1 Ohm stable amplifiers (inexpensive)

[bandphan]

From martin logan usa...
Q. Do MartinLogan speakers require big or expensive amplifiers?

A. Absolutely not. MartinLogan speakers are quite efficient and are capable of providing from 89-91 dB output from only 2.83 volts of input. This makes them suitable for use with a wide range of discrete and integrated amps, receivers, and A/V receivers. Our hybrid designs will perform well with either a tube or transistorized amplifier, and will reveal the sonic character of either type.

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Q. What size (power) of an amplifier should I use?

A. The power amplifier is one of the most important elements in any A/V system, as too little power will not allow your system to live up to its full potential. In general, we recommend an amplifier with 100 to 200 watts per channel for most applications. Probably less would be adequate for our smaller hybrids or when used in home theater where a subwoofer is employed. Our hybrid designs will perform well with either a tube or transistorized amplifier, and will reveal the sonic character of either type. However, it is important that the amplifier be stable operating into varying impedance loads: an ideally stable amplifier will typically be able to deliver nearly twice its rated 8 Ohm wattage into 4 Ohms and should again increase into 2 Ohms.

That said, you should consider both your musical tastes and the size of your listening room. What type of musical content do you prefer and what listening level do you like the best-ambient, loud, or somewhere in between?

For instance if your listening preferences lean more toward chamber music, solo, or acoustic performances, then a smaller power amp will be adequate. On the other hand, if you enjoy symphonic music or rock-particularly at live listening levels-then you will need a larger power amplifier. This is because, for the most part, chamber music doesn't require the extended volume range that symphonic or rock music performances do to fully reproduce the performance.

Another important consideration is the size and character of your listening room. Character refers to its acoustic qualities. Does your room have a bright (reflective) or dull (absorptive) quality? Bright rooms are distinguished by their large flat hard surfaces, and dull rooms by their draperies and wall-to-wall carpeting. As a general rule larger rooms and duller rooms require more power to get the same live performance level.

Also, most multi-channel home theater/music systems incorporate amplified subwoofers (the .1 in 5.1, 6.1 and 7.1 channel home theater)which rely on your processor's bass management calibrations to reproduce the lower bass and sub-bass frequencies (80-100Hz and below). In this case, a portion of the power amp's output will be handled by the subwoofer amplifier, leaving more power available to the rest of the system. This allows the use of more moderately powered amplifiers while maintaining high levels of performance.

Your amplifier should also be capable of stable operation into a varying impedance load-delivering more power into lower impedance loads. This is because most musical content presents a constantly varying load to your amplifier with power requirements tied to the frequency of that content-as frequency rises, impedance drops and power requirements increase. The main idea is to have enough reserve power to handle transients like explosions, cymbal crashes, and other loud passages without overloading your amp.

 

[WmAx]

How about the Yamaha amplifiers you are using? I would rather fanless operation.

Well, it's easy to do the fan replacement.

The Yamahas cost more. In addition, do you have an actual impedance plot for the speakers at subject here? The Yamahas also will not drive as demanding of a load as the EP2500. But until you show the impedance plot I really have no idea what the actual load demand of these speakers may be.

-Chris

 

[PENG]

That doesn't change the simple fact I currently don't understand it. Is there a simple equation for this?

The equations are quite simple but let me try to show you some worked examples but please realize that I am using fictitious numbers.

For a resistive load:

Power = I² x R ----------- (1)

For a reactive load:

Power = I² x Z x cos θ ---------(2), where Z is the impedance (when it is not purely resistive), θ is the phase angle between the voltage and current phasor. (A phasor is a rotating vector that is used to represent a sinusoidally varying quantity)

Let’s say at rated output the amp applies 40V (rms) across an 8 ohms load, and consider a resistive load first:

I = V/R (Ohm’s Law) = 40/8 = 5A, substitute this into the power formula (1),

P = 5x5x8 = 200W

Across a 4 ohms load,

I = 40/4 = 10A,

P = 10x10x4 = 400W

Across a 2 ohm load,

I = 40/2 = 20A,

P = 20x20x2 = 800W

Across an 1 ohm load,

I = 40/1 = 40A,

P = 40x40x1 = 1600W

So the amp doubles down as long it can deliver the current according to Ohm’s Law, hence the term “high current” amp.

For a “cheap” amp that you are talking about, I would not assume it can double down all the way to 1 ohm so let’s assume the worse case, that is, the amp cannot deliver more than what it can deliver into an 8 ohm load.

Applying the same formula, across an 1 ohm load,

P = 5x5x1 = 25W, in other words, the amp that outputs 200W across an 8 ohm load can only output 25W across an 1 ohm load.

Now, let’s consider a reactive load, as 3 dB says some speakers are highly reactive such that the phase angle between the voltage and current can be as high as 75 degrees. In this case we need to use formula (2) above:
That is Power, P = I² x Z x cos θ, so again assuming the amp cannot output current higher than 5A,

P = 5x5x1xcos(75) = 25x0.258819 = 6.47W

Of course the above example represents one of the possible worst case scenarios. In reality even a cheap pro amp can output higher current into an impedance lower than 8 ohms; and very few speakers will be so highly reactive in the power demanding low frequency range.

In fact many amps (http://www.crownaudio.com/amp_htm/cdi.htm) will approximately double down to 4 ohms or even 2 ohms, after that it would likely begin to approximate “half” (if there is such a term) down to 1 ohm and below as it reaches its current limit if it is not allowed to clip.

 

[lsiberian]

The equations are quite simple but let me try to show you some worked examples but please realize that I am using fictitious numbers.

For a resistive load:

Power = I² x R ----------- (1)

For a reactive load:

Power = I² x Z x cos θ ---------(2), where Z is the impedance (when it is not purely resistive), θ is the phase angle between the voltage and current phasor. (A phasor is a rotating vector that is used to represent a sinusoidally varying quantity)

Let’s say at rated output the amp applies 40V (rms) across an 8 ohms load, and consider a resistive load first:

I = V/R (Ohm’s Law) = 40/8 = 5A, substitute this into the power formula (1),

P = 5x5x8 = 200W

Across a 4 ohms load,

I = 40/4 = 10A,

P = 10x10x4 = 400W

Across a 2 ohm load,

I = 40/2 = 20A,

P = 20x20x2 = 800W

Across an 1 ohm load,

I = 40/1 = 40A,

P = 40x40x1 = 1600W

So the amp doubles down as long it can deliver the current according to Ohm’s Law, hence the term “high current” amp.

For a “cheap” amp that you are talking about, I would not assume it can double down all the way to 1 ohm so let’s assume the worse case, that is, the amp cannot deliver more than what it can deliver into an 8 ohm load.

Applying the same formula, across an 1 ohm load,

P = 5x5x1 = 25W, in other words, the amp that outputs 200W across an 8 ohm load can only output 25W across an 1 ohm load.

Now, let’s consider a reactive load, as 3 dB says some speakers are highly reactive such that the phase angle between the voltage and current can be as high as 75 degrees. In this case we need to use formula (2) above:
That is Power, P = I² x Z x cos θ, so again assuming the amp cannot output current higher than 5A,

P = 5x5x1xcos(75) = 25x0.258819 = 6.47W

Of course the above example represents one of the possible worst case scenarios. In reality even a cheap pro amp can output higher current into an impedance lower than 8 ohms; and very few speakers will be so highly reactive in the power demanding low frequency range.

In fact many amps (http://www.crownaudio.com/amp_htm/cdi.htm) will approximately double down to 4 ohms or even 2 ohms, after that it would likely begin to approximate “half” (if there is such a term) down to 1 ohm and below as it reaches its current limit if it is not allowed to clip.

This is my kind of post. Once you get Math involved I understand. And it's not even Calculus.

So as the phase angle goes to 90 degrees the power goes to zero. So if one where to truly have a 90 degree phase angle one couldn't have any power in a reactive load. Because the cosine would go to zero.

So the current required to drive a speaker is dependent on the phase of the reactive load. Where 20 amps is the maximum an ep2500 can pull

20^2 x 1 x Cos of 75 is kind of a worst case maximum power of an ep2500.

which translates to 100watts.

Where if it's driven with a 10 amp load we are looking at 25 watts and so forth. I know there is a bit more to it than that, but still I find it interesting.

 

[3db]

Doing some more reading on electrostats and it turns out that their high impedance devices .. aleast according to this article..

http://www.music.mcgill.ca/~wes/docs/Electrostatic.pdf

I just wish they would publish what their phase angle is becuase its almost a pure capacitor when compared to that of a cone type speaker. This in turn does make the phase angle a worst case scenario.

 

[TLS Guy]

Doing some more reading on electrostats and it turns out that their high impedance devices .. aleast according to this article..

http://www.music.mcgill.ca/~wes/docs/Electrostatic.pdf

I just wish they would publish what their phase angle is becuase its almost a pure capacitor when compared to that of a cone type speaker. This in turn does make the phase angle a worst case scenario.

That's the very point I made earlier. An electrostatic speaker is a capacitor and most amps hate that type of load.

His best bet for powering an electrostatic on the cheap is a vintage Quad 303. For apartment use a Quad 303 will power it just fine and sound sweet.

This auction it is going for $80 at the moment with only two bids. Shipping would be about $120. If he got it for 100 GBP it would still be a bargain.

If he feels he wants 100 watts, he should wait for a Quad 405 2 to come up, or an updated 405. He will have to be prepared to give around $400 to $450 for one of those though. All Quad amps drive these high capacitance loads perfectly. Good 405s are highly sought after so the bidding can get intense.

The other option is to get a any 405. If no updated they go for under $200.

There are lots of US sites even that will update and restore a 405 for about $200 or a little less.

 

[Seth=L]

I'm ditching electrostats for the moment, I just made my big purchase for the month.

 

[Lordoftherings]

Music = Yeah! // Movies = Maybe, maybe not!

I'm ditching electrostats for the moment, I just made my big purchase for the month.

I think that for 2-channel stereo listening, there are some great electrostat speakers.

But I'm not convinced yet for movie watching, as they are much more fussy about placements and room treatments, unless you have the room for them.
And of course, amps with low impedance drives.
And you might is well go for the full system setup with all electrostatics, for the best integration (electrostat sub? ).

That's just my opinion, based on some research about this subject.

Bob

 

[3db]

That's the very point I made earlier. An electrostatic speaker is a capacitor and most amps hate that type of load.

His best bet for powering an electrostatic on the cheap is a vintage Quad 303. For apartment use a Quad 303 will power it just fine and sound sweet.

This auction it is going for $80 at the moment with only two bids. Shipping would be about $120. If he got it for 100 GBP it would still be a bargain.

If he feels he wants 100 watts, he should wait for a Quad 405 2 to come up, or an updated 405. He will have to be prepared to give around $400 to $450 for one of those though. All Quad amps drive these high capacitance loads perfectly. Good 405s are highly sought after so the bidding can get intense.

The other option is to get a any 405. If no updated they go for under $200.

There are lots of US sites even that will update and restore a 405 for about $200 or a little less.

Maybe I misunderstood some posts but I think I saw people drive ELs with tube amplifiers. Are thye less susceptable to the effects of large phase angles?

 

[AcuDefTechGuy]

The Audio Critic tested the Denon PMA-2000 and it produced 399 watts into 1 ohm load.

 

[3db]

The Audio Critic tested the Denon PMA-2000 and it produced 399 watts into 1 ohm load.

Into a regular speaker and not an electrostat whose phase angle is really large. Not a ood thing.

 

[Lordoftherings]

Maybe I misunderstood some posts but I think I saw people drive ELs with tube amplifiers. Are thye less susceptable to the effects of large phase angles?

Not a good idea in my book.

The Audio Critic tested the Denon PMA-2000 and it produced 399 watts into 1 ohm load.

Any link from that review, perhaps?

 

[AcuDefTechGuy]

Not a good idea in my book.



Any link from that review, perhaps?

Man, you can't just take my word for it?

Fine, here it is (Page# 34, integrated amps):

http://www.theaudiocritic.com/back_issues/The_Audio_Critic_25_r.pdf

 

[jliedeka]

The only phase/impedance graph I could find for an ES speaker was in a Stereophile review for a Quad ESL-989 here. It looks like the worst phase angle is in the low bass at around 58 degrees but the impedance is not especially low.

Jim

 

[bandphan]

The only phase/impedance graph I could find for an ES speaker was in a Stereophile review for a Quad ESL-989 here. It looks like the worst phase angle is in the low bass at around 58 degrees but the impedance is not especially low.

Jim

That tends to be correct, and if Seth is looking at logan panels, they are hybrid and a woofer covers most of the low/mid bass regions.

 

[Lordoftherings]

here it is (Page# 34, integrated amps):

http://www.theaudiocritic.com/back_issues/The_Audio_Critic_25_r.pdf

Thank you very much so, sir.

Oh, and I did believe you, I just like to read some more, to further my education.

 

[PENG]

Maybe I misunderstood some posts but I think I saw people drive ELs with tube amplifiers. Are thye less susceptable to the effects of large phase angles?

I can't imagine tube amps can do better driving loads of low impedance and/or large phase angles. As far as I know they do better with higher or at least not too fluctuating impedance loads that are resistive to slightly inductive.

 

[PENG]

Into a regular speaker and not an electrostat whose phase angle is really large. Not a ood thing.

399W into 1 ohm still not a good thing, you are kidding right?
You can't look at phase angles in isolation. You have to see both the impedance and phase angle vs frequency curves at the same time. Most curves I have seen tend to have impedance dips and phase angle peaks happening at different frequencies and in relatively narrow bandwidths. Further, consider this:

cos(30)=0.866
cos(45)=0.707
cos(60)=0.5
cost(70)=0.342
cost(80)=0.174

Until the phase angle get to be larger than 60 degrees, its effect on current demand is no worse than that of a dip in impedance from 8 to 4 ohms (resistive) except that if the phase angle is leading (capacitive), it will make it worse for lesser amps including tube amps.

 

[PENG]

Thank you very much so, sir.

Oh, and I did believe you, I just like to read some more, to further my education.

Want more?

http://www.symphonysound.com/articles/tubefriendly.html

 

[3db]

399W into 1 ohm still not a good thing, you are kidding right?
You can't look at phase angles in isolation. You have to see both the impedance and phase angle vs frequency curves at the same time. Most curves I have seen tend to have impedance dips and phase angle peaks happening at different frequencies and in relatively narrow bandwidths. Further, consider this:

cos(30)=0.866
cos(45)=0.707
cos(60)=0.5
cost(70)=0.342
cost(80)=0.174

Until the phase angle get to be larger than 60 degrees, its effect on current demand is no worse than that of a dip in impedance from 8 to 4 ohms (resistive) except that if the phase angle is leading (capacitive), it will make it worse for lesser amps including tube amps.

I understand the math PENG and I'm not knocking the Denon's output. But I'm also not blindly pumping out the specs without a real understanding of them. I also never just looked at phase angle below and if you see my other posts about that, I even stated that a 4 ohm dip wasn't a bad thing as long as the phase angle was small at a non bass frequency.