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  1. audioguru2

    transistor off

    I think a class-A power amplifier is a crazy way to heat your house. It gets hot even if it doesn't have a signal. I was wrong before. The Mosfet won't have a high voltage gain because the low resistance of the load is its drain load, not the very high impedance of the LM317 current source.
  2. audioguru2

    The relationship of Amplifier vs Power vs Frequency

    I think the power output of an amplifier at a certain frequency depends on the design of the amplifier. The amplifier could have terrible low or high frequency response.
  3. audioguru2

    120VAC to a2VDC 30A power supply circuit needed

    19VAC makes an unregulated 24.9VDC which is much too high for a 12V/25A regulator. The regulator will heat with (24.9V - 12V) x 25A= 323W! If the transformer was 12VAC then its unregulated voltage would be 15VDC and the regulator would dissipate "only" 75W.
  4. audioguru2

    transistor off

    Hi Elix, Your opamp has a very low input impedance of only 1.5k ohms which is too low for many audio sources. The Mosfet has a very high voltage gain at low frequencies but there is no volume control. If negative feedback is added then I think the poor high frequency response of the LM317...
  5. audioguru2

    3 Channel Spectrum Analyzer - question

    The LM3900 is a quad "Norton" opamp and the list shows that a BM3900 is the same.
  6. audioguru2

    3 Channel Spectrum Analyzer - question

    Three datasheet companies online have never heard of a BM3900.
  7. audioguru2

    12 V DC to a 220V AC Inverter AMplfier Design

    150W output plus 38W of heat in the inverter circuit = 188W total. 188W/12V= 15.7A from the 12V battery, into the low voltage winding of the transformer and is the average current in the Mosfets. 15.7A is the average continuous current, the peak momentary current is higher. If you overload the...
  8. audioguru2

    12 V DC to a 220V AC Inverter AMplfier Design

    Nobody makes a step-up transformer. Buy an ordinary step-down transformer and connect it backwards. Don't think of current, think of power. Then calculate the current.
  9. audioguru2

    12 V DC to a 220V AC Inverter AMplfier Design

    You cannot buy a transformer that is 8.5V-0V-8.5V to 220V. You buy one that is 220V to 8.5V-0V-8.5V instead. For it to pass 188W continuously then its 8.5V winding must pass 15.7A continuously. The current rating for its high voltage winding is not mentioned. 188W is a lot of power. If you use a...
  10. audioguru2

    white led

    How can you power two 3.5V LEDs in series (7V) with only 5V from a 7805? I didn't check the datasheet, but a 3.5V LED could be 3.0V, 3,5V or 4.0V. Some of them are 3.5V. Its absolute max current is probably 350mA. Do you want to operate it at its limit? You need two current regulators set to...
  11. audioguru2

    alarm circuit using lm555

    The thyristor circuit you want me to comment on uses an SCR thyristor. Like a triac, it turns on and stays on until its power is turned off. In the first circuit you showed, if the 555 timer was wired properly then the thyristor would have turned on and stayed on immediately, without a delay.
  12. audioguru2

    alarm circuit using lm555

    The frequency of a buzzer is built into it. An AC  light dimmer is a resistor in series and a capacitor to neutral which can delay the AC signal from the mains. If it is fed to the gate of a triac (an AC thyristor) then the triac turns on late for each half-cycle so the average power to its...
  13. audioguru2

    Switch off, Curcuit on

    Brendan, Just buy the switch. A double-pole switch has two separate sections. A double-throw switch has two positions. Get a double-pole, double-throw switch then one section can turn on something while its other section turns off something.
  14. audioguru2

    3 Channel Spectrum Analyzer - question

    You can use the Panasonic AN6884 LED drivers and I can use the National Semi LM3915 LED drivers if I change the wiring for them. You can order an LM3900 and I can buy one or change the wiring so that an ordinary quad opamp can be used.
  15. audioguru2

    THINGS YOU NEVER KNEW YOUR CELL PHONE COULD DO

    My cell phone shovels the snow from my driveway and takes my dog for a walk. I don't believe most of those myths that came from a circulating e-mail.
  16. audioguru2

    AM transmitter

    Hi Cecilia, Welcome to our forum. ;D The microphone is an electret type. It is shown as a 3-wires one but I have seen only 2-wires ones. We don't know which type is used with your laptop. R1 powers the FET transistor inside the electrret mic. C4 couples the mic signal to Q2 and blocks the DC...
  17. audioguru2

    Electrodes...

    9V is too low a voltage to cause a shock. A tens machine boosts the voltage to at least 100V and pulses it. Shocking somebody is dangerous. Find something more useful to do.
  18. audioguru2

    Adding current boost to voltage regulator TL783

    The TL783 has a dropout voltage of about 12V. So current-boosting transistors must be paralleled to be able to dissipate the high amount of heat.
  19. audioguru2

    3 Channel Spectrum Analyzer - question

    Yes. The circuit can be modified so it can use ordinary opamps. But I looked for the old Panasonic LED driver ICs in two of the largest American electronic parts distributors and they don't have any. It is a big job to redesign the circuit to use ordinary opamps and common LM3915 LED driver ICs...
  20. audioguru2

    3 Channel Spectrum Analyzer - question

    Here is a link to our 3-Channel Spectrum Analyser project: http://www.electronics-lab.com/projects/audio/037/index.html Here is its schematic with its errors marked:
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