Class D

Been thinking of trying a D amp to reduce clutter. Most that I see are not rated at 2 ohms.  My PSB Stratus gold's will drop to 3 ohms or lower at some frequencies. So my question is will these types of amps handle this impedance ?
Thanks in advance. Chris
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Certain Class D amps thrive, others not so much.  AVM and Rogue I know from personal experience are fine and more than stable at these lower impedances.

Other brands I know struggle a bit.  
Some class D amps can have problems with more difficult speaker loads, but it's hard to know without trying if the manufacturer isn't saying.
I use Hypex, Ice and Behringer. ALL will push 1 ohm loads.

I don't like the sound of ICE or Behringer for anything other than BASS.
Both the 2K ice and the 12K Behringers, are PURE workhorses. I use them for what they are intended for. I use 3 12K double amp modules when we want a little THUMP for a block or two... Still cooling down from New Years. LOL

Hypex on the other hand.. Night and day to me.. I use Nords with revision D buffers..and NC500 modules. I opted for 2590 sparko pros for the opamps. I've used a LOT of different opamps through the years.. THAT one is a real keeper. My speakers are wired at 3.1 ohm. Small planars.

They did dip to under 2 ohms, before I split the circuit. 1.7ohms in the bass region..

I went to pure class D on the bass and Valves from 300hz and up.. I've NEVER looked back.. 5 years now..

I did some mods to the Behringers. I put HQ toggles on the PS fan and disconnect the other two and put them on a thermal ONLY switch. LOL They came on New years for the first time.. 8 12" UM, 4 15" UM and 2 18" UM. Ultimax Daytons 2496 Active XOs

About 100 CF of cabinets.. BOOM BOOM...VERY well behaved...

100+ db for over an hour.. We didn't need fire works.. KIDS..

Summer it's all class d for 3-4 months, come fall winter and spring, Class ds and Valves...Just a match made in heaven.. I'm pretty picky..

I don't care WHO makes it, I'll figure out if its worth a hoot. right app goes a long ways...

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Most that I see are not rated at 2 ohms.
Because there’s a reason for that they don’t fair well or shut down. Be careful with your choice

Look for independent bench tests, like this Stereophile one.

Your PSB Stratus gold need an amp that breeze through very low "EPDR" (combined impedance/-phase angle) in the bass 50hz-100hz, also low impedance in the mid bass.

Look for amps that can come "close" to doubling their 4ohm wattage into 2ohms (eg: 4ohm-200w/2ohm-400w) this means they have no problems with current into 2ohms.
Stereophile: Its impedance curve (fig.1) also suggested that it needs to be partnered by an amplifier capable of a healthy current delivery. Not only does the impedance drop to a low 2.72 ohms at 97Hz, but the -phase angle is quite severe through the midbass region.
Cheers George
Nah the kids around here use, UMs. They literally roll them out of the Garages over to my shop for a block party every now and then.. I just provide the cheap amps, they have TRIED to BLOW UP... Haven’t. Yet.. LOL. Use to use 4 Adcom 565s mono blocks..

I have a pair of 15", and 4 12".. Not an audiophile speaker.. UMs.. my opinion.

New Years and Halloween, LOOK OUT. The power meter is spinning.:-) 3 seperate circuits...

The Behringer 12K are 500.00 EACH brand new... Excellent bass amps when used with a 300.00 2496 active... Better than any plate amp out there...3400 watts at 4 ohms.. full blown DSP...onboard PEQ, delay, 6-48db slope, threshold limiting. FUN and ear plugs come to mind, Mine NEVER came out...New years...

A NC1200 is RATED 1200 W @2 ohms.
You looking for stereo, dual mono or monoblocks?
Rogue Audio - your choice of an integrated amp to fit your budget.
If you are OK with an analog unit.
No DAC. Just good old days analog.
My Rogue Sphinx is handling my B&W, 85 dB Sens. bookshelves as they have never been before. Performance at 4 ohms is not a problem at all.Personally, I think the Sphinx will drive most anything.
Doubt the PSB's temporary dip to 3 ohms would be an issue.
Most of George's post is wrong. EPDR has no meaning really for ClassD.  As well, doubling power with half impedance has little meaning.  All that matters is distortion with low impedance loads.  Most amps that double in power start at comparatively low power at 8 ohms but are still "large" amplifiers. They have relatively low rail voltages. ClassD don't have the same design restrictions as linear amps. An amp that is 400 watts at 8/4/2 ohms has as much capability as an amp that is 100/200/400 watts at 8/4/2 ohms.  What matters is what is the limiting factor.

zappas OP

Some here have no idea, believe Stereophile’s tester JA and his measurements that I posted, he has more knowledge in his little toe, than most of the self proclaimed know all’s here.

Cheers George
I run a class D amp which doubles output from 8 to 4 ohms and is stable at 2 ohms. Also sounds fabulous ( Aavik U-300}. There are other good sounding class D which are stable at 2 ohms.
You can source second hand Aavik U-300s as it has been replaced by a new model. . It has a great DAC and adjustable phono stage. Would expect heavy heavy discounting too as list on Aaviks are frankly ridiculous
EPDR, what ever...

Some time back I asked for the opportunity (I also paid for it!) to test an amp that uses less idle power than my Pass X350.5.
~450 watt in my case, standby = 5 watt though!

So here came a pair of Mola Mola monos, claimed by someone experts - being the 'Rolls Roys' of class D amps. 

Well, so why not? 

Long story short, whether it was an EPDR issue or what else ever, they just didn't 'cut it'. 

Clean as a fiddle they'd sounded, they just could not match the authority of my class A / A/B Pass.
This into a 89dB, 4ohm, quoted Burmester 961, ~35 kg/speaker. 
8“ bass drivers, but by no means a current guzzling monster speakers. 

Anyone think I'd try some more Class D 'Rolls Roys'... not very likely as I feel at present. 

Just sharing for what it's worth... 😏 
Michélle 🇿🇦 
Stereophile tester JA does not say what George thinks he says and JA is not an amplifier designer. Neither is George hence why he keeps making wrong statements about Class D.  Read some other threads. George can never justify his statements and can never communicate why they are true.

You have the floor George. Tell us exactly the effect of EPDR on Class D. Go for it.
The only class D is in my subwoofer in my surround sound system. I do hear the Rogue Sphinx is class D and has some great reviews, however it Is a hybrid with Tubed preamp and so it most likely helps it sound better. Also, the Marantz ruby is a class D integrated. 

It does seem the Mola Molas were overhyped, or the reviewers connected them to more efficient speakers, proper impedance matched preamps... but in the real world, they are likely cabled with impedance mismatched preamps, or hard to drive speakers, or...

I have used quite a few different Mfgs class D amps over a decade, none came close to the EVS1200 of based on dual mono IcePower AS1200 modules that he then sprinkles decades of moding know how pixie dust. Needless to say, they are powerful, especially with my 96dB Emerald Physics Open Baffle 3.4s + 2 SVS powered subs.

Unfortunately (for the rest) he is no longer making the EVS1200. PS Audio has the M1200s with tube buffer, but none of EVS’s magic and a hefty $6000 price tag, though it's a pittance compared to the Molas. Im not suggesting the M1200s are superior, but for rockers, probably. Last night I listened to the MoFi SACD of Dire Straits Love Over Gold. The SVS 12" subs were the weak link

It's not an integrated but the March Audio P502 stereo amp is rated to 2 ohms. Sounds very good with Revel speakers. If you're looking for silly tweaks that either do nothing or degrade the amp look elsewhere this guy doesn't buy into the voodoo just gives a great performing amp for a decent price.
I have Classe Sigma Amps - they sounded exceptional, but they could not drive the bass on my Wilsons.  I had other amps go into protection at concert levels (Bryston / PS Audio).  I moved the class D's to surround duty and put Rowland Monoblocks in to drive the Wilson load which can dip to 1 ohm.  Pure bliss.
Well, not that I’m aware of what you suggest, as his review speaker were SIBELIUS of 87 dB.
Those Mola Mola monos are supposed to ’do’ some 400 odd watt/channel (into 4 ohm...) - somewhat more than my X350.5 Pass.
So - no go with my power saving notions.
This issue is/was some often mentioned with class D amps, and can strip music of its musicality. 
Was happy to go back to my present set up.
Michélle 🇿🇦
My 4 ohm Apogee Duettas were driven very nicely by a pair of Bel Canto Ref 1000 monoblocks. I'm sure they would work fot you Zappas.
What's wrong with getting a competent Purifi-based class D power amp from Apollon, March, Nord, etc., and then sticking a nice tubey tube preamp in front of it?
I hooked my $80 Fosi integrated amp (with Bluetooth) to a pair of kef ls50s and have been frankly flabbergasted how good it sounds.  I have heard some highly regarded “audiophile” amps totally strike out with those.  
Just saying.  Can’t go wrong for the price that is for sure.   Returnable off Amazon and nothing to lose to try for peanuts by high end audio standards. 
D amp to reduce clutter. Most that I see are not rated at 2 ohms.
As said in my first post, they don’t give it as they either turn off going into protection mode, or they are current starved into 2ohms, or the worst oscillate.
Your speakers present a very hard load especially the combined impedance together with - phase angle (EPDR)
And for @justmetoo here’s a link to "try" and understand how speakers torture amps, especially EPDR. (page2)

Cheers George
Hi Zappas,

I've used IcePower based Class D with Focal Profiles which drop to a little under 3 Ohms.  They performed just as well as my Parasound A23s in the bass. Maybe better.


Yes, please read about EPDR, then you can tell George he does not understand it just like every other person who understands amplifiers has told him.

Equivalent Peak Dissipation Resistance - i.e. EQUIVALENT resistance to equal peak thermal dissipation. Not peak current supply. Not minimum impedance. The EQUIVALENT (not actual) resistance that would equal the peak THERMAL dissipation.

This only has meaning for traditional amplifiers that operate in the linear region, i.e. Class A, AB. It is where the (current output * (rail voltage - output voltage)) is at a maximum.  With a linear amp, let's say the current output is 10A, and the voltage difference = 40V at some point in time. That would be 400 watts dissipated across the output devices. That is the thermal dissipation in a linear amplifier.

In a Class-D amplifier, the average (as they are switching) voltage in the output devices, while they are conducting, will be a small fraction of a volt. Let's say it is 0.1V at 10A.  The dissipation in the output devices is now 1W.  Notice that the rail voltage does not enter the equation?  Now practically there is a small contribution from the rail voltage, but there is not a direct correlation like in a Class A/ AB amplifier because obviously they don't work the same way.

Now one thing a Class-D amplifer may due is hard limit current which they will "measure" or at least check for a peak on every single switching cycle.  This provides short circuit protection and protection that the output inductors do not enter saturation. As that current will be fixed, this is why in a Class-D amplifier the output power probably does not keep doubling with halving of the output impedance. The power will probably increase a lot between 8 and 4 ohms, because in this case the major limitation in output power is due to the power supply rail voltage. It will likely not double into 2 ohms because you will run into the current limit before the voltage limit.

What does this mean?  As long as the amp does not have stability issues at 2ohms, which most newer ones will not, and you don't drive the amplifier into clipping, then the class-D amp will be just fine into low impedance loads no matter what some people who make claims, but don't understand the underlying technology make.

As @audio2design points out, EPDR does not apply to class D amplifiers. However, the efficiency at which a class D amplifier operates is reduced as load impedance goes down since the output transistors will be conducting more current during their switching and on-phases for the same power into the load. 

Class D amps are theoretically 100% efficient if the output transistors had zero on-resistance, infinite off resistance, and switched infinitely fast. But, of course, this isn't the case. Typical class D amps are 90% or more efficient into 8 ohms (at max output power), but efficiency drops by approximately 40% into 4 ohms, and 40% again at 2 ohms.

Under normal circumstances, this isn't a huge problem because an audio amplifier in a normal home music environment is typically operating at a small fraction of it's peak power. But under heavy demand (or test conditions), the lower operating efficiency into lower impedance loads will eventually cause the amplifier to get too hot and shut down. The good news is that modern class D amps all have circuitry to protect the amplifier under these conditions. 

As @audio2design also points out, class D amps will also incorporate maximum current limiters which will also limit maximum power into low impedance loads. Since this circuitry operates almost instantaneously (checking current on every switching cycle), this is more likely to limit maximum power into low impedance loads since music peaks can often be many times higher than average power requirements. But these current limits are generally quite high. For example, the Purifi module, which is rated at just over 200w into 8ohms, has a 25A current limiter, but this is what ultimately limits the peak power into loads below about 2 ohms.
But, of course, this isn’t the case. Typical class D amps are 90% or more efficient into 8 ohms (at max output power), but efficiency drops by approximately 40% into 4 ohms, and 40% again at 2 ohms.

I am not sure you wrote this correctly. I think you mean losses go up 40%, or stated as efficiency, the reduction in efficiency goes up by 40%, i.e. 10% reduction becomes 14%?

Conduction losses are I^2 * R. At the same wattage, half the resistance, current goes up sqrt(2) = 41.4%, so losses must go up 100% due to conduction losses, but realistically total losses are going to be a quiescent component (in this case about 11 watts), plus a linear component and a squared component to come up with a very good model.

For reference as example, the NCORE 500 OEM module is about 95.2% efficient at 400W/8 ohms, about 92.6% efficiency at 400W/4 ohms, but drops down to about 87.5% at 400W/2 ohms. Losses are 20, 32, and 67 watts at 8/4/2 ohms, 400W output.

For the NC500, the current limit is 26A. That puts maximum possible RMS power at 2ohms = (26/sqrt(2))^2 * 2 = (26*26/2)*2 = 676W, not too far from the rated power of 550W as a ratio, and even closer if you add losses above to the 550W.
@audio2design Yes, that is what I meant. Sorry if my language wasn't clear. 
zappas OP

Just use your "common sense" when asking why? when ever Class-D is bench tested, why it is they never give the 2ohm wattage, or advertised and compared to the 8 or 4ohm wattage
And sometimes even stated that they try 2ohms but the amp switches off, before they could turn up the test signal level, to get some current flowing into the 2ohm load.

We heard an A/B of what the sound was like into Wilson Alexia with 0.9ohm EPDR bass loading, the 150w-8ohm Gryphon Antillion’s bass sounded absolutely magnificent, but with my 2 x more higher wattage 300w-8ohm Belcanto Ref 600Mono clones (NC500) with linear power supplies, were not anywhere near in the same league. And that can only be due to current delivery into the low impedance.

Cheers George
zappas OP

Ask yourself why all the Ncore data sheets have the 2 ohm power ratings in the data sheet right near the top. Some people never move forward and have to bring up a one time comparison of a $40,000 dollar amplifier against $10,000 amplifier that no one can verify.  Well not really $10K. They were clones of the Bel Canto, so unknown pedigree, and unknown performance. Now we are talking $40,000 something that has likely never seen a measurement that confirmed performance.

One day George will discover that EPDR is not the same as current delivery. That day is not today.
I think I may understand Equivalent Peak Dissipation Resistance which I had never heard until recently in one of the class d amplifier threads. Audio2design and Jaytor have nicely explained that.  It is very informative and interesting. Thanks
Like I said  zappas OP don't trust anything the manufacturers or shillers say, independent test figures are much closer to the truth, they tell the real story.

Cheers George 
One D amp that won't "reduce clutter", as OP says, but can easily handle a 1-ohm Apogee Scintilla is the H2O Audio S250 Signature.
Uses older Ice modules, 250W/8-ohm, doubling down, a really healthy power supply, dual mono in one chassis with two toroids, 70-lbs.'s also rare on the used market so don't hold your breath. 
I'm sure there's some special circuitry somewhere but it's pretty basic otherwise. It's all in the design and execution. Point is, class D can properly drive 1-ohm, not just be stable there, if so designed. I don't know why more manufacturers don't make the effort.

Hi, has this conversation degenerated to fake data, or specifications that have no bearing on actual listening experience?

If so, I'm in!

No, not on my end. An amp that can easily handle a Scintilla, not just handle but do it beautifully, is a breeze with any other speaker. Several users on the old Apogee forum agree and they are fanatical about their Apogees! I was less fanatical for mine especially when they needed restoration and I had to let them go - along with the amp.

Price is not bad at around $3500, if I recall. Problem is Henry Ho is tough to get a hold off, as it seems this is a sideline for him. I can pass along his email to anyone interested.
As said in my first post, they don’t give it as they either turn off going into protection mode, or they are current starved into 2ohms, or the worst oscillate.
Your speakers present a very hard load especially the combined impedance together with - phase angle (EPDR)
And for @justmetoo here’s a link to "try" and understand how speakers torture amps, especially EPDR. (page2)
This is fake news.

If you have a class D amp, and a speaker that dips to 3 ohms or even 2 ohms, don't worry- just hook it up. EPDR won't be an issue- the output impedance of any modern class D amp is only a few milliohms; what's happening at 2 or 3 ohms is thousands of times higher impedance and the amp won't care.

It may not double power into 2 ohms though, but that's not important except at clipping. What's important with most speakers is the amp behave as a voltage source, which it will do just fine.

With regards to that bit about 'oscillate': most modern class D amps already oscillate as part of their modus operandi. You can't somehow make them oscillate *more*; the idea is rubbish.

This is fake news.
Just like *****, into protection mode for his own interests, the new Class-D must be coming soon.

It may not double power into 2 ohms though, but that’s not important
That more fake than anything!
Most Class-D’s, independent tests, can’t better the 4ohm wattage with the 2ohm load, if they don’t turn off first, let alone double it. That’s how "strangled" they are for current.

With regards to that bit about ’oscillate’: most modern class D amps already oscillate as part of their modus operandi. You can’t somehow make them oscillate *more*; the idea is rubbish.
No you are. You know exactly what was meant by that, don't play the arrogant card, just another ***** side step to protect an upcoming Class-D from you

Entertainment in georgehifi relentlessly defending inferior technology.

A typical response from a snake oil "fuser"
Thanks for the reminder! I need to see about potential fuse change in this new Class D amp! Total fun!  :) 
I fail to understand one thing - people spend "their own money" to buy the class D amp they like. So what bothers George? Don't know what he is trying to achieve jumping on all the Class D threads and making a mess. The only reason I can think of is - his light attenuator must not be compatible with Class D and hence he does not want people to adapt them. George, can your attenuator drive Class D amps? I might look into Purifi or GAN based amp if I upgrade in the future. So what is your agenda?