toy organ emf?

Discussion in 'The Projects Forum' started by ale2121, Apr 12, 2009.

  1. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    so i made this toy organ with a 555 chip.
    http://www.ecelab.com/circuit-toy-organ.htm
    It's pretty exact to the schematic, no changes. I made it at home, plugged it into my amp, and it was lots of fun. So, I bring it to band practice to play, along with my amp, and it won't work. There were 3 other amps plugged in with all sorts of other music equipment. Could it have been an emf issue? I checked all the connections while i was there, and nothing was lose. I got it to play really faintly (which i'm considering as nothing, except for purposes of trouble shooting) when I used the cheap unshielded dollar store cable, but when I used a shielded cable, I couldn't even get the faint sound. So, I plugged it back in with the unshielded cable, got a faint sound, then tried moving it closer to the amp, and got nothing. hmmmm. the circuit is still on a breadboard, all the parts are exposed. Anyways, I brought it back home, plugged it all back in, and it worked fine. why is it that it works fine at my house, but not at my friend's practice space?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Sounds like his mixer input is not exactly compatible with the odd arrangement on the 555 circuit. You need to swap the speaker/capacitor arangement, the capacitor should be on pin 3, and the speaker going to ground. To help your friends electronics add a variable 1KΩ resistor in there too.
     
  3. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    what does the 1k resistor do? and you think grounding the speaker will help with the emf, if that is in fact what it is? as i said, it works fine at my house. dumb, i know. his? sorry, no, there was no mixer. it was the exact same arrangement I had when it was working in my (her) room.

    and where do i put the 1k resistor? a volume knob, right? i don't hav variable one, but i put a 1k fixed resistor in there and nothin.

    i just tried the capacitor switch and it's not really helping. it's having weird problems in my room now too. and now I'm picking up a radio station every time i touch the switch?
     
    Last edited: Apr 12, 2009
  4. Wendy

    Moderator

    Mar 24, 2008
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    You are feeding the input of an amp. The 555 has a strong DC component with the AC, which is why there is a capacitor. Not knowing your friends arrangement, I can only speculate that feeding a 555 output directly into the mixer can do real damage. You need a capacitor between your setup and the mixer input. The circuit doesn't care if the capacitor or speaker is on top or bottom.

    The other thing is the volume level out of the 555 is LOUD. Again, not good for your friends electronics. A variable would reduce that too, you could make it adjustable. I'll be back in a bit with a sketch of what I'm talking about.

    From what you said, your friends amp has several inputs, you are trying to use one of them. That is a mixer, and you are mixing several signals together.

    **************************

    Rereading your first post, you said you plugged into your amp. I assume (since you didn't post a schematic) that you removed the capacitor and speaker altogether, that or connected in a manner shown in the first picture.

    The last picture was what I was talking about.

    [​IMG]
     
    Last edited: Apr 12, 2009
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The output at the speaker should be buffered through an op-amp circuit that will give a 1V peak-peak output, centered on ground.

    Option 2: put a microphone in front of the speaker
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    The OP has modified the design, but we don't know how it was modified. My solutions would work, but we were posting at the same time, and we'll need input how he did it. I assume (again that word) he used a 9V battery.

    [​IMG]
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    A quick side note, I used to do something very similar in my college days (as a noob), but for a darker purpose. The 555 Hysteretic Oscillator is an extremely simple oscillator, and will go well into the ultrasonic region. Coupled to a stereo it will drive neighbors and pets crazy. <evil laugh>

    Another side note: you will get a much more melodious sound from pins 6 and 2, although it will screw up the tuning somewhat. If you want to persue this I'll be glad to go into it.
     
    Last edited: Apr 12, 2009
  8. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    ok, its just me. there is no mixer. it's just my amp. I replaced the 8 ohm speaker in the schematic with a quarter inch out. now I can't even get the circuit to work with my original 8 ohm speaker. ok, this op amp business. I've been asking around about this and can't really get a clear answer. is it the same as a preamp? and I have an LM 358, data here.. http://www.national.com/mpf/LM/LM358.html

    will that work, and keep me from getting radio stations in my toy organ?

    ps the hysterics is cool. i'd like to build lots of little instruments like this, but one working for starters would rock.

    oh, and, as far as the loud goes, it sounded great with my amp. when it worked. which is why i was confident enough to show up to practice, psyched to play it. doh.
     
    Last edited: Apr 12, 2009
  9. Wendy

    Moderator

    Mar 24, 2008
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    You may have zapped your 555. Personally I pay about 25¢ each for them, so I don't view it as serious. The capacitor is needed on the 3rd picture to prevent that, and the resistor will isolate the 555 somewhat from the amp.

    I'm one of the local 555 gurus hereabouts, and I like helping people experiment, so don't be afraid to ask questions or explore. They are fun little chippies.

    ***************************

    My computer glitched in the middle of this post, Anyhow, the out my 555 Projects.
     
    Last edited: Apr 12, 2009
  10. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    hmm. i popped the 555 into my flashing led circuit and the led is just on and not flashing. so, i'm guessing yeah i blew TWO out. no, it's not that big of a deal, unfortunately the only chips i have left at the moment are 556. if i were to use a 556, is it just a 555 on each side of the chip? except for vcc and ground? like 2 - 7 is one 555 and 8 - 13 is another?

    ok, sooo just to avoid destroying more of them, what exactly am i do to this circuit? change the cap to the 3 pin side of the speaker? and add a volume knob.

    and even if i don't need op amp, that's fine, but it would still be cool if someone could explain in laymans terms what it is and when it's useful. Even if I don't NEED it would it be helpful?
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    That melodious sound I was talking about is a triangle wave, the op amp will allow you tap into Pin 2/6 without affecting the circuit. For this application a transistor would also work. A triangle wave is much closer to a sine wave, which is a pure sound. A 555 sound wave is normally a square wave, which sounds a lot like bagpipes.

    I'm attaching a document I made for such a purpose (showing the difference between a 555 and a 556 connection). Connect the equivalent pins for pin4 to ground, it will shut down the unused 555 in the 556.

    [​IMG]

    If you check out my AAC blog you find a lot of info like this.
     
    Last edited: Apr 12, 2009
  12. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    what makes the triangle wave? the op amp added to the 555? also, I've heard using two 555s or a 556 will even out the wave. more like a sine wave vs a square wave?
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    Pin 2/6 in a 555 oscillator already has a triangle wave (reread my Hystertic Oscillator article), but it is a sensitive point. Touching it changes the circuits operation. To tap into it requires minimum interaction, which means extra circuitry.
     
  14. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    cool. ok, i think i will make a new circuit tomorrow with a 556, and include both 555s on the 556 to get a better sound. I've seen some of those schematics around, i think the Forest Mimms book has them in it. I will keep you posted on how it turns out. I'm sure I will have just as many questions tomorrow. Thank you :)
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    The 555 has a max allowed output current of 200mA. The circuit with a new 9V battery will try to feed 375mA into the 8 ohm speaker and it might blow up the 555.

    You don't need an opamp. You just need to connect the capacitor to pin 3 of the 555, a 10 ohm resistor in series with the speaker to limit the current and connect the capacitor and resistor to the hot wire of a shielded audio cable (to stop radio interference) and connect the shield to the 555 ground and to the amplifier's ground.
     
  16. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    sweet, i will try this too.
     
  17. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    ok, so i'm still working on this. i have the circuit as posted earlier in this thread. I've made the following changes based on suggestions: 1, the 4.7 electrolytic cap goes from pin 3 to one hot end of a 1/4 inch mono out. the other hot end of the mono cable goes to a 5k pot which is then connected to ground. the ground end of the 1/4 inch mono connector is also connected to ground. It did eliminate a lot of noise, but I'm still getting a radio station when I either touch the ground on the 1/4 inch connector, or when i touch the raw wire connected to pin 1, which is also grounded.

    how can i eliminate this? I think I don't really understand proper grounding when it comes to audio.

    also, what is a ground loop? is that what causes the radio station pickup?
     
  18. Wendy

    Moderator

    Mar 24, 2008
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    I'll have to get back with you later, but I will be back.

    ****************************************

    Schematics, even crude ones, are always much better than verbal descriptions. Try the diagrams I suggested.

    As to the radio noise, partly it is a fuction of unsheilded wires (which make dandy antennas), and partly there is some unlinearity in your input. You can filter this out, but first we need to get the 555 end working the way you want.

    You are using batteries on this 555 circuit, right?
     
    Last edited: Apr 23, 2009
  19. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    hey, sorry I didn't realize you updated this post. which wires are unshielded? the cable going to my amp is technically shielded though I'd be willing to bet it's not as good of shielding as it could be, they were cheap cables. But, if you mean the switch wires, how would I ground these? the switch, from pin 1, actually is grounded. but when i touch it, it picks up radio stations.

    what is unlinearity? the 555 does work the way i want. the whole circuit works quite well, just the occasional radio station noise.
     
  20. Audioguru

    New Member

    Dec 20, 2007
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    Shielded audio cable is used to shield the signal wire from picking up radiated mains hum and radio stations.
     
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