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  1. audioguru2

    +- 15vdc Dual Converter

    Hotwaterwizard, Where is the power source for TR1 and TR2 going to come from?
  2. audioguru2

    Lasersound

    Hotwaterwizard, 1) I saw an advertisment for an ultrasonic "sound beam" about 3 months ago but have lost the source. Apparently when the modulated beam hits an object (like a statue in a museum) then the sound demodulates and appears to originate from that object. Only people near the object can...
  3. audioguru2

    Electronic Stethoscope

    Hi guys, Sorry for this late post. This project has attracted a lot of attention but has also created much frustration and confusion, due to schematic and parts list errors in the original article. Let us stick to the original circuit using standard parts and having 9V batteries. Dpak showed a...
  4. audioguru2

    4N25 Schematic check

    MP, If a back-EMF protection diode is built into a fan then it would be in parallel, not in series. So if you connected it backwards then the diode would be forward-conducting across the power supply which may blow-up the diode and/or the power supply. Amps, Maybe you misunderstood my...
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Mastrila, Maybe when your parts got hot they were damaged. The guys who are talking about modifying this power supply to get 5A of current output are having problems similar to yours with the original circuit. Their post is here...
  6. audioguru2

    4N25 Schematic check

    That's right, MP. Please let me elaborate. The motor has coils of wire around a core, just like a relay. They are inductors. When you energize an inductor then a magnetic field is built-up around the core. When you remove the power source then the collapsing field induces a high voltage across...
  7. audioguru2

    PLL FM Transmitter

    Hi Mayo, I hope that you do not want to transmit on the FM broadcast band of 88 to 108 MHz because the VCO in the 4046 has a typical max. frequency of only 0.8 to 2.4MHz (page 7 on data sheet). A broadcast band FM transmitter needs an 88 to 108MHz VCO which feeds a very high frequency digital...
  8. audioguru2

    4N25 Schematic check

    Amps, your revised circuit shows 12V relay coils powered by only 5V. Use 5V relays. When you turn-on the computer, it will be cold and the switch or temp.-controller will apply only 8V to 1 fan. Will it start running on this low voltage? Most fan controllers apply full voltage for a moment to...
  9. audioguru2

    Car stereo amplifier output ratings

    MP, you are absolutely correct. Some of those monster sized and heavy weight car amps produce very much power by drawing up to 100A from the battery, stepping-up the voltage and using high-power circuits with many power transistors. But others cheat the numbers by stating a non-standard 1 or 2...
  10. audioguru2

    Car stereo amplifier output ratings

    Thanks, Sec, for that excellent link. I've seen the site but not that article before. Maybe the advertisers should spell Watt as What. There is another link somewhere that examines the cheap junk that is built into a well-known and expensive home surround-sound sub-woofer and amps with satellite...
  11. audioguru2

    0-30 Vdc Stabilized Power Supply

    MP, to boost the current output of a regulator, a power PNP transistor and input sense resistor is recommended to be wired across the regulator, as shown at fig. 10 in the datasheet of the MC78XX series by ON Semi here: http://www.onsemi.com/pub/Collateral/MC7800-D.PDF This way, their superb...
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    MP, I was replying to Tom in his reply #9 in this post where he asked if he could parallel 2 of these Stabilized Power Supplies to get more output current. My reply refers to paralleling these supplies, any other regulated supplies and IC regulators in general.
  13. audioguru2

    Car stereo amplifier output ratings

    Hello all, Looking for a car receiver or amplifier and saw 200W? Well it has 4 channels so each one delivers 50W, right? Maybe, but what kind of watts? If you measure a car battery to be 14.15V when charging, then use it to power an amp that incorporates the very latest low-saturation FETs...
  14. audioguru2

    When to use a heat sink

    Hi Firefly, a heatsink is used to carry heat away from a component conducting the heat to the surrounding air, since the heatsink has a large surface. Heat is caused by the power that the component is dissipating (power = the current through it X the voltage across it). The 2N3055 can have up...
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hello Tom and others, You CANNOT put stabilized power supplies in parallel since you cannot ensure that they have EXACTLY the same output voltage. The supply with the slightly higher voltage will carry the whole load while the lower voltage one(s) will tell its regulator that the voltage is high...
  16. audioguru2

    0-30 Vdc Stabilized Power Supply

    Do not use a 2N2222 instead of a 2N2219 for Q2 since it must dissipate up to 5W and therefore is shown with a heatsink. The 2N2219 has a larger metal case and is designed for use with a heatsink. The 2N2222 has a small plastic case and cannot dissipate more than about 1/3W. With 5W in a 2N2222...
  17. audioguru2

    OPAMP questions

    Most general-purpose or audio voltage-feedback opamps have a low frequency gain of 100,000 or more and then start a 20 dB/decade roll-off at 10 Hz to 100 Hz. They have the built-in roll-off so that at a high frequency such as 1 MHz or more, where the op-amp circuit will have close to 180 degees...
  18. audioguru2

    sensitive low frequency filter

    MP, let's hope that Rich can get the circuit working. Don't you count 4 equal RC networks on your filter? It looks like two 2-pole filters cascaded, but the first 2-pole filter isn't quite a multiple-feedback type since the feedback resistor doen't connect to the junction of the 1st resistor and...
  19. audioguru2

    sensitive low frequency filter

    OOps, the bulb won't be very bright, not loud. Why not use a super-bright LED in series with a current-limiting resistor instead of a bulb? Then adjust the resistor for the maximum brightness.
  20. audioguru2

    sensitive low frequency filter

    MP: Isn't your circuit a 4-pole filter? Rich: Russ's classic 3-pole filter will filter the bass very well but will not have enough gain for a microphone unless it is placed right up against a very-loud speaker. But don't simply increase the gain of the 1st stage becuse it will overload during...
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