High Current vs High Voltage Amplifiers

Jigesh Patel · 10-06-2003, 07:22 AM

Given the same power ratings, which type (high current output vs high voltage output) of multichannel amplifier should sound better with speakers of around 8-ohm nominal impedance and around 89 or 90dB sensitivity? The intended usage is 65% movies and 35% hi-rez music.

Thank you.

Jigesh

Yogi · 10-06-2003, 08:53 AM

With speakers of higher impedance (easy to drive 8 Ohms), amps with higher voltage output can perform good, however speakers with low impedance (tougher loads, 4 ohms that drop down to 2 ohms like electrostats) one needs an amp that can deliver high current. Tube amps operate at higher voltages while SS amps operate at higher currents. Thats why tube amps perform well with easy speaker loads while you almost always need a good SS amp to drive large electrostats.

MHO

Michael R Price · 10-06-2003, 09:13 AM

I don't think either of those terms really mean anything, when you think about it. Given the same power ratings, current is voltage divided by resistance, no matter how you slice it! Seriously, though, I don't think you should pay much attention to claims like that. It's a good thing if the amplifier is *capable* of delivering a lot of current, because that means might distort less under load. The only reasonable way to gauge that is by looking at how much the power rating increases with lower impedances (4 or 2 ohms).

Actually, what specific speakers do you have? Some of them aren't actually 8 ohms, especially in the bass.

Jigesh Patel · 10-06-2003, 09:19 AM

I have Paradigm Reference/40, CC and 20 (front, center, surround) with SVS 25-31PC+ and the receiver is Denon AVR-3802. The speakers are said "compatible with 8 ohms" on Paradigm website and I understand impedance dips occasionally with frequency. I was considering an outboard amplifier (like Parasound HCA-1205A, where HCA stands for high current amplifier despite its being a Solid State amplifier).

Thanks.

Jigesh

Shiu · 10-06-2003, 08:11 PM

I think Yogi's example (Tube vs Solid State)is an interesting one. While it is true that current = voltage divide by impedance, a high voltage, low current system can theorectically delivers the same power as a low voltage, high current system. A high impedance coil (lighter gauge wire and more turns) with a lower current rating in a speaker, should be able to produce as much force as a low impedance coil (heavier gauge wire and less turns) that has a higher current rating. I am not sure if I remember correctly, but in my vague memory, there used to be amplifiers that drove speakers with as high as 800 ohms.

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Chu Gai · 10-07-2003, 04:39 AM

Ummmm, not sure what you mean by low current, but if it's low enough, there's no way those two units are equivalent. You've got to have some amps in order to deliver the power especially if the impedance is low.

Jason.Soko · 10-07-2003, 04:45 PM

Current drives speakers, that is all their is to it. Thereis a reason why they sell 1000watt amplifiers at walmart for $100 dollars while my 70w amplifier cost $2500.

Jonathan M · 10-07-2003, 06:23 PM

An amplifier is simply something that takes a given voltage, and amplifies it by some set factor.

This is all fine and dandy until you actually hook a speaker up to your amplifier in order to get sound out.

The speaker represents a load on the amplifier which is generally some complex impedance that varies with frequency. Usually the impedance is high at any resonance (port or loudspeaker) and low in between the impedance peaks. It also tends to rise as frequency increases.

Given this impedance, the amplifier will try and amplify it's source voltage by it's constant factor, and present it across the load. This inturn produces a current in the load, equal to the voltage divided by the impedance.

Where does this current come from? The power supply of the amp (ie this current comes from the DC supply rails of the amplifier which comes from the mains via (generally) a transformer, rectifier, and capacitor filter bank. If these components, as well as the mains itself, are capable of supplying the required current, then everything is peachy, and the speaker will produce what is was asked for (subject to it's response variations). Problems occur when one or more of the links in the chain are unable to supply the required current. In this case, they'll supply as much current as they can, and thus force the voltage rails to droop, which then lowers the voltage at the output (so that it still satisfies ohms law V = IZ).

As for which is better, high current or high voltage, the answer is it depends on what the impedance is, and how much it varies, along with how sensitive the speaker is, and what sort of volume you require.

Hope this helps, or at least has been a little informative!

Cheers,
Jonathan

Shiu · 10-07-2003, 06:37 PM

Chu, may be I should have said "lower current", instead of low current. It is just "relatively" speaking. Example, a coil with 10 turns passing 10 amps compare to a coil with 20 turns passing 5 amps. The product "ampere-turns" is the same.

Chu Gai · 10-07-2003, 07:18 PM

This may be a bit of confusion upon my part in possibly misunderstanding what you've written, but the vast majority of speakers are designed to give a flat FR when driven by a voltage source. Now that doesn't mean that current isn't needed. Perhaps we're saying the same thing.
What's the 1000 watt wallmart amp that's going for $100?