2 ohm stable amp recomendations please

[SuperKris]

ive seen denon 4400 and 6600 monoblocs used on those speakers.

 

[rabbit]

Are these the correct figures for your example?

Here is what 100A of current represents at typical impedances

8 ohms = 1,250 watts
4 ohms = 5,000 watts
2 ohms = 10,000 watts

Your example assumes the amp is capable of doubling down.

The amp isn't capable of continuously deliver 100 amps into the load. Because music is transient in nature it is only required to do this momentarily which is why the rating is for instantaneous current capability.

 

[JimJ[VT]]

and in doing so many people would think "Wow, that must be a great "high current" amp because it doubles down all the way to 2 ohms". However, QSC would never sell any into the intended pro audio market because the amplifier cost for the "double down" sandbagged watt ratings wouldn't be in the ballpark with the competition.

That reminded me of what it used to be like in car audio competition, a lot of organizations went off 4-ohm rated power for determining classes...so of course, it led to amps that did "1 watt" at 4 ohms, but were able to run down to a half-ohm or lower...that 1 watt amp would do 4kW down there

 

[whoaru99]

The amp isn't capable of continuously deliver 100 amps into the load. Because music is transient in nature it is only required to do this momentarily which is why the rating is for instantaneous current capability.

Doesn't matter, it's still impossible at any normal impedance.

The voltage required to deliver 100A to the following loads is:

100A @ 8 ohms requires 800 volts.
100A @ 4 ohms requires 400 volts.
100A @ 2 ohms requries 200 volts.
100A @ 1 ohm requires 100 volts.

All of those, I expect, greatly exceed the rail voltage of that amp.

Again, just to be clear, I'm not trying to say anything bad about the amp. It's only the "HCC" spec and the "high current" thing in general that I'm grinding on.

 

[rabbit]

Doesn't matter, it's still impossible at any normal impedance.

The voltage required to deliver 100A to the following loads is:

100A @ 8 ohms requires 800 volts.
100A @ 4 ohms requires 400 volts.
100A @ 2 ohms requries 200 volts.

All of those, I expect, greatly exceed the rail voltage of that amp.

If you read Matti Otala's paper he talks about certain asymmetrical waveforms producing 6 times the peak current into a reactive load compared to a resistive load, albeit for a millisecond or so. The big question is whether or not these signals are actually present in music ??

For example an amp that delivers 50 watt into 8 ohms requires a peak current capability of 3.5 amps or 7 amps into 4 ohms. However it is possible for a reactive 8 ohm load to draw 6 times this or 23 amps with some asymmetrical waveforms.

 

[whoaru99]

Are these the correct figures for your example?

Here is what 100A of current represents at typical impedances

8 ohms = 1,250 watts
4 ohms = 5,000 watts
2 ohms = 10,000 watts

Your example assumes the amp is capable of doubling down.

I believe my figures were correct. Calculation of power from current and resistance, using the 100A as a constant (I), varying the load (R) in the formula to get watts (p)


P = I^2 x R

 

[whoaru99]

If you read Matti Otala's paper he talks about certain asymmetrical waveforms producing 6 times the peak current into a reactive load compared to a resistive load, albeit for a millisecond or so. The big question is whether or not these signals are actually present in music ??

For example an amp that delivers 50 watt into 8 ohms requires a peak current capability of 3.5 amps or 7 amps into 4 ohms. However it is possible for a reactive 8 ohm load to draw 6 times this or 23 amps with some asymmetrical waveforms.

That's fine. I don't doubt it.

But, afaik, it doesn't significantly change what the amp can deliver to the load...which is what we're discussing.

 

[SoCal Sam]

I believe my figures were correct. Calculation of power from current and resistance, using the 100A as a constant (I), varying the load (R) in the formula to get watts (p)


P = I^2 x R

I wish I was born an electrical engineer so my apologies for taking baby steps. I believe the correct formula to arrive at watts is:

P (watts) = I (Amps)^2 / R (Ohm)

or

Watts = Amps^2 / Ohm

 

[whoaru99]

I wish I was born an electrical engineer so my apologies for taking baby steps. I believe the correct formula to arrive at watts is:

P (watts) = I (Amps)^2 / R (Ohm)

or

Watts = Amps^2 / Ohm

I'm still coming up with P = I^2 x R...

Here it is and here again. Unless I'm missing something on both those sites, or they're both wrong.

 

[Susurus]

How about a nice set of Klipsch RF-7's? 250wpc continuous, 1000 RMS peak and 104dB/1 m on axis means 125 continuous SPL and peak SPL 131. Add a couple of subs if you want to.

If what you want is a way to make your model Infinitys sound louder, it doesn't matter what you do--Eliot is right on the nose.

Some speakers react to higher than optimal wattage by actually sounding lower!

The VC overheats, the xover handles it poorly, and the drivers are pushed beyond design specifications--even bouncing onto the back plate of the motor, pulling the VC lead wires taut, all of which won't help. :sigh:

 

[Elliot Thompson]

How about a nice set of Klipsch RF-7's? 250wpc continuous, 1000 RMS peak and 104dB/1 m on axis means 125 continuous SPL and peak SPL 131. :

With speakers like those and assuming Patrick likes volume, you may have just given him an eviction notice from his wife. :thmbsp:


A pair of these would solve the volume issues as well...

Best Regards,

 

[tarior]

He may as well go all the way and get some Jubilees.

 

[SoCal Sam]

I'm still coming up with P = I^2 x R...

Here it is and here again. Unless I'm missing something on both those sites, or they're both wrong.

Your example of 8 ohms = 80,000 watts is correct but we have to look at the voltage. Voltage is 800 which is an improbable figure for output as is 80,000 watts for an amplifier.

However, 100V is a plausible output voltage. I think we have the labels confused. So the better formula to use is:

Watts = Volts ^ 2 / Ohm

 

[KentTeffeteller]

There is one make of amplifier I trust driving a 2 ohm load day in and day out. That amp is any McIntosh with autoformers. Costs more up front but is cheaper over the long haul when repair costs are considered.

 

[whoaru99]

Your example of 8 ohms = 80,000 watts is correct but we have to look at the voltage. Voltage is 800 which is an improbable figure for output as is 80,000 watts for an amplifier.

However, 100V is a plausible output voltage. I think we have the labels confused. So the better formula to use is:

Watts = Volts ^ 2 / Ohm

100V is a plausible voltage output, I agree. Not, however, from the amps being discussed in this thread.

I agree the formula above produces the correct result for power calculation. Another power forumla is Watts = Volts * Amps. Which one is best depends on what information is at hand.

"Watts = Amps^2 * Ohms" was, IMHO, more appropriate for the example at hand because a defined current (100A) was given, and the commonly-accepted 8, 4, and 2 ohm ratings could be used in the formula.

 

[whoaru99]

There is one make of amplifier I trust driving a 2 ohm load day in and day out. That amp is any McIntosh with autoformers. Costs more up front but is cheaper over the long haul when repair costs are considered.

I'd trust my Levinson driving two ohms all day. In fact, maybe even 1 ohm since the manual says it is capable of driving 2 ohm loads in the bridged mode. That is equivalent to 1 ohm in the stereo mode.

Also, every one of my pro amps is rated for operation at 2 ohms. No restrictions for duration/duty cycle are given.

 

[SoCal Sam]

100V is a plausible voltage output, I agree. Not, however, from the amps being discussed in this thread.

I agree the formula above produces the correct result for power calculation. Another power forumla is Watts = Volts * Amps. Which one is best depends on what information is at hand.

"Watts = Amps^2 * Ohms" was, IMHO, more appropriate for the example at hand because a defined current (100A) was given, and the commonly-accepted 8, 4, and 2 ohm ratings could be used in the formula.

Good to give the brain cells a twirl...

From Rabbit's HK PA2400 specs:

High Instantaneous Current Capability (HCC) : +/-100amps

This looks a lot like a Dynamic Headroom figure so the load would be I'm guessing 2 ohm and the power 5,000 watts. Not out of the question but I am skeptical. IMO, continuous power at 2 ohm will give a better idea of an amp's capability.

 

[whoaru99]

Gotta be way lower than 2 ohms. Twice I've asked H/K for the test criteria used to determine the HCC number, but no reply in either case.

The only thing that makes sense is something very low, like 0.1 ohm; maybe even lower.

If we go back to the forumulas, 5,000W at 2 ohms doesn't match up with the 100A HCC spec nor the plausible output voltage for this amp.

 

[automojo]

All this numbers are nice, great for shop talk, and "trusting" ? a amp to drive 2 ohm loads all day long can be comforting to some.
The big test is really how it performs with these loads. Doesn't surprise me H/K doesn't respond, the designers of those amps have long left the company. Unless you have actually tested the amp with said speakers and musical program material, all your mathmatical figures are mere assumptions on how the amplifier may perform, little else.
Again, how it sounds-most pro amps put out lots of power, but most to my ears aren't very musical regardless of their specs so to me what's the point?
Usually there is a reason most choose a audiophile amp over a proamp for home listening-it's the sound, not marketing. And most proamps are considerably cheaper spec wise than there audio conterparts.
I have both a PA2400 (direct coupled design) and a H/K Signature 1.5 (built my Mark Levinson- the USA). The 1.5 will double it's power (200wpc) into 4 ohms (400wpc), according to the designer (will foward thread when I find it) of the Signature 1.5 (no current limiting switch or design), and will drive 2 ohm loads all day long as well at around 750 wpc, according to the designer, but H/K the manufactor doesn't recommend it
So we have to conflicting specs and perspectives on one amp, the H/k 1.5 from the desinger, and the manufactor.
I have also driven a pair of Infinites with the PA2400 in the 8 ohm setting for hours with no problems, or excessive heating. Both amps recently tuned to specs. It uses 8 15amp outputs and 48000 total filter caps
To me, this means that the specs are only a starting point, and nothing more till you actually try the amp in real world conditions.
Both these amps have very stout power supplys, very large torodial trannys, and 15 amp outout transistors. The 1.5 uses a toal of (24) 15 amp output transistors, 65,000 total filter caps, so the ratings the designer specs of this amp aren't out of line. But again, it's all talk till you hook up the wires and press the power button, how it sounds driving the speakers is what matters.
In my experience, and given a wide range of rating on amps (conservative-not), instead of saying this amp should put out 5400 watts @100amps current vs 350 watts etc, borrow one and see how it works.
I don't take any offense to the H/k comments, interesting-but performance, not specs are what matters.

 

[rabbit]

People are confusing instantaneous current capability with continuous current rating.

An instantaneous current rating of +/- 100 amps does not mean the amp can deliver this current on a continuous basis. It means it can deliver high current in short bursts in accordance with the program material and reactive speaker load which may demand high current for only a small amount of time.

Having said that I have used a H/K PA2400 with my RS4.5's and have had no problems with it driving these difficult speakers. This is more than I can say for some of the Japanese high power rated receivers which are built like the proverbial battle ship but just can't deliver the goodies when it comes to driving difficult loads such as the Infinities. The H/K cuts through the task like swiss cheese.