pre outs-line outs

Discussion in 'Home Theater Projects' started by jeff hedderson, Feb 6, 2005.

  1. jeff hedderson

    jeff hedderson Auditioning

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    I have a onkyo surrounds receiver tx-ds595 the only line out is for the sub.i also have a onkyo 2 channel amp m282.I am building a set of 12 in mains to add to my front speakers,and wanting to use the m282 to drive them,with control from the receiver.With no preouts,or line outs for the mains how can this be done? thanks.
     
  2. Mark Tranchant

    Mark Tranchant Stunt Coordinator

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    You could build a potential divider (two for stereo) and connect it to you speaker outputs. You'll want to divide the speaker voltage by a factor of very roughly 100, so something like 100 ohms and 10k ohms would do the job. You may need to experiment a bit here, or use a potentiometer with safety limiting resistor.

    Connect the two resistors in series across the speaker outputs with 10k ohm resistor "on top" (connected to + or red), and the 100 ohm connected to black or -. Take the feed for the 2-channel amp across the 100 ohm resistor using some shielded cable.

    IMPORTANT: there are a number of unusual situations in which the speaker ground connection may not be actual ground. This setup may well damage something if that is the case.

    This is a hideous botch, but it should work. Ensure that the series combination of resistors is high with respect to the speaker impedance, but not much higher than the 10k suggested here.

    Don't blame me if it all disappears in a cloud of smoke.
     
  3. Scott Giles

    Scott Giles Auditioning

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    Jeff,

    I know there are commercially made "attenuators" as well, but I bet the principle is the same. Designed to take speaker level outputs to line level for input to switching or processing device, if I understood what you want to do.

    I don't know right where to send you to buy, but I think Boston Acoustics offers one.

    good luck.

    Scott
     
  4. jeff hedderson

    jeff hedderson Auditioning

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    Thank you guys i am playing around with some circuits,got one to work but not enough out put.wondering at what voltage i can apply to simulate speaker out then measure line out to do my testing thanks guys. Jeff
     
  5. Mark Tranchant

    Mark Tranchant Stunt Coordinator

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    You can work it out easily enough. Voltage is the square root of the power times the impedance. If you also know the input voltage you need to drive your amp to maximum power, you're sorted.

    For example, if you put up to 50W into 8 ohms, you're looking at 20V. If your other amp wants 1V input, you need to knock up a 1:20 attenuator.

    I guess my 1:100 figure was a touch high in my original post.
     
  6. Allan Jayne

    Allan Jayne Cinematographer

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    Are the main amp's subwoofer line outs full range or bass only? Do a quick test disconnecting them from the subwoofer and connecting them to your separate front speaker amp.

    Subwoofer line outs intended to feed a sub which in turn has regular speaker daisy chained need to be full range.

    I am guessing that you could put two 1:2 attenuation networks across each main amp. subwoofer line out and feed both the sub and the separate front speaker amp. from that. For each channel take four resistors each equal to the line out impedance (1K-ohms?) and connect them in a square. One corner is ground, the opposite corner goes to the line out, the remaining corners go to the sub and the other amp. respectively. The 1:2 attenuation is needed to prevent undesirable interaction between the three items connected together. Sorry, useless if there is only one, monaural, sub line out.

    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  7. AeroDigirati

    AeroDigirati Auditioning

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    Subwoofer line outs intended to feed a sub which in turn has regular speaker daisy chained need to be full range.

    New to this: my addendum ...

    When a subwoofer is configured in this way, ie, AVR-->SW-->SPKRs do you still need to specify "yes" to whether you have a subwoofer configured or not? Seems as though you could configure SW=No and the AVR & SW manages the LFE, etc.? Am I off or on track? Thanks.
     
  8. AeroDigirati

    AeroDigirati Auditioning

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    Subwoofer line outs intended to feed a sub which in turn has regular speaker daisy chained need to be full range.

    When a subwoofer is configured in this way, ie, AVR-->SW-->SPKRs do you still need to specify "yes" to whether you have a subwoofer configured or not? Seems as though you could configure SW=No and the AVR & SW manages the LFE, etc.? Am I off or on track? Thanks.
     
  9. Grant B

    Grant B Producer

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    You might be able to use a 'tape output' feature running that output to a amp.

    You will not have volume control but if the amp does or if you hook up a volume control to the amp out, it shouldn't be a problem.

    That's the easy way.
     

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