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  1. audioguru2

    5 Watt Audio Amplifier

    Hi Clemson, I am sorry to correct those other guys, but the LM383, TDA2003 and TBA810 are all designed to deliver a fairly low output voltage to a 4 ohm speaker when supplied by a 12V car battery. To get 5W into 8 ohms requires a signal that is nearly 18V peak-to-peak. Since an amplifier is not...
  2. audioguru2

    ECG for home use

    Hi Oli, I would just use a single cheap, common and low-noise TL072 dual opamp to replace both of those rare expensive ones.
  3. audioguru2

    Electronic Stethoscope 2

    Thanks Oli, My new project, Electronic Stethoscope-2, has been submitted and should be highlighted on this site's home page any minute now.
  4. audioguru2

    Audio amplifier

    Hi Atheos, Welcome to our forum. The schematic figure 6 on page 11 of the datasheet is complete and should work fine.
  5. audioguru2

    555 timer help

    Hi Suraj, The 555 is a dedicated timer IC. The problem that it has with long time periods is that the timing capacitor must have a high accurate value. Electrolytic caps are not accurate and they have a fairly high leakage current. If you are rich and have lotsa space, you could use 100 or more...
  6. audioguru2

    ECG for home use

    Hi Oli, Greetings to Hong Kong. Your English is excellent! I buy parts on the web from the local division of Farnell and they guarantee next day delivery. Millions of parts at pretty good prices. At www.farnell.com I can see Hong Kong's flag! Try them. Notice that the amplified signal is fed to...
  7. audioguru2

    555 timer help

    Where is the timing capacitor for the 555? You are using a piece of wire instead.
  8. audioguru2

    AA battery power rating

    Hi Quantum, Simply compare the size and weight of AA and AAA battery cells. They are full of chemicals, not majic. Of course the biggest one will supply more ma/hr. (This does not apply to their "almost empty" Ni-MH D cells, that only have a little AA cell inside). You could also compare their...
  9. audioguru2

    ERRORS

    It is not OK now. I just got the same error trying to reply to you. Let's see how it is in about 14 hours.
  10. audioguru2

    Electronic Stethoscope 2

    Hi Doctor Emad, You don't need the blinking LED. Without U4, the new (TL072) corrected circuit has only two ICs and is very small.
  11. audioguru2

    ERRORS

    Hi Ante, At about the same time today as you posted your errors, I sent an e-mail to Mixos attaching exactly the same errors! ;) I suspect that "footer-linkman" is having difficulty fetching advertisment #30, and others. It is very bad at that certain time of the day. I just simply give-up...
  12. audioguru2

    ECG for home use

    Hi Oli, You don't need to use those particular IC's, many manufacturers make inamps and opamps that would be OK. Where on this planet are you at? Maybe I can direct you to a good international supplier. On another electronics web-forum, a guy is having trouble with exactly the same circuit that...
  13. audioguru2

    Electronic Stethoscope 2

    Hi Doctor Emad, I am happy to hear that you got your corrected project working properly and am glad to have helped you. Thank-you for helping me prove that my ideas, corrections and simplifications work very well. I will post my corrected circuit as a new project. ;D ;D ;D 8)
  14. audioguru2

    Auto electronics ?, 24V gauges in 12V circuit

    Hi BBC, Welcome to our forum. It might be very difficult or impossible to use a 24V instrument cluster in a car that is designed for 12V. The speedometer will work if it is the old mechanical kind and the cable fits. It will be wrong if the wheels are a different size. If it is electric or...
  15. audioguru2

    Electronic Stethoscope 2

    Hi Doctor Emad, Which circuit did you constuct? (We have many, now). I don't know why it doesn't work, when it worked before but was noisy. It should work fine and with less noise with the TL072. The "auto" stethoscope that you posted is very similar to our corrected one, but uses a 3-wire...
  16. audioguru2

    Transistor tester

    Hi Steven, Sorry, but its switch is labeled backwards. It is shown in the "NPN" position (NPN emitter-follower). It is a waste of a 9V battery since most of its voltage is wasted in the 470 ohm current-limiting resistor. It could use cheaper and longer lasting two AA cells (3V), if it was...
  17. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    Hi Kain, Don't worry about stability, if your heatsinks don't work well then the output transistors will be destroyed! If the project is powering a low voltage or accidently shorted load at 5A, the output transistors must dissipate about 200W. You were talking about using a flat heatsink. But...
  18. audioguru2

    part replacement

    Of course they were used. Nothing else was available in the early days of opamps. Even my very old speakerphone used one. Nowadays, a low-noise, wide bandwidth, low distortion TL072 costs less than a noisy, narrow-bandwidth, high distortion LM358. A noisy, narrow-bandwidth 1458 costs the same.
  19. audioguru2

    Re-chargeable Batteries

    Hi Ante, Your shop has a good battery. I think that I have been looking at too many American manufacturers. Sanyo has one that is 9000ma/hr but they are not available in small quantities. I can't remember which of my suppliers sells a European battery, Saft or something. Which manufacturer is...
  20. audioguru2

    How to get low level from high (audio)

    Hi John, I am assuming that the car radio's amps are bridged without a transformer, with a + non-inverting amp and a - inverting amp for each speaker. Each amp's common is ground, not floating. Since your circuits have the lowest value resistor in the - inverting side, their outputs are also -...
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