Background noise from ??

Discussion in 'General Electronics Chat' started by Tryin2learn, Oct 7, 2017.

  1. Tryin2learn

    Thread Starter Member

    Nov 11, 2016
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    Hiya can anyone help me . I have been trying to add a microphone to my CCTV system but although I can hear sound I have a lot of background noise .The set up is like this I have a microphone amp mains powered ' connected to this is a speaker ' and a microphone 12 vdc powered by a adapter.I have tried everything that I know I have tried swopping the microphone' the microphone cable 'the 12 vdc cable 'the 12 vdc adapter it is now a linear one ' swopped the mains cable to the amp ' changed the speaker ' and still I get background noise from the speaker ???. Any ideas thanks Keith
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi T,
    What sort of background noise,? eg: hiss, rumble, wind, buzz ?
    E
     
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  3. Tonyr1084

    Well-Known Member

    Sep 24, 2015
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    Yes, my question as well. If it's a buzz noise it's either from your power supply or the power line is picking up AC hum. If it's hiss then your amplifier is oscillating. If it's rumble or wind it's likely exactly that - wind. Can you post a recording of the noise? That way it's likely someone here can identify exactly what the problem is. Solution could be as simple as a couple filter capacitors or a wind screen over the mic.
     
  4. Tryin2learn

    Thread Starter Member

    Nov 11, 2016
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    Hiya it sounds more like a hiss to me when I turn the volume up it gets louder . I should have said it's not wind as I have a sponge wind sock on the mic . I don't know how to post a recording of the noise . Thanks keith
     
  5. Tryin2learn

    Thread Starter Member

    Nov 11, 2016
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    Thanks for replying .like below I think it's more like a hiss . I have tried plugging the amp into different circuit's of the house and the noise is still there .I have even tried using a 12 vdc battery supply to the mic to rule out the 12 vdc adapter's . Keith
     
  6. Tonyr1084

    Well-Known Member

    Sep 24, 2015
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    OK, sounds like it's in the amplifier circuit. Can you tell us about your amp? Is it home built? Is it a cheap amplifier that you bought?
     
  7. Tryin2learn

    Thread Starter Member

    Nov 11, 2016
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    Hiya no I bought it .I wouldn't say it was cheap I paid if my memory is working about 50 -60 pounds and you can get them for a lot less . You see I only wanted a small compact amp because it was only to use with my CCTV.Maybe it is the amp though as I have tried everything else . Is there not a filter that I can use ?? Thanks for your replies keith
     
  8. philba

    Active Member

    Aug 17, 2017
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    No, you can't filter out the noise because it's originating inside the amp.
     
  9. Tryin2learn

    Thread Starter Member

    Nov 11, 2016
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  10. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi Keith,
    Do you still get the noise when the input to the audio amp is shorted out.?[ ie; mike unplugged and the amp input linked across]
    E
     
  11. Audioguru

    AAC Fanatic!

    Dec 20, 2007
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    You can easily filter out the hiss. But then you also filter out the high audio frequencies and the audio will sound very muffled.
    I suspect that a power amplifier is being used as a preamplifier.
     
  12. Tonyr1084

    Well-Known Member

    Sep 24, 2015
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    Another question to consider: What type of microphone are you using? Maybe you've mis-matched impedances. I'm often saying I'm not the expert, and I gladly share that I know what I know AND that I know there are things I do not know. So beyond basic electronics, I stink. Still, it might be possible you are using the wrong type of microphone.
     
  13. Tryin2learn

    Thread Starter Member

    Nov 11, 2016
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    Hiya thanks for the reply .how do you link the amp input ??. Keith
     
  14. Tryin2learn

    Thread Starter Member

    Nov 11, 2016
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    Hiya I don't know maybe your right I have have 2 different mic's and it is the same with both of them they are decent mic's not the 5 pound ones of eBay but i suppose it's possible both of them are wrong .thanks Keith
     
  15. Tryin2learn

    Thread Starter Member

    Nov 11, 2016
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    Hiya this amplifier has two 6.5 mm jack socket's on it and input's for a CD player 'dvd player 'aux and line ( don't know what that is ) I thought
    These type the of amplifier's had a pre amp built in ??..thank's keith
     
  16. Tonyr1084

    Well-Known Member

    Sep 24, 2015
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    Dynamics
    Dynamic microphones employ a coil of wire, magnet, and a thin diaphragm. The diaphragm attaches to the coil and moves the coil in relation to the magnet. This is a very durable design. Consequently, a trade-off of this strength is a loss in clarity. Additionally, they may not have the character that ribbons offer. Dynamics are typically cardioid microphones and capture sound from the front. Place them in front of loud sources, and percussive elements. Most close drum microphones are dynamics. You will also find them in front of guitar and bass cabinets as well.

    Condensers
    Condensers suspend a very thin material or diaphragm in two plates. Sound waves excite the plates, changing the distance between them. Altering this distance affects the voltage or signal carried to your preamp. This design creates a microphone that is extremely detailed and clear. So much so that some use tube power circuits, in place of phantom power to add missing character and warmth. Others forego tubes, and transformers further pushing the clarity envelope.

    Condensers are used on any source needing pristine focus, and accurate representation. The diaphragm itself comes in different sizes. Small diaphragm condensers have a frequency response focusing on upper midrange and trebles. Large diaphragm condensers are considered full range, use them to capture sources spanning the entire frequency spectrum. Condensers come in a vast array of polar patterns. Furthermore, some are switchable from cardioid to figure 8 to Omni. Vocals, guitars, strings, and pianos, all benefit from the clarity condensers provide.

    Ribbons
    Ribbon microphones suspend a conductive “ribbon” element between two magnetic poles. As the ribbon moves a voltage is created in the magnetic field. This voltage is sent to your microphone preamp. Their warm nature is useful in taming shrill, overly harsh sounds. It’s important to note, the ribbon element is very fragile, and should not be subjected to high sound pressure levels. Also, ribbons have the weakest output of the three types and require more gain from the preamp to get to nominal levels. Ribbons pick up sound in a figure 8 pattern, from the front, and from the rear. They work wonderfully on acoustic guitars, stringed instruments, brass, and some vocal applications.

    Summary
    Armed with this knowledge, approach each source with thoughts on how it will sit in your final mix. Different microphone types will suit different purposes. For high volume applications, grab the dynamics. For absolute clarity, use the condenser that meets the frequency needs of the source. Finally, reach for your ribbons to create density and weight.

    { source: https://www.masteringbox.com/microphone-types-uses/ }

    The use of a dynamic mic acts like a closed loop circuit across the input of your amplifier. It may tend to (and I'm not the expert) hold the amp from oscillation. Whereas condensers act more like a capacitance across the input, and thus, may allow more oscillation. May even encourage some, but again, I don't know. Where the condenser microphone needs a power source, such as a battery or an external supply, they don't generate a voltage, nor do they act like a capacitance. They use the available power and convert it into a sine wave representing the sound. They can be very sensitive, and I don't think they will lend themselves to oscillation (hiss) in your amp.

    Someone (I could look back) said to short the input to your amp. In other words, the two wires forming the input (one may be chassis grounded) can be shorted, supplying the pre-amp with a ZERO input signal. If your amp still hisses then it's not likely a problem caused by use of the improper microphone. All microphones have an impedance, and need to match what the amp is looking for. A wrong impedance might (again, IDK) cause some hiss.

    I've always loved the sound of a record player playing through a magnetic cartridge. Ceramic cartridges would produce a much louder signal, but the magnetic cartridge would produce a much better sound (IMO). So I can imagine changing microphones of the same type won't make any real difference, whereas choosing the right microphone for your amp will.
     
    Last edited: Oct 8, 2017
  17. cornishlad

    Member

    Jul 31, 2013
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    If you short out the mic connection does the noise go away ?
     
  18. Tonyr1084

    Well-Known Member

    Sep 24, 2015
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    Depending on the input type, yes, or no. With something that is already preamplified, no. Things like a DVD player; no. But with a microphone that is not preamp'd, yes, you need to amplify the signal.
     
  19. Tryin2learn

    Thread Starter Member

    Nov 11, 2016
    101
    1
    Hiya thanks for the reply .I don't know how to short out the mic connection .how do you do it ?? Thanks Keith .
     
  20. Tryin2learn

    Thread Starter Member

    Nov 11, 2016
    101
    1
    Hiya if anybody has the time if you Google KAD-2 Digital stereo amplifier mine is the one without the led display and like I said two microphone socket's but I got it wrong it's 6.3 not 6.5 . The microphone that is now connected to the amp Google Microseven M7WP microphone . The microphone is a waterproof outdoor type . Thanks
     
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