60dB per decade. If its source impedance and its load impedance are correct then it will have a flat response from DC up to its cutoff frequency.
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    The voltage across your D7 is only 0.7V because it is also probably connected backwards. The cathode end of diodes is marked with a black band. 33V across 1.5 ohms is a current of 22A! When the voltage dropped to 4.5V then the current was 3A.
  9. audioguru2

    communication with crystals

    Even the transmitter and receiver circuits in a cheap $10.00 radio controlled micro car are fairly complicated. Their range is about only 4m.
  10. audioguru2

    My 12 watt x2 stereo amplifier

    Hi Ben, There are lots of bridged amplifier ICs made for car radios that produce 14 real Watts per channel continuously with low distortion into a 4 ohm speaker with your 13.2V battery powering them. About 7.5 Watts into 8 ohm speakers per channel. A TDA7240A is a single channel bridged...
  11. audioguru2

    building a generator

    There is a project on the internet about using a big AC motor as a generator. It has "residual" magnetism that starts it generating then it makes its own strong magnetism as it gets going.
  12. audioguru2

    communication with crystals

    A radio and a radio transmitter are complicated if you want them to work well. Copy the cheap circuits inside radio controlled toys if you want simple circuits that do not work well.
  13. audioguru2

    My 12 watt x2 stereo amplifier

    Hi Ben, Your amplifier looks nice and looks identical to the 2 x 5W amplifier I made for the beach many years ago. Mine used a 7.2V Ni-Cad battery (inside its case) and its bridged amplifier ICs produced 5 real Watts per channel at low distortion into my 4 ohm speakers. Are your Kemo amplifier...
  14. audioguru2

    alarm circuit using lm555

    Programmable Unijunction Transistor. Look in Google. It is something like an SCR but you can set the voltage that triggers it.
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    The circuits won't work properly without the -5.6V negative supply. C2 and C3 should be replaced to see if they are bad. The output of the opamp connects to Q2. Q4 cannot work and the output cannot work without Q2. Something is shorting the output of the opamp to Q4 or to the output. maybe D10...
  16. audioguru2

    12 V DC to a 220V AC Inverter AMplfier Design

    Use two of those Mosfets on each side for a 150W modified sine-wave inverter.
  17. audioguru2

    transistor off

    I connected the Mosfet as a source-follower that has a low output impedance. I used AC negative feedback to reduce distortion, to control the gain and to make the output impedance even lower. I used DC negative feedback to control the biasing of the Mosfet. The BIAS pot should be adjusted for...
  18. audioguru2

    12 V DC to a 220V AC Inverter AMplfier Design

    www.digikey.com They are in some countries. www.farnell.com and click on the flag of your country. I look at Canadian and United States pages.
  19. audioguru2

    Looking for datasheet: STK 090

    I think a number is missing. www.datasheetarchive.com lists STK0040, STK0040II and STK2040. Which one? 
  20. audioguru2

    12 V DC to a 220V AC Inverter AMplfier Design

    I don't use high current Mosfets. The online catalogs of Digikey and Newark have hundreds of them. Some can conduct over 100A. I don't know what you can buy.
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