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

[TheOctopus]

Serge you don't even pretend to understand or care , hahaha ..


Im now beginning to understand how such a stalwart company is laughed upon in the modern hi-end era and considered junk by many..

:disbelief:

Regards

Over the decades of reading Stereophile, I've seen plenty of comments of cooking and blazing hot amps that were too hot to touch, etc.. etc. while being bench tested/tortured. What's there to not understand? Music is not a continuous sinewave at 1/3 rated power....

Music flows, it has ebbs, quiet passages, music had my MC501s, D'Agostino Momentums, ARC, amps that actually offered a "visual" reference to what is going on with the power output, they were all cruising at fractional power output. Mostly somewhere in the 3-40w range with peaks of perhaps 100w when really rocking out on occasion. I don't listen to music at simulated rock concert levels... Never have.

So McIntosh has both thermal and clipping protection. No fried tweeters, no melted transistors that were outside the SOA. It is true that McIntosh operates at class A for the first few watts and sounds great doing it but no amount of heat sinks would keep it within that range if the loud knob is cranked over on the preamp... It leaves class A and will keep on huffing and puffing, delivering, typically way more than the advertised power with the autoformer. What's there not to understand? The thermal circuit is there to protect your investment from your own stupidity.

Don't like McIntosh? Fine, that's your personal bias. I see nothing wrong with the design that has never let me down personally and everyone else I know that owns McIntosh amps.

 

[a.wayne]

 

[TheOctopus]

This is how most folks listen in real world applications... Long way to go to clipping and thermal protection circuits activating LOL...

 

[TheOctopus]

Then there are the MC1.25KWs for the bigger scale/room/speaker applications.

 

[Sujay]

Burmester 909 mk5! Or 911mk3 mono. But 909 mk5 better for that load

 

[ALUCARD19]

Anthem P2 stable down to short circuit 0 ohms

 

[Hear Here]

Re: Power amplifiers that excel with VERY low impedance - and low efficiency - loads

Looking for recommendations for a client.

Please - submissions not from hearsay, but from actual user experience - Thanks!

Jim - I bought a pair of low efficient, low impedence Martin Logan electrostatic 13A speakers a couple of years ago, but after using Avantgarde for 15 years, I had no suitable amplifier. Looking at sources such as Martin Logan Owners forum, I went for the Sanders Magtech amplifier. Sanders build electrostatic speakers and found a dearth of suitable amps, so he designed his own with those particular features. It was a good amp for this type of speaker, but sadly the speakers never sounded good in my difficult room. Both the ML and Sanders were sold and I'm back with Avantgarde. My GamuT D200 also did well with the MLs. Peter

 

[Mr Peabody]

I heard the Sanders amps were built by either ATI or Coda, I can't remember which. I personally wouldn't use Coda for a bass amp but ATI are beasts. I'm sure Sanders were built to their spec though. The Coda use no feedback, they are high current but don't have the definition I like in the low end. I wish I had more time with the ATI in my system, I have never heard an amp with that much low end power at any price. A friend brought his over for a quick listen back when I had Revel F52's.

 

[audio.bill]

I heard the Sanders amps were built by either ATI or Coda, I can't remember which. I personally wouldn't use Coda for a bass amp but ATI are beasts. I'm sure Sanders were built to their spec though. The Coda use no feedback, they are high current but don't have the definition I like in the low end. I wish I had more time with the ATI in my system, I have never heard an amp with that much low end power at any price. A friend brought his over for a quick listen back when I had Revel F52's.

Sanders amps are built by CODA but are OEM to Sanders design, not the same as any Coda model. ATI also builds OEM amps for several other companies.

 

[ALUCARD19]

Like I stated earlier you should try the Anthem P2 power amp 325WPC @8ohms,500WPC @4ohms,675WPC @2ohms, and stable all the way down to 0 ohm impedance.
Just go to the Anthem website and under products go to P2 power amps

 

[ALUCARD19]

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

 

[Puma Cat]

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.

 

[greystoke4]

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,

 

[Jim Smith]

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,

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.

 

[Puma Cat]

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.

 

[atmasphere]

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.

 

[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..

 

[ACHiPo]

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

 

[atmasphere]

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.

 

[a.wayne]

Harshness and Brightness is usually associated with clipping and or too low of compensated for class A bias at desired listening levels, these are known knowns with SS amps and how high is SS distortion vs Toobs distortion in General Ralph ..?

Distortion quantity either matters or it dont you cant have it both ways ...

Boulder 2150 :

Even at 4 ohms it register very little and JA using 40V is a very high irrelevant number as nobody domestically will be using 40V , a more realistic 1 watt at 8&4 ohm would be more relevant but distortion numbers were well into his test equipment noise floor ..

Now if you look at the still very low numbers of distortion at 4 ohm
(Magenta vs blue) its easily compensated by the lower distortion achieved from running multiple drivers Even with the lower ZMin from the Loudspeakers ..