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Hi all.
My speakers are rated 4 ohms. A local audio store tells me to throw the switch on my SLI-80 integrated amp from 4 ohms to 8 ohms as it will improve the sound. Risks? Benefits? Your experience?
Thx
CJ
Follow Ups:
All the posts I have read here present some valid points. I prefer Chucks overall. The amp probably sounds the best from the 8 ohm tap and I'm sure this one was used when the amplifier was measured for specification purposes. With tube gear there really is no great advantage gained by using the 4 ohm tap as the phase angles the amp 'sees' at various frequencies make the 4 ohm rating of the loudspeakers almost meaningless. Tubes are voltage amplifiers and solid-state are current amplifiers.
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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.
Normally speakers with nominal 4 ohm impedence have dips below 4 ohms and benefit from the use of the 4 ohm taps. Using those taps can improve the bass performance. The trade off is that the sound in the mids and highs can benefit from use of the 8ohm tap. In both cases the operative term is 'can', not 'will'.
Try both, listen to both carefully, and pick that which sounds best to you in your system.
Usually the 4ohm-8ohm switch on the amplifier reduces the rail voltages and the peak voltage swing capability in the four ohm mode. This is so the amplifier can pass its FTC power test. Doesn't effect the sound until you reach the lowered clipping point. Or you can reverse the logic and say that the switch in the 8 ohm mode raises the rail voltages and the peak voltage capability when the current demands of the loudspeaker load are not as severe. As long as you are not testing the amplifier with sine waves you are probably OK in the 8 Ohm mode.
Let your ears be the judge. No real risks that I'm aware of. With my 4 ohm Salk SongTowers, I prefer the 4 ohm tap on my Latino ST70. As always, however, different systems may yield different or even inconclusive results.
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