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I had a look at another Exchange question, and couldn't quite understand.

I have a set of cheap speakers, 8ohms each with a combined output of 6 watts.

If sqrt(6w/8Ω) = 0.866 v, and the post says line level is approximately 1 volt, what should my amperage be?

How can I calculate for an appropriate resistor?

I have about 10 150Ω resistors at home... will wiring them half and half between speakers attenuate the signal? How many do I need of each?

EDIT (CLARIFICATION):

I want to know how to calculate the resistance needed to reduce a powered signal (6w) to line level.

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  • \$\begingroup\$ I think your calculation's a bit wonky. 0.866V into 8 ohms won't give you 6W. \$\endgroup\$
    – Simon B
    Commented Jun 1, 2017 at 13:59
  • \$\begingroup\$ It ought to be \$\sqrt(3W * 8R)\approx5V\$, \$I\approx0.6A\$ per speaker. However, no idea what you are asking re the resistors.....question is unclear. Voting to close. \$\endgroup\$
    – Trevor_G
    Commented Jun 1, 2017 at 14:10
  • \$\begingroup\$ You seem to be confusing all sorts of nomenclature. Line level is not used to drive speakers, it is used to send audio signals to devices expecting line-level (nominally 1-2Vpp) inputs, like power amps (used to drive speakers), audio interfaces, or studio effects units. \$\endgroup\$
    – Chris M.
    Commented Jun 1, 2017 at 14:57
  • \$\begingroup\$ @ChrisM. Hence my question says reduce to line level, not from line level. I have speakers that are powered, but I want to cut the wires to them and output them to a jack at line level. \$\endgroup\$
    – yeeeeee
    Commented Jun 2, 2017 at 6:24
  • \$\begingroup\$ @Trevor, I don't come from any electrical background at all. Don't "vote to close" because of my naivety. \$\endgroup\$
    – yeeeeee
    Commented Jun 2, 2017 at 6:25

1 Answer 1

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schematic

simulate this circuit – Schematic created using CircuitLab

Something like the circuit shown should work. I'm assuming that the amplifier will be happy driving a 18 ohm load, rather than 8 ohm. Doubling the resistance halves the power dissipated. Even so, R1 needs to be something chunky, such as a 2W resistor.

I chose the relative values of R1 and R3 so that you don't have to run the amplifier at full volume. Turning down the volume a bit significantly reduces the distortion.

If the impedance is important, you'd have to halve the values of both resistors, and use an even bigger resistor for R1, such as 5W rated.

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  • \$\begingroup\$ In a random turn of events, this circuit (with halved impedances) helped me salvage a 1995 Tiger Electronics "Talkgirl Jr." today. You are my Wife's hero, Simon B. LOL! \$\endgroup\$
    – iwolf
    Commented Jun 10, 2020 at 23:17

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