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Hello Im new this is my first post, I have lots a questions.

Discussion in 'General Electronics Discussion' started by morbe, Feb 8, 2012.

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  1. morbe

    morbe

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    Feb 8, 2012
    Hello everyone, I'm new both to this website forum and the interesting world of electronics. to include circuit building and repairs etc.
    Just to introduce my self my name is Mike, I work as an information systems. I'm a musician as well which is the reason to come in here and pick every one's brain! I have 3 tube amps one dies on me and one I'm slowly restoring by sending it to amp tech and dropping hundreds of dollars on a techs eagerness to work in high powered amps confidently without worrying about getting shocked or killed. I have read minimal web sites and books on electric circuits and power amplifiers and I have skills with a solder gun, which I know makes me one of the most dangerous persons on earth. But I recently purchased a book today from radio shack "Getting Started in Electronics" and my knowledge of this subject is growing every day. Eventually I would love to buy a DIY Tube amplifier kit and build it with the confidence that I too have built a high powered amplifier in hopes that I dont kill my self by simply plugging a guitar into it. LOL.

    Well enough with the introduction i will just get into the "meat and potatoes":
    you have to crawl before you can walk and you have to walk before you can run.

    I recently purchased a pre amp kit and 7 watt amplifier from velleman. These kits are for like kids to learn I think. The skill level is 2. but I want to connect them using the same power supply.

    1. The pre-amp power supply needs to be 10-30vdc/10mA and the power supply for the amplifier requires a power supply of 8-18vdc/0.5A. I have found in the far reaches of my attic a power supply that is rated output of DC 12v / 2A. can I use this power supply to run the devices simultaneously?

    2. Also I have to cut the tip of this power adapter off to connect it to the devices and use it to power the device. The power Adapter output again is DC 12V / 2A. as this is my first real project I'm a bit worried that I might be entering the realm of danger. everywhere I read says that 2 amps is more than enough to kill you. I understand that I am opening a can of worms here, but I can never get a straight answer. what happens if I plug that adapter in and touch the wire wires with each hand will it send electric death though my heart and body? I know enough to make sure every thing is soldered properly and not to touch the device while its plugged in and if I do have one hand behind my back. but I plan to make this a travel guitar amp and well when the guitar is plugged into the amp the operator becomes part of the circuit because the strings are attached to ground. Is there a chance that if I design this makeshift guitar amp I will kill myself attempting to play a guitar though it?

    Thanks in advance folks, I have my favorite Music, Amps, Guitar, forums. that I go to I hope to make this my electronics home forum.
     
  2. davenn

    davenn Moderator

    13,865
    1,956
    Sep 5, 2009
    hi morbe,
    welcome to the forums

    12V at 2 amps isnt going to kill you. You wouldnt even feel a tingle. The voltage is too low to break down the outer skin resistance. you may feel something if your hands were wet.

    at 240VAC ~ 25 - 30mA is enough to put your heart into fibrillation if the supply wires were held, one in each hand. As a general rule anything over 50V is deemed hi voltage and needs to be treated with respect is there are a few amps flowing

    that plugpack should be ok for your project. even tho the supply is 12VDC @ 2 amps
    ... that is an indication of its maximum capability. the circuit(s) will only draw what they need. in your case 10mA and 500mA (0.5 A)

    cheers
    Dave
     
  3. Rleo6965

    Rleo6965

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    Jan 22, 2012
    Its much safer if you use isolation transformer . Specially if your using a Vacuum tube amp.
     
  4. Laplace

    Laplace

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    Apr 4, 2010
    Your power supply has the appropriate voltage and sufficient current capability for your needs; however, this being an audio application, I would check that adequate electrical filtering is included to suppress AC hum. Even though the unit may have large electrolytic capacitors, who knows for how many years they have been degrading in a hot attic. Your power supply may need some fresh capacitors installed, especially if it is not a regulated voltage design.

    The danger from electricity is proportional to the current flowing through the body which can be calculated from the applied voltage and the electrical resistance of the body. This resistance is primarily due to the skin resistance in contact with the electrode. I=E/R The 'normal' contact resistance is on the order of 5,000 ohms but this can go down to 1,000 ohms if the skin is wet (damp, sweaty, salty), or can increase to the megohm range if the skin is extraordinarily dry. If the electrode pierces the skin to contact the blood underneath, then the resistance can be as low as a few hundred ohms. See the table below to compare the danger from increasing levels of current. I have been shocked at the 5mA level by a 6 volt battery when my hands are clammy.

    Current,mA........Probable Effect on Human Body
    1mA.............Perception level. Slight tingling sensation. Still dangerous under certain conditions.
    5mA.............Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary reactions to shocks in this range may lead to injuries.
    6mA-16mA........Painful shock, begin to lose muscular control. Commonly referred to as the freezing current or "let-go" range.
    17mA-99mA.......Extreme pain, respiratory arrest, severe muscular contractions. Individual cannot let go. Death is possible.
    100mA-2000mA....Ventricular fibrillation (uneven, uncoordinated pumping of the heart.) Muscular contraction and nerve damage begins to occur. Death is likely.
    >2,000mA........Cardiac arrest, internal organ damage, and severe burns. Death is probable.
     
  5. morbe

    morbe

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    Feb 8, 2012
    Thanks every one.
    This by no means is going to be a tube amp. Maybe one day i will make one. Right now im just taking baby steps. I feel a little bit more comfortable working with this ac adapter until i read that last post were it said 2000mA can start cardio problems and death it likely stuff. I guess what im getting out of this is, even though im messing with amps with pontential deadly levels, its more than likely not dangerous because the volts are not high enough to penetrate my body efficiently to kill me.
    I would have loved to put an output transformer but i dont understan yet how it puts out electricity and how i could match it up to what i need from both devices. Plus this is my first project i didnt want to waste too much money. So far im in the whole about 50 bucks including both project parts and a book to learn as i go. This make shift amp will be in a chassis built from spare wood i have at my house. Power adapter was found and speaker is being donated.
    Should i be worried that my guitars electronics are grounded and this power adapter is.not grounded. Most power adapters and plugs have a ground is that to protect me or the equipment.
     
  6. jackorocko

    jackorocko

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    Apr 4, 2010
    But only at the right voltage. As davenn said, you need high voltage to break down the resistance in the skin. What this means is that anything below 50V with normal dry hands will do zero damage to yourself.

    Also remember the golden rule of thumb, don't ever double dip. What this means is keep only one hand in harms way and the other far away. If you create a path across your heart for current to flow it is indeed worse then letting current flow from your left hand to your left foot. Or so they say, I know it has worked for me because I been hit by 240V before and it hurt like a bitch, but I am still here. :) I have actually been shocked quite a lot. So don't let fear stand in your way, it only hurts for a second.

    milliamps of current is what kills, but it needs high voltage to do the damage.
     
    Last edited: Feb 8, 2012
  7. jackorocko

    jackorocko

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    Apr 4, 2010
  8. morbe

    morbe

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    Feb 8, 2012
    Yeah i know what yoy mean about safety. I was poking around in an amp i had but i was using drum sticks and wearing leather work gloves. It must have been a site. Im still worried that s dont have a wire in my adapter that connects to ground. Any one know if this is a bad thing? I read alot that all electronics should have a ground wire to be considered safe
     
  9. morbe

    morbe

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    Feb 8, 2012
    I built the amp it was easy from set up to clean up it took about 4 hours. I thought that the preamp stage would give more but I'm not sure yet as the speaker I was using Im sure was not the ideal speaker, it was part of a stereo system we used to have. any how here are some pics.

    [​IMG]

    The electronic kits actually came in a clear case. I used this to make a prototype case, Of course I plan to make a mini head out of it.

    [​IMG]

    Not sure if the speaker was the correct to test with. but this was just to make sure it worked.

    [​IMG]
     
  10. morbe

    morbe

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    Feb 8, 2012
    Here is a video, I wasnt trying to make a great sounding amp I was just starting to learn electronics.

    [​IMG]
     
  11. jackorocko

    jackorocko

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    Apr 4, 2010
    I don't think pre-amps are meant to drive loud speakers, that is why they are called pre-amps and not amps. But, anyway, good work and now on to bigger things I presume?
     
  12. morbe

    morbe

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    Feb 8, 2012
    Well i put in the preamp so i could boost the signal of the guitar. Well this was a kit. Im lookinh at schematics and trying put a plan out in paper how it would fit in a board but for some reason my mind is having a hard time converting schematics to a physical circiut. Any good web sites that explains how to do this? Or any good books? Im afraid im limited to kits untill i figure out how to do this. The bigger things will have to wait for now.
     
  13. jackorocko

    jackorocko

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    Apr 4, 2010
    I am very fond of diyaudio.com if you are into do it yourself amplifier kits. When I used to visit their frequently they used to always be running bulk PCB sales/kits. Someone makes a really good design and so someone else decides to make a PCB and get it massed produce. The best part, it comes cheaper and the work is already done. All you need do is solder the pieces together. BTW, nelson pass is a frequent visitor of diyaudio.com if you know who that is.

    Also, I would like to recommend you to the chipamp if you want a extremely cheap but rather nice amplifier kit. Google it, plenty of versions around but brian from chipamp.com I believe is who I bought my kit from. It will make that cheesy speaker you got jump right off the table. :)
     
    Last edited: Feb 10, 2012
  14. morbe

    morbe

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    Feb 8, 2012
    Well some time has past and I know I'm bumping an old thread, sorry if the moderators are against reviving old threads.
    And the times have been slow to learn. I have gotten a new few books on electronics. Learned a little more but not much. My confidence level has raised. I'm not as timid to rip something apart and test what component was bad. Im confident with building simple circuits from schematics. I can mod guitar pedals. But I still stay clear of the high voltage guitar amps. I'm just not that confident yet. But I'm getting there. I can follow instructions extremely well and I've been looking into trying to build my own stuff. I still have the 7 watt amp I built but took the pre amp out. I'm brainstorming how I can connect a tube driven pre amp to it. And try to run it off a 9 volt power supply. Ive seen tube based pedals and looked over how to convert the schematics to place in a guitar style amp. But then here is the choice " to do or not to do"? This is the question. I've proven that I can follow instructions time and time again. So why not take the leap of faith and buy the fender champ amp kit? It's a simple circuit and every one claims It's the gate way diy amp kit. One day I will build one, one day.
    Btw thanks for having such an awesome forum.
     
  15. davenn

    davenn Moderator

    13,865
    1,956
    Sep 5, 2009
    cool OK next step in learning.....

    mounting the circuit boards using small nut and bolts. Two reasons
    1) looks a lot neater and tidier and makes it easier to fault find at a later date
    2) stops boards touching each other and shorting out causing the "magic smoke" to be released

    keep up the good learning well done

    Dave
     
    Last edited: Aug 1, 2012
  16. morbe

    morbe

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    Feb 8, 2012
    Yes, will do. Though screws were all I had at the time. I didn't even think it was going to work. I'm a bit more conservative and neater now.
     
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