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External Amp for DIY Tempest

Discussion in 'Home Theater Projects' started by Theon, May 10, 2004.

  1. Theon

    Theon Active Member

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    I am toying with the idea of powering a DIY Tempest with an external amp. Can I use any stereo amp to power the sub, or will I need an amp with certain inputs?

    The crossover of my Yamaha receiver is set at 90Hz and is unadjustable.

    Thanks.
     
  2. Mike SJ

    Mike SJ Well-Known Member

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  3. TimForman

    TimForman Well-Known Member

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    I've been using an external pro amp for a couple of years and it's fine. There's plenty to choose from like QSC, Pyle Pro, Crown, etc.. A older stereo amp will work fine. Some of the old Realistic receivers had hefty power supplies and work nice if you can scrounge one up at a thrift store.
     
  4. Theon

    Theon Active Member

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    Thanks for the responses guys. Here is what I think would work: Sub out on my primary receiver to any input (CD, Cassette) jack on my external sub amp. Then I use speaker cables between my external amp and the subwoofer. Sound good?

    One thing I'm unsure of: since the Sub out on my receiver is giving out a mono signal, how would that affect how I hook up my sub? As I understand it, the Tempest is a dual-coil woofer and I would benefit from having an external amp powering it through two channels (more power).
     
  5. Brian Fellmeth

    Brian Fellmeth Well-Known Member

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    This just came up in another thread. Yes, you can split the sub out line and plug them into the R and L RCA inputs of the receiver, say CD, Aux, anything but phono if it has one. Then use both the R and L speaker wire posts- one pair to each voice coil. Do not reverse the polarity. That way you will use both channels of your stereo amp and get the most out of it.
     
  6. Theon

    Theon Active Member

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    Thanks Brian.

    One more question (for now): should I just drill/cut a hole one in of the walls of the sub big enough for the speaker wire to pass through? I'm building a sealed sub so I'm unsure to as how this will affect it's performance.
     
  7. TimForman

    TimForman Well-Known Member

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  8. Bhavesh

    Bhavesh Well-Known Member

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    Theon,
    Using speaker terminals would add a really nice, professional touch to your sub. The one I got from Parts Express had its own gasket so there's no need to worry about air leaks.

    Plus this way you have the option of using the shorting bars to wire it in parallel if/when you buy a better amp.GOLD PLATED BI-AMP TERMINAL
     
  9. Theon

    Theon Active Member

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    Ok, I bought a "Y-coupler" which I hope will separate a mono signal into stereo (part # 274-511 at radioshack canada). I also bought a terminal cup similar to the one Bhavesh recommended above. At the back of the cup, there is a bar connecting the negative terminals and another connecting the positive terminals. Since I want to wire my Tempest in parallel, should I keep these bars? I am planning to do as Brian sugessted and run one pair of wires to each voice coil.

    Also, I am unsure on how to physically connect the Tempest to the terminal cup. I am going to use speaker wire, but will I need spades or some other connector to acheive a reliable connection with the Tempest?

    TIA
     
  10. Brian Fellmeth

    Brian Fellmeth Well-Known Member

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    This can be done with any spade type thing that is very snug on the lugs, but I strongly recommend that the speaker wire be soldered to the lugs on the driver and on the terminal cup. If necessary, dragoon some friend or relative who knows how to solder to help you. There will be so much energy and vibration in that cabinet that I would not trust any connection based on friction alone.
     
  11. Theon

    Theon Active Member

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    Brian, thanks for the quick and thorough response. As I don't have a friend or relative to solder for me, would a tight connection and electrical tape work? (I hope that question didn't reveal my complete ignorance...:b )

    Also, does the Tempest driver come with any connectors?

    Finally, running each channel at 8 ohms would equal a 4 ohm load total? (I want a 4 ohm load since my amp isn't very powerful).
     
  12. DustinF

    DustinF Active Member

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    I don't believe you need a "Y-coupler" to seperate the mono signal.

    You run speaker cable from your stereo's left speaker connection to one of the voice coils on the Tempest. Then run another speaker cable from the stereo's right speaker connection to the other voice coil.

    In your stereo's setup menu, make sure it's set to stereo. If it's a 5.1 receiver then make sure the speakers are set to large, turn off the center speaker and sub output and rear speakers.
     
  13. Mike SJ

    Mike SJ Well-Known Member

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  14. Brian Fellmeth

    Brian Fellmeth Well-Known Member

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    What you need to understand is that your amp is really 2 amps- one for each stereo channel. Your choice is to use both amps, each seeing a single 8 ohm voice coil as a load, or just use one channel and give it both voice coils wired in parallel for a 4 ohm load. While it is true that halving the load will increase the power, it will not double it. Using both amp channels instead of one won't double the power either (both amps share a power supply) but it will probably get much closer to doubling the power.
     
  15. Theon

    Theon Active Member

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    I bought some female interconnects which seem to be doing the job on the lugs.

    You've convinced me that one channel to each coil is the way to go. I won't need much power anyway since I only went halfway up the volume scale with my old 120 watt Sony SA-WM40.

    Now all I'm waiting for is the Tempest driver itself...
     
  16. Theon

    Theon Active Member

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    Well, my Tempest is up and running. It sounds great but there is one curious detail that I wonder about. It seems that the sub is receiving high frequency signals (I've even heard voices coming from the sub). The reason I know this is because I can isolate the sub by turning of my main speakers. My Yamaha 5560 manual says that the crossover is an automatic 90Hz. I have my setting set to Bass = Sub, and my Mains are set to "Small". Does anyone have a theory?
     
  17. Joe Mihok

    Joe Mihok Well-Known Member

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    wish I could help but I have no idea. Does it do this for all movies ? Or have you only tested with a particular one ? I know some voices can be pretty deep (example, FRAILTY) and can possibly be passed the the sub ......
     
  18. Theon

    Theon Active Member

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    I'm experiencing the high frequencies coming from the sub in music. It sounds as if the 15" woofer is receiving a full range signal, but due to it's size cannot reproduce the high frequencies well enough.

    And to Joe: Congrats on getting your sub finished! I learned lots from your thread.
     
  19. Andrew Pierce

    Andrew Pierce Well-Known Member

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    I suppose it may be possible that the LFE channel of the movie(s) in question have high-freqency information encoded into it and your receiver is not sorting it out right, assuming you don't have it plugged into the wrong channel. In any case, you could try using some sort of low-pass filter on the line. Do a search on PE for 'fmod', which are usually used for car stereo applications, but might do the trick for you.
     
  20. minhG

    minhG Well-Known Member

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    just to chime in. i know that most high pass filters and low pass filters have some kind of slope so you get a blending of frequencies aboce and below the xover point.

    is it possible what you're hearing is normal?

    for example if i high pass a speaker at 80hz, i would not expect a straight line drop off of frequencies, i would expect it to be gradual so that the sounds blends together.

    i noticed my sub does something similiar with the front speakers off i can hear a faint distance bit of the sound.
     

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