Bizarre Mini Amplifier + White Noise Generator?

bma_finished_a

[Jordi] made this awesome looking mini amplifier which has a rather unusual feature. He’s calling it the Bizarre Mini Amplifier because it also has a white noise generator built right into it! Bizarre right?

Now, most people would just find a suitable amplifier and put it into a nice box, but not [Jordi]! He’s designed the amplifier circuit from the ground up! It features four distinct stages like most typical amplifiers:

  1. Impedance Adapt Stage: Two OPAMPS for both the left and right channels — The high input impedance allows for different audio sources to be connected without affecting the output.
  2. Mixer stage: Combines the left, right and noise signals into one, using a third OPAMP. A potentiometer is the output resistor which allows for the volume control.
  3. Filter Stage: A simple filter stage that uses a R-C low-pass filter, another potentiometer controls the tone.
  4. Power Stage: A final power amplifier to boost the output.

After building the circuit, there was a bit of troubleshooting to get it to work properly, so if you’re interested [Jordi] has done a great write-up of this on his blog.

Finally, he decided to add a white noise generator after he discovered it helps him sleep. This is the one part of the project that he didn’t actually go into detail for! But, considering it’s just white noise, we could probably figure out what he did. Stick around after the break to see the device in action!

There’s just something about the retro style look to this thing that we love. We know it’s just a plain old white project box, but between the clear speaker, chrome switches and old labels, it just looks… great!

Comments

  1. anyone got an idea where to find those embossed labels? They look sick.,

  2. jaromirs says:

    Using a lot of unneeded opamps into circuit doesn’t make it better.
    – Using voltage follower U1A is pointless, when input impedance is nailed down to R1,R2,R3 to approx 3kOhm.
    – Follower after mixer is not needed, mixer has low output impedance anyway.
    – Mixer could be done as three resistors with no opamps, afer all.
    – Opamps should be TL07x, not TL08x

  3. Bob says:

    WhiteNoiseBaby on android has saved my sanity with the new born.
    Never thought of trying it on myself too…

  4. Bogdan says:

    1. LM386 is not a 5W amplifier.
    2. What @jaromirs says.
    3. Waaaay to huge capacitor for filtering 10.000uF? Also poorly connected with too thin wires in a wrong topology(after the regulator, really?)

    • tekkieneet says:

      With that large of a capacitor, better have reverse bias diodes
      connected between the In/out pins of LM317 to protect it when you cut
      the power. Should read up on Ripple Reject graph of LM317 in page 7 of
      the datasheet. The large cap should be at LM317 input and a small one at
      LM317 output.

    • bryan says:

      too many op-amps and yes, the filter cap is on the wrong side of the regulator. 1000uf should be enough before and maybe 10 or 100uf after the reg is more typical.

      I would not have a pot across the feedback of the op-amp either. suppose it opens up (even for just a short time); you now have infinite gain which is not what you want. I would have a safety resistor in parallel with that; or better yet, use a conventional pot at the input of the OA and not setting the gain factor like you did.

  5. Chris Rennie says:

    I like the look of your bizarre amp a lot! But as several folk here (jaromirs etc.,) have pointed out, what your actual circuit provides and your description of it, aren’t the same.

    • Jordi says:

      What you see working in the video is what is described in the circuit. The only thing that is different is the huge 1000 uF capacitor, that I placed by error in the schematic after the regulator, and in the real circuit is placed before. The rest is exactly what you can see in the video. It was more than 10 years since I didn’t use operationals, so I’m sure that there are some things that could be improved.

  6. Trav says:

    I love the look. Is it me or are the volume knobs rotating backwards?

  7. Where do you find clear speakers? Just searched and am only finding speakers in clear enclosures.

  8. jg says:

    Nice build.

    I have to say that while white noise blocks out background noises and is nice for sleeping, I prefer to sleep using ‘calm sea waves’ – it’s a 3+ hour .mp3 file rigged to repeat on whatever’s playing it. Sometimes I’ll cycle through sound tracks of showers or a waterfall or rain – rain with thunderstorms is great.

    But my real distraction problems are ADHD (treated with meds) and the ever present ringing in my ears (treated with learned ignoring), and I’ve found pink noise works best for me – better than white noise or brown noise.

    • pcf11 says:

      Background noises? What background noises? It is quiet like a crypt around here. You can hear your own heart beating. You just got to love the peace and quiet of the country.

      • Greenaum says:

        Try living across the road from a pub. A busy one! With crappy windows from somewhere close to the dawn of time. Good job I’m a good sleeper.

        • pcf11 says:

          I live across the street from a farm field. Some years my neighbors are all ears too when the farmer plants corn. It is true that you can hear corn grow. You have to listen really hard in order to hear it though.

          A little bit of my front yard

          • Greenaum says:

            YOU CAN HEAR THE GRASS GROW!

            Actually I didn’t think much of that song.

            OTOH where I am now, I can walk 10 minutes to the centre of town, or to the houses of most of my friends and family, so I do ok. The town has a stupid 1-way traffic system on most roads, which means you can get a bus to somewhere, but not back again. So it’s a good job it’s a smallish town. 30,000 people.

            I’m a city boy originally, from a very cosmopolitan town, half a million people, I miss culture! By which I mean anything that stupid heterosexual white idiots wouldn’t want to do. Nothing against white heterosexuals, obviously, but a mix of everyone is cultural riches. There’s all sorts of different people back home, but you only appreciate what you have when it’s gone!

            My home town also has the wierd advantage of being a major urban centre, connected to several other big cities, but you can catch a bus and within 20 minutes be in the middle of beautiful Yorkshire countryside.

            Still, nothing wrong with peace and quiet, I could happily spend a few weeks somewhere like your place. It IS a good job I’m a heavy sleeper!

  9. jon2wyslyd says:

    Nice build.

    I have to say that while white noise blocks out background noises and is nice for sleeping, I prefer to sleep using ‘calm sea waves’ – it’s a 3+ hour .mp3 file rigged to repeat on whatever’s playing it. Sometimes I’ll cycle through sound tracks of showers or a waterfall or rain – rain with thunderstorms is great.

    But my real distraction problems are ADHD (treated with meds) and the ever present ringing in my ears (treated with learned ignoring), and I’ve found pink noise works best for me – better than white noise or brown noise.

  10. Syrus says:

    ermehgerd.
    LM386.
    TL082
    Never seen that done before. Ground up?
    Wrong values used captures more of the essence :/

    Similar and much older products/projects:
    Runoffgroove – Beavisaudio – Smokey amp.

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