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  1. audioguru2

    Connecting An Audio Output to 20 Headphones...

    Shahrier, 1) Check the spec's for your VCR to see whether it can drive the parallel combination of the TV and amplifier. 2) You have 2 posts about this subject. Please see my reply in your other post about using gold-plated relay or switch contacts for audio.
  2. audioguru2

    Audio Signal Switch

    Hi GPG, I think that a 74HC4051 or regular 4051 will be noisy and make switching "pops" when used with mic levels. Shahrier, What is an 89c51? Since microphones have a very low signal level, relays or switches should have gold-plated contacts. It doesn't cost much more since the layer is very...
  3. audioguru2

    Demagnitize reception of radios

    Quantum, Then what will you do if they play MP3s, CDs, cassette tapes or vinyl records? Or if they go LIVE? Or Kariokee? I think that Rap is just yapping to a big beat. Sometimes it rhymes. Just be thankful that they don't play bagpipes! Don't you have noise laws down there? I was at the St...
  4. audioguru2

    Connecting An Audio Output to 20 Headphones...

    Shahriar, Your FET Audio Mixer will work fine if you select a FET that has a correct amount of self-bias current. But your Microphone Mixer looks like a line-level mixer, that needs a separate mic preamp for each mic. If you design it with enough gain for direct mic connection, and you use...
  5. audioguru2

    PWM using 555 timer

    Wait a minute, Darrin, You mentioned, Triac. All along we thought that you were PWM'ing from a DC supply. A TRIAC works like a latch, since once it is triggered, then it conducts and stays-on until the current through it drops very low (when the mains voltage crosses 0V for resistive loads)...
  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    DjZero, Welcome to our forum. I'm sorry to hear that your project doesn't work. 1) What are the ratings of your power transformer? a) AC voltage at full load. b) AC current at full load, or VA rating. c) AC voltage with no load. 2) What is the DC voltage at the base of the 2N3055...
  7. audioguru2

    PSU 0-60Volts

    Ante, It must need a VERY LARGE (300W!) heatsink. (or liquid nitrogen).
  8. audioguru2

    TV Signal Amplifier

    Wazzamatta with it? It can't be any cheaper!
  9. audioguru2

    Who is using the oldest computer?

    Ante, Kindof extreme. My 486/100 doesn't even have a fan.
  10. audioguru2

    PWM using 555 timer

    Ante, I grow hair on my face most of the time, and especially when I see a circuit with its common-mode input voltage limit exceeded. Have you seen what happens to a TL07X? Its output suddenly inverts! It makes really bad overdrive distortion. I relate the moon being full with Murphy's Law, and...
  11. audioguru2

    Connecting An Audio Output to 20 Headphones...

    Shahriar, Your "black box" headphones distribution amplifier will be a 10 to 20W (for 8 ohms load) PA amplifier with 2 or 3 line-level inputs. Each headphone connects to its output through a 120 ohm/1W resistor in series (use 2 for stereo). Your microphones "Amp" will be a 20-input microphone...
  12. audioguru2

    Perhaps a 555 circuit

    Hi Stu, 15 minutes is a long time for a 555 timer. It will need a high value capacitor with extremely low leakage. Instead, I suggest using a CD4060B oscillator/counter IC. A timer project that uses it is here: http://www.mitedu.freeserve.co.uk/Circuits/Timing/24hour.htm
  13. audioguru2

    Demagnitize reception of radios

    Quantum, Yeah, I know. Your neighbours' radio bothers you and you want to mess it up for them. Right? Creating sparks makes large, low-radio-frequency AMPLITUDE variations, which causes static in AM (Amplitude Modulation) radios. FM (Frequency Modulation) radios ignor amplitude variations, and...
  14. audioguru2

    Who is using the oldest computer?

    Vainajala, I've seen refrigerators with plumbing hoses attached, but never a computer like yours has. Good idea.
  15. audioguru2

    Passive audio filters

    Hi Vainajala, That should be better, but I hope that your step-compensation doesn't mess-up the phase at crossover too much. How did you manage to have a tweeter rolloff that is much more than 12dB/octave? Did your sim program screw-up?
  16. audioguru2

    PWM using 555 timer

    Ante and Darrin, Do your simulation programs know what happens to the 555's comparators when the pin 5 voltage exceeds their common-mode voltage limit? I think that the comparators won't work if pin 5's voltage is higher than 1 or 2 volts below the supply voltage, or lower than 2 or 3 volts...
  17. audioguru2

    Demagnitize reception of radios

    Quantum, You want to MAKE a radio sound distorted and fuzzy???? Huh? ??? FM radios have a specification called Capture Ratio, which allows them to lock onto the strongest signal and ignor any weaker signals including noise. That is one reason that they sound so good, and why it would be...
  18. audioguru2

    Demagnitize reception of radios

    Hi Quantum, You don't say what your radio sounds like to make it not "clear sounding". You also don't say if it is AM or FM. Your radio may have a cheap, tinny-sounding little speaker, or have a simple circuit that picks-up interference. It may have a poor amplifier with lots of distortion. What...
  19. audioguru2

    how can i find...

    Or if you need 3 ohms, then use a liltle more than 1/2 foot of AWG47 wire (if you can see it), but it won't carry much current nor be a good inductor. Coils are rated in current (size of wire) and inductance (number of turns of wire around a magnetic core). So if you are making a coil, then be...
  20. audioguru2

    Trying to build a project, need parts

    Hi Stu, Over here, RS sells only "war surplus" stuff, and some simple kits. I think that it is British, not Radio Shack. Don't you have better British suppliers such as Mapplin (Mappin?) or Farnell?
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