High current amplifier?

Question

What is the difference between a high current amplifier and "regular amplifier, as far as performance is concerned?

Answer 1

In order to give you a proper answer there are a few basic concepts that are VERY important to the understanding of the complex interaction between a loudspeaker and an audio power amplifier.

AC electrical signals, including the (‘small’ and ‘large’) audio signals between an audio power amplifier and a loudspeaker, behave in a complicated but well-understood manner. The behavior of AC electrical signals, unlike simple DC electrical signals, is far more complicated by virtue of the fact that current lags voltage by a phase angle of θ. Further compounding this complicated behavior is a phenomenon known as electrical impedance, or simply impedance, which greatly influences the interaction between an audio power amplifier and a loudspeaker. Impedance is a mathematically “complex” electrical quantity possessing both real and complex components. With few exceptions all loudspeakers, particularly moving coil loudspeakers, have a complex impedance that varies widely over the audible frequency range being reproduced by the loudspeaker. What you end up with is a ‘system’ that has fairly complex, yet well-understood behavior; (well-understood thanks in large part to the electrical engineers Richard H. Small and A. Neville Thiele, after whom the well known Thiele-Small loudspeaker parameters were named.)

Simply stated, electrical impedance is the opposition to the flow of alternating current. As mentioned earlier impedance is a “complex” electrical quantity comprised of not only a resistance component but also complex inductive and capacitive reactances that vary with frequency. Impedance has a familiar counterpart in DC circuit theory known as resistance. Resistance is the opposition to the flow of direct current. Unlike impedance resistance is essentially constant with respect to frequency.

Resistance forms part of a fundamental relationship between voltage and current known as Ohm’s Law. Ohm’s Law states that the direct current (I) passing through a conductor is directly proportional to the voltage (E) and inversely proportional to the resistance (R) as measured between any two points along the conductor. This relationship may be written mathematically as follows: I = E/R. Impedance (Z) is also related to voltage and current in much the same manner as resistance, that is, the alternating current (I) passing through a conductor is directly proportional to the voltage (E) and inversely proportional to the impedance (Z) or I = E/Z. It is also worth noting that power, P = IE = I²Z = E²/Z.

Virtually all audio power amplifiers (including the power amplifier section in audio receivers) function as a constant voltage source, i.e., voltage levels remain essentially constant (though with some power amplifier designs voltage levels may be dynamically stepped-up or down as needed) while the amount of current varies in proportion to the loudspeaker’s impedance and the musical demands of the audio signal.

With all of this in mind it is very important to remember that virtually all loudspeakers (some more than others) pose a complex electrical load to an audio power amplifier. This complex (or “reactive”) electrical load, i.e., the impedance of the loudspeaker, often varies substantially over the frequency range being reproduced by the loudspeaker. There are invariably one or more points throughout the frequency range where the impedance may dip well below the nominal rated impedance of the loudspeaker. When this occurs the amplifier must be capable of delivering additional current without distorting (or “clipping”) the amplitude of the audio signal. This is further complicated by the fact that there are several types of music, as well as musical instruments, that are very dynamic in nature—capable of generating very demanding transients—that can easily overwhelm lesser audio power amplifiers, especially in parts of the frequency range where the impedance of some loudspeakers dip dangerously low. If your power amplifier is unable to handle this type of dynamic audio content—and depending on your volume control settings—then one of two things will most likely occur: either the protection circuits will kick-in or the amplifier will clip, either of which will spoil your listening enjoyment and perhaps—where one is using a poorly designed audio amplifier (or audio receiver)—destroy one or more of the drivers in your loudspeakers.

Aside from transformer-based vacuum tube audio amplifiers, the better audio power amplifiers, as well as audio receivers, are capable of delivering significant amounts of continuous current into low impedances, e.g., 4 ohms or even 2 ohms and below, and even more when it comes to dynamic headroom requirements, and are usually specified as such. To accomplish this feat a power amplifier must utilize a well-designed power supply that is capable of supplying a sufficient quantity of current to the amplifier’s output stage as needed; this is often what is meant by the term “high current” power amplifier. (Note: power amplifiers capable of delivering continuous power into loads of 2 ohms and lower will usually carry a fairly high price tag; beyond the price range of the average consumer.)

So yes a high current audio power amplifier is beneficial, perhaps even important, depending on your audio and musical preferences, especially if you value audio quality and/or your loudspeakers.

 
Heavy Load: How Loudspeakers Torture Amplifiers
Keith Howard, Stereophile, Vol.30No.7, July, 2007
http://www.printthis.clickability.com/pt/cpt?action=cpt&urlID=23237810&url=http://www.stereophile.com/reference/707heavy/index.html
Hot Stuff: Loudspeaker Voice-Coil Temperatures
Keith Howard, Stereophile, Vol.29No.11, November, 2006
http://www.printthis.clickability.com/pt/cpt?action=cpt&urlID=20309033&url=http://www.stereophile.com/reference/1106hot/index.html

Questions of Impedance Interaction
Thomas J. Norton, Stereophile, Vol.17No.1, January, 1994
http://www.printthis.clickability.com/pt/cpt?action=cpt&urlID=8836822&url=http://www.stereophile.com/reference/810/index.html

Audio Basics: A Is For Ampere
J. Gordon Holt, Stereophile, Vol.14No.3, March, 1991
http://www.printthis.clickability.com/pt/cpt?action=cpt&urlID=8276863&url=http://www.stereophile.com/reference/62/index.html

Power Amplifiers and Real-World Speaker Impedances
http://www.fmacoustics.com/pdf/audiophilpoweramp.pdf
Like a Swiss Watch
http://www.fmacoustics.com/pdf/swiss_watch.pdf

Power Supplies by Nelson Pass
http://www.passlabs.com/downloads/articles/powersupply.pdf
Current Source Amplifiers and Sensitive / Full-Range Drivers
http://www.passdiy.com/pdf/cs-amps-speakers.pdf

Solid State Power Amplifier Supply, Parts 1-3
http://www.tnt-audio.com/clinica/ssps1_e.html

Audio Power Amplifier Design Handbook, Fourth Edition
Douglas Self
ISBN-13: 978-0-7506-8072-1
ISBN-10: 0-7506-8072-5
Newnes / Elsevier
http://books.elsevier.com/us//communications/us/subindex.asp?maintarget=&isbn=9780750680721
The Amplifier Institute
http://www.dself.dsl.pipex.com/ampins/ampins.htm

High Performance Audio Power Amplifiers
Ben Duncan
ISBN-13: 978-0-7506-2629-3
ISBN-10: 0-7506-2629-1
Newnes / Elsevier
http://books.elsevier.com/us//communications/us/subindex.asp?maintarget=&isbn=9780750626293

Peak Transient Current and Power into a Complex Impedance
Preis, D.; Schroeter, J.
AES Preprint Number: 2337
http://www.aes.org/e-lib/browse.cfm?elib=5093

Computing Peak Currents into Loudspeakers
Authors: Vanderkooy, J.; Lipshitz, S. P.
AES Preprint Number: 2411
http://www.aes.org/e-lib/browse.cfm?elib=5019

Peak Current Requirement of Commercial Loudspeaker Systems
Otala, Matti; Huttunen, Pertti
JAES Volume 35 Number 6 pp. 455-462; June 1987
http://www.aes.org/e-lib/browse.cfm?elib=5198
AES Preprint Number: 2293
http://www.aes.org/e-lib/browse.cfm?elib=11462

Input Current Requirements of High-Quality Loudspeaker Systems
Martikainen, Ilpo; Varla, Ari; Otala, Matti
AES Preprint Number: 1987
http://www.aes.org/e-lib/browse.cfm?elib=11775

Transient Intermodulation Distortion in Commercial Audio Amplifiers
Otala, Matti; Ensomaa, Raimo
JAES Volume 22 Number 4 pp. 244-246; May 1974
http://www.aes.org/e-lib/browse.cfm?elib=2763
AES Preprint Number: G-3
http://www.aes.org/e-lib/browse.cfm?elib=2556

Load Handling Capability of Commercial Power Amplifiers
Sekiya, Mamoru; Otala, Matti
AES Preprint Number: 2237
http://www.aes.org/e-lib/browse.cfm?elib=11518

Transient Analysis: A Design Tool in Loudspeaker Systems Engineering
Mills, P. G. L.; Hawksford, M. J.
AES Preprint Number: 2338
http://www.aes.org/e-lib/browse.cfm?elib=5092

Dynamic Linearity and Power Compression in Moving-Coil Loudspeakers
Gander, Mark R.
Volume 34 Number 9 pp. 627-646; September 1986
http://www.aes.org/e-lib/browse.cfm?elib=5251
AES Preprint Number: 2128
http://www.aes.org/e-lib/browse.cfm?elib=10241

Dynamic Range Issues in the Modern Digital Audio Environment
AES Conference Paper Number: MBB-02
Fielder, Louis
http://www.aes.org/e-lib/browse.cfm?elib=10206

High Performance Loudspeakers, 6th Edition
Martin Colloms
ISBN-13: 978-0-470-09430-3
ISBN-10: 0-470-09430-3
Wiley
http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470094303.html

Measuring Loudspeakers, Part One
John Atkinson, Stereophile, Vol.21No.11, November, 1998
http://www.printthis.clickability.com/pt/cpt?action=cpt&urlID=8477388&url=http://www.stereophile.com/features/99/index.html
Measuring Loudspeakers, Part Two
John Atkinson, Stereophile, Vol.21No.12, December, 1998
http://www.printthis.clickability.com/pt/cpt?action=cpt&urlID=8709087&url=http://www.stereophile.com/features/100/index.html
Measuring Loudspeakers, Part Three
John Atkinson, Stereophile, Vol.22No.1, January, 1999
http://www.printthis.clickability.com/pt/cpt?action=cpt&urlID=8709064&url=http://www.stereophile.com/features/103index.html

(Don) D. B. Keele, Jr. - Papers and Publications
http://www.xlrtechs.com/dbkeele.com/papers.htm
 

Answer 2

High Current Amplifier

Answer 3

Hi. Ideally, an Amplifier should produce a constant voltage across the speaker terminals whatever the load. Let's say the Amplifier is producing 20 volts at the output terminals. That means 50 watts are being fed into an 8 ohm speaker.
(Watts equal voltage squared divided by impedance) If we connect a 4 ohm speaker,halving the original load ,the same 20 volts would now produce 100 watts, and further,200 watts into 2 ohms.Each time the load resistance is halved, the Amplifier should ideally double its output. This high current capability is important if the loudspeaker impedance dips into a very low range.To make this happen,the Amplifiers' power supply must also double its current delivery to the output transistors.Most Solid State Amplifiers have high current capability.

Tubes,unlike Transisters, are not capable of producing large amounts of current.Most Tube Amplifiers would not be the ideal choice to power very low impedance Speakers.Tube Amplifiers tend to be of lower power than a similarly priced Solid State unit.The sensitivity of the Speaker,then, becomes another important cosideration when mating a Speaker with a Tube Amp.

As far as performance goes, both high current and low current Amplifiers can both perform very well,if they are designed properly, and matched to suitable Speakers.

Answer 4

A high-current amplifier is simply one in which the power supply and output stage can pass enough current to drive low-impedance loads. The "high-current" label is pretty much a marketing label, it gets tacked onto even entry-level receivers with slightly beefier power supplies than one usually sees at that level, but not much else (there is still only one pair of output transistors per channel, driving low impedance loads with a single pair can push the transistors out of their safe operating area - this is why many receivers have a "4-ohm" mode, it limits the supply rails and engages current limiting in the output stage to keep from blowing outputs.) When an amplifier attempts to swing a given voltage into the load, the load will attempt to draw a certain amount of current, and if the power supply cannot provide it or the output transistors cannot safely pass that current, output either sags (and the amplifier clips, and you can toast your tweeters if the distortion harmonics are strong enough) or you toast outputs (and if the protection circuit doesn't trip, possibly your woofers as well since up to 30-50VDC could pass through whichever transistor shorted to the speakers.)

To deliver large amounts of current, you need a beefy power supply, multiple output device pairs, and GOOD heat sinking. The amplifier can be class A, AB, B, D, whatever...the physics still apply. Also, you really can't divorce power in watts from current in amperes, since P = IE (P is power in watts, I is current in amperes, E is potential in volts.) If an amplifier cannot deliver the current a speaker asks for, the power in watts dissipated into the load will not be there either.
https://www.electrikals.com/

Answer 5

This gets a little tricky.

Power is Voltage times current.

So a 50 watt amplifier could be any of the following:

50 volts with 1 amp current
25 volts with 2 amp current
...
1 volt with 50 amp current

So a "High Current" amplifier tends to be just what it says - more current for the power instead of low-current, high voltage.

The internal circuity has to be built beefier to handle higher current so these units tend to be heavier, run cooler, last longer and yes - sound better.

Answer 6

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Some audio amps will work at DC. I had a Hafler amp that was blocked from responding to DC via an input cap that could be removed. Amps used for vibration tables are at that power level and respond to DC. They have limited upper frequency response, but you only need 500 Hz. The last reference is a 8000 watt amplifier. It doesn't respond to DC, but I suspect it's an easy mod. .

Answer 7

It's just an expression used by pimps in sales departments.

If an amplifier is to drive an 8 ohm load to 100W then it has to deliver 3.53 amperes.

For it to drive a 4 ohm load to 100W it would have to deliver 5 amperes.

And 100W in 2 ohms would require 7.07 amperes.

Nothing mysterious about it.

To call an amplifer "high current" is really playing with words.

It 's just a way of saying that it can develop the stated power in low impedance loads. But it sounds impressive.

Answer 8

look at dovebid or ebay they are used for vibration and provide megawatts for shaking airplanes... unholtz dikie bruel & kjaer ac power sources like ?? forgot