How get oscilation balance in amplifier and out speaker impedance?

Discussion in 'General Electronics Chat' started by Sprenc, Dec 16, 2012.

  1. Sprenc

    Thread Starter New Member

    Dec 16, 2012
    3
    0
    well, i have two amplifiers, the firstone is a tdaxxxx build by me and the second is a old 90's aiwa modular amplifier bassed in stk4142II.

    This amplifiers has as out impedance speakers 6 Ω as minimum, but if i have connected speakers with 4 Ω or less, the amplifiers starting to make an unexpected oscillation with the risk to burn' em out.

    My doubt as i could have control of this effect in a component level? :( please i have working over this doubt over many time ago back, THX you all.



    well i hope someone can help me in this question which has tormented me time ago.
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You said that the minimum allowed speaker impedance is 6 ohms. The amplifier, its heat sinks and its power supply must be re-designed to drive a speaker that is only 4 ohms.
    Simply do not overload the amplifier.
     
  3. Sprenc

    Thread Starter New Member

    Dec 16, 2012
    3
    0
    uhm ok im conscius i must redesign it, but why i should be setting on that amplifier or any amplifier, i don't believe just the power supply?
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    If the maximum allowed current used by the amplifier occurs with a 6 ohms load then it must be re-designed to use more current for a 4 ohms load.
    Same with its heat sinks.
    Same with its power supply.

    There are hundreds of amplifier circuits to do what you want but you have only one of them to be modified.
     
  5. Snowflashdrop

    New Member

    Dec 16, 2012
    1
    0
    Hi sprene,
    I would try adding a 2 ohm resistor in series with the 4 ohm speaker. I realize you will have a loss in volume but at least the load (speaker+resistor) will match the source (Amplifier). If you cant find a 2 ohm resistor with the wattage you need, I suggest you use incandescent light bulbs. Here in the US since we use 110vAC, I would need a 220 watt light bulb (W=E*I).
    NOTE: I know someone will chime-in about Impedance, but from a practical point, we are trying to get rid of the ocillations due to the load miss-match, and the light bulb filament acts more like a resistor than an impedance device.

    You can use an ohm meter to check the resistance of the light bulb, and if needed, you can put lower wattage ones in parallel to get the 2 ohms that you need. I suggest to use light sockets, but if you are careful, you can solder wires directly to the light bulbs.

    I have used light bulbs for current limiter several times in the past, with good success. Let me know if you want to discuss further, I am on Skype or e-mail.
    Regards
    PAul
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    No.
    A resistor in series with a speaker destroys the damping of resonances provided by the extremely low output impedance of a modern amplifier.
    Then the speaker sounds "boomy" like a bongo drum (boom boom) or sounds awful (shriek shriek) or both.
     
  7. Sprenc

    Thread Starter New Member

    Dec 16, 2012
    3
    0
    good point that with incandescent bulbs, i thinked in the bright over a 220 watts on 110 vca, good point, just as audioguru has said try to set the current, ok i've understood uhhm but why i could moves there? the feedback resistor? the inverse or non-inverse input components? i tried all about of this wau im desperate, lol.
     
Loading...