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  1. Audioguru

    Simple SW receiver on 3V?

    Headphones connected in series (without re-wiring the plug) end up out-of-phase and sound weird.
  2. Audioguru

    SPST LED Rocker Switch Wiring

    You do not step down to 2.2V. Instead you add a current-limiting resistor in series. The resistor will be (12V - 2.0V)/10mA= 1k ohms or use 510 ohms for brighter 20mA. A 1/4W resistor will be fine. Correct polarity of the LED is important.
  3. Audioguru

    Simple SW receiver on 3V?

    Sure, use a little 9V battery with a simple class-A audio power amplifier made with only one transistor. With a 3V supply and an 8 ohm speaker then for low distortion the speaker must have 1.5V across it and the speaker must have the remaining 1.5V across it. The resistor also must be 8 ohms...
  4. Audioguru

    Simple SW receiver on 3V?

    Do you want to listen on headphones or on a speaker? Restricting the battery voltage to 3V when the battery is new or is 2V when the battery needs to be replaced reduces the maximum loudness. To reduce battery current all the time even when not playing, a class-AB amplifier should be used, not a...
  5. Audioguru

    Will covering ring on male TRS jack with tape work?

    I was thinking about a balanced output done with opamps that are not isolated from the shield ground like a transformer would be.
  6. Audioguru

    Will covering ring on male TRS jack with tape work?

    I did not finish reading the other thread. Half of a balanced output T and S (where the S is the cable shield) is the same as an unbalanced shielded signal. If you get a ground loop and its noises then you should use balanced to balanced.
  7. Audioguru

    Will covering ring on male TRS jack with tape work?

    The "ring" output on a balanced connector is a signal that might cause damage if grounded. Connecting the T as a signal and the S as the cable shield and ground wire should work fine with a -6dB signal loss.
  8. Audioguru

    Will covering ring on male TRS jack with tape work?

    You have a balanced TRS "stereo" plug and you have a balanced TRS jack instead of a unbalanced TS "mono" jack. Simply connect the T live wire and the S ground wire to the jack with its R terminal not connected to anything.
  9. Audioguru

    Will covering ring on male TRS jack with tape work?

    Simply do not connect your unbalanced circuit to the ring terminal of the jack. The tip will be the live signal and the sleeve will be ground.
  10. Audioguru

    Is transistor faulty or something else amiss

    A simple FM transmitter sounds awful without producing low and high audio frequencies. Also its radio frequency wanders all over the place. My FM transmitter uses the oscillator trimmer capacitor to select a vacant radio frequency and the trimmer capacitor on the RF amplifier is broadly peaked...
  11. Audioguru

    Is transistor faulty or something else amiss

    The 680 ohms resistor is the current-limiting resistor (to ground) for an LED I never installed. The 470 ohms emitter resistor R5 is 0.1" to the right of the emitter wire of Q1. C2 and R6 are on the bottom of the circuit board.
  12. Audioguru

    Is transistor faulty or something else amiss

    I forgot to say that the original C1 and C2 audio coupling capacitors have such a low value that they cut all low audio frequencies causing a man's voice to sound like a chipmunk. The values of the original R6 and C3 are also wrong and cut high audio frequencies. Then the sounds heard on an FM...
  13. Audioguru

    Is transistor faulty or something else amiss

    A multimeter is made to accurately measure the voltage at 50Hz or 60Hz. It works poorly at 1kHz and the FM radio frequency of 100MHz is 100 hundred thousand times higher and a multimeter measures nothing. That is the same circuit that I fixed 14 years ago: 1) The mic preamp transistor is...
  14. Audioguru

    Video signal amplifier.

    You showed a very slow opamp as non-inverting with a single negative feedback resistor. Its input might or might not be biased properly by the signal source. Your opamp circuit showed no power supply connections. It did not have a series input resistor used in an inverting opamp amplifier. Since...
  15. Audioguru

    Strange voltage variation in circuit

    If you have an old 741 opamp that works when its power supply is only 9V (its datasheet shows only a 30V power supply) then almost any sound will cause it to have an AC output which will trigger the flipflop thousands of times. You need a "peak detector" circuit that produces a DC output...
  16. Audioguru

    Video signal amplifier.

    An antique LM747 has such a slow output slew rate that your sync pulse input is gone before the output of the opamp does anything. What are you trying to boost? The opamp circuit has a voltage gain of only 1 at low frequencies.
  17. Audioguru

    12V power supply

    The 100uF main filter capacitor value is low for a 100mA load so it is probably producing a lot of ripple. Maybe that is why the transformer output voltage is so high.
  18. Audioguru

    dc measuring

    On the other website the circuit had some instructions in a foreign language (German?):
  19. Audioguru

    Schematic for the philips BT100 bluetooth

    The important specification details about the dangerous cheap charger are not shown: 1) It does not say it is certified to be safe. The manufacturer's name is unknown or is hidden. 2) It does not say the charging stops. Then it will over-charge and cause an explosion and fire. 3) It does not say...
  20. Audioguru

    Class AB Power Amplifier Design

    ICs are fine if you check to see that they are still being made and when you do not buy cheap fakes from China (Ebay, Banggood, AliExpress, Amazon, etc). On Elliot Sound Products website there are many amplifier circuits, most made with components. Years ago he used excellent Toshiba output...
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