Constant Power

[amirm]

You would want to ask them specifically about the older Watt/Puppy. I can't speak to newer designs, although so far our stuff sounds fine on them.

Steve has the Alexandria Series ll so would be good to know the answer in that case just the same.

 

[microstrip]

(...) You have a good relationship with Wilson folks. Do you want to run this argument and ask them what they think? Clearly they either intended this to happen to or not. If they intended, then we need to know what range of amp impedance they assumed and no one should use their speakers with anything else if they expect accurate reproduction. I recall them always use your LAM amps at shows in the last couple of years I have heard them so perhaps there is something there.

Amir,

You really have a good sense of humor! I do not think that Wilson folks have the same definition of sound accuracy as F. Toole.

Besides David Wilson has expressed several times his opinions about what are the best amplifiers for his speakers - mostly the ones you prefer and have power enough for your application. He once referred in a interview about the Grand Slamm that Lloyd uses that he had people using it successfully with 7W SETs and 1000W solid state.

 

[Steve Williams]

The conclusion therefore would be that such a speaker would not sound correct with vast majority of amps that have very small output impedance. In the specific, your Wilson speakers would never sound right with a solid state amp.

not sure that I agree with this statement. Ask Christian how his X2 series ll's sound with his SS amps. Before I went all tubes the SS amps driving my speakers were Krell 750Mcx and they sounded darn good

 

[Roger Dressler]

It depends on whether your top priority is sound quality or virtually carefree system matching. If the latter, then solid state amps with large amounts of global negative feedback offer all you could ever ask for.

Why do you assume global negative feedback is the only way to achieve a low output impedance? That seems very prejudicial, let alone false.

 

[andy_c]

Why do you assume global negative feedback is the only way to achieve a low output impedance? That seems very prejudicial, let alone false.

Also, there's the false assumption that trouble-free system matching and best sound quality are somehow mutually exclusive.

 

[Atmasphere]

Steve has the Alexandria Series ll so would be good to know the answer in that case just the same.

We already know that one works... The MA-2 works very nicely with the Alexandria- we've even built them custom with matching finish. Whether that is by design or not is unknown (although the national sales manager for Wilson had a set of MA-1s and later had a set of MA-2s), but so far I have yet to hear of an incompatability with Wilson and our amps. We have a customer that used our little S-30 very successfully on his later Watt/Puppy setup, eventually he graduated to a set of M-60s. As Wilson stated, you can use them with an SET if its enough power; that is what our customer was using before he got our stuff. At any rate I have been able to recommend Wilson to our customers for the last 20 years with no worries.

How about a speaker that does not work so well with an amplifier with no feedback? One example I like to use is the B&W 802. This speaker is nominally 8 ohms in the mids and highs but it 4 ohms in the bass where the load is two 8 ohm woofers in parallel. The efficiency of the drivers is such that the woofers are 3 db less efficient than the midrange and tweeter. But there are two in parallel so we know that the sensitivity of the woofer array is increased by 3db. If your amplifier can double power from 8 to 4 ohms it will work fine with this speaker. OTOH if the amplifier does not double power the result will be a 3db 'shelf' of reduced output operating in the woofer region. IOW the amp will sound a little weak in the bass, even though it may have good extension. You can improve this by adding feedback to the tube amp but you will also pay the price of the amp getting brighter and less musical.

So here is where I see the Power Paradigm as better: if the speaker requires the amp to have feedback in order to work, it inherently will be violating one of the most fundamental rules of human hearing, that of being how we perceive sound pressure. In addition a tonal coloration (brightness) is introduced. Thus such a speaker might sound like a good stereo, but it has no chance of sounding like real music.

 

[Duke LeJeune]

Bold 1: Perhaps you should, because so far all you've done is provide evidence that given enough care in matching amp and speakers, one of OTL's classic weaknesses might be overcome. And by smoother, I assume you mean more linear?

Bold 2: This "real" reason for the use of OTL amps, I'm sure you've noticed, is almost universally accepted by the devotees of OTL amps, but it doesn't get any traction outside the club. While you're making your case, if you really have an interest in doing that, you may want to show some statistical evidence of which distortions matter to human hearing, at what levels, and some examples of OTL amps audibly reducing the distortions that do (once you've established that), relative to SS amps of equal quality. Otherwise, you're just another OTL fan praising that thing you like the sound of. This is an audiophile board; we don't need to be convinced that some people enjoy THD. I do need to be convinced that the presence of a bunch of it audibly reduces distortions that have been demonstrated to be more audible and objectionable to more listeners, not just anecdotally reported as such by fans. Don't get me wrong, this is a OTL discussion with a chart in it; I appreciate the progress, but we're still barely lifted above he said/he said.

I don't really have any issue with Ralph's terminology, but I think it is useful to know when "engineering" terminology is really not - not universally defined, understood or used -- but is, instead, the invention of the author and adds no credibility, substance, or even a point of reference beyond the author's position.

Tim

Bold 1) I'm not engineer enough to come up with mathematical proofs (of my claim that "an OTL amp + optimized speaker will, for a given box size and efficiency, give you deeper and smoother bass extension than you'd get from the same size box and efficiency optimized for a solid state amp"), so I'd have to resort to modelling examples. And I'd probably be accused of picking examples that prove my point. So how about I give you a chance to participate here, no one is going to accuse you of intentionally picking an example that supports my position.

Refer back to the example system I described in post #41 (Faital 12FH520, 6 cubic feet, 35 Hz tuning, 4 ohm amplifier output impedance). That woofer has a calculated efficiency (based on T/S parameters) of 96.2 dB/1 watt. Pick any woofer you want that has approximately the same efficiency, adjust the Vas until the calculated efficiency actually is the same (so that we're comparing apples to apples) and model it in a 6 cubic foot vented box tuned however you want, adjusting the input voltage so that both speakers are seeing the same wattage based on their voice coil resistance, 5.1 ohms in the case of the Faital. See if you can get BOTH a lower F3 AND a smoother response curve using an amp with negligible output impedance.

This should be a total piece of cake for you, because the example in post #41 is not optimized. I just picked that woofer, box size, tuning frequency and output impedance off the top of my head without doing any modelling (though I did subsequently model it to see if it would make my point, but did not optimize it further).

Once you've proven me wrong there, we'll move on to Bold 2.

 

[Roger Dressler]

On the other hand, there are still many open questions, the most important of which for me are:

a) No one has yet come forward to name *current-day* SS amplifiers or other tube amplifiers that are not following the power paradigm;

You mean voltage paradigm, no? Are not most amps voltage paradigm? Certainly true for SS amps. I'd say also the case for tube amps. First, we have to use the correct criteria. This "same power for different impedance" is being misinterpreted as a criterion for power paradigm. This has a) nothing to do with the max output (i.e. 10% or 1% THD) power, and b) it has nothing to do with a nice tube amp such as McIntosh that offers the same total power into 2, 4, 8 ohms, as that only happens when the speaker of that impedance is connected to those three different sets of output transformer taps.

Every illustration of how amp/speaker matching interaction affects sound quality ignores all of this, and focuses (rightly) on how the varying impedance of a speaker over frequency interacts with the output impedance of the amp. If the nominal 4 ohm speaker has an 8 ohm impedance at the crossover, changing the connections to the 8 ohm taps is not an option.

So if we can ignore power supply stiffness and output transformers, we'll much more quickly arrive at the operative characteristics of the amp/speaker interaction that affect sound quality.

A modest SS amp might have a damping factor of 40 into a 4 ohm load. That means an output impedance of 0.1 ohm. What would be the damping factor of a McIntosh tube amp? Anyone? They state >40 wideband for the MC302. So it exhibits the same 0.1 ohm source impedance as a SS amp. Sure, you can find SS amps with higher damping factor, but after 10 - 20 feet of speaker cable, it might not matter.

b) No one has directly discussed amplifier output impedance and how that fits into either the so-called voltage paradigm or the the power paradigm; more importantly, what is it that makes a design follow one paradigm vs/ the other - we would like to see formulas that also involve the load itself. We don't even know what the true output impedance characteristics of Atmasphere's OTLs are.

Based on my previous paragraph, I would assert that the McIntosh amps are voltage paradigm, since they behave essentially the same as far as the amp/speaker relationship is concerned as SS voltage paradigm amps. Atma-Sphere stated a power paradigm amp exhibits "moderate output impedance (1-20 ohms is typical)". An easy way to make an amp with a 10 ohm output impedance is to add a 10 ohm resistor in series with the speaker. Or pick whatever value makes the speaker sound best.

 

[Duke LeJeune]

When you design a set of speakers for these power paradigm amps are you aiming for as flat an impedance as possible, or at least trying to minimize nasty impedance peaks?

Yes, I'm aiming to keep the impedance as flat as possible over most of the spectrum. Here's what one of my impedance curves looks like:

No smoothing applied - that's the raw data. The scale is kinda hard to read - the bottom-most line is 12.6 ohms, and the one above it is 26 ohms. The "nominal impedance" of that speaker is 16 ohms.

Obviously we still have major peaks in the bass region, but I use those as a "cheat" to get deeper and smoother bass than I otherwise would have when that speaker is used with an OTL amp (Ralph's S-30 in this case).

When it's used with a solid state amp, I tune the box a bit higher, and aside from losing about 1/3 octave of low bass, the frequency response is virtually unchanged.

 

[Roger Dressler]

How about a speaker that does not work so well with an amplifier with no feedback? One example I like to use is the B&W 802. This speaker is nominally 8 ohms in the mids and highs but it 4 ohms in the bass where the load is two 8 ohm woofers in parallel. The efficiency of the drivers is such that the woofers are 3 db less efficient than the midrange and tweeter. But there are two in parallel so we know that the sensitivity of the woofer array is increased by 3db. If your amplifier can double power from 8 to 4 ohms it will work fine with this speaker. OTOH if the amplifier does not double power the result will be a 3db 'shelf' of reduced output operating in the woofer region. IOW the amp will sound a little weak in the bass, even though it may have good extension. You can improve this by adding feedback to the tube amp but you will also pay the price of the amp getting brighter and less musical.

Or you can use a McIntosh tube/transformer amp (or the like) which has an output impedance of <0.1 ohms.

So here is where I see the Power Paradigm as better: if the speaker requires the amp to have feedback in order to work, it inherently will be violating one of the most fundamental rules of human hearing, that of being how we perceive sound pressure.

This constant hammering on feedback is getting a little tiresome. There are other ways to achieve low output impedance without global negative feedback. Dismissing all feedback as harmful is baseless.

And what does feedback have to do with how we perceive sound pressure? Please explain the fundamental rule to which you refer. Thanks in advance.

 

[amirm]

Amir,

You really have a good sense of humor! I do not think that Wilson folks have the same definition of sound accuracy as F. Toole.

Wha I said has nothing to do with Floyd Toole. I am repeating the argument being made by people posting here. If they are not saying that they produce more accurate reproduction then I don't know what they are saying.

 

[amirm]

not sure that I agree with this statement. Ask Christian how his X2 series ll's sound with his SS amps. Before I went all tubes the SS amps driving my speakers were Krell 750Mcx and they sounded darn good

Then your practical experience is disputing the case being made here for constant power, etc. That argument falls apart if amps regardless of output impedance sound great.

 

[Phelonious Ponk]

Bold 1) I'm not engineer enough to come up with mathematical proofs (of my claim that "an OTL amp + optimized speaker will, for a given box size and efficiency, give you deeper and smoother bass extension than you'd get from the same size box and efficiency optimized for a solid state amp"), so I'd have to resort to modelling examples. And I'd probably be accused of picking examples that prove my point. So how about I give you a chance to participate here, no one is going to accuse you of intentionally picking an example that supports my position.

Refer back to the example system I described in post #41 (Faital 12FH520, 6 cubic feet, 35 Hz tuning, 4 ohm amplifier output impedance). That woofer has a calculated efficiency (based on T/S parameters) of 96.2 dB/1 watt. Pick any woofer you want that has approximately the same efficiency, adjust the Vas until the calculated efficiency actually is the same (so that we're comparing apples to apples) and model it in a 6 cubic foot vented box tuned however you want, adjusting the input voltage so that both speakers are seeing the same wattage based on their voice coil resistance, 5.1 ohms in the case of the Faital. See if you can get BOTH a lower F3 AND a smoother response curve using an amp with negligible output impedance.

This should be a total piece of cake for you, because the example in post #41 is not optimized. I just picked that woofer, box size, tuning frequency and output impedance off the top of my head without doing any modelling (though I did subsequently model it to see if it would make my point, but did not optimize it further).

Once you've proven me wrong there, we'll move on to Bold 2.

I think you've got this backwards. You're the one making the claims. Specifically that a properly matched OTL amp/speaker combo can deliver both deeper and smoother bass than an unnamed SS amp/speaker combo. The burden of proof is yours. I won't trouble you to do any modeling, though. Just some independent measurements of the response of a speaker/amp combo you consider appropriate would be a good start, as I'm not really looking for "proof," just some evidence more substantive than the opinion of someone with a vested interest in the outcome.

Tim

 

[amirm]

We already know that one works... The MA-2 works very nicely with the Alexandria- we've even built them custom with matching finish. Whether that is by design or not is unknown (although the national sales manager for Wilson had a set of MA-1s and later had a set of MA-2s), but so far I have yet to hear of an incompatability with Wilson and our amps.

I am taking what you say at face value. If so, then there has to be the case that solid state amps with the same speakers produce worse fidelity and speaker manufacturer agrees with that. It can't be that both amps as I mentioned to Steve sound great.

We have a customer that used our little S-30 very successfully on his later Watt/Puppy setup, eventually he graduated to a set of M-60s. As Wilson stated, you can use them with an SET if its enough power; that is what our customer was using before he got our stuff. At any rate I have been able to recommend Wilson to our customers for the last 20 years with no worries.

I hope you appreciate that we need objective independent data on such things. Anecdotal information from parties with an interest in the outcome don't travel far .

How about a speaker that does not work so well with an amplifier with no feedback? One example I like to use is the B&W 802. This speaker is nominally 8 ohms in the mids and highs but it 4 ohms in the bass where the load is two 8 ohm woofers in parallel. The efficiency of the drivers is such that the woofers are 3 db less efficient than the midrange and tweeter. But there are two in parallel so we know that the sensitivity of the woofer array is increased by 3db. If your amplifier can double power from 8 to 4 ohms it will work fine with this speaker. OTOH if the amplifier does not double power the result will be a 3db 'shelf' of reduced output operating in the woofer region. IOW the amp will sound a little weak in the bass, even though it may have good extension. You can improve this by adding feedback to the tube amp but you will also pay the price of the amp getting brighter and less musical.

The B&W has some certain design flaws. So I would buy that if you messed around with how you drove it, maybe subjectively it would sound better. A better solution would be to get a speaker that doesn't have such serious directivity problems (B&W is speaker B):

And looks like you are right about lower output in low frequencies. Instead of trying to mate it with an amp to fix its issues, why not use the speakers that don't have these problems?

So here is where I see the Power Paradigm as better: if the speaker requires the amp to have feedback in order to work, it inherently will be violating one of the most fundamental rules of human hearing, that of being how we perceive sound pressure. In addition a tonal coloration (brightness) is introduced. Thus such a speaker might sound like a good stereo, but it has no chance of sounding like real music.

The problem is that we can't demonstrate these issues in listening tests. Solid State amps with negative feedback routinely sound like real music.

 

[mep]

mep, your Appeal to Authority here is a classic Logical Fallacy. Just because Bob didn't know of the amp in bold does not mean it does not exist. For that matter I don't know of one either, in strict terms, but if we speak in terms of decibels than I can name quite a few. Further, the constant current amps he mentions of course are not constant power. The comment actually points to his ignorance on the topic. His closing argument is also a Strawman- I never made the stereotype he suggests.

Your argument is a "classic Logical Fallacy." I didn't bold the statement in the article, you did. I didn't refer to that sentence about the power amp, you did. I simply stated that Cordell didn't agree with your paper in general. I didn't call out out one part and bold it as you did. It's clear to me now that when people don't write things you agree with, you have no problems changing their words around so you can accuse them of strawman arguments or logical fallacy. You have done it to me twice now. And based on your last comments above where you slam Cordell, it appears that people who don't agree with you are destined to be told they are ignorant and use strawman arguments.

 

[mep]

One question for mep, do you believe that you have more experience and knowledge of amp design than Ralph Karsten? Because, IF you don't, what is the point of this thread?

I would love to say that I can't believe you asked me either question, but I can believe it. I have never stated that I have "more experience and knowledge of amp design than Ralph Karsten." And your next question is bogus on several counts. This thread was not/is not primarily about Ralph's OTL designs. This thread was started to discuss the voltage paradigm and power paradigm amplifiers as outlined in Ralph's paper. So your second question which states that if I don't know more about designing amps than Ralph that makes me unqualified to comment on his paper is pure nonsense. Talk about a strawman argument... If you have paid any attention at all to this thread, I think you would have seen by now there are other people who understand why I started this thread and agree with the points I'm trying to make. I don't know if this is over your head or if you just wish to make baseless attacks on me.

 

[amirm]

Let's cool off on personal comments guys. There is plenty to discuss on technical front that such commentary is not needed.

 

[mep]

Do you have any papers you could reference with regards to McIntosh being leaders in the voltage paradigm? Since both McIntosh tube amps and all but their cheapest SS amps use output transformers, that puts them in the “power paradigm” camp and not the “voltage paradigm” camp. And it would only follow that if McIntosh amps were designed following the rules of the “power paradigm” that their speakers would be designed the same way.

You are mistaken- output transformers have nothing to do with this one way or the other. It is more about global loop feedback.

Really now? You described the Power Paradigm as follows:

"The Power Paradigm
The Power Paradigm assumes that amplifiers produce power and speakers are power-driven. Current produced by a power amplifier is not ignored and is considered in the amplifier's power response. Under this model, the ideal amplifier will make the same power into all loads, 4, 8 and 16 ohms. The typical amplifier, in this case, is a vacuum tube amplifier which usually makes its power into these loads via taps of its output transformer."

You state in your paper the “typical” amplifier that meets the power paradigm model is a vacuum tube amplifier that makes its power into these loads via taps of its output transformer. McIntosh makes tube amplifiers with output transformers. McIntosh also makes SS amplifiers with output transformers (autoformers). According to your paper above, that puts McIntosh squarely into the power paradigm camp. Now output transformers have nothing to do with the paradigm an amp fits into and “it is more about global feedback”? And again, I asked you if you had any papers you could reference with regards to McIntosh being leaders in the voltage paradigm, but I received no answer one way or the other.

 

[mep]

Let's cool off on personal comments guys. There is plenty to discuss on technical front that such commentary is not needed.

Amir-I hope they do. I have been at the receiving end of personal comments from both Ralph and DaveyF and I'm very tired of it.

 

[Atmasphere]

Also, there's the false assumption that trouble-free system matching and best sound quality are somehow mutually exclusive.

So far, they are. This is partially because the industry really does not have a good equipment matching conversation- tubes are after all still around. It is possible to get a low output impedance without feedback, the Ayre and Ridley Audio amplifiers are examples. The Ridley is one of the best amps I have heard (its also SS), but its 100 watts and over $100,000. Plus it has a heater that heats up the output devices such that the amp is as hot as a tube amp and draws the same power (the technique is patented BTW).

That leaves the Ayre as one of the very few contenders otherwise. One concern you have with many semiconductors is that there is a non-linear capacitance that is inherent to the junctions of the device. This capacitance is magnified by current through the device. There is one semiconductor, the varactor diode, that takes advantage of this effect and is used a lot in the tuning of FM radios (apply a different voltage and change the capacitance and therefore the tuned frequency of the radio). This non-linear capacitance is one of the reasons semiconductors make more odd ordered harmonics. BTW you can reduce this by less current through the devices- IOW by driving a higher impedance loudspeaker. Although you will loose some power, the amp will sound smoother and more detailed.

In case it is not obvious this is all about not violating human hearing/perceptual rules. If we can acheive that then it follows that the system will sound better. I regard the Ayre as being on the cutting edge in this regard. If I could build a SS amp that sounded as good as the tubes I would do it in a heartbeat. But I can't and no-one else seems to have been able to do so either. So the Power Paradigm is the next best alternative; a means of obtaining flat frequency response without the tonal coloration that loop feedback causes.