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  1. Audioguru

    Math Question, How Do You Really Figure This Out

    An LED is not a white hot piece of an accurate length and diameter of wire that can be made to draw certain current at a certain voltage (incandescent light bulb). Instead an LED cannot be made accurately so its datasheet shows a range of forward voltage, a minimum, a typical and a maximum. Some...
  2. Audioguru

    Building a Microphone should be easy, right?

    Told ya so.
  3. Audioguru

    Capacitor In Line?

    Today I had two plugpack power supplies that had labels saying 5V/1A so I measured their voltages with no load. One measured 9.2V and the other measured 5.3V so I used the 5.3V one and my new circuit did not blow up. Cheap power supplies have poor control of their voltage.
  4. Audioguru

    Can an old Ni-Cd battery charger be used for Ni-MH batteries?

    I have four chargers for AA and AAA cells. They charge 2 cells as a pair in series then they cost a little less.
  5. Audioguru

    Vacuum Tubes

    A vacuum tube and a transistor do not pass AC, instead they pass DC that is modulated with an AC signal.
  6. Audioguru

    Help with Pot and LM3914

    What is the function of the LM3914? Instead of showing the levels of the music, don't you simply want to show the setting of the volume control? Then since the audio is stereo that uses a dual volume control (one for each channel) then you need a volume control that has 3 pots in it that is rare...
  7. Audioguru

    Rat Zapper Power Supply

    Why would a mouse or rat live in a very hot attic?? It is not a lizard.
  8. Audioguru

    Help with Pot and LM3914

    Aren't you using a stereo pot as a mono volume control and as a feed to the LM3914 circuit to show the volume setting of the pot? I showed you how to connect the 500k pot to the LM3914 circuit. Connect the other 500k part of the stereo pot as a volume control. Since your power supply is only 5V...
  9. Audioguru

    Help with Pot and LM3914

    The datasheet says the maximum input current is 100nA so into your 500k pot the input voltage from the bias current is 100nA x 500k ohms= 0.05V which is almost nothing so the calibration at half pot setting will be accurate. The datasheet says the max useable input voltage is the power supply...
  10. Audioguru

    Class A amp with NPN BC547 transistor

    Hi Steve, The 11< is not 11k, it is 1k.
  11. Audioguru

    Class A amp with NPN BC547 transistor

    There are many articles on the web about how transistors work. Yours is called "common emitter" and its voltage gain is roughly Rc/Re so your gain is an attenuation of 90/1000= 0.09 times. Your collector current is not 100mA, it is 1V/1k ohms= 1mA and the voltage at the collector is not 90mV it...
  12. Audioguru

    Help with Pot and LM3914

    The datasheet for the LM3914 shows exactly how to connect it. The LM3914 is a linear voltmeter. For audio you should use a logarithmic volume control and a logarithmic LM3915 IC that has much more range than a \n LM3914.
  13. Audioguru

    LED Wiring

    If each LED uses 3.2V then the resistor has 4.5V - 3.2V= 1.3V across it and the total current is 1.3V/20 ohms= 65mA. with 16 LEDs in parallel then each LED uses 65mA/16= 4.1mA. If the LEDs are 1.9V red LEDs then the resistor has 4.5V - 1.9V= 2.6V across it, the total current is 2.6V/20 ohms=...
  14. Audioguru

    How to connect tweeter with speaker, series or parallel?

    Piezo tweeters sound awful. They have a few strong resonance peaks with low levels in between. The horns make it sound worse. The diagram shows exactly how to connect a capacitor in series with the tweeter and how they and the bass speaker are connected to the amplifier. Google has never heard...
  15. Audioguru

    Building a Microphone should be easy, right?

    A mono plug shorts the mic terminals in the 4-wires jack. You need a 4-wires plug for your electret mic. You need a 2-wires electret mic. Some electret mics have 3-wires. Connect the mic to the plug with shielded audio cable, not 2 wires that will be antennas that pickup hum from mains...
  16. Audioguru

    Building a Microphone should be easy, right?

    I have a few electret mics from cell phones and child's toys and they all work fine. Maybe you have the extremely tiny mic from the cord of a headset? It is very difficult to make connections to it.
  17. Audioguru

    Building a Microphone should be easy, right?

    Your mono plug is shorting the mic connections on the plug. Get a 4-connections plug. I found this schematic of a 4-connections headphones plug in Google:
  18. Audioguru

    How could I connect sound input to this circuit?

    The pins are labelled: GND (power supply 0V), GND (input ground), (IN) input, and VDD (positive power supply). The module should have supplied a matching connector for the pins but instead you can solder wires to them.
  19. Audioguru

    Building a Microphone should be easy, right?

    If you plug into a microphone input then the built-in microphone should be disconnected by the jack. A microphone input jack on a laptop has nothing to do with a speaker. Maybe the symbol for a coil mic looks like a speaker to you? A coil mic is called a "dynamic" mic. Look up what type of mic...
  20. Audioguru

    5v from 12v is this viable?

    Here is an electric guitar Jfet "preamp" and its explanations. Here is a graph of the high frequency boost that a high impedance load has on a magnetic guitar pickup. Guitar speakers are usually just a simple woofer without a tweeter so the high frequency boost is important.
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