Impedance and volume

[Quickie]

I will use a classic SVT tube head for my example question. When playing in the 4 ohm output mode, you get full power (300 watts)....but at a higher voltage than when in 2 ohm output. In the 2 ohm output you still get 300 watts....but at a higher current and lower voltage. Voltage = volume. Am I correct with this example?

Voltage is after all what gives you volume. Watts are not watts in other words. Am I totally off base or is this true?

[billfitzmaurice]

Originally Posted by Quickie

Am I totally off base or is this true?

Your half off base. You can't use the higher impedance tap to get a higher voltage swing as the amp won't like it. That's why they have different taps.

[okcrum]

volume is proportional to watts = volts X amps, so they both count. An SVT will output the same power at both impedance settings.

The higher the impedance, the higher the voltage needed to attain a given power level. Perhaps this is leading you astray.

[billfitzmaurice]

Originally Posted by okcrum

volume is proportional to watts = volts X amps, so they both count.

He's actually right on the voltage, it's voltage swing that determines volume, not watts. Where current, and therefore power comes in, is how much is required to deliver the voltage swing across the impedance load.

[Bassmec]

Originally Posted by Quickie

I will use a classic SVT tube head for my example question. When playing in the 4 ohm output mode, you get full power (300 watts)....but at a higher voltage than when in 2 ohm output. In the 2 ohm output you still get 300 watts....but at a higher current and lower voltage. Voltage = volume. Am I correct with this example?

Voltage is after all what gives you volume. Watts are not watts in other words. Am I totally off base or is this true?

Well its speakers that makes sound, not watts, if one gets an ac voltage then its impedance will determine the overall wattage.
The transformer taps are arranged to provide an ideal match to the tube Impedance and operating voltages and the loads that are connected to the secondaries.
There is no advantage to a tube amp to operate at lower impedance in fact there are small but good reasons to apply a load impedance as high as 16 ohms if its catered for in the secondary windings.

[okcrum]

Originally Posted by billfitzmaurice

He's actually right on the voltage, it's voltage swing that determines volume, not watts. Where current, and therefore power comes in, is how much is required to deliver the voltage swing across the impedance load.

Yup, either way you end up heating something.