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Old 15th April 2008, 11:09 PM   #1
kvk is offline kvk  United States
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Default OPT impedance vs. speaker

suppose you have a SE amp with a 5K:8Ohm OPT. Now lets say you run that with 16ohm or 4ohm speakers. What does that do to the OPT impedance? Does it make it 2.5K or 10K respectively?
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Old 15th April 2008, 11:16 PM   #2
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Impedance is reflected straight through an output transformer. If the primary impedance is normally 5,000 ohms with an 8 ohm load it will be 10,000 ohms with a 16 ohm load and 2,500 ohms with a 4 ohm load.

Wade
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Old 16th April 2008, 05:20 PM   #3
kvk is offline kvk  United States
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So what would then be the implications if one did run an 8ohm SE amp at 4Ohm or 16Ohm?

I would guess that there'd be less output at 16 Ohms?

At 4Ohms, I would guess there would be more output but also more distortion and more stress on the tube? If you were to just turn the volume a bit, would you still get acceptable performance?
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Old 16th April 2008, 05:24 PM   #4
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2.5K SE is a reasonable impedance for some tubes, including 2A3's and 300B's.
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Old 16th April 2008, 05:37 PM   #5
EC8010 is offline EC8010  United Kingdom
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Loudspeakers are not resistors. Just because a driver claims 4 Ohm impedance does not mean it is 4 Ohms from 20Hz to 20kHz. Far from it. Here's a typical 150mm "8 Ohm" driver. I use the 4 Ohm tap for everything.
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