Current, Amperage
Julian Hirsh also said that all well designed amplifiers sound the same.He was certainly wrong about that, but it depends on what is considered 'well designed'. If the amp is designed to have good specs and that's considered good, that's one thing. If the amp is designed to adhere to the human hearing perceptual rules, that's another thing. Two such amps won't sound the same- the specs on paper don't take human perceptual rules into account. |
Efficiency and sensitivity are not the same thing, although many people think so. https://www.galaxyaudio.com/education/efficiency-vs-sensitivity |
No doubt elevick's math is correct, however there is more to consider. Those SPL's are at 1m, and the further away they decrease, but there's 2 speakers and room gain. If it's a 4 ohm speaker, the sensitivity spec is at 2 watts unless it states 1 watt. If nothing is stated or it says 2.83v, then 2 watts, so a 1 watt rating is 3db lower. The power necessary is for a maximum peak SPL, not the average. Depending on the type music, some peaks can be as much as 20-25db higher than the average. The recommended minimum power of this speaker being 40 watts is likely due to it's varing impedance, 8 ohms nominal, 2.9 ohms minimum. But that wattage spec can be misleading as well. I'm sure a 30 watt Pass would have no trouble, where as a budget 100 watt receiver would struggle. |
current and wattage, courtesy of Atmasphere http://www.atma-sphere.com/Resources/Common_Amplifier_Myths.php |
@lilmsmaggie yes, sorry, my ‘pre-amp’ is a VTL 2.5. I had an Mcintosh MC252 but sold it a few years ago and my stuff has been in storage. I’m now looking for a new amo as I want to setup my system again. Not sure I want to soend that much again on an amp. I also had seem the Focal ‘power suggestion’ of 40-250, but that is a big range. Bottom line, will the current/ amperage in a less expensive amp of 100-150 watts be enough to provide the right power? Rotel, etc? Also, what about Class A, A/B, D - does this come into play and is it a big variable depending on your speakers, etc? Thank you. |
| Post removed |
Most focals require extra current in the 100Hz range due to relatively low 3 ish impedance. Not an amp killing situation, but I do find that they sound a little soft in the bass unless the amp is stiff. Don't need a high power ratimg, but they will are relatively "discrimimating" when it comes to amplifier current delkvery. An unfortunate trait for otherwise highly praised and affordable line |
| Post removed |
The amperes/channel spec is basically meaningless along with most other ampere ratings. Current is a function of (ohm) load and will swing as the load varies across the frequency range. My rule of thumb is picking a reputable (voltage source) amp that doubles its power as the load is halved is usually a good starting point. Adding a class A design is icing on the top if the extra heat is not a concern. Current source amp tend to pair much better with (very) high efficiency single driver speakers, based on my albeit limited experience. |
Kalali 5-12-2018+1. Amplifier current ratings are meaningless and should almost always be ignored. For example, as stated above the MC602 is described as being capable of providing 150 amperes. 150 amps into 2 ohms corresponds to 45,000 watts. 150 amps into 4 ohms corresponds to 90,000 watts. 150 amps into 8 ohms corresponds to 180,000 watts! Meanwhile the amplifier’s rated continuous power capability is 600 watts into any of those impedances, and it is described as being capable of providing 1000 watts on tone bursts. What the 150 ampere number most likely represents is how much current can be supplied into a short circuit (zero ohms) for an unspecified number of milliseconds (thousandths of a second), at which point the amplifier’s self-protection mechanisms would shut it down. And according to comments Ralph (Atmasphere) has made in the past about amplifier current ratings in general, it may not even represent that capability at the output of the amplifier, but rather at the output of its internal power supply. Regards, -- Al |
So, how much ‘current’ do I need? And, is this a rating or spec that is provided?Don't worry about the current! What is needed is the power to drive the speaker in such a way that its frequency response is flat and that its loud enough without audible distortion. These two can be quite different, but the thing to understand is that the current cannot exist without power! There is an immutable law that binds them together. It is Power = Current x Voltage where power is in watts, current in amps and voltage in volts. This law is unlike a speed limit in that it simply cannot be violated without creating a new branch of physics which isn't going to happen with amps and speakers :) The big deal here is that the amp must be able to act like a voltage source with this speaker. What that means is that over the entire range of impedances expressed by the speaker, the amp must be able to make the same voltage (if a simple sine wave were applied to the input of the amp, and swept over the range of the speaker). This can be done by a tube amp or solid state, as **this ability has more to do with output impedance than it does anything else (like 'current')**. In tube amps a low output impedance is achieved by application of negative feedback. Solid state amps often have a low enough output impedance without feedback, but usually are non-linear without it so they have feedback too with rare exception. The feedback induces a servo control aspect to the amplifier- the output voltage is fed back into the amp as a correction; this essentially tells the amp to make more power into lower impedances and less into higher impedances. This comes with a price, like all things in life. Feedback adds distortions of its own when applied to an amp, even while suppressing distortion in the amp. This distortion can be heard in any amplifier as brightness and harshness (since it is composed of higher ordered harmonics to which the ear is keenly sensitive). This is why there are amplifier designs that don't use feedback, and complementary speaker designs that don't expect the amp to be a voltage source. |
| Post removed |
@elizabeth Thank you. I agree, and this IS the point of the discussion; What is enough [we know too little is bad, but how much overkill does one need ]? I had a McInotsh MC252 - 250 WPC on either 2, 4 or 8 ohms, and I loved it, but do I need that again in a 12x12 room? used for $3500 for my type of setup is a lot. I don;t need the 'Wow' blue lights factor again :) Can a Rotel 200 wpc or something else provide enough [that will be good] without having to spend more than $500-1000 used? Thanks; this is an interesting topic for all of us that have decent systems but maybe not more than $5-$10K into them. |
| Post removed |
It's more about synergy, not math. I have a 300 wpc Mac but usually am using my 10 watt triode. Running out of power can ruin a speaker and/or your experience but quality is much more important than quantity. My math was a generalization but you do need a frame of reference on these things. Generally speaking you gain 3db for doubling your wattage is a great way to understand why going from 40 to 60 watts is virtually inaudible all other things remaining equal. |
