Title.
Some amplifiers are marketed with “Current of XX Ampere in each channel”. I googled it and the only thing I managed to find was some forum expert saying “Current is more important than wattage rating”. But I still don’t understand why. Ohms law is still ohms law. Doesn’t matter if you advertise one or two of the factoring numbers from the equation.
Parasound advertise their amplifiers with current rating. Does is matter and why don’t other brands do it as well?
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wasn’t able to put this comment so I made a thread for it: Do see.
Disclosure: I am not a EE. But as I have understood it, current capacity is aligned with an amp’s ability to to drive a speaker’s reactance throughout its impedance variations, which follow no simple Ohm’s Law calculation. In audible terms it means more powerful and controlled bass from your woofer. But I’ve heard amps with huge current ratings sound pretty poor in other respects. Krell was the first company to tout current doubling as the holy grail. But McIntosh always used their autoformers to trumpet “Full power to any load”. NAD now tells us “load invariance” is a virtue, and give their Hybrid Digital amps the same rating at all impedances….and are widely considered outstanding. The takeaway for me is don’t get hung up on these numbers. The FTC preconditioning requirement made it much tougher to give high 4 ohm ratings and caused a lot of over engineered over priced products to be marketed. You wouldn’t want an amp with less current than needed to drive your speakers, but having way more than enough doesn’t buy you anything.
NAD uses small power supplies, that is their “virtue”. Show me an amp with high dynamic range and I’ll show you an amp with an undersized power supply.
NAD Hybrid Digital amps, whether Hypex nCore, uCD, or Purifi, all use PWM power supplies that are highly efficient, unlike conventional supplies, and all their power ratings are conservative. It’s a big point for them. The era of soft clipping and +3dB headroom was the 80s, long before Class D was in vogue.
Wattage is directly correlated to current, Wattage = Resistance * Current^2. Wattage rating is current rating.
High current means it has a good power supply and sufficient output devices to provide it. It doesn’t really mean much unless they tell you the load impedance.
I remember a review a long time ago where a 45W Pioneer receiver put out the same 12.5A as a 50W Mark Levinson separate amp that was touted for it’s current output ;)
https://www.worldradiohistory.com/Archive-All-Audio/Archive-HiFI-Stereo/80s/HiFi-Stereo-Review-1987-01.pdfTalk to Young Ahn he makes his own power supplies for his Fluxion Amps
Running out of voltage is harmless – the amp clips, it sounds bad, you turn the volume down, and life goes on. (The ostensible purpose of level meters is to help avoid clipping but we all know they just look cool.)
Running out of current can damage an amplifier. It can overstress the output devices and damage them, maybe catastrophically.
Fancy amplifiers have circuitry to protect against this, either nicely by momentarily reducing volume, or crudely by cutting off current output. The latter causes the amplifier’s output to momentarily present a high impedance to the speaker. That sounds bad and might damage tweeters, if flyback current from a moving woofer ends up in the tweeter since it can’t return to the amp.
Bob Cordell has a chapter in his amplifier book where he talks about how you don’t really need the protection circuitry. If the amp’s output stage has enough current capacity it becomes impossible to overstress it with a speaker of a given impedance.
My rule of thumb based on Mr. Cordell’s math is: if an amplifier has one pair of output transistors per 50W rated power into 8 ohms, it can safely drive any 4-ohm-rated speaker (regardless of its demand phase curve!) and will never be overstressed. Note this assumes dynamic speakers, not electrostatics.
For example if an amplifier is rated 150wpc @ 8 ohms, and it has 3 pairs of output devices per channel, it’s safe to drive a 4 ohm speaker. But if it only has two pairs of outputs, you’re on thin ice. (And you could double that number of output devices if you want to be safe into nominally 2 ohm loads, or halve it if you only care about nominally 8 ohm loads.)
Yea… not actually how it works. Running out of voltage results in square waves. Short peaks of 200 watts is not going to burn out a tweeter’s voice coil. Clipping results in square waves. Continuous 30 watts can easily melt a tweeter’s voice coil.
As many note, when the speaker impedance is low, more current is needed to maintain the same power (watts) level. Generally, the lowest impedance is in the bass range, where you want to have maximum power available.
I notice that when I use a high current capable amp, such as a NAD or my Adcom, the bass sounds deeper and more full on my 4 ohm speakers than when I am using a receiver that does not have the same current capacity. For Class AB amps, weight is a good indicator of current capacity (heavy transformer).
Current is more important if you have a speaker that goes down to 4 ohm.
If you have an 8 ohm speaker that is 82dB sensitivity, you should focus more on watts.