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If they stay in class a up to a point and then get into class b and since music at high enough volume driving speakers with high enough efficiency requires very little power do high power amps ever get out of class a and into class b?
For example how often would Bryston 28Bł Mono amps or 7Bł Mono amps actually operate in class b?
Thanks.
Follow Ups:
Not a brick wall OR a 'cliff'......
With music with a 10db crest factor? You might be in 'A' a low levels and fully transitioned during the loudest parts....Say.....3 watts to 30 watts.....
Too much is never enough
A class A/B power amp assuming it's a high current design with a very stable power supply can potentially operate on the Class "A" bias around 10-15% of its power output before it'll slide into Class "B" bias operation. For example, if a Class A/B power amp has a power output of around 100 watts/c the first 10 watts/c of its power output would be on a Class "A" bias operation. However, there are some exemptions to the rule for example Krell, Mark Levinson, Pass Labs just to name a few power amps designs are known to exceed the 10-15% rule as some can output up to 40% of their power output on Class "A" bias operation.
What this means is if you have very efficient speakers with sensitivity at around 105dB and you happen to drive them with a Krell power amp you'll always going to be listening on a Class "A" bias operation. Unless you decided to unfurl Krell's sails then all bets are off as you're reliably be catching one of the woofers on your lap.
Anyone know what the percentage is for Quad II amps?
If your speakers are highly efficient, your amp(s) likely will probably
always operate in class A mode.
I second Abe's comments about Bryston amps. Further, you don't need the
power of which they are capable with high efficiency speakers.
Whether or not you can observe a thing depends upon the theory you use. It is the theory which decides what can be observed. - Albert Einstein
Over on the Emotiva forum? You read guys with a Pair of the XPA monoblocks and Klipsch speakers.
THAN? to add insult t injury? the pair of amps AND the remainder of the system in ONE shared outlet.
No amount of 'you only need 50 watts' will convince. No amount of 'You need a 20 amp service JUST for the amps' helps, either.....
Too much is never enough
Oh I see what you mean! On a Klipsch group, there's a guy using 400watts on the high pass and 2000watts (?) on the low pass of his bi-amped Klipsch Heritage speakers, because otherwise he would "run out of steam". I told him I used to throw parties at my place with techno DJ with a 10watts amp on LaScala but he didn't seem convinced. ^^
that's how I was sold a 'flame linear' in the 70's
Waste of ink trying to convince those guys.
When I tell 'em.....that the 400 or whatever watts of the BIG EMO amp when run on a 15 amp circuit AS A PAIR is maybe some fraction of the possible bench power? But I've got all those Capacitors!!
the guys at EMO who SELL the stuff are MUTE. I tried without luck to get some buy in on a standard dummy load for speaker testing. Less traction tha a Bald Tired F-150 on an ice hill.....
Too much is never enough
Great observation about the Emos; living in a 75 year old building
even with a 20 amp circuit I have to use a power re-generator which enables me drive the speakers at lower power levels. And using a 20 amp circuit for one amp and 16 amp circuit for another you can hear the difference in the sound of the speaker-had to make room and placement adjustments to balance them out
Please tell me more about that.
Iti s especially noticeable on live recording that have excellent spatial qualities ;BLUE NOTE JAZZ
Also the bass seems slightly extendened and the pulse or pace of the music is quicker on the 20 amp circuity. Oddly and I have switched the speakers to check the highs are more refined on the 15 amp circuit. Hope this is not madness. Also had my hearing checked which might also explain a little of this. Better hearing on the 15 amp speaker side. The amps are mono blocks.
Nope, just wanted to know
thanks
These days> EMO has gone to a SMPS to 'save' efficiency.
So? While the amp continues as an A/B amp....and without the G2 amps had in the form of a 'A-A/B' switch, which was just a bias adjust scheme the NET efficncy of the amp is hardly changed at all.
And add to THAT the fact that a speaker of 5% efficiency is a LOT and you have a plug to speaker limit BELOW the speakers efficiency. For someone like me, with panels? Hopeless!!
The standard EMO user? Looks at the Capactance in the PS. It took me a LONG time to figure this out. It's not capacitance but the VOLTAGE which matters. A tube amp with say 300mfd @500 volts holds a huge amount of energy.......IN JOULES. The true measure. Energy goes up much more quicly with voltage than capacitance.....MUCH....
Score one for TUBES. And I suspect one source of the 'apparent' power of tube amps.....
I lived in a HOUSE in Fullerton CA which had Knob and Tube wiring. ONE outlet in the kitchen and another in the living room. This is a MAJOR PROBLEM and hazardous in the extreme. My dad, who came for a visit, freaked out. And recommended an 'immediate move' to a real apartment.
Too much is never enough
I shouldn't say anything. I know what you mean. You're asking if the output devices (tubes or transistors) in a high powered Class A/B amp ever get to the point where those devices reach cutoff if the amp is never ask to provide much power. I'm not going to answer your question. Instead I am going to point out....... Class A/B amps never run in Class A and they never run in Class B. They run in Class A/B. It is it's own thing.
With a Class A amp the output devices are biased at the midpoint between saturation and cutoff. With Class B the devices are biased to just reach cutoff with no signal present. A Class A/B amplifier meets neither of these requirements. It is it's own thing.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
!
The Mind has No Firewall~ U.S. Army War College.
but there has to be some idle current flowing otherwise there wouldn't be .7 volts at the cathode at idle.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Finally someone got this right.
The amps don't magically shift between operating modes.
Dan Santoni
Pass: " Class B has no bias current, Class AB has a moderate bias current, and Class A has a high bias current. Class AB push-pull amplifiers are hybrids between Class B and Class A. Class AB run Class A at low power levels, and become Class B amplifiers at output currents determined by the bias . " {emphasis added}Pass: " Push-pull amplifiers generally operate in Class A mode up to a point where the output current is twice the value of the bias current. In the Class A region, both halves of the circuit share the signal simultaneously. Beyond that the signal is handled solely by the push (+) half of the amplifier or the pull (-) half. "
What might be fair to say is that A/B amps don't cease being class A when more power is demanded: only the peaks , '+' or '-' of the signal operate in class B mode. There is nothing magical about the shifting.
Dmitri Shostakovich
Edits: 02/03/22 02/03/22
"What might be fair to say is that A/B amps don't cease being class A when more power is demanded: only the peaks, '+' or '-' of the signal operate in class B mode. There is nothing magical about the shifting."
Then the definitions (and distinctions between) of Class A and Class B and Class A/B have lost their meanings.
I think Pass said what he said, the way he said it, just to get a point across to the non technical reader.
I think he was really saying something like this,
The amp is not Class A at low power but it has something in common with a Class A amplifier, the output devices don't reach cutoff (***like in a Class A amplifier***) when at low power. The amp is not Class B but it has something in common with a Class B amplifier when at higher power levels, the output devices do reach cutoff (***like in a Class B amplifier***).
But just because those two thing are "like" Class A and Class B that doesn't make the amplifier a Class A or a Class B amplifier. It is neither, it is a Class A/B amplifier. Class A/B amplifier are there own thing. Nelson was just trying to get non technical people to understand how they do what they do. He was not trying to re-define the meaning of Class A and Class B or Class A/B. All three are already well defined.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It would appear that you have a new definition of amp classes because Nelson Pass is spot on when it comes to the original definition of Class A, AB and B.
I think I get what you are saying.
In order for class A and B to integrate into A/B, the basis for each is there, but they never truly work as pure now that they are called upon to work together vs how they would work on their own.
It would be like asking an 8 cylinder motor in 4 cylinder variable management mode for better gas mileage, response and RPM's, to give you the identical benefit of a pure 4 cylinder motor. Close but not quite the same.
Motor analogy aside, I wonder if the class B portion of A/B is also somewhat less pure and perhaps audibly different vs a pure class B amp at high volumes.
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
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Dmitri Shostakovich
Devialet amps have what is called "Analog Digital Hybrid ". The voltage gain is Class A, while the current gain is Class D. They have a patent on this.
It's the best sounding set of amps I've heard to date.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
!
The Mind has No Firewall~ U.S. Army War College.
Check out this link
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
They didn't exactly love it; see link below.
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Dmitri Shostakovich
Check out the Stereophile review of the D-Premier. One will get a MUCH different perspective. BTW, JA also measured the unit. Virtually every review of Devialet amps outside of ASR provides the strongest positive recommendations, especially if configured in mono.There are other measurements that reviews could conduct that would provide better insight as to how gear sounds in real world usage. Reviewers don't provide those. I take ASR reviews with large grains of salt.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 02/04/22 02/04/22
If you did, you would see that Amir mentioned John Atkinson's Stereophile review, (see link).As Amir points out, Atkinson's measurements do also reflect the high frequency power limitation. Atkinson is a sort of "glass half full" guy where as Amir is more of a "glass half empty" guy.
Personally I feel that JA too often glosses his reviews to deemphasize components' shortcomings.
Personally I don't think measurements are everything, OTOH I believe there is usually some correlation between measurements and SQ.
Dmitri Shostakovich
Edits: 02/04/22
Read any other review of Devialet, especially the D-Premier. 250, 250 pro, and they universally rate them among the very best available at any price. Some of the sound quality is due to the slick method the DAC is integrated into the power amp section. The fact that the voltage operates in Class A means practically that there is no crossover notches in the audio signal. No one else has come up with this approach. Since pretty much every reviewer greatly praises the Devialet, one naysayer who uses a subset of measurements that don't fully translate to the design objectives does not carry much weight with me, nor dare I say the many other reviewers and owners.
Tweeters aren't meant to take or need a lot of power.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
I'd LOVE to hear you and Pass talk this over. He seems intent on 'high bias' designs, weighing about 1lb per watt and having a very high output in what HE calls 'A' than sliding into A/B
Read up on his panel meter which Does Not move....until the amp is beginning to transition to A/B. It stays mid-range, mostly......
Too much is never enough
My conclusion is based on his article I link below.
It seems to me Pass is saying that class A operation and class B operation are discrete states though the A/B amp will pass seamlessly and often frequently between them.
Sliding bias is an arrangement where the bias is adjusted depending on the power level in the interest of increasing efficiency by modulating input power as the demanded output power rises and falls.
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Dmitri Shostakovich
"Class B has no bias current, Class AB has a moderate bias current, and Class A has a high bias current. Class AB push-pull amplifiers are hybrids between Class B and Class A. Class AB run Class A at low power levels, and become Class B amplifiers at output currents determined by the bias."All I can say is, Nelson is wrong. (What I really think is that Nelson is just saying it that way to get his point across to none technical people)
A/B amplifiers do not "run Class A" at low power levels and then "become Class B amplifiers".
He said it himself, in a Class A amplifier the output devices have a high bias current. Class A/B amplifiers do not run their output devices at high bias.
What is true about Class A/B amplifiers is at low power the output devices do not reach cutoff, like a Class A amplifier, but that does not mean they are Class A amplifiers.
A horse has four legs, a dog also has four legs but that does not make a dog a horse.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/03/22
That's because the designer isn't intending to produce a whole lot of power in class A mode -- class A mode simply means that the amp is producing only the power output possible below the bias setting. A class A/B amp is a class A amp while operating under these conditions; when the power spikes above that limit, it operates in class B mode. This transition happens seamlessly and continually.Or as Pass says, " Push-pull amplifiers generally operate in Class A mode up to a point where the output current is twice the value of the bias current. In the Class A region, both halves of the circuit share the signal simultaneously. Beyond that the signal is handled solely by the push (+) half of the amplifier or the pull (-) half. "
So, e.g. the Pass X150.5 amp that I owned for several years puts out 16 wpc into 8 ohms in class A mode according to Pass.
Dmitri Shostakovich
Edits: 02/03/22 02/03/22 02/03/22 02/03/22
"A class A/B amp is a class A amp while operating under these conditions; when the power spikes above that limit, it operates in class B mode. This transition happens seamlessly and continually."
I guess it's a matter of semantics but in a proper Class A amplifier the output devices are biased halfway between saturation and cutoff (in the most linear region of the transfer curve). In a proper Class B amplifier the output devices are biased so they just reach cutoff with no signal present.
In a Class A/B amplifier neither of the two conditions above are meet.
Here's why is matters. Output devices are not perfectly linear. The most linear part is the center of the transfer curve. When the output device is biased right in the middle of this curve (in the most linear part of the curve) then the first watt (or so) is the cleanest. In a Class A/B amp the output devices are biased well below the most linear part of the transfer curve. The devices do not operate exclusively in the most linear part for the first watt or two like they do in a true Class A amplifier. So even though the output device don't reach cutoff (while the A/B amplifier is in the so called "Class A" mode) it's still not the same operating point as a true Class A amplifier would be.
I may be blind but I can't understand why people are not seeing my point.
Class A is a particular type of operation, Class B is a particular type of operation and Class A/B is yet a different type of operation, not a mix of A then B.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Thank you Tre' for taking the time and effort to explain this to us less technically knowledgeable inmates.
Your posting is the first time the discussion made any sense to me!
Don't wrestle with pigs. You both get dirty and the pig likes it.
Mark Twain
You're not blind. The reason folks are misunderstanding is because the definition of Class-A (in the audio world) has really become squishy in the last few decades. Even Nelson Pass is playing fast/loose with the wording and descriptions of this.
These sort of things become entrenched into the audiophile lingo and it becomes impossible to make any headway reversing it.
Your description is absolutely correct. A device biased halfway between cutoff and saturation is Class-A. Anything else is....something else.
Dave.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Strangely enough I was going to add a blurb about refraining from the sliding bias thing in answering my question but I convinced myself that it was not required.
I also used Bryston as it was easy to get technical info on their power ratings.
What was I thinking there!
He might be doing something with sliding bias. That's different than a traditional Class A/B amplifier.
An amplifier with sliding bias can be a Class A amplifier that changes to a Class A/B amplifier when the extra power is needed.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
My PSAudio GCC 'integrated' had a 'Gain Cell' input which made it a CLAIMED 'variable gain' amp.
But I never figured that one out....
Too much is never enough
PS Audio GainCell:
The gain of the preaamp stage itself is electronically controlled as needed to adjust volume level. This is different than most preamps where the gain is fixed and the signal feeding it is attenuated. The traditional volume control (attenuator) does not exist in the GainCell and is not in the audio signal path.
Paul claims to have invented the GainCell. He may have invented the name but the technology has been used by others. I don't recall the details but the concept has been around before Paul's "GainCell".
He uses the little GainCell module in various PS Audio products.
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Bruce Rozenblit of Transcendent Sound has produced a variable gain tube preamp kit - with an MM phono stage! Would be my first choice if I needed a new preamp...
Don't wrestle with pigs. You both get dirty and the pig likes it.
Mark Twain
Whatever class of operation my Bryston 7BSST2 mono amps operated in, they sounded thin and cold to me. Bryston likes to boast about their power and distortion specs so I suspect they are running mostly Class AB.
Bryston seems to be about specs and warranty. I was not a fan of my hefty 7BSST2 monoblocks and after trying to make them sound "musical" with various tube preamps - and tube rolling the tube preamps, I eventually gave up after a few months. That's not to say they are bad amps, just not what I like to hear in amplification. Too lean clean clinical analytical cold and dry for my taste. Nice tight bass though.
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I never owned Bryston amps, but heard them several times at various audio shows. Typically they were matched with one model Maggie or another. They always struck me as lifeless and musically unenvolving, regardless of the speaker.
"The only cats worth anything are the cats who take chances. Sometimes I play things I never heard myself." Thelonious Monk
I had some of Bryston's first products including thr 4b when introduced and can agree to that the sound was more suited to "pro" application way back then. I can't comment on their recent products.
I've had many amplifiers over the years of all different typologies: tube, SS or combinations of both. running my Klipschorns that I've been using steadily for between 40 -50 years now.
In my recent total equipment upgrade I'm running what I consider by far the best sounding and performing amplifier that I've ever heard with these speakers and it's a very powerful current capable class A/B. Nothing else has come close to the attributes of this combination.
Goes to show that maybe it rests with the capabilities of the amplification design and execution. I've never been more satisfied.
IMHO too many people get hung up on amplifier class of operation. There are excellent and not so great sounding amps across nearly all classes. Some will insist that Class A is the best sounding so they pair their under powered HOT running Class A amp with a speaker that requires more power and the sound is compressed or congested. They would have been better off with a good Class AB amp with more power. I've been there myself! I'm at the other end of the spectrum running Class D these days.
As for Bryston, I auditioned a 4B series amp back in the 1990's then bought Classe instead ;-) I much preferred the Classe sound. Bryston back in the 90's sounded harsh and grainy to me to go along with their thin and cold sound. The more recent 7BSST2 pair that I had was better. They weren't harsh or grainy but still on the lean thin and cold side for me. I prefer more "meat on the bones" and a warmer more robust and "musical" sounds.
My Pass Labs Aleph 3 from years ago:
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This true Class A 30-wpc amp runs HOT and draws nearly 250-Watts from the AC mains. Coupled to my reasonably easy to drive Tannoy Definition D500 towers the setup sounded dynamically compressed and congested. Even the modestly easy Tannoys require more power. The photo was staged but you get the point ;-)
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Great amplification design is a result of both technological and artistic capability. Art of sound is the objective. I do believe the amplification I'm using now, an Alluxity Power One Stereo Amplifier out of the Danish Vitus family displays these attributes admirably. Never expected so much improvement in so many areas. Pays to check what's out there.
Not my taste in sound also.
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