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  1. Audioguru

    New Stompbox Project

    An electric guitar needs a very high load resistance to sound like it is playing into an old vacuum tubes amplifier. A pair of 200k bias resistors have values that are Much Too Low. Instead use a vacuum tube amplifier or an opamp with Jfet inputs and a high value input resistors or like in this...
  2. Audioguru

    New Stompbox Project

    The extremely old (52 years) uA741 opamp is too noisy (hiss) and the 4558 dual opamp have a minimum input resistance of only 300k. Electric guitar pickups need the extremely high input resistance of a vacuum tube or Jfet input opamp. The LF353 and TL081 opamps have Jfet inputs but are also too...
  3. Audioguru

    Testing a Polyester Cap

    When my digital multimeter says OL then it is set to measure resistance and the resistance is higher than 40M ohms which means the capacitor is not shorted and has no leakage current. Why do you think this capacitor is bad?
  4. Audioguru

    My Li-Ion Battery Charger Circuit Is Not Working As Expected

    DO NOT use a solderless breadboard. Its contacts are cheap and very poor quality. Did the poor quality breadboard produce some smoke? Instead, solder the parts close together on stripboard or a pcb.
  5. Audioguru

    Need Help with simple 9V circuit design.

    A motor and a switch are rated for voltage and for current. You did not say the maximum current for the motor and the spec's for the switch does not say its maximum allowed current.
  6. Audioguru

    Why do I not get e-mails about replies to threads I am involved in here?

    I have the notifications ticked but I do not get e-mails about any replies to threads I watch. I was not notified about your reply. Here is a copy of my preferences:
  7. Audioguru

    Why do I not get e-mails about replies to threads I am involved in here?

    My e-mail address is correct in my settings.
  8. Audioguru

    Short wave radio on breadboard

    The video is missing a schematic and parts list. The antique 741 opamp was designed 52 years ago. It should be buried. Use a modern amplifier. The opamp has positive feedback instead of negative feedback. The radio is missing a Power Amplifier to drive a speaker.
  9. Audioguru

    Question hdd badblock interference and dvd burn

    I am glad that my replacement computer has a Solid State Drive that is extremely fast. It is in an HP that is very new and I got it as a refurb last Black Friday for low cost.
  10. Audioguru

    Question SSD china aliexpress

    "Cheap" means low quality and poor reliability. Is that what you want?
  11. Audioguru

    The Theremin Stretch

    In the video, I liked the bubbles playing sounds and the pedal making chords. The woman with the severe English accent was talking in a room that had severe echoes. She has a speech problem that causes every sentence to fade away like she was running out of breathing air.
  12. Audioguru

    My Li-Ion Battery Charger Circuit Is Not Working As Expected

    Tests for that Chinese "9V" Li-Ion battery say and show it was pretty good (were they paid so say that?). It had over-voltage and low voltage protection cutoffs. Some tests were 6 years ago. Is the battery the same today?? A test of the Soshine battery charger showed that the test guy pulled on...
  13. Audioguru

    tens of years battery life ?

    Energizer guarantees a 10 years shelf life for their alkaline batteries. I have used many and never had one leak. I have seen many leaking Duracell and Super-Heavy-Duty batteries.
  14. Audioguru

    The Theremin Stretch

    The Jfets you purchased are probably not identical. Some have a 2mA spec and others have a 20mA spec. You need to test them and hope to match them if you bought extra ones.
  15. Audioguru

    My Li-Ion Battery Charger Circuit Is Not Working As Expected

    I have never seen a 9V Li-PO in an ordinary 9V Alkaline package. I guess the weakest cell will become over-voltage when charged without balancing then the metal case absorbs the shock of an explosion or holds in the resulting fire.
  16. Audioguru

    The Theremin Stretch

    Some Jfets draw a high current and other Jfets draw a low current even when they have the same part number. The datasheet shows the range of current. The circuit resistances for the biasing must match the Jfet, or the Jfet actual current must match the biasing resistances. Then the Jfets must...
  17. Audioguru

    Part Replacement in Circuit

    Digikey says that the MPF102 is obsolete and is not made anymore. They have a 10:1 range of current so you need luck to find some that will work in that circuit. I hope that whoever made the ones you bought used the standard pin-out:
  18. Audioguru

    Part Replacement in Circuit

    I did not hear in the video about the radio frequency it uses and I did not calculate it because of all the stray capacitance. The video mentions that it picks up radio stations. The antenna length depends on the radio frequency and amount of stray capacitance.
  19. Audioguru

    Powering car 5000w 500rms amplier and with xbox 360 psu

    Many car amplifiers are rated in Whats instead of real Watts. The 5000W is actually only about 100 Watts.
  20. Audioguru

    My Li-Ion Battery Charger Circuit Is Not Working As Expected

    The low cost chargers for my radio controlled model airplanes charge my 2-cells Li-PO batteries to 8.35V which is close to the 8.40V full charge voltage. The chargers are balanced to avoid a cell with a lower capacity from over-charging and exploding. When the 8.35V is reached the battery is far...
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