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In Reply to: RE: update on web search posted by cpotl on July 08, 2017 at 05:56:22
Got to stay with the Kiss principle to avoid trouble. i will do a little research on what size resistors to use.
FWIW, vintage tube amps and receivers with a headphone jack had a problem similar to yours; how to load the amp when the headphones were connected thru a dropping resistor of ~ 200-500 ohms - essentially open circuit. Typically they inserted a 25-50 ohm resistor across the output when the headphones were plugged in. I would expect a load in this range of values would be a reasonable starting point, esp if your amps are inherently stable.
But wouldn't the output required for headphones be different than that required for speakers? Would the amp still drive my speakers properly?
I'm suggesting you parallel a 25-50 ohm resistor across the output of each of your amps. When the speaker is connected to the amp it sees ~ 6-7 ohms assuming 8 ohm speakers. When you disconnect the speaker the amp will see 25-50 ohms depending on the resistor value you choose to use. Most amps should tolerate both 6-7 ohms and 25-50 ohms across 8 ohm taps with signal applied w/o issue.
I was using an 8 ohm resistor in parallel, but a quick on a calculator program shows that 25 ohms would give a more even effective resistance when the amp is in use. I had meant to do this earlier as another poster had mentioned this as well, but I forgot to do it. Thanks for the reminder, I will give it a try.
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