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  • Off Topic: Amplifier Schematic

    This is entirely non-organ related, it's more of an electronic/hobbyist question. I'm trying to build a simple, small amplifier for a homemade megaphone-type thing. It needs to be small enough to fit in the back of a little horn I already have, and it needs to be decently loud. I found what seems to be the perfect circuit here: http://www.radio-electronics.com/inf..._amplifier.php

    The problem is, none of the components have values or part numbers! Are these values not critical? Also, what are good transistors to use, when none are specified? Also, there are six lines coming off the schematic-and I can't tell which is for V+, signal in, ground, etc. I'm guessing the signal goes into the capacitor to filter DC, but my electronics knowledge is pretty shaky. I also don't know how powerful the amp would be!

    So if anyone can point me in the right direction, it would be great. Thanks!


  • #2
    I wouldn't go that way if you're not sure in electronics. Also, what is your input (microphone?), how much voltage do you have and what's the impedance of the speaker? All that is important in finding a fitting amplifier.


    • #3
      Okay, thanks, I'll find another that's more specific. It's not really a hi-fi audio project, it's actually for a crew coxswain. A friend and I found an old siren compression driver/horn, so we were going to use an earphone as a microphone (since they're the same thing, just switched around) and try to amplify stuff through the speaker-like a homemade megaphone, of sorts.

      I believe the driver is 8 ohms, so I'll take that into account when I'm looking up diagrams.

      As for voltage, it's going to be in a boat, self contained, so it needs to be able to run off a battery!

      I'll keep poking around and see what else I can find. Thanks for the tips!



      • #4
        With what you are going to use as a microphone, most of these amps wouldn't have enough gain to get much volume out of it. You might want to just buy a kit with all the parts and a PCB and solder it up yourself. Check out this link.
        There are many more companies that also supply audio amp kits. Just search for them.



        • #5
          Okay, battery powered was obvious but said you already had a housing I tought there would be a battery compartment already in so you knew the voltage. But I see now you are adapting something else. So let's say you'll have about 6-9V available (4-6 AA cells).

          The CK701 amp in the link HenryK provided would be something usefull. If you don't want to build the kit then the schematic with values is on the site. One Watt may not seem much but with a horn it can be really loud. Also you only have batteries, so try to limit the power.

          I wouldn't use a headset in reverse. As HenryK said that will need a lot of amplification and probably sound really bad as well. I'd go with an electret mic. They can be found easily and are not difficult to use. It is a proper mic and as such will also need a lot of amplification but it will likely behave better. A good schematic and a lot of info on using them can be found here:
          http://www.instructables.com/id/Pre-...-electret-mic/ This is a very simple version.
          A bit more elaborated to get the most out of the microphone:
          http://sound.westhost.com/project93.htm Look at figure 6 for a transistor version. For your application you could omit C6, R13 and the connection to F2 and connect C8 to GND (connection 1)


          • #6
            Sorry it took me so long to respond, I haven't had access to a computer for the last few days, but I read your posts on a phone!

            I'll go for a real mic-it's an entirely fun-based project so it's no big deal if the headphone doesn't work, but why not do it right the first time!

            I'll figure out a 1-watt amp and make this thing work. Thanks!