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Audiophile help please - Ohms and power

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dzseki:
Also in practical amplifiers the power supply has a limited power output (this is where they can cut cost), so while in theory the output power ratio for the amplifier at 4 Ohm / 8 Ohm load would be 2 : 1, this rarely happens as the power supply is usualy underspecified and drops the output voltage too soon. Specification for amplifier that is putting 30W in to 4 Ohm and 20W into 8 Ohm is very common.
Also some amplifiers (mostly NAD I think?) had switches on the back for 4/8Ohm setting, which increased the supply voltage for the power amplifier, then it could drive 4 and 8 Ohm speakers with roughly the same power

DW1961:

--- Quote from: ejeffrey on July 31, 2020, 05:27:14 am ---24 volts is the DC supply voltage to the amplifier.  It's a constant input voltage, so peak, RMS, average are all the same.  When the amplifier has to produce a varying waveform from the 24 V input source, it can produce any voltage up to (slightly less than) 24 V. The voltage is dropped across the amplifier's power transistors.  So if you want to produce a sine wave with maximum power output, it would have a 24 V peak.  In that case the RMS voltage would be 17 V.  (17 V)^2/(8 ohm) is 36 watts into an 8 ohm speaker.  In reality it won't be able to go all the way to 24 V, there will always be some voltage drop on the power transistors, hence the 30 W rating.

--- End quote ---

OK I get that. So is the voltage drop constant or depends on the amp chip? It looks like they are losing 16% from an RMS of 17V.

It looks like they lose 16% in the conversion?

24V @ 8 Ohms = 72 watts / 2 =36 watts

36 -30 = 6 watts lost.
16.6% loss? Is that linear for each voltage?

DW1961:
Just one other thing before I pass out tonight.

If you need to double power to increase volume 3dBs, then is there any loss using less voltage.
e.g. @ 8 ohms
24V gets you 60 watts total
19 volts gets you 37 watts total

What about a difference is bass power needs? Would the extra power help?

dzseki:
At different loudness levels the human ear perceives the bass and treble notes differently, consult with the Fletcher-Munson curves. Some amplifiers until the 90's had a "loudness" button to mimic the human hearing.

SiliconWizard:
As said already - as a reasonable estimate for classic audio amps: max power is basically U^2/R, with U the "compliance" voltage (basically the supply voltage of the output stage minus some unavoidable drop-out voltage), and R the nominal impedance of the load. Of course the  output stage also has a max power rating, meaning that you can estimate the max power at a given load if you increase the load's impedance, but if you decrease it, you won't be able to exceed the max rated power. Depending on the amplifier's design, it may just limit the power, blow a fuse or even burn if you use a load with too low an impedance.

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