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  1. audioguru2

    part replacement

    The 1458 and LM358 are very noisy and have poor audio high frequency response. The LM358 also has crossover distortion. They are not suitable for an audio project.
  2. audioguru2

    Re-chargeable Batteries

    Hi Guys, I have been shopping for high-capacity Ni-Mh re-chargeable batteries. I know that the AA cells have a capacity that is about 4.4 times what the old Ni-Cads had, but I need more. In the good old days, a D cell Ni-Cad had 8 times the capacity of an AA cell. So I thought that a D cell...
  3. audioguru2

    Circuit You've Ever Made?

    Hi Quantum, Welcome back! I like to make things work better. You should hear my little clock radio. It looks the same as the original. It weighs 10 times more than the original (audio amp circuit, bass-boost circuit, lots of solder and a new tiny speaker with a big magnet). It has so much bass...
  4. audioguru2

    How to get low level from high (audio)

    Hi John, That's a nice attenuating "balun" circuit. But it provides a signal that is out-of-phase. While investigating swapping its inputs to swap the phase, I wondered what a null would sound like. Complete cancellation? Just distortion? So I changed your resistor values and came up with this...
  5. audioguru2

    Electronic Stethoscope 2

    Hi Doctor Emad, You are correct. You don't need U4. It just flickers the LED during each heartbeat which looks nice. U4 and the LED also waste battery power.
  6. audioguru2

    Logic Level MOSFET switching off

    Hi Cyberfreak, Now I am really confused. Your schematic doesn't show a load to ground. It shows instead an external power supply, +12VI, which is used as a backup charger on a rainy day when the solar cells can't charge the battery. Here's how I think it works: 1) The Mosfet is turned off and...
  7. audioguru2

    Logic Level MOSFET switching off

    Hi Cyberfreak, Why are you using two P-channel Mosfets connected in series, with the top one with its drain and source backwards? ??? The bottom Mosfet by itself will work fine (its source connected to the positive supply) but the supply for the Cmos gate driver IC must be at the same supply...
  8. audioguru2

    ECG for home use

    Hi Oli, I was worried that you wanted an early indication of an inheiritance! If you can afford the high price of that instrumentation-amp IC and can obtain one, it would be interesting to experiment with building an ECG. Try the author's circuit and see how much hum is on the output. Then try...
  9. audioguru2

    Logic Level MOSFET switching off

    Hi Cyberfreak, I wish that you posted your schematic because I am just guessing that you are using the Mosfet as a source-follower. A source-follower can't switch current to a load unless its gate voltage is much higher than its source voltage when turned on. So for its source to be at 11.95V...
  10. audioguru2

    help! transistor as diode

    Thanks Suraj, You have found a good article that clearly explains that our "Super Diode" will have the same voltage across it as the base-emitter voltage of a transistor. Since our "Super Diode" has current gain, the collector will handle most of its current and the base very little, reducing...
  11. audioguru2

    Logic Level MOSFET switching off

    Hi Cyberfreak, Your answer is there in the datasheet. 1uA is the maximum spec (for leaky ones that were made late on a Frday), most will conduct much less. Most people would consider that a high-current Mosfet with a conducting current of only 1uA or less is turned off.
  12. audioguru2

    Logic Level MOSFETs

    Hi Cyberfreak, Your Mosfets are tiny little things so you must be careful with power dissipation. Use your CD4001 driver with the 12V supply to drive the Mosfets to their best conduction. If your 1.8A load is continuous, each Mosfet will dissipate 292mW worst case (max. Rds). If both Mosfets in...
  13. audioguru2

    Logic Level MOSFETs

    Hi Cyberfreak, A logic-level Mosfet does not abruptly switch off with a gate voltage of 0V, nor switch on at 5V. Just do a Google search and look at a datasheet. I have used a little 2N7000 Mosfet, and its datasheet is here: http://www.fairchildsemi.com/ds/2N/2N7000.pdf The datasheet says that...
  14. audioguru2

    ECG for home use

    Hi Oli, That ECG circuit is too simple. It is like only part of circuits on the web and in the IC's datasheet. It doesn't even have a shield on its cable, which is very important to have on a circuit with such a high gain. Most ECG circuits use another opamp to drive the cable's shield. The...
  15. audioguru2

    Electronic Stethoscope 2

    Hi Trigger, The power source (battery) doesn't produce any noise. The noise comes from inside a noisy opamp, U1, and is amplified by its high gain. If you divide R1 (10K) into two 5K resistors with their junction decoupled to ground, you will decrease the output of the microphone, because its...
  16. audioguru2

    solid state toggle switch

    Hi Merrill, Please post a link to the datasheet for your piezo switch. Some manufacturers call it a proximity switch. Another link explains that its output pulse rise and fall times are too slow to directly trigger a 4013 flip-flop! Maybe that is your problem. They cure it by adding a 4050...
  17. audioguru2

    help! transistor as diode

    Hi Kevin, A forward-biased zener diode performs like an ordinary diode where its voltage will increase when its current increases. A transistor "Super Diode" (its base connected to its collector) will have the base-emitter junction monitoring its output voltage and varies the collector...
  18. audioguru2

    solid state toggle switch

    Hi Merrill, What is a piezo switch? If you tap on a piezo, it produces a high voltage that can damage an IC's input. Ante's 4093 circuit is small and simple and will toggle well. It will be on at power up. It can drive the resistor/transistor that drives your opto. The capacitors are backwards...
  19. audioguru2

    TRIAC question

    No Kevin, A Triac turns off only when its current reduces below its holding value. Reducing its conducting voltage or reversing its gate bias won't turn it off. Its current will reduce and it will turn off when its load voltage crosses near 0v. If you short-circuit a Triac then its current will...
  20. audioguru2

    Electronic Stethoscope 2

    Hi Doctor Emad, A TL072 or a KIA358 has two opamps inside. Your preamp circuit used only one of them. My latest schematic shows how to connect its pins for use as U1 and U2. Before you said that your circuit just made a noise sound like shshshshshshsh. Now you say it was a satisfactory result...
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