High current amplifier?

Question

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

Answer 1

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 2

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 3

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

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Questions of Impedance Interaction

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Audio Basics: A Is For Ampere

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Power Amplifiers and Real-World Speaker Impedances

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Power Supplies by Nelson Pass

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Current Source Amplifiers and Sensitive / Full-Range Drivers

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Solid State Power Amplifier Supply, Parts 1-3

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Audio Power Amplifier Design Handbook, Fourth Edition

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ISBN-10: 0-7506-8072-5

Newnes / Elsevier

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The Amplifier Institute

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High Performance Audio Power Amplifiers

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ISBN-13: 978-0-7506-2629-3

ISBN-10: 0-7506-2629-1

Newnes / Elsevier

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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...



Computing Peak Currents into Loudspeakers

Authors:   Vanderkooy, J.; L******z, S. P.

AES Preprint Number: 2411

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Peak Current Requirement of Commercial Loudspeaker Systems

Otala, Matti; Huttunen, Pertti

JAES Volume 35 Number 6 pp. 455-462; June 1987

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Input Current Requirements of High-Quality Loudspeaker Systems

Martikainen, Ilpo; Varla, Ari; Otala, Matti

AES Preprint Number: 1987

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Transient Intermodulation Distortion in Commercial Audio Amplifiers

Otala, Matti; Ensomaa, Raimo

JAES Volume 22 Number 4 pp. 244-246; May 1974

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AES Preprint Number: G-3

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Load Handling Capability of Commercial Power Amplifiers

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AES Preprint Number: 2237

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Transient Analysis: A Design Tool in Loudspeaker Systems Engineering

Mills, P. G. L.; Hawksford, M. J.

AES Preprint Number: 2338

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Dynamic Linearity and Power Compression in Moving-Coil Loudspeakers

Gander, Mark R.

Volume 34 Number 9 pp. 627-646; September 1986

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AES Preprint Number: 2128

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Dynamic Range Issues in the Modern Digital Audio Environment

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High Performance Loudspeakers, 6th Edition

Martin Colloms

ISBN-13: 978-0-470-09430-3

ISBN-10: 0-470-09430-3

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Measuring Loudspeakers, Part One

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Measuring Loudspeakers, Part Two

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Measuring Loudspeakers, Part Three

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(Don) D. B. Keele, Jr. - Papers and Publications

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Answer 4

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.