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Thread: "Pure Class A"

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    frenchmon frenchmon's Avatar
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    "Pure Class A"

    So what is "pure class A". Just about every "pure class A" amp is low in wattage and very expensive. How does a "pure class A" amp at 35 watts per channel compare to a non-pure class a amp at 200 watts per channel?

    frenchmon
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  2. #2
    Ajani
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    Quote Originally Posted by frenchmon
    So what is "pure class A". Just about every "pure class A" amp is low in wattage and very expensive. How does a "pure class A" amp at 35 watts per channel compare to a non-pure class a amp at 200 watts per channel?

    frenchmon
    The benefits are lower distortion (none of that switching distortion caused by typical Class AB amps) and allegedly sweeter sound (I've never tried one so I can't comment... Whereas a 200 watt class AB amp would give you greater dynamic range...

    Trying to decide between a Musical Fidelity M6i and AMS35i???? (The price difference would be my deciding factor )

  3. #3
    frenchmon frenchmon's Avatar
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    Quote Originally Posted by Ajani
    The benefits are lower distortion (none of that switching distortion caused by typical Class AB amps) and allegedly sweeter sound (I've never tried one so I can't comment... Whereas a 200 watt class AB amp would give you greater dynamic range...

    Trying to decide between a Musical Fidelity M6i and AMS35i???? (The price difference would be my deciding factor )
    Well the price over there is $6000 for the AMS35i. Don't know what it would be over here. Maybe to much for my pocket. The M6i is reachable.

    Kinda scary Ajani...you reading my mind like that. Dont put no voodoo on me.

    frenchmon
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  4. #4
    Ajani
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    Quote Originally Posted by frenchmon
    Well the price over there is $6000 for the AMS35i. Don't know what it would be over here. Maybe to much for my pocket. The M6i is reachable.

    Kinda scary Ajani...you reading my mind like that. Dont put no voodoo on me.

    frenchmon
    If I remember correctly the AMS35i is supposed to go for 9,000 USD (so triple the M6i)... though I'm not sure when it will reach the US, as last I know MF lost its American distributor (though it still has a few products available on AudioAdvisor)...

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    The easiest way to understand the difference between class A and AB is to picture a sine wave.

    Half of the sine wave is above the mid-point and half below.

    In a class B amp, the top half of the signal is amplified by one output device and the bottom half by the other. The two halves are joined together at the output to create the full sine wave.

    Unfortunately, the point where the top and bottom halves are re-mated is somewhat imperfect so you get a notch or crossover distortion.

    In a class AB amp the output devices are partially biased in the "on" state which helps reduce this distortion but does not eliminate it.

    In a class A amp, the whole sine wave passes through one device so nothing has to be matched up at the output. This completely eliminates any notch distortion. (Note it doesn't reduce other types of distortion.)

    The penalty is that the bias level has to be set very high which means the device is always "on" even when there is no signal. At best a class A amp is no more than 50% efficient (meaning 1 watt is wasted in heat for every watt delivered to a speaker.) Many are less efficient than this.

    That is why class A amps tend to be lower power than AB. The heat generated and wasted energy are issues that need to be considered in the design. However, class A advocates are quite enthralled with the purity of the signal, particularly at lower volume levels where the notch distortion would be a higher percentage of the signal.

    Higher output vs low-level signal purity is the trade off. Only you can make the call as to which you prefer.

  6. #6
    Silence of the spam Site Moderator Geoffcin's Avatar
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    Quote Originally Posted by frenchmon
    So what is "pure class A". Just about every "pure class A" amp is low in wattage and very expensive. How does a "pure class A" amp at 35 watts per channel compare to a non-pure class a amp at 200 watts per channel?

    frenchmon
    I think what your trying to ask is if class "A" power amp is somehow more powerful per watt than an A/B amp. A pure "Class A" is no more powerful per watt than a more common A/B amp. However it uses a lot more power as the circuit is always on.

    Some of the more expensive high power amps from the likes of Pass Labs and such give you the best of both worlds with the first few dozen watts or so in pure class "A" before switching over to class A/B.

    There's a good primer on "Class A" amps on the web;

    http://www.electronics-tutorials.ws/...ier/amp_5.html

    Don't let the schematics bother you, the text is an easy read.
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  7. #7
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by frenchmon
    So what is "pure class A". Just about every "pure class A" amp is low in wattage and very expensive. How does a "pure class A" amp at 35 watts per channel compare to a non-pure class a amp at 200 watts per channel?
    It is a qualitative difference. Perhaps a discussion by Nelson Pass would help. He has designed countless leading edge amplifiers for over thirty years and is the father of the sliding bias class A concept. Take a look here.

    Virtually all preamps and other line level stages are class A for their better distortion characteristics - not lower levels per se, but the distribution with fewer high order products. Most amps today are of the AB design. Which means they act in class A for a portion of the range, then switch to class B at higher output levels. The point at which they transition is very different from amp to amp. Those with richer bias tend to be heavier and run hotter. I find that those with richer bias offer better low level resolution.

    rw

  8. #8
    frenchmon frenchmon's Avatar
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    Quote Originally Posted by Ajani
    If I remember correctly the AMS35i is supposed to go for 9,000 USD (so triple the M6i)... though I'm not sure when it will reach the US, as last I know MF lost its American distributor (though it still has a few products available on AudioAdvisor)...

    Ouch...that hurt.

    frenchmon
    Music...let it into your soul and be moved....with Canton...Pure Music


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  9. #9
    Ajani
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    Quote Originally Posted by frenchmon
    Ouch...that hurt.

    frenchmon
    If you really want MF Class A... you could pick up a discontinued A1 (also 35 watts) for $1K... it's a cheap way to test one out... I've been tempted to get one, but I live in Jamaica, so the last thing I need is an amp to perform double duty as a room heater...

  10. #10
    Forum Regular blackraven's Avatar
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    My Parasound Halo A21 is an example of an AB amp that runs in Class A for the first 10wpc.
    Its heat sinks are massive.
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  11. #11
    frenchmon frenchmon's Avatar
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    Thanks gents for the knowledge...and yes Geoffcin I was trying to ask about the power difference though I still did not understand how it worked but know I do. But as Ajani said, the pure A is just to expensive for my wallet. I'd get put out if I bought that thing home at triple the price of the M6i.


    frenchmon
    Music...let it into your soul and be moved....with Canton...Pure Music


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  12. #12
    Forum Regular blackraven's Avatar
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    If you want a high power Class A amp you need to buy this one- But get the fork lift ready!

    http://www.lelong.com.my/Auc/List/20...td10975475.htm
    Pass Labs X250 amp, BAT Vk-51se Preamp,
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  13. #13
    frenchmon frenchmon's Avatar
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    Quote Originally Posted by blackraven
    My Parasound Halo A21 is an example of an AB amp that runs in Class A for the first 10wpc.
    Its heat sinks are massive.
    I've got a friend that has the Halo A21 and that thing is huge. Sounds good as well

    Ajani I love Musical Fidelity's sound, and I really love my Xray, even better now that I got use to the way it looks. But the looks of those A1 products from MF just dont do anything for me. I know, I know....I should not be worried with looks, but man those things just don't do anything for me.
    Music...let it into your soul and be moved....with Canton...Pure Music


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  14. #14
    frenchmon frenchmon's Avatar
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    I'm concerned with good sound rather than another heater for my house. So does the pure class A mean better audible sound quality? And what makes class A so expensive?

    frenchmon
    Music...let it into your soul and be moved....with Canton...Pure Music


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  15. #15
    Ajani
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    Quote Originally Posted by frenchmon
    I've got a friend that has the Halo A21 and that thing is huge. Sounds good as well

    Ajani I love Musical Fidelity's sound, and I really love my Xray, even better now that I got use to the way it looks. But the looks of those A1 products from MF just dont do anything for me. I know, I know....I should not be worried with looks, but man those things just don't do anything for me.
    LOL... I can't even lie, if the heat wasn't an issue then the ugliness of the A1 would ruin it for me...

    You could look into getting a matching X-T100 Amp (Wally at Underwood HiFi has one available for sale as part of a set with the XRay and power supply.. I suspect he'd be willing to sell you the amp by itself and sell the CD and power supply to someone else)...

    I auditioned the set a few years ago (X-T100, XRay V8 and power supply) and sold my Rotel gear with the intention to upgrade to the MF set... (However, job changes and migrating killed that plan)...

  16. #16
    Silence of the spam Site Moderator Geoffcin's Avatar
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    Quote Originally Posted by frenchmon
    I'm concerned with good sound rather than another heater for my house. So does the pure class A mean better audible sound quality? And what makes class A so expensive?

    frenchmon
    Now that's the question!

    Certainly the people who pay the premium for a pure class A amp would say so. As to why they cost more, that I cannot answer you definitively. For all intensive purposes they are constructed with the same components, with a class A amp actually needing LESS complex circuitry. Of course generating so much heat those components must be robust, and the designer has to provide generous heat sinks too, so there's an extra cost compared to an A/B amp.
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  17. #17
    Shostakovich fan Feanor's Avatar
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    Quote Originally Posted by Geoffcin
    .... As to why they cost more, that I cannot answer you definitively. For all intensive purposes they are constructed with the same components, with a class A amp actually needing LESS complex circuitry. Of course generating so much heat those components must be robust, and the designer has to provide generous heat sinks too, so there's an extra cost compared to an A/B amp.
    The power supplies of Class A amps must be much more robust for a given power output than Class A/B. I'd say that's the major reason they are more expensive.

  18. #18
    Shostakovich fan Feanor's Avatar
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    Quote Originally Posted by E-Stat
    It is a qualitative difference. Perhaps a discussion by Nelson Pass would help. He has designed countless leading edge amplifiers for over thirty years and is the father of the sliding bias class A concept. Take a look here.

    Virtually all preamps and other line level stages are class A for their better distortion characteristics - not lower levels per se, but the distribution with fewer high order products. Most amps today are of the AB design. Which means they act in class A for a portion of the range, then switch to class B at higher output levels. The point at which they transition is very different from amp to amp. Those with richer bias tend to be heavier and run hotter. I find that those with richer bias offer better low level resolution.

    rw
    Speaking of Pass Labs and Class A, I'm thinking I'd really covet a pair of XA200.A's, (400 wpc @ 4 ohms), to power my Maggies.




    A pair of these beasts is in the range of $35,000, weighs 360 lbs, and sucks 1400 watts at idle.

  19. #19
    Silence of the spam Site Moderator Geoffcin's Avatar
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    Quote Originally Posted by Feanor
    Speaking of Pass Labs and Class A, I'm thinking I'd really covet a pair of XA200.A's, (400 wpc @ 4 ohms), to power my Maggies.




    A pair of these beasts is in the range of $35,000, weighs 360 lbs, and sucks 1400 watts at idle.
    What, only a pair? How about a quad for bi-amping!.
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  20. #20
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    Any one heard of these? http://www.jamnaudio.com/claytonaudio.html

    Frenchmon, care to guess why they are called "Clayton" Audio? They are pretty expensive as well. Not like a Pass monoblock but several thousand. I heard a pair of the CA monoblocks drive the Dynaudio Sapphires and it was amazing.

    That KSA would be a sweet amp.

  21. #21
    RGA
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    Another factor on this topic involves negative feedback. Proponents like me prefer as little feedback or no negative feedback as possible. High Damping factor amplifiers (usually high power not Single Ended solid state amplifiers) tend to have more negative feedback and IMO that means worse sound. UHF magazine in their book does not recommend amplifiers with Damping factors over 40.

    Power with reasonable high efficient speakers do not need more than about 8 watts to play loud with bass and treble and dynamics. Since there are no advantages of owning hard to drive speakers why spend more to get more power on worse sounding amplifiers? Not a lot of sense to me in that approach.

    And as Martin Colloms noted in Stereophile - Against some of the top Solid State designers Colloms had those SS designers pit their amplifiers against eachother - Colloms put in a no negative feedback 10 year old used Tube amp - all the SS designers in a blind listening session chose the 10 year old tube amp for $100 over their $3k models. http://www.stereophile.com/reference/70/

  22. #22
    Suspended Smokey's Avatar
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    Quote Originally Posted by RGA
    Power with reasonable high efficient speakers do not need more than about 8 watts to play loud with bass and treble and dynamics. Since there are no advantages of owning hard to drive speakers why spend more to get more power on worse sounding amplifiers? Not a lot of sense to me in that approach.
    I think if you add distortion (THD) to the mix, you will get a different picture of what you stated.

    As you said 8 watts of power will certainly get loud, but distortion will be high due to not having enough Dynamic Headroom to handle power spikes. This is where more power is welcome to keep [even&odd] distortion low.

    In another word more power is not about quantity, but rather quality

  23. #23
    Forum Regular audio amateur's Avatar
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    Quote Originally Posted by Smokey
    I think if you add distortion (THD) to the mix, you will get a different picture of what you stated.

    As you said 8 watts of power will certainly get loud, but distortion will be high due to not having enough Dynamic Headroom to handle power spikes. This is where more power is welcome to keep [even&odd] distortion low.

    In another word more power is not about quantity, but rather quality
    If your speakers are a little efficient & your not listening at ear bleeding levels, then there should be no need for more than 8 watts, even to handle dynamics peaks without distortion.

  24. #24
    One of Jerry's Kids Jim Eck's Avatar
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    http://dozin.com/godzilla/amp.htm#

    The Godzilla Class A amplifier, check out the link, this is one very high powered Class A amplifier, they where used by Bob Weir and Phil Lesh of the Grateful Dead, an amplifier that can double as a welder! Unfortunately they only made 23.

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  25. #25
    Silence of the spam Site Moderator Geoffcin's Avatar
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    Quote Originally Posted by audio amateur
    If your speakers are a little efficient & your not listening at ear bleeding levels, then there should be no need for more than 8 watts, even to handle dynamics peaks without distortion.
    Well that leaves my speakers out as I've pushed every amp I've ever owned into clipping. (and I've had some brutes too) Really though, most modern amps have more than 8 watts, unless we're talking about S.E.T. amps and that's a discussion for another thread. (even though SET's are all Class "A" in design)
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