Question about high current amps versus "not high current amps"

@thecarpathian 'Output devices' means components in the output section of the amplifier; usually power transistors mounted to a heatsink. We make both class D amps and tube power amps so in their cases either GaNFETs or power tubes.

@atmasphere

Thanks again.

I don’t know if you get told this often, but I really appreciate that you take the time out from what I’m sure is a full dance card to offer your insight here and to educate.

Some amplifier manufacturers do take current measurements on the outputs of the amp, the Krell I400 has 62 amps of peak current on the output. I'm sure those are taken for only brief milliseconds before the outputs fry.

@gregm , @steakster

+1

 

Amps measure the provided flow of electric current.

Watts measure the amount of electrical power being used.. Watts are calculated by multiplying the current in amps by the voltage of the source.

Sufficiently beefy amps needed are dependent on the speakers you are running. A high-current amplifier is simply one in which it has a robust power supply and output stage that can pass enough current to drive low-impedance loads. If you have 4 ohm speakers that might drop down below that at times, you’ll need something with a fair chunk of available and fast delivery of current to run them decently.

To deliver large amounts of current, you need a beefy power supply (or plural independent channel power supplies) with multiple output device pairs, and GOOD heat sinking. The amplifier can be class A, AB, B, D, whatever...

The top end build (…and price ) amplifiers are “ dual mono”. amplifiers.
- A dual-mono amp contains two mono channels that are independent of each other.

-A simple stereo amp consists of two shared channels which always share a single common power supply and thus are always dependent on one another.

Essentially, in a dual-mono setup, these are two separate amplifiers with the same design, with matched or high manufacturing tolerance (read: more expensive) components. The pic below (Dual-Mono) shows that the left and right signal paths are entirely independent of each other ….each with their own independent high-end , robust & beefy power supplies.

 

WHY WPC Ratings can be misleading and prone to marketing crap Now ….. think multichannel AVR’s that share a single power supply for all its channels with a stated, say, 100 wpc rating, ….. The big power sharing between channels dilution is obvious .

The stated marketing blurb of quoted number wpc without reference to the available current delivery and other output metrics is now split across all the channels, Each channel that an AV receiver supports will need the power to run. The more channels you have, the more power-hungry the AVR will be to make full use of its capabilities.Thst is why most AVR’s flunk out in 2 channels optimal performance as underpowered units that fail the performance of the speakers.

The FTC 1974 Rule? If a standard is selected and adhered to by all, then at least we’d have a method of comparing products in terms of their available power output on a fair basis.
More than 50 years ago, before the arrival of surround sound and multichannel products, there was a universal standard set up by the Federal Trade Commission (FTC), which established a method for rating stereo (two-channel) receivers and amplifiers.

The FTC’s 1974 rule specified that stereo amplifiers be rated with both channels driven simultaneously into 8 ohms across a specified bandwidth (20 Hz to 20 kHz) at a specified level of distortion (THD), and that’s how things went until the appearance of multi-channel AV receivers.

Some real life examples of the fallacies on current AVR power ratings re: WPC as a true measure of amp power

120 watts per channel; all channels rated at 0.05% THD”
(no bandwidth mentioned; no impedance load, no mention of any channels driven simultaneously)

“7 x 125 watts per channel”
(No frequency range stated, no distortion rating, no mention of number of channels driven, no mention of impedance load)

“Front L + R: 85 watts per channel, 20 Hz to 20 kHz, at 0.08% THD, into 8 ohms, both channels driven.”
(Very good ratings for two stereo channels; other channels were similarly specified, in pairs, but no ratings for all channels driven)

“No power output specified”
(unbelievable!)

“100 watts per channel x 7; 20Hz — 20 kHz; 0.03% THD, 8 ohms; all channels driven”
(Excellent but still needs each channel’s maximum output)

Except for the last unit, a lot of confusion ensues about exactly what sort of per channel output capabilities each receiver has.
 

tt should be stated that no matter how you decide to test an AV receiver’s amplifier output section, it will always involve a test signal that bears little relation to music signals from a CD, DVD, or other source.

Music signals, by nature, are always varying, not just in level but also by frequency, so it’s impossible to generate a test signal that exactly duplicates music or soundtrack signals since they vary every moment.

TAKEAWAY

Difficult speakers needing “ grunt” to drive means a beefy need for amperes (current) ….not just confusing WPC ratings in isolation.Match your amplifier accordingly wisely.

Those are formulas for static case, i.e. single wave. But is amp capable of delivering a lot of current on high transients QUICKLY? It may be high current capable when single is stable, but what about transitions (which is what music is)? Is it able to raise current and provide energy fast enough?