high current vs high power

Rare is the speaker that presents a constant load all the way across the audio spectrum. In my experience, speakers tend to dip to lower impedances more than bump to higher ones, respective of the advertised impedances. Most amps are spec'd for what they can drive at a specific frequency, into a specific load impedence, and do it continuously and what they can do for a very brief period. Higher current amps are able to briefly, or continuously, supply more current when needed. Remember that power is not just ExI, It is also I2R. What that means for us, is that the amp is able to handle lower impedances, either briefly or continuously. Some speakers just require amps that can supply the extra current that may be may needed at various places across the spectrum.

Output impedance vs load impedance is important in such regards.

I prefer amps that can do it continuously. Hence they are spec'd for lower speaker impedances from jump street, like the Yamaha M80, or M85, which are spec'd to drive 2 ohm loads all day long. Concept receivers can push more current than normal, but only briefly, but that is still a good thing.

Bottom line: high current amps can be an important consideration in the audio equation.

Enjoy,
Rich P
This is an excellent point.
 
Ha! This thread is done. I have purchased a McIntosh 2155 amplifier because McIntosh is like honey badger...honey badger don't care what the Impedance is, lol. It also looks as though I will be replacing the Cornwalls with B&W speakers. I have an audition coming up Wednesday night. I am not sure if crossing over the signal at 80 Hz on the Cornwalls will result in sound as good as the 801 S3. I guess I will have my answer next Wednesday.
 
2155 like its larger brother the 2255 were great continuous duty power amps. Like other macs they would give you about 25 to 30% more power to a given load than rated. But they aren't the high current amps like later Macs. What they will do is operate 24 hours a day upside down if you wish with out any sign of strain. Later amps like the 501, 252, and 1000 will give you much more peak energy, be able to drive a 4 ohm load from an 8 ohm tap for instance, but don't ask them to do it 24/7, they heat and shut down every time. That one hour test at 33 to 40 % power will cause a lot of the later Macs to over heat and shut down. Now I realize for the home owner we don't put that kind of strain on our amps only using about 1/8 to 1/10 the average power of the highest peak which is usually a small percentage of the capability of the amp. So it makes no real difference most of the time to most folks. But some of us like to push the pedal to the metal with in efficient speakers and thats where the trouble begins. Also operating an amp with the Power Guard flashing squeezes the signal pushing the demand for higher current levels over time.
 
Interesting discussion.
In my mind I've always, rightly or wrongly, associated "high current" with studio/pro-type amps....never though of it in a more general sense.

Also interesting to me in relation to Class D amps, which in many cases apparently qualify as high current.
With a sufficient power supply they commonly double 8ohm rated output at 4ohms.
In mono mode many are rated down to 3ohms with proportional increase in wattage.

According to Texas Instruments, their TPA 3255 EV module will do over 500 watts into 2ohms in mono mode at 1% THD if run at 52VDC.
 
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My understanding is that hugh DF has more to do with negative feedback than current capability.

Feedback definitely is a big part of it, but having a high current capability also helps lower output impedance. An amp with a single pair of output devices vs the same amp with 6 pairs will be different.
 
I worked for an audio amplifier manufacturer for a decade. What I learned was that most of what manufacturers espouse about their product's high current capabilities is really nothing more than marketing speak. There exists a device called the AudioGraph Power Cube which can be an excellent tool for engineers to develop true high current power amplifiers. Problem is, most don't have access to them.

OP - the inventor of the AD-1 amp dyno ( aka the honey badger ) is one of my buddies.
 
This is a good discussion! High current amplification is what I was missing earlier in my return to Audio. I seem to like speakers that are power hungry (but not like those infinity’s or others), and now I try to keep Higher current amps in my collection. I’ve given up on receivers. I just don’t trust they will give me the best the speaker gave provide. Of course there are lower power amps that sound excellent, just not with the same speakers.
 
Much of the popular discussion about high current amplifiers stems from the Linn/Naim/Linn systems which were irresponsibly touted as the World's Best systems by jigoistic/biased/bought journalists in the UK. The Linn Isobarik loudspeakers dipped down to 1 ohm in the bass. This placed the spotlight front and center on the amplification. Most Japanese receivers couldn't deal with that load. Many non-Japanese amplifiers couldn't handle that load. The Naim 250 could. This with the fact that the Naim preamps were known to integrate well with the Linn Sondek made for a system which worked together extremely well. Was it the world's best system of the time? Nope. But undeviating promotion of a particular party line appeals to those who are looking for an authoritative voice. Much product was sold. Legions of blind faith followers were spawned. The benefit is that discussion was opened about the amplifier requirements of low impedance loudspeakers.
 
It would seem like synergy with the speakers that are being powered would be the most important. My Yamaha P2200 & P2201 amps have a current limiter that comes into play with loads just under 2.5 ohms. I run my P2200/P2201 amps bridged, which means the current limiters come into play with loads just under 5 ohms, but the setup is otherwise good for ~700wpc @8 ohms. Especially with the ~5 ohm limit, I imagine that is similar to what many might think of when they think of an amp that is high power but not high current. Thankfully the speakers I use with them are 8 ohm nominal and ~5.7 ohm minimum impedance. I've certainly never felt limited, if anything, the opposite.
 

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It would seem like synergy with the speakers that are being powered would be the most important.

Absolutely. As was posted earlier in this thread, some speakers sound much better with low damping factor amps. They were designed to work with low DF amps and sound much much better with them. In Audio it is always 'Horses for courses'.
 
2155 Later amps like the 501, 252, and 1000 will give you much more peak energy, be able to drive a 4 ohm load from an 8 ohm tap for instance, but don't ask them to do it 24/7, they heat and shut down every time.

I chose the 2155 for one very obvious reason - cost. I can accomplish my amplification goals with 2 amps for less cost than what one of the newer Macs would run. In my system, the 2155 will handle signal down to some frequency between 80 and 200 or so depending on what my guy recommends. Since it will not be called upon to amplify the deep bass, the 2155 will deliver all the signal/current I could ever need to the Cornwalls. The real power hungry speakers/signal - 200ish Hz on down - will be amplified by a class D professional amplifier. For both amplifiers, actual measured output (Not manufacturer claimed output) was used in calculating the size of amplifier needed in order to met the 50% rule. Essentially, the responses on this thread, the messages, and just a tad bit of research led me to using two amplifiers in order to play at irresponsible levels without the music crapping out. All of this for less than one of the newer Mac pieces. For $1800, I have all the amplification I will ever need in my current system with the neat bonus of an extra $5k in my pocket.
 
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Below is the Thevenin Equivalent Circuit for a typical cone type speaker/driver. Re (far left R symbol) is the dc coil resistance + other resistances/reactances, including the amplifier's output reactance. As one can see the maximum current is limited by Re's value. Re can be ~3 ohms for a 4 ohm speaker and ~6.5 ohms for an 8 ohm speaker.

Speaker Thevenin Equivalent Circuit 4.jpg

As an example, we have an 8 ohm speaker, say minimum resistance Re of 6 ohms, and 30 volts rms at the speaker, the maximum rms output power possible is 150 watts. The rms current is 5 amps, the peak voltage is ~42.3 volts while the peak current is ~7.05 amps.

keep on truckin

joe
 
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