[diofan56]

Hi all!

What is the difference between a high current amplifier and an amplifier that is not high current?  Is there a difference that can actually be heard?

Would a more powerful amplifier be about the same as a lower wattage high current amplifier?

Thanks in advance for your replies!

Dave

[I.Greyhound Fan]

The link below may help to answer your question-

http://forums.klipsch.com/forums/p/33606/292494.aspx

[modular747]

"High current" capability only means that the amp can produce more power into very low impedance speakers - i.e. 2 or 1 ohms - than a "lesser current" amp with the same power rating into 8 ohms.

Unless you have very low impedance speakers or are running speaker sets in parallel, you won't hear any difference, assuming the amps are otherwise identical.

High current amps are a better choice if you are running them in bridged mode for very high output into 4 ohm speakers.  They also are the amps of choice to use for arc welding...

[rlee8394]

"High current" capability only means that the amp can produce more power into very low impedance speakers - i.e. 2 or 1 ohms - than a "lesser current" amp with the same power rating into 8 ohms.

Unless you have very low impedance speakers or are running speaker sets in parallel, you won't hear any difference, assuming the amps are otherwise identical.

High current amps are a better choice if you are running them in bridged mode for very high output into 4 ohm speakers.  They also are the amps of choice to use for arc welding...

Not exactly true in the real world, although your premise is perfectly accurate theoretically. Unfortunately, there are very few loudspeakers that maintain a fixed impedance over frequency. Some actually dip to very low impedances, sometimes down to 2 or 3 ohms, at certain frequencies. This is where a high current amplifier can make a difference in sound quality. If an amp can't maintain the proper signal voltage due to current limiting at certain frequencies, then the output will not be a faithful representation of the input signal and fidelity will suffer. This problem is exacerbated with playing the system at high volume levels. If you do have loudspeakers that maintain a constant impedance over frequency, then, as modular747 states, the benefits of a high current amp are less important provided you have adequate power (voltage x current) for the speakers at the volume levels you intend use. Just my $0.02 worth.

Ron

[modular747]

In solid state power amps, the current capacity rating has to do with the safe operating zone, not what can be delivered.  To a lesser extent, it involves the power supply limits, but these won't be exceeded before the output devices in any competent design.  With AVA models, the standard and alternative "hc" models have identical power supplies and differ only in the number of output MOSFETs.

Solid state power amps, unlike preamps and tube amps, never current limit, regardless of the rating.  When the output current exceeds the safe zone of the output devices, the amp will blow a fuse or shut down.  (There are a few exceptions such as McIntosh which have current/voltage limiting protection).  Reactive speaker impedances may have impedance dips at some frequencies, but these are well away from the bass/midrange zones and carry little current with music signals

In the case of AVA amps, which I believe the OP was referring to, the "hc" version of some models can drive very low impedance loads to higher levels without blowing power supply fuses or damaging the output devices.  In no case will the "regular" version current limit into reactive loads.

[avahifi]

Note that our current inexpensive "double die" high current option for new AVA amplifiers takes advantage of a new Exicon power mos-fet series.

The actual die area of a big power mos-fet transistor in a TO-3 case is only about half the size of your smallest fingernail.  Exicon figured out that they could actually put two high powered mos-fet dies in one TO-3 case.  This effectively doubles the current and thermal capacity of the device - -  the same as having twice as many output devices, but needing only the mounting space and wiring complexity of a single device.  Since these devices share nearly perfectly - no current hogging as in bipolar power transistors and no need for thermal bias tracking circuits at all - the double die option allows us to build amplifiers with double the current reserves as our "normal" amplifiers, and our normal ones are very rugged in their own lights.

Because each double die output mos-fet is working less hard and because the ultimate power from the amplifier is limited by the on resistance of the devices (limiting output power to below the actual potential of the power supply rails, doubling the output devices lowers the on resistance as the devices are in parallel, and thus allows higher output voltage swing and power from the same power supply and audio circuit configuration - -  essentially free extra power.

Finally remember that the current capacity of our amplifiers are limited by the final speaker fuses.  4 amps allows 200 watts per channel into 8 ohms.  We supply speaker fuses built into our amplifiers to protect your speakers from use accidents and "parties" and protect your amplifier from problems such as "my dog chewed up my speaker cables".  If you use speaker fuses that are too big, this will save you the cost of replacing the fuses when a sudden accidental overload destroys your woofers.  A general rule of thumb is reasonably efficient small 2-way designs, start with no more than 2 amp quick blow fuses.  Bigger or less efficient 2-way speakers, 3 amp quick blow is probably rational, big floor standing 3-way designs, no more than 4 amps, and real inefficient monsters, probably 5 amps should be the maximum. Low impedance speakers may require one amp more fuse per application.  Remember that 200 watts into a speaker is the same heat as putting two 100 watt light bulbs into a small metal breadbox and leaving that on for an hour or so.  Not the kind of heat your voice coils can withstand for long.

We offer the "high current' options simply to allow great amplifier performance into really difficult and widely varying speaker loads.  If your speakers are reasonably rational designs of 85 dB efficiency or higher, and you have the power rating to drive that load, you will probably never hear the difference.

Regards,

Frank Van Alstine