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  1. Audioguru

    A really small and cheap audio stereo amplifier 3w/3w from 5V psu

    When the supply is 5V, the PAM8403 produces 3W per channel into 4 ohms with horrible 10% distortion, 2.5W per channel with less distortion and only 2W per channel when clipping begins. The PAM8610 datasheet says "Not Recommended", Use PAM8006A".
  2. Audioguru

    Power supplies

    Your opamp has a single positive supply and 0V. Then its + input must be biased with a DC voltage that is half the supply voltage so that its output can swing up and down. Many opamps are powered with a dual polarity supply that has positive, 0V and has negative. Then its + input is biased at...
  3. Audioguru

    LiPo Battery voltage difference across cells

    A cell with a voltage too low might have physical Lithium metal plated where ions should be there. When some chargers detect a low voltage then they attempt charging at a very low current and if the voltage slowly rises without the battery temperature rising then the battery will be fine. The...
  4. Audioguru

    LiPo Battery voltage difference across cells

    That is a very powerful battery when it is new. Your charger is smart enough to detect damage in the battery and refuse to charge it preventing an explosion and/or fire. A Li-PO battery might have physical damage or internally have one cell with a voltage too low (less than 3.0V) or too high...
  5. Audioguru

    MP3 player hum

    If the hum is a pure sinewave with no harmonics (but it probably has harmonics) then a filter for that frequency will cut some parts in music and in speech. But with harmonics then you must cut all bass frequencies which is bad for music and makes male adult voices sound like chipmunks. My...
  6. Audioguru

    MP3 player hum

    Hum is simply filtered away by cutting all the bass sounds.
  7. Audioguru

    Back to the Breadboard

    The 1nF was calculated to cut 160Hz and lower for the Jfet-inputs TL081 opamp. The 4558 opamps have ordinary input transistors with a minimum input resistance of 300k ohms which in parallel with the 1M biasing resistor produces a minimum of 231k and cuts 693Hz and lower. The input resistance of...
  8. Audioguru

    Back to the Breadboard

    Where is a 1nF capacitor? The circuit does not have one.
  9. Audioguru

    MP3 player hum

    There are programs available for stripboard layout but I like using my brain instead. A drill bit or one made with a handle on it cuts the strips.
  10. Audioguru

    MP3 player hum

    Here is an example of a circuit made on stripboard. The parts and a few jumpers are all soldered on the bottom where the copper strips are. Some of the copper strips are cut to length then the same strip is used again in a different location. The parts are close together and there are no long...
  11. Audioguru

    MP3 player hum

    Breadboards guarantee hum and interference, don't use a breadboard for audio or video. The contacts on a breadboard corrode and wear out causing intermittent connections. In my career and hobby I made thousands of prototype circuits and they all worked perfectly because I planned a perforated...
  12. Audioguru

    Back to the Breadboard

    The circuit is a very common pedal circuit that you are copying. Will you pay me $50 if I take one?:)
  13. Audioguru

    Back to the Breadboard

    No. The input signal is already AC probably with an average of 0V so it goes positive and negative. Your opamp circuit has a single positive supply, not a positive and negative supply so it cannot use the negative part of the input signal. The opamp must be biased at half the supply voltage so...
  14. Audioguru

    MP3 player hum

    Every audio system built on a breadboard produces hum and other interference. Each wire and each strip of contacts on the breadboard is an antenna that picks up electrical 50Hz or 60Hz that is all around the breadboard. ALL home audio systems are connected together with shielded audio cables.
  15. Audioguru

    Back to the Breadboard

    A guitar pickup works best when loaded with 1M or higher. The input of an old vacuum tubes guitar amplifier always had a 1M resistor. A TL081 single or TL082 dual opamp have Jfet transistors which have the same extremely high resistance of a vacuum tube. The old 4558 opamp has ordinary...
  16. Audioguru

    Back to the Breadboard

    The 1M resistor biases the + input of the opamp to +4.5VDC then the gain pot provides DC negative feedback with a gain of 1 so that the opamp output will also be at +4.5VDC and can swing equally up 3.5V to 8V and down 3.5V to 1V with the audio.
  17. Audioguru

    Back to the Breadboard

    Here is a video of a guitar pedal with soft clipping diodes and hard clipping diodes and different opamps:
  18. Audioguru

    Back to the Breadboard

    Good, it does what you want. Of course I noticed the hum and midrange noise before you began playing. The tone is midrange with very high frequencies and most low frequencies reduced.
  19. Audioguru

    Back to the Breadboard

    Each unshielded audio wire is an antenna that will pickup mains hum and all kinds of other interference. The metal cases on the pots should be connected to the circuit's 0V to avoid more interference. Chinese high voltage green film capacitors are old fashioned and are huge. My European (Epcos...
  20. Audioguru

    Repair stereo transformer ~ possible?

    I think the transformer burnt because the over-voltage caused a few hundred amplifier parts to short which overloaded the transformer. Repairing or replacing the transformer will not fix the problem.
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