Can a subwoofer amplifier (-)output be grounded ?

Discussion in 'General Electronics Chat' started by Externet, Sep 1, 2014.

  1. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    On a mobile monophonic power amplifier, can the minus output for the subwoofer speaker be grounded ?
    Or are forced floating terminals ? Or depends on manufacturer ?
     
  2. MikeML

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    If it for automotive use, almost for sure the speaker must float because it is driven by bridged (opposite phase) amplifiers.
     
  3. SgtWookie

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    Jul 17, 2007
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    I wouldn't try it if I were you. Wire might be expensive, but the repair bill would be a lot more.
     
  4. Lestraveled

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    It is never a good idea to ground a speaker terminal. At minimum you will pick up noise. A bridged amp will most likely smoke.

    WHY would you want to ground a speaker terminal?
     
  5. Shagas

    Active Member

    May 13, 2013
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    If the mobile device was powered by an ungrounded source such as a battery then it would be safe to connect one of the speaker terminals to ground but I can't think of a reason why you would need to do that.
     
  6. Externet

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    Thanks.
    A couple of the responses above mention bridged amplifier. ¿? ----> For a monophonic (single channel single output subwoofer amplifier) ?

    A couple of responses wonder why I would do that. Will be used/operated as an AC power supply of variable frequency /amplitude /waveform by feeding an unbalanced audio signal generator to its input, and may need a common negative with the 12VDC battery that powers it. (An unbalanced audio signal generator on steroids)
     
  7. alfacliff

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    Dec 13, 2013
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    a bridged amploifier is two amplifiers fed out of phase to increase the power. with only 12 volts supply, the power output is limited. with one amplifier output going positive and the other going negative, that efectivly doubles the available power. the speaker is connected between the two amplifiers.
     
  8. MikeML

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    Hook it up with the speaker (load) connected to the two output pins (A &B, my names), powered with +12V and oV(gnd). Apply signal (sine, music) to the amplifier input. Use two-channel scope to observe the voltage at A and B with scope-gnd-clip connected to 0V. If you see equal, but opposite phase signals, each having a DC offset of ~6Vdc (centered halfway between 0V and 12V), you have a typical bridged amplifier.

    If so, you could drive a load with one end grounded by doing the following: get a huge electrolytic capacitor (several thousand uF, >10Vdc). Connect +end to either A or B. Connect the load between the - end of the capacitor and 0V. Now you are driving a grounded load, but with 1/4 of the rated power of the amplifier.
     
  9. Externet

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    alfacliff; MikeML... It is a monophonic amplifier as from the original post. No bridging. There is no A, B outputs for L,R. There is speaker out +,- , period
    Its internal power supply pumps the 12VDC battery supply up to +/- 60V rails. Checked continuity, (-) output is internally to chassis. I will ground commonly battery supply and speaker minus. I will come back with the color of the smoke later...

    Edited - added: This type of amplifier----> http://g-ecx.images-amazon.com/images/G/01/electronics/detail-page/DCT5001D_diagram.jpg
     
    Last edited: Sep 2, 2014
  10. MikeML

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    I never thought it was a stereo amp. Everything I said above assumed it is a Mono bridged amp.

    My A is your speaker+, my B is your speaker-.

    If it has a step-up switcher, then there is a chance that speaker-(B) is internally connected to 0V.

    Added: after looking at the link, I believe that it is a single-ended (not-bridged) amp. However, not connecting load- to speaker- would be a huge mistake. Since that thing can push 64A, returning the -end of the load to 0V will create a huge ground-loop through the power supply wiring, and the thing will likely oscillate.
     
    Last edited: Sep 2, 2014
  11. alfacliff

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    Dec 13, 2013
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    thats right, subwoofer amps are usually mono. that dowsnt mean it isnt bridged. a stereo bridged amp would have 4 or more amps. bridging is used to get more power out of amplifiers, not to produce stereo or mono.
     
  12. GopherT

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    Nov 23, 2012
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    There is a switch in back for Mast/Bridge/Sla modes. Likely need two units to do bridging setup.

    Still not sure if the (-) speaker would be all the way down to ground in a non-bridged mode or only at 1/2 of supply (6 volts). Testing, as previously suggested, would be required.
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
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    As you say - bridge tied load can't be grounded - there are 2 amplifier outputs, one driving each end of the speaker coil.

    IWHT the DC resistance from an amplifier output would be vastly different to one that is grounded inside the amplifier - the resistance to any convenient ground point from a grounded output should be near enough zero.

    Should be possible to tell using any decent DMM without pulling the amp apart and tracing into the innards.
     
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