Is there a spec or a trustworthy definition of what a "high current" amplifier is?

[caesar]

Many claim to make high current amps, but when you put them to a test of driving a tough load, they poop out. Is there a way to know if an amp is "high current" via a spec or a definition?

 

[mep]

Instead of making general statements, why don't you provide a list of so-called high-current amps that "poop out" when driving a "tough load." After you provide a list of those amps, list the speakers that were used with them that caused them to "poop out."

 

[caesar]

Instead of making general statements, why don't you provide a list of so-called high-current amps that "poop out" when driving a "tough load." After you provide a list of those amps, list the speakers that were used with them that caused them to "poop out."

MEP,

Simple example: MBL 101. But regardless of the speaker, my question is general: is there an indicator, a sign, or a spec that could hint that an amplifier is "high current".

 

[mep]

MEP,

Simple example: MBL 101. But regardless of the speaker, my question is general: is there an indicator, a sign, or a spec that could hint that an amplifier is "high current".

First sign to look for is an amp that truly doubles its output power as the impedance halves.

 

[dallasjustice]

Some manufacturers have a spec for max amps. Krell and Soulution come to mind. Usually it's the amplifiers that are really big with massive transformers that can really deliver the current, as long as it's not powered by SMPS. Bridged designs usually struggle to get it done in the low impedances.

 

[DonH50]

Interesting comment on switch-mode power supplies. In the designs I work with, SMPS' are the "go-to" architecture for very high current delivery. Linear designs are too slow, far too bulky, and waste far too much energy. And our noise specs are extremely stringent over a very wide bandwidth. But, SMPS' are perceived as "worse" and "cheap" in the audio realm by virtually everyone I have spoken with about them.

I agree with Mark about looking for amps that double power with halving of impedance, and cite the ability to drive very low-impedance loads. Bridged designs will struggle much more to drive low-impedance loads by their very nature.

 

[dallasjustice]

I was referring to size only. I only mentioned SMPS because they are not big. I didn't say they don't deliver current. I've had a couple of class D amps with SMPS recently and they deliver unlimited current.

Interesting comment on switch-mode power supplies. In the designs I work with, SMPS' are the "go-to" architecture for very high current delivery. Linear designs are too slow, far too bulky, and waste far too much energy. And our noise specs are extremely stringent over a very wide bandwidth. But, SMPS' are perceived as "worse" and "cheap" in the audio realm by virtually everyone I have spoken with about them.

I agree with Mark about looking for amps that double power with halving of impedance, and cite the ability to drive very low-impedance loads. Bridged designs will struggle much more to drive low-impedance loads by their very nature.

 

[amirm]

This is a hard question to answer. "Double down" on resistive loads is a good measure but it doesn't say how it works on a real load. I can tell somewhat by looking inside of a machine, sizing up the number and type of output transistors, power transformer and filter bank size, etc.

 

[DonH50]

I was referring to size only. I only mentioned SMPS because they are not big. I didn't say they don't deliver current. I've had a couple of class D amps with SMPS recently and they deliver unlimited current.

Sorry, must have read more into this than you meant:

"Usually it's the amplifiers that are really big with massive transformers that can really deliver the current, as long as it's not powered by SMPS."

Now I am confused by what you did actually mean, help? Maybe the opposite of what I thought, that with SMPS there are no big transformers so does not fit the "usually big transformers" part? That makes more sense now that I read it back.

Long week... - Don

 

[dallasjustice]

I didn't write well on that post. I was just trying to offer a dumb visual inspection rule of thumb based strictly on size. As you point out, that rule wouldn't apply to most amps with an SMPS because they are usually much smaller.

Btw, I think audiophiles give SMPS an unfair wrap. They can be spectacular, IME. I've heard they are much more difficult to design but cheaper to build. Is that so?

Sorry, must have read more into this than you meant:

"Usually it's the amplifiers that are really big with massive transformers that can really deliver the current, as long as it's not powered by SMPS."

Now I am confused by what you did actually mean, help? Maybe the opposite of what I thought, that with SMPS there are no big transformers so does not fit the "usually big transformers" part? That makes more sense now that I read it back.

Long week... - Don

 

[DonH50]

I am not really a "power" guy. In our products we base the designs on manufacturer's reference designs and factory support so they are fairly straightforward. SWAP and cost are factors in what we use; no way a 30 A linear supply would fit on a RAID card and a penny is important when you sell millions of them.

 

[JackD201]

Since gobs of power are typically not required all the time and are usually only needed for peaks, I usually look at the capacitance storage figures (in micro farads) as a rough guide on top of "doubling down".

 

[RogerD]

circuit breakers instead of fuses might be a tipoff.

 

[andy_c]

You can get a decent approximation of the peak current capability if you have access to Stereophile measurements of output power into two Ohms or the lowest impedance measured. You can calculate it this way:

I[sub]peak[/sub] = sqrt(2 * P / R)

where P is the measured output power and R is the resistance used to measure it. For example, the Parasound JC-1 was measured into 1 Ohm at 4200 Watts. This gives:

I[sub]peak[/sub] = sqrt(2 * 4200 / 1) = 91.6 Amps peak

This is actually conservative, as the amp is still voltage clipping in this test (its power supply voltages are about +/- 95 Volts). Parasound claims in excess of 100A peak current and I don't doubt this.

Another example is the Halcro DM88. It measured 266 Watts into two Ohms. Peak current for this is:

I[sub]peak[/sub] = sqrt(2 * 266 / 2) = 16.3 Amps peak

This calculation will almost always yield a conservative estimate.

 

[LL21]

Since gobs of power are typically not required all the time and are usually only needed for peaks, I usually look at the capacitance storage figures (in micro farads) as a rough guide on top of "doubling down".

Is capacitance the ability for the amp to effectively 'store' energy that is then used during playback? Like charging a battery from the wall, and the battery is what is driving the musical signal?

If something like that...how closely does this approximate true battery supplies in terms of sound when the capacitance is as significant as some of the bigger amps (the Gryphon Mephisto monos are 1 million microfarads (1 farad) of capacitance)?

I imagine on louder levels and particularly highly dynamic music with enormous sudden peaks...having significant capacitance is important because the amp does not need to draw from the wall immediately, but first to the well of stored energy in the capacitors first?

 

[JackD201]

Pretty much Lloyd. It's partially why, say, some 100wpc amps can run out of gas slower than others of the same rated RMS wattage.

 

[LL21]

Pretty much Lloyd. It's partially why, say, some 100wpc amps can run out of gas slower than others of the same rated RMS wattage.

Thanks and good to get confirmation.

 

[dallasjustice]

Capacitance is being restored in SMPS a lot faster than a LPSU due to the switching frequency. This is why a switching PSU can much more easily deliver current to low impedance loads.

 

[Atmasphere]

MEP,

Simple example: MBL 101. But regardless of the speaker, my question is general: is there an indicator, a sign, or a spec that could hint that an amplifier is "high current".

The MBL101 is not that hard to drive! A 200 - watt tube amp will be plenty of power in most rooms. The real issue with the 101 is not whether the amp can make the power, but if it will throttle its power back properly when encountering that 8 ohm load in the upper midrange. If not, the result will be brightness.

More about that at this link: http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

A secondary issue is whether its a good idea to demand high current out of an amplifier even if its capable of it. The evidence of measurements is that it is not. If you look at the specs of any amplifier you will see that the distortion of the amplifier while driving 4 ohms is always higher than that when it is driving 8 ohms. The distortion drops further into 16 ohms.

So the question really is whether that increase of distortion is significant, as in- can you hear it? The answer is, yes, you can hear it, as the distortion product is mostly higher ordered harmonics, to which the ear is keyed to detect the sound pressure level. IOW we are more sensitive to higher ordered harmonics in a sound than almost anything else, due to the fact that its actually really important to our survival.

The bottom line is if you are making an investment in an amplifier for home audio purposes, that investment dollar will be best served by a loudspeaker of higher impedance, all other things being equal, entirely on account of how human hearing/perceptual rules work (which does not vary from human to human, unlike taste). If you are more concerned about sound pressure, where sound quality is secondary, there is a weak (3db) argument for four ohms over 8 ohms.

 

[dallasjustice]

I agree with all of what you say here.

The problem I have is that I believe that the speaker/room is the most important component in all systems. So what if my favorite speaker/room combo places a heavy load on the amp?

I have heard some excellent high impedance speakers like the voxativ horn. But there are also many awesome speakers that place a heavy load on the amplifier. For me, it's the speaker that determines which amp works best, not the other way around.

Michael.

The MBL101 is not that hard to drive! A 200 - watt tube amp will be plenty of power in most rooms. The real issue with the 101 is not whether the amp can make the power, but if it will throttle its power back properly when encountering that 8 ohm load in the upper midrange. If not, the result will be brightness.

More about that at this link: http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

A secondary issue is whether its a good idea to demand high current out of an amplifier even if its capable of it. The evidence of measurements is that it is not. If you look at the specs of any amplifier you will see that the distortion of the amplifier while driving 4 ohms is always higher than that when it is driving 8 ohms. The distortion drops further into 16 ohms.

So the question really is whether that increase of distortion is significant, as in- can you hear it? The answer is, yes, you can hear it, as the distortion product is mostly higher ordered harmonics, to which the ear is keyed to detect the sound pressure level. IOW we are more sensitive to higher ordered harmonics in a sound than almost anything else, due to the fact that its actually really important to our survival.

The bottom line is if you are making an investment in an amplifier for home audio purposes, that investment dollar will be best served by a loudspeaker of higher impedance, all other things being equal, entirely on account of how human hearing/perceptual rules work (which does not vary from human to human, unlike taste). If you are more concerned about sound pressure, where sound quality is secondary, there is a weak (3db) argument for four ohms over 8 ohms.