Thread: Power amplifiers that excel with very low impedance - and low efficiency loads

The Anthem P2 does not get hot beyond ambient air temperature, I have used a P2 amp for over 8 years and have never had it get hot or shut down and I have driven speakers down around 1-2 ohms for 10-12 hours at a time at 3/4+ power and this amp will just keep going. If you want look up the reviews for this amp they have been made for at least 10 years.
This amp is basically 2 mono amps in one chassis, no fuses, and I have never had the reset buttons pop to reset this amp, they run around 5k new but used can be had from 2-3k

Originally Posted by Jim Smith

Thanks again for all of your replies. It looks to be an exceedingly difficult issue for him to overcome, but at least there have been some interesting suggestions.

Jim, my recommendation would be to give any of the Constellation amps a serious look. Caelin uses them in his audio showroom at Shunyata, and he says they will drive any impedance load into any speaker and never break a sweat. Also, he says they sound as good upon start-up as they do fully warmed up. They are also incredibly reliable, and having heard them first-hand at his showroom, I can say they sound...absolutely fabulous. Even that Argo integrated is really something else.

The other solid-state brand that comes to mind is DarTZeel...again, we're talkin' next level here, in my experience.

There are reasons why you never see Constellation or DarTZeel gear for sale at the used gear sites...'cause the folks that own them...NEVER sell them.

To be honest i'm finding it very hard, to understand why we can not know what the speaker is, if it's a new company, so what, it will become common knowledge soon anyway, and if a new company is producing a speaker that you can hardly drive, unless you buy a pair of Dan D relentless amps at £250,000, then i really don't give them much of a chance anyway, so to be honest this thread is pointless,

Originally Posted by Jim Smith

As I said, the client is the one that has restricted me from giving that info. I do not lie to my clients - when I agreed to his request, he felt safe.

I do understand your position, it's just that I cannot reveal it.

Professional integrity. 👍👊

Originally Posted by Jim Smith

Thanks for all of your replies!

The speakers are a fairly new brand, from outside the USA.

While my client doesn't want to be involved with pointing out publicly an issue about which he is concerned, and perhaps causing a bad outcome for the new manufacturer, I can say that this is the bass driver in a multi-way high end speaker.

The driver's impedance is 1.4 ohms.

He has been thinking of using direct access to only that driver with an appropriate amplifier. The remainder of the sound (maybe 80%) from that speaker is quite nice, it's only problematic with the inefficient/low impedance bass driver in action.

Such a driver is going to cause any and I mean any amplifier to make excess distortion, so keeping it corralled to one driver (or more likely, array) is a good idea.

If it is an array, it might be possible to wire the drivers in a series/parallel arrangement to get a higher impedance. Since the output of the amp has to be controlled by a level control to allow it to work with the rest of the speaker, doing this shouldn't be weird. But it would make the speaker easier for a wider range of amplifiers.

I know that you're not talking about what speaker. But you might be able to pass some information along to the manufacturer thru their customer, which is that there is no benefit using any amplifier made to running such a low impedance in the bass region. You're simply going to get into drive problems, the speaker cables will be a nightmare (since their DCR will become a thing) and it will make it hard to sell speakers. Look at how hard it is to get an amp that's suited for this kind of duty and you're not even the seller!

So he might consider a minor redesign.

Just FWIW Dept,: there's no good argument for low impedance speakers if audio excellence is your goal. You might have a weak argument if sound pressure is your goal. You'll simply force whatever amp can survive the application to make more distortion and if that amp is also driving the mids and highs make no mistake: that distortion will be audible as brightness and harshness. A simple way to make any speaker sound smoother and more detailed would be to somehow go to a higher impedance without changing anything else.

Now some people on this thread know I'm a manufacturer of tube amps (now for over 46 years). But I've worked on thousands of solid state amps in my career (I put myself through engineering school servicing audio equipment). Right now we're working on a class D amp of our own design. IOW I'm not being hyperbolic, I'm not making this stuff up; I'm simply being pragmatic.

As far as what amp to use, the first thing to know is how much power you need. Do you have any sensitivity specs and do you know the size of the room? Sorry if you posted that but I went through this thread and didn't see it.

Originally Posted by Jim Smith

Thanks for all of your replies!

The speakers are a fairly new brand, from outside the USA.

While my client doesn't want to be involved with pointing out publicly an issue about which he is concerned, and perhaps causing a bad outcome for the new manufacturer, I can say that this is the bass driver in a multi-way high end speaker.

The driver's impedance is 1.4 ohms.

He has been thinking of using direct access to only that driver with an appropriate amplifier. The remainder of the sound (maybe 80%) from that speaker is quite nice, it's only problematic with the inefficient/low impedance bass driver in action.

Jim,
The Speltz Zero autoformers increase the impedance the amp sees. I run them on my AtmaSphere M60 OTL amps driving Kef Reference 207/2s which dip to 3 Ohms and they definitely do not add transformer euphonics. It could be an option that widens the choice of amps.

Evan

Originally Posted by a.wayne

Haha OK Ralph ..

Here we go, for an OTL toob amp you are 100% correct , for a transformer coupled toob amp you’re 50% correct , for an SS amplifier designed for low Z operation not so much.


A low Z operation SS amp will have both Bias and feedback scheme as well as output/driver stage designed for such a low impedance operation , only low to zero feedback amplifiers will have issues driving low Z loads, to be specific the loudspeaker should be of such a design to take advantage of being such a low load , case in point , direct drive ribbons, as the removal of meters of wiring thru inductive voice coils and resistors is easily overcome by being able to drive the diaphragm directly..


Regards

PS : For an high impedance 8 ohm easy to drive loudspeaker i would use a toob amplifier and not an SS amp , a well designed SS amp is at its best on low Z difficult loads , i do realize the current trend is low feedback SS amps for 8 ohm load type speakers and those type of amplifiers will suffer on difficult low Z loads with increased distortion and a lack of stability..

I've yet to see a solid state amp (or class D) whose distortion did not go up when driving a 4 Ohm load as opposed to an 8 Ohm load.

If you know of one I'd be interested.

But you can see this in the specs if they are published. The thing is, that little difference you see is audible- since the ear converts all forms of distortion into tonality, and since it also uses the higher ordered harmonics to sense sound pressure, that slight amount of increased distortion (which is almost entirely higher ordered harmonics) is audible as increased harshness and brightness- and a loss of detail.

Harshness and brightness is the sort of thing that lowers WAF and if you have any hearing left, reduces your enjoyment of the actual music- it allows your brain to know that what you're listening to is a mechanical reproduction of some kind- electronics instead of music. This is just me of course- my goal in high end audio is to get the result to sound real and the more you spend at that effort, the more it had better pay off. So things like 4 Ohms (or less) loads play counter to that.

You're pointing out exactly what I'm talking about.

The thing is, the industry has spent a lot of time telling audiophiles that the slight difference you see in the charts is 'negligible' and 'inaudible'. Quite simply it isn't. What is being ignored here is that the ear has over a 120dB range and uses the higher orders to sense sound pressure- and so is keenly sensitive to them, far more so than anything else. As a result we can hear these 'tiny' (because that's how they look on paper) differences- that's why audiophiles hear differences in amps, not so much due to FR variation, but due to the distortion signature.

For the application the Boulder is probably one of the better choices! But saying that its going to sound its very best is an entirely different matter- the ability to drive low impedances isn't what makes an amp sound good or bad. Distortion is what does affect that and clipping has nothing to do with it. IOW the differences we hear between amps is due to the distortion they make when they are not clipping, because the ear pays a lot of attention to the tonality created by that distortion. Again, that's why you can have two amps on the bench that both measure perfectly flat, but one is bright and the other is not. The brightness is the result of non-clipping distortion.

That BTW is why the tube industry is still very much around; for the last 60 years we've been hearing solid state amps be bright (and of course the guitar world plays an enormous role). You might want to read what Bruno Putzeys has to say about distortion (if you've not already).

I can,

This is an example of how the distortion signature affects the sound you hear. A large 2nd and 3rd harmonic helps mask the presence of the higher orders. This helps keep the amp sounding smooth even though it has more higher ordered harmonic content than most solid state amps.

Put another way, the distortion signature is pretty important to how smooth the amp sounds. The trick is getting it down overall- tube amps in general are not very good at that since its hard to build them with enough feedback to do the trick (IOW phase margin is an issue).

One other thing: the distortion really should be the same at 1KHz and 10KHz as it measures at 100Hz. Many amps have insufficient gain bandwidth product, which is another way of saying that as frequency is increased, the feedback decreases, so we see distortion rising with frequency.

The problem is that feedback introduces distortion in the form of higher ordered harmonics through the process of bifurcation (see Norman Crowhurst- he was writing about this 60 years ago). In addition you can get intermodulations at the feedback node if you're not careful. Since feedback suppresses the innate distortion of the amp, the remaining distortion is often that of the feedback itself and it is unmasked, so easy to hear.

If you have enough feedback you can get around this problem. Imagine a bell curve; feedback does its worst damage between 15-25 dB (which is an amount commonly used). If you get over 35dB the amp can clean this problem up and you can have a much smoother sounding amp. Class D seems to offer a nice way to do this in self-oscillating examples.

You can get tubes to sound just fine but not every manufacturer of tube amps is successful. Plus you do want to be careful to not use them with speakers that they are simply a bad match. But I've found that latter bit true of transistors as well: not every speaker works with every amp and vice versa.

Originally Posted by a.wayne

Class D or any SS has its sound same as high distortion toobs and or low distortion high feedback toobs, Only amps with bad open loop gain tend to have NFB issues ...

If I understand you correctly I partially agree. I'll make it a bit more clear: If they have the same distortion signature it won't matter what kind of amp it is, it'll sound the same. But what is meant by 'bad open loop gain'??

Again a lower THD high dynamic low Z operating loudspeaker is superior sounding to a high Z variant with less drive area , this will more than compensates for any small increase in amplifier THD ....!

It may well- but increase the Z and you have the best of both worlds.

A committed low Z designed SS can be of low distortion and flat bandwidth 20-20K same as 8 ohm if optimized in its design phase..

Of course!! Why did you bring this up?

Lamm M1.2 Reference in low Z operation mode optimized , "1–6 ohms," THD+N (%) vs frequency at 8.95V into: 8 ohms (blue), 4 ohms (magenta), 2 ohms (red).

Is that flat enuff for you ...?


Regards

Sure! But what does its distortion signature look like? I've heard that amp a few times so I think I can take a good guess that its low in 2nd and 3rd harmonic content. IOW another example of exactly what I've been talking about. You can't know how the amp sounds by looking at the THD; you'll have a greater understanding by knowing what its primary distortion product actually is. In audio amps you tend to get two types of non-linear functions- quadratic and cubic. A fully single-ended circuit will exhibit the former while a fully differential circuit will exhibit the latter (and so be lower in overall distortion). If both types are present you'll get some algebraic summing, like you see in a Dyna ST70 or the like where the 5th will have a bit more amplitude. I recommend the writings of Norman Crowhurst and Bruno Putzeys regarding this particular aspect of topology. Sorry if this seems off in the weeds but its directly related to the issue of distortion being audible.

Loved my Lamm M1.2 hybrid monos. Should have kept them.

Originally Posted by a.wayne

Yea ,

unlike your Mac those can handle the Pre-conditioning test at 1/3 power ..

Never had a problem with either.

Originally Posted by a.wayne

I’m familiar with Crowhurst , Geddes , Putzeys, et al , its not relevant to the discussion about low Z SS amps as we are not debating distortion signature, we are debating your comment on why low z is bad in loudspeakers...



Regards

Hm. If you really think that then you missed the point of my comment. It was in fact entirely about how low Z loudspeakers cause all amps to have increased distortion. And yes, the writings of those authors are quite relevant. They can be quite helpful in guiding one towards something more musical as opposed to something less musical.

And with a lot of solid state amps that have a distortion signature that allows the higher ordered harmonics to be heard as brightness and harshness, this simply means that the system will sound less 'real'. But in the OP's situation, the distortion is corralled a bit by being limited to the woofer or woofer array, thus limiting the effect somewhat (unless the woofer also has a choke in series, some of that distortion will be reproduced).

By simply employing a higher impedance (which might be as simple as changing the series/parallel arrangement if its an array) this distortion will be reduced.

BTW you didn't answer my question about what is meant by 'bad open loop gain'. I'm very curious what you meant by that.

Originally Posted by a.wayne

Well..


You missed my point entirely Ralph , mainly how SS amps designed for low Z operation( proven and shown as you requested look at lamm ) can have low distortion as well as how low Z loudspeakers if designed correctly has less distortion than high Z , making the whole combination superior granted far more technically difficult and not as easy as say an high Z , 2 way or 3 way system with usually higher Thd

As to your umpteen time Strawman argument about distortion signature , that’s all getting into subjective audio blah blah as to who likes what and is a total side step of the point being made.

Measured thd , not subjective likes and dislikes ...!

This is almost entirely false. All humans use the same hearing perceptual rules- for example all humans use the higher ordered harmonics to sense sound pressure. That's not a matter of taste. The masking principle is also common to all humans. There's no strawman going on; simply the nuance of what happens when you try to use any amp to drive an impedance that low.

The 'almost part' is the THD of the Lamm, which is unusual. But without knowing the distortion signature you can't just say that 'lower THD is better'. Lower THD and a proper distortion signature such that higher orders are masked is what will result in an amp that is musical and not bright. Low THD on its own can easily result in a bright sounding amp. You can try to make the argument that such is subjective, but its also well-known that humans find the higher orders unpleasant and that understanding was published way back in the 1930s. If you're going to subject an amplifier (including the Lamm in this case) to a situation where you know its going to make those higher orders you can count on the result being less musical and you don't have to hear it to know that. All you have to know is the science of how the amps work and how that interacts with human hearing perceptual rules.

If you design an amp without paying attention to the aspects of human hearing you stand a good chance of making something that will sound bad. Its not subjective so much as its engineering applied to physiology.

BTW , your suggestion of simple change of series / parallel to increase impedance load is nothing more than band aid for what is really an amp mis-match situation , you should investigate how series coils affects the sound vs parallel circuits, in regards to loudspeakers ..

I have investigated that and it works fine as long as all the drivers are the same kind and interacting in the same way in their enclosure.

Originally Posted by a.wayne

Well i guess everyone hears the same and like the same sound, it’s settled then, err , if not for the unsettling Irony ...

Regards

That's not what I'm saying. I am saying that the rules that govern how we perceive sound are the same rules- this is how MP3s are possible. They rely on the masking principle to compress the file size. And its also true that humans don't like higher ordered distortion components - that's why most guitar amps are tube amps, although to be clear in the case of the OP I'm not talking about an overdriven amp.

Originally Posted by a.wayne

You’re obfuscating ,

It’s apples and oranges , the discussion has nothing to do with distortion harmonic (complete different discussion) structure its all academic really, these are all known knowns , yet you keep wanting to keep this circular Strawman argument, waffling between objective and the subjective ..

Whats your thoughts on Specialized vs Trek ..?


Regards

If you think I'm obfuscating or waffling, then you've missed my point.

Class D offers a way (through self-oscillating design) to allow for a large amount of feedback (+35dB) that is otherwise difficult to design into traditionally-designed solid state or tube amplifiers. This is done by intentionally exceeding the amp's phase margin, so it oscillates. The oscillation is then used as its switching frequency. This allows for an amp that lacks the typical brighter/harsher presentation than the prior art (otherwise to avoid this you have to avoid feedback altogether). A very nice benefit is they are also cooler running, more efficient and lower cost. Class D amps have a different artifact that is actually similar in some ways to tube amps. Dead time causes distortion; but it tends to be of the lower harmonic variety, as do non-linearities in the encoding scheme. This allows for an amp that not only has the right distortion signature, but also low THD, the best of both worlds. Of course if you overdrive it, it will clip like any other solid state amp. So don't clip it.

Originally Posted by atmasphere

Right now we're working on a class D amp of our own design.

Could you hurry that up please? I would love a cool-running, high-power, great-sounding amplifier that I can lift.

All too frequently it is over 100 degrees here so no Class-A. Tubes are relegated to winter use but swapping amps is getting harder every year. Every Class-D amp I have tried did everything right--except make music. At least to my ears.

Originally Posted by Dizzie

Could you hurry that up please? I would love a cool-running, high-power, great-sounding amplifier that I can lift.

All too frequently it is over 100 degrees here so no Class-A. Tubes are relegated to winter use but swapping amps is getting harder every year. Every Class-D amp I have tried did everything right--except make music. At least to my ears.

We'll be building our next production in November.

Originally Posted by a.wayne

Over a 100deg , must be Global warming Central and For clarity , Ralph had told me he is doing a class D 7-8 yrs ago ..

Are you saying I should exhale? i.e. Not hold my breath.

Originally Posted by a.wayne

Ralph had told me he is doing a class D 7-8 yrs ago ..

This statement is incorrect. Our first work started more like 4 years ago and prior to that we had not discussed with anyone outside the company anything with regard to making a class D.

Wow, this thread has taken such a digression from the subject of Jim's original post, maybe all the amp "techical side-bar dicussion" should be moved to it's own thread. Lots of good info here, but pretty far from JIm's original post.

Jim: I'd go with Constellation if it's in your customers budget. Just sayin'....


'

Originally Posted by Randy Myers

Not sure this qualifies, but here is the NAD C 298 specs:

Rated output power into 8 Ohms (Stereo) 185 W at 8 ohms (ref. 20 Hz-20 kHz at rated THD, both channels driven)
Rated output power into 4 ohms (Stereo) 340 W at 4 ohms (ref. 20 Hz-20 kHz at rated THD, both channels driven)
Rated output power into 8 Ohms (Bridge mode) 620 W at 8 ohms (ref. 20 Hz-20 kHz at rated THD, both channels driven)
THD (20 Hz – 20 kHz) <0.005 % (1 W to 185 W, 8 ohms and 4 ohms)

Sure looks like they claim same low distortion for both 8 and 4 ohm. Am I missing something or are they claiming that the distortion figures do not raise at 4 ohm?

Dunno! But it would be interesting to see how it actually behaves. The amp doesn't double power- in sufficient heat sinks or power supply?? With a limitation like that imposed I would expect to see it affect distortion too.

Your memory fails you, we have had this and that discussion maybe 100 times already ....

This statement is false.

No Ralph your response is , not calling you out just saying your memory maybe failing you...


Regards

Originally Posted by Puma Cat

Wow, this thread has taken such a digression from the subject of Jim's original post, maybe all the amp "techical side-bar dicussion" should be moved to it's own thread. Lots of good info here, but pretty far from JIm's original post.

Jim: I'd go with Constellation if it's in your customers budget. Just sayin'....


'

i think we are ok continuing the thread this way since jim (i think) is no more in search.

the client has a speaker with a nasty load. what can he do?
well, sell the speaker or buy an amp that can handle the load.
however, the client (if i understood correct) wanted to buy an amp on top to the existing one and drive the bass separately.

to make that sound good, you will need an extra crossover that will be capable of adjusting phase etc, you will need more cables and actually the SAME amp you already have.
so if your first amp cant handle the load why buy it again.
bottom line, if you do it right, it will be very expensive.

Originally Posted by a.wayne

No Ralph your response is , not calling you out just saying your memory maybe failing you...


Regards

It isn't. Your use of hyperbole is failing you however. '100's of times?? Nope. Eight years ago we had no plans of a class D amp. None. That didn't happen until about 4 years ago. So how could I have talked to anyone about the project eight years ago?? The answer is simple: I didn't. In fact I kept silent about the class D project for about a year.

So please cease and desist about attacking me regarding the state of my memory. Reporting your post as the abuse that it is failed to get any response out of the moderation team (and being a moderator on another site I know the definition of abuse) so I'm simply stating here how to deal with this: if you disagree with someone on a topic, attack the post, not the poster. Get it??

If a person is going argue with Ralph about amplifiers I have just one suggestion for that person. Do not enter into a battle of wits unarmed.