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Speaker Asylum General speaker questions for audio and home theater. |
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Speaker Asylum General speaker questions for audio and home theater. |
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In Reply to: 8 ohms into 4 ohms posted by cj3 on January 5, 2009 at 21:30:05:
Your amp has output transformers with separate feedback windings (I wonder if they borrowed this idea from Henry Wolcott?). The secondary windings are tapped so that the transformers can match either 4 ohms or 8 ohms to the tubes. A toggle switch is provided to select the secondary winding tap.
Tubes have an ideal load impedance, but usually a lot of tolerance for variation from this impedance. Speakers usually show a lot of impedance variation over frequency. Thus, it is not clear which tap would give you the better overall balance of sound until you do the experiment. The risk of making the load impedance too small would be shortened tube life, but I would only expect this if you routinely operate the amps near full power.
The 8-ohm taps use the full secondary windings, while the 4-ohm taps use about 71% of the windings. This means a portion of each winding is unused and unloaded when the switch is set to 4 ohms. These unused portions can ring and degrade the sound, but the design of the separate feedback windings may control this problem.
I would do the test with a good recording of intimate vocals, and see which tap gives a more life-like presentation.
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Follow Ups
- Risks and benefits. - Al Sekela 10:45:50 01/06/09 (0)
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