555 Synth only works if....

Discussion in 'The Projects Forum' started by mxabeles, Apr 25, 2009.

  1. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    I have been making some 555 timer synths. I use 2 timer chips that when combined get nice chaotic results (also have pots for both R1 and R2 of each chip).
    The problem lies in that these synths won't produce sound unless a smack the back of the project enclosure hard.
    I am using a 12v DC power suppler (800mA) and a 5V+ regulator in the circuit. The capacitors are all pretty low (none above 10uf) except for the cap going to audio output (100uf).

    Ok, any suggestion would be appreciated!!

    Thanks,
    Max
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Schematics please?

    Have yo done any power measurements? I'm thinking power supplies mostly, but it sounds like an intermittent connection.
     
  3. CDRIVE

    Senior Member

    Jul 1, 2008
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    The most likely thing to look for is a cold solder joint. Open it up and probe and tap each component and wire with an insulated tool while the power in on. You should also be able to make basic voltmeter test at the 555's Vcc, Chg, Out, Thld and Gnd pins. If neither 555 is producing output then I would be looking at the connections common to both chips like power. I also hope that you don't have the output pins connected together. I doubt that this would cause an intermittent but it's not healthy for the 555's or the power supply. ;)
     
  4. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    cool thanks for the fast replies.

    To check for cold solder joints with a multi-meter do I just have it set to read DC voltage and have power on?? (and even if a joint is physically connected with solder it still might not work?)
    Also, yes I have a toggle switch that CAN connect both outputs. It sounds good audio wise- but don't think that is the problem in regards to turning on/sound output though because I made a new piece and the VERY first time I tried turning it on it needed to be spanked so to speak.


    Best,
    Max
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Cold solder is usually pretty visable. I'd use a large magnifiying glass (or a microscope, if you have access) and look at them. You will see where the metals are actually separated (usually).
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    You can do it that way. You can also check with power off, using the DMM on the Ohms scale.

    It takes some practice to be able to spot "cold" solder joints. A good solder joint has a shiny, mirror-like finish, and is properly "flowed" without a lot of excess solder applied. If the solder's surface looks grey and/or coarse/pitted, you may have moved the connection when the solder was in it's "plastic" state (between liquid and solid). 63/37 solder is "eutectic"; it has no plastic state.

    If your soldering looks like large blobs of grey solder, you need to practice. My own first efforts were pretty awful. :rolleyes: It takes awhile to get really good at it.

    Starting off with clean parts is a must. Isopropyl alcohol works quite well; you can get 91% isopropyl alcohol at your local Wal-mart pharmacy pretty inexpensively. Don't use 70% isopropyl; there is far too much water in it. Acid brushes work well for cleaning parts/boards with the alcohol; you can get them at a hardware or auto parts store. They have black nylon bristles with rolled sheet-metal handles.

    Don't leave the alcohol bottle open; it absorbs moisture from the air. It's also flammable, and burns with a blue flame that's difficult to see in normal room lighting.

    This is not a good idea; your pair of timers will be "fighting" each other. While one timers' output might be sourcing current, the other will be sinking it. Effectively, this is practically a dead short across the power supply, and your timers will overheat rapidly.

    You need some additional circuitry to prevent a melt-down of the timers; at a minimum use 25 Ohm resistors on both timer's output pins, which will limit maximum current to 100mA.
     
  7. CDRIVE

    Senior Member

    Jul 1, 2008
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    (1) When trouble shooting with a multimeter for node voltages (power on) it's best to connect the negative probe to common with an alligator clip. This will free up one of your hands and also insure a constant connection. If checking in Ohmmeter mode the power should always be off.

    (2) The fact that you stated that you built another model that is also experiencing the same intermittent problem leads me to believe that your problem is most likely in the power pack cable or plug.

    (3) Since you haven't posted a schematic I'm not sure how you are mixing the outputs from each 555 but outputs from separate 555's should never be directly connected together. This is because the output pin both sources and sinks current. If one chip's output pin is high while the other is low you have created a momentary short! :eek:
     
  8. CDRIVE

    Senior Member

    Jul 1, 2008
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    SgtWookie, sorry for echoing your reply. You typed faster than me! :D
    By the way, your avatar is the most impressive I've ever seen. You look sharp. You look proud. You look Marine!

    Thank you and God bless you.

    Old Grunt.
    Chu Chi 1965 - 1966
    588th Combat Engineers
     
  9. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    Sorry about messiness, first time trying to make a proper schematic with a drawing program. Wish I had Windows w/ Eagle (X11 on my Max)....:confused:

    Thanks, maybe this will shed some light on the issue. Or just shroud everything in total darkness;)

    PS. ignore red lead above "audio - out" blue line


    Best, And thanks for all the replies. Very informative!
    Max
     
    Last edited: Apr 25, 2009
  10. CDRIVE

    Senior Member

    Jul 1, 2008
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    OK, in it's current position SW2 has both U1 & U2 outputs tied together. Get rid of that for the reasons previously stated. When SW2 is switched to its other pole you are frequency modulating U1 from U2's output using the Control Input on U1. That's OK.
     
  11. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    actually in both cases it was a matter of forgetting to solder a bus or lead on the perfboard! Thanks for telling me to check! Awesome.......



    In terms of connecting both outputs of the 555 i'm sure it is bad but i did it for a while and touched the 555 timer and it wasn't too terribly hot. Actually felt hotter when output of timer 2 was connected to voltage control. Oh well.



    Thanks problem fixed

    Best,
    Max
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    If you really liked that sound effect you got with the switch shorting the outputs, you could just connect 25 to 50 Ohm resistors from the outputs (pin 3) of each 555 timer to the switch connections. That way, the resistors will take the heat rather than the timers.

    If you're really using a 78L05 regulator (not a 7805) you were probably subjecting it to a lot of stress; increasing the resistances on pins 3 to 50 or 100 Ohms would be better.
     
  13. CDRIVE

    Senior Member

    Jul 1, 2008
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    Max, a wiring technique that I've used forever is this: Make a copy of your schematic and grab a highlighter marker. As each wire and component lead or pin is soldered highlight the item. If only one end of a component was soldered ( because another component has not been installed at that node yet ) then don't run the highlighter to the end of the component until it's soldered. As your projects grow in complexity you will really appreciate this system.

    As far as your design of having the output pins of two 555's fornicating with each other is concerned.... I really think you should take Sgt. Wookie's advice.

    One last thing. I noticed that your schematic did not include any bypass caps on the Vcc line, which is a good habit to get into. The output pin of the the 7805 regulator should also include a small electrolytic about 10uF. Also, when I use wall packs I rarely rely on them to provide proper filtering, so the input of all my Vreg's nearly always have an electrolytic >= 500uF. Remember that most wall packs were designed to operate with a battery in the circuit which is a filter in itself. So (quite often) the manufacturer is not going to give it much attention. Besides that, large filter caps take up valuable real estate in the pack, in a world that puts a premium on small packages. ;)
     
  14. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    kudos, thanks alot for cap info
     
  15. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    Hi All, I built a larger synth consisting of 4 LM555 timers. Two "seperate" (all sharing same power supply) oscillators with their own LFO.
    I created a patchbay that can connect the output of the 2nd audible oscillator to various inputs of the first 555 group (output of first LFO, voltage control of 1st LFO, output of audible 1st LFO etc.). Its sounding ok and I took the sarges advice and threw some 30ish ohm resistors in series with all the outputs of the timers.

    My new question is this:
    It seems with every sound, even the most chaotic, there is base frequency "tied" to it. The sound is a hum; basically what you hear when you touch an audio plug to your finger or a jack while the power is on. This is a problem because now no sound is truly "wild." There is always a faint harmonization with this base hum.
    Any suggestions?
    CD Drive suggested putting caps around the Vcc and Vreg (I don't know what Vreg is). I also have no volume knob. Would adding a volume knob take the hum away??????

    OK, cool. This forum is one of the best online forums around. You guys rock!!!!:D
    PS yes i know. its missing knob
     
  16. Wendy

    Moderator

    Mar 24, 2008
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    The hum can be from several sources, it is likely 60Hz. It is in the air waves, and a lot of amps will pick it up if the equipment isn't shielded. It can also be from the equipment from their power supply, power supply filters don't always work as they are supposed to.
     
  17. CDRIVE

    Senior Member

    Jul 1, 2008
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    Actually the Vcc and Vreg are the same node on your circuit. I said that I didn't see any filter caps on the input or output pins of your 7805. Don't rely on a wall pack to provide proper filtering. Please re-read what I posted. Also, don't leave any control pins hanging, as they can pick up 60Hz hum and modulate the 555. If a Control pin is not being used you should bypass it to gnd with a small cap≈ .1uF.
    The wall pack is both a positive and negative thing for electronics experimenters and students. It's a positive because it simplifies the circuit. It can be a negative thing because proper power supply design seems to have been lost in the mix.
    One quick way to determine if the hum is from the power supply is to replace the wall pack with a battery and test again.
    Answer to your volume control question: No!
     
  18. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    ok thanks guys.
    So i will put caps next to the 7805 input/output. I am using a "headphone" 8" jack as my jack for the wall wart. Is that bad?

    In terms of the output pins of the 555, due to the fact I am using a SPDT center of switch to control their output destination, when the switch is centered they are connected to nothing. Thus should I put a .1uf cap running from pin three to ground? Would I still be able to modulate the output?







    THANKS!
     
    Last edited: May 1, 2009
  19. CDRIVE

    Senior Member

    Jul 1, 2008
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    I didn't say the output pin. I said the Control pin, which is pin 5. The electrolytics for the 7805 should be 500uF to 1000uF for the input pin but no more than 10uF for the Vreg output pin.
     
  20. CDRIVE

    Senior Member

    Jul 1, 2008
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    What are you implying? Please elaborate. :confused:
     
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