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    • #3487
      LectronFan
      Participant

      Hi all,

      When working at the amplifier circuits, I noticed that the Lectron speaker box produces too many high end frequencies. This resulted in poor and ear unfriendly sound.

      When I opened the box (for measuring the signals), I noticed there is enough place to mount a 7,7 mm or 3 inch speaker.

      So I went to the electronics shop and found a neat and more powerful speaker :

      Here you will find all info

      After fitting it quite easily into the housing, I was surprised with the audio quality. There are more deeper tones and less high. This improved the sound quite a lot and I enjoyed listening the whole evening with the 3 stage amplifier connected to my smartphone. I fiddled a bit with the equalizer to find the sweet sound.

      There are certainly better speakers (and more expensive) than this one, but I’m very pleased now.

      Greetings

      • This topic was modified 3 months, 3 weeks ago by mwpeters75.
      • This topic was modified 3 months, 3 weeks ago by mwpeters75. Reason: Changed font and size styling for easier reading
      • This topic was modified 3 months, 2 weeks ago by mwpeters75. Reason: Changed font and size styling for easier reading
    • #3490
      mwpeters75
      Keymaster

      Great idea Frank!

      Check out this video of the 50th anniversary FM Stereo radios that were created by Guenther Stabe and Gerd Kopperschmidt!  https://www.youtube.com/watch?v=cf0KpAie-Vw

    • #3717
      LectronFan
      Participant

      Hi Michael !

      Thank you for the link and the comparison between the radio modules. I have one of those  FM radio modules and together with the improved speakerbox and 3 stage amplifier, it forms a really well functioning FM radio with amazing selectivity, no noise and great sound ! And it even works with no antenna attached !

      Here is a picture of the setup :

      FM radio setup

      And here is a comparison between the two speakers. I used the 3 stage amplifier to test the new larger speaker against the original small speaker in the box. A signal was introduced into the amplifier. This was a sine wave going from 150Hz to 15kHz. You notice that the larger speaker has more low and mid range. The small speaker has only high end (peaking at max around 4kHz). Strangely enough the larger speaker reduces this 4kHz, resulting in a warm sound.

      Speaker comparison

      And here is a close up picture of the new speaker inside the box :

      New speaker

      Greetings

    • #3722
      mwpeters75
      Keymaster

      Hi Frank,

      What is the light bulb’s function in the circuit?

      Thank you for the contribution!

      • This reply was modified 3 months, 2 weeks ago by mwpeters75.
      • #3740
        LectronFan
        Participant

        Hi Michael !

        Well observed ! The lamp is used in this circuit as a small resistor (about 12 Ohm).

        This is needed for setting the correct current for the transistors.

        Greetings

         

        • This reply was modified 3 months, 2 weeks ago by mwpeters75.
        • This reply was modified 3 months, 2 weeks ago by mwpeters75. Reason: Changed font and size styling for easier reading
        • #3744
          mwpeters75
          Keymaster

          Hi Frank,
          Does the bulb illuminate at all or modulate based on the AF being late in the signal chain?
          Would you be interested in doing some video demos that I can add to my Lectron System video page on YouTube?  With uploading, YT optimizes the videos for streaming and I just add the link and embed it as a short code unless I am using a video gallery widget.  It would be fun to have your experiments demonstrated with video!

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