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  1. Audioguru

    Signal mixer, voltage mixer.

    When you say "control voltage" do you mean the "modulating signal"?
  2. Audioguru

    Line splitter.

    It passes AC signals, not DC control voltages. Since there is only one input then it mixes nothing. If you bypass the coupling capacitors then it amplifies the DC input up to 30.86 times up to about +10V.
  3. Audioguru

    Signal mixer, voltage mixer.

    You said the signal generator has a steady output of 3.4V regardless of the frequency. Is it 3.4V AC or 3.4V DC? You said that you want the mixer to work with "control voltages". If the control voltages are DC then why are you using an AC signal generator?
  4. Audioguru

    Amplifying piezo buzzer

    We do not know if the piezo buzzer has its + terminal at the positive supply and its - terminal is driven to ground with "something", or the opposite. If it is known then a transistor can be used to drive the piezo buzzer from a higher supply voltage. EDIT: Sometmes the sound hole in a piezo...
  5. Audioguru

    Different Pass filters for different speakers.

    SL is surround Left and SR is surround Right. Most cars have 4 speakers, 2 in the front doors and two on the rear shelf. I have never heard surround sound in a car. The output power with the 15V supply shown and 8 ohm speakers is about 2.6W per channel and into 4 ohm speakers the power is about...
  6. Audioguru

    12VDC Backup supply

    Look at Energizer's Ni-MH Battery Applications Manual on their website. It says to have a trickle charge current that is 1/40th of its capacity or less so that the extreme pressure caused by overcharging does not cause the battery to fart and release its goodies. Its life is shortened if it...
  7. Audioguru

    12VDC Backup supply

    A new Energizer Ni-MH 9V battery is rated at 175mAh. It should not be trickle charged higher than 175/40= 4.4mA. Its voltage is about 8.4V at half a charge and your 12V source might be 13.2V then the diode drops the source 0.7V to 12.5V and the resistor value for 4.4mA is (12.5V - 8.4V)/4.4mA=...
  8. Audioguru

    12VDC Backup supply

    The Huosuli battery is probably Chinese. Then it might be very poor quality and not produce its rated 1300mAh and it might use old fashioned chemicals then it will not hold a charge for more than a few weeks. It has 10 cells that average 1.2V during a discharge and it is about 14V to 15V when...
  9. Audioguru

    LED buck drivers and reducing current

    How will you cool the LEDs? They will need a pretty big finned heatsink or they will quickly melt.
  10. Audioguru

    12VDC Backup supply

    Energizer says that their old Ni-Cad batteries are fine charging at the 14 hour rate continuously but Ni-MH must have the trickle charge reduced to 1/40th or their life is shortened. New (the last 2 years) Energizer Ni-MH cells are the new kind (like Eneloop) that come pre-charged and hold a...
  11. Audioguru

    12VDC Backup supply

    A little 9V rechargeable battery today is 7 cells of Ni-MH and its fully charged voltage is about 9.8V and its average voltage during a discharge is 8.4V. Its load should be disconnected when its voltage has dropped to 6.3V so that its weakest cell does not become reversed and destroyed...
  12. Audioguru

    Basic speaker setup

    A speaker that is as cheap as 1.5W will sound awful. But it will play smoke alarm beeps and baby crying sounds pretty well but not loud.
  13. Audioguru

    NPN transistor still working? Strange ..

    Years ago when I used the emitter-base junction of a transistor as a low power zener diode I did not connect the collector. Maybe when the emitter-base has avalanche breakdown then the transistor conducts from emitter to collector? Years ago I used a PUT as an oscillator.
  14. Audioguru

    30W and 4x8W audio amplifier circuit?

    The National Semi (now owned by Texas Instruments) LM1875 single amplifier is almost the same as each amplifier in a TDA2005 dual amplifier that you have.
  15. Audioguru

    30W and 4x8W audio amplifier circuit?

    You are looking at the exaggerated power ratings shown on amplifier datasheets. It says 10% distortion that sounds awful because the amplifier is clipping like crazy. The old TDA2005 produces 2 x 8W into 3 ohm speakers (two of your 6 ohm speakers in parallel) at low distortion when its supply...
  16. Audioguru

    NPN transistor still working? Strange ..

    It takes time for the capacitor to charge to the voltage that causes the transistor to conduct, then the capacitor is discharged by the transistor and its LED load to a voltage (or current) that is low enough for the transistor to turn off, then the capacitor slowly charges again and it all...
  17. Audioguru

    NPN transistor still working? Strange ..

    It is the reverse emitter-base voltage that causes the transistor to conduct avalanche breakdown current. The voltage causes the breakdown and the result is current flowing in the transistor.
  18. Audioguru

    Loud mains hum with Jaycar short circuits Vol 3 #12

    Usually an amplifier has more than enough gain so it can be used with input levels that are lower than normal. Then it has volume controls (not gain controls) that yours might not have.
  19. Audioguru

    30W and 4x8W audio amplifier circuit?

    VS = ± 16V is the + and - power supply for that 34W bridge amp. The datasheet does not say its distortion or how much heat it produces. There are many class-D 8W amplifiers available. Look at the Texas Instruments website.
  20. Audioguru

    NPN transistor still working? Strange ..

    The capacitor does not fully charge because the reverse-biased emitter-base has avalanche breakdown at about 6V and is in series with the forward-biased base-collector diode. Then the transistor conducts from emitter to collector and dumps some of the capacitor charge into the LED.
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