True Class A Amps

Just curious, who of you own one,
Not an Audiophile, just a dude who loves music, and decent gear to hear it with.

Comments

  • pitdogg2pitdogg2 Posts: 14,316
    3 that I recollect
  • afterburntafterburnt Posts: 5,633
    Emo's must be class A because they burn the front lawn.
  • BlueFoxBlueFox Posts: 12,050
    Not pure. Class A for the first 20 watts, which is fine for me.
    Bud - Silicon Valley

    Lumin X1
    Sony XA-5400ES SACD
    Pass XP-22 pre, X600.5 amps
    Magico S5 MKII Mcast Rose speakers, SPOD spikes

    Shunyata Triton v3/Typhon QR on preamp, Denali 2000 (2) on amps
    Shunyata Sigma XLR analog ICs, Sigma speaker cables
    Shunyata Sigma HC (2), Sigma Analog, Sigma Digital, Z Anaconda (3) power cables

    Mapleshade Samson V.3 four shelf solid maple rack, Micropoint brass footers
    Three 20 amp circuits.
  • nooshinjohnnooshinjohn Posts: 21,321
    edited April 27
    retracted.....
    The Gear... Carver "Statement" Mono-blocks, TriangleArt Reference SE with Pass Labs Xono Phono Preamp, Walker Precision Motor Drive, ClearAudio Goldfinger Diamond v2 cartridge and Origin Conquerer Mk3c tonearm, Polk Audio "Signature" Reference Series 1.2TL with complete mods, Pass Labs X0.2 three chassis preamp, PS Audio PerfectWave DAC MkII, Pioneer Elite SC-LX701, Oppo UDP-205 4K Blu-ray player, Sony XBR70x850B 4k, Polk audio AB700/800 "in-wall" surrounds.

    Saying that it's "too hard" to pursue your dreams is no different than admitting to yourself that you are too lazy to achieve them.

    “If it moves, tax it. If it keeps moving, regulate it. And if it stops moving, subsidize it.”
  • motorstereomotorstereo Posts: 1,297
    edited April 27
    I had a pair of Monarchy sm70 monoblocks that were class A. Ran hot as a firecracker, weren't my cup of tea sonically and required putting a grease fitting on the power meter. I did the happy the dance the day they left a few months ago.
  • mhardy6647mhardy6647 Posts: 22,990
    edited April 27
    oh, oh, oh! pick me, pick me!

    46602617645_e324754511_b.jpgDSC_4280 (2) by Mark Hardy, on Flickr
    Single Ended Class A direct heated triode (2A3) JE Labs "Simple 2A3" variant.

    Or, if you prefer soiled solid state:
    (courtesy of @ALL212 and an anonymous benefactor who actually directed it to me -- which was/is very much appreciated):

    44366482421_f50c8978d1_b.jpgDSC_2871 (2) by Mark Hardy, on Flickr
    Single Ended Class A "Amp Camp Amp" variant.

    Or even vintage?

    wn2dekvdjeq4.jpg


    OK, this one has switchable Class A PP operation (for something like 10 wpc), but it does sound good when so switched, even forty years after it rolled (or whatever) off the assembly line.

    There are others here (mostly SE vacuum tube amps, which operate in Class A by definition).

  • gfonggfong Posts: 1,077
    edited April 27
    got one! Unison Research
  • Gerres26Gerres26 Posts: 483
    My Aragon is a class A/B amp but is biased into class A for the first 26 watts...sounds excellent to me
  • txcoastal1txcoastal1 Posts: 10,584
    Owned Threshold Stasis and like Gfong a Unison research

    Also owned an XA30.5

    2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
    Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
    Gear on standby: Melody 101 tube pre, Unison Research Simply Italy Integrated
    Gone to new homes: (Matt Polk's)Threshold Stasis SA12e monoblocks, Pass XA30.5 amp, Usher MD2 speakers, Dynaudio C4 platinum speakers, Modwright LS100 (voltz), Simaudio 780D DAC
  • heiney9heiney9 Posts: 24,112
    edited April 28
    I had a pair of Monarchy sm70 monoblocks that were class A. Ran hot as a firecracker, weren't my cup of tea sonically and required putting a grease fitting on the power meter. I did the happy the dance the day they left a few months ago.

    Pure class A is considered "single ended". The Monarchy's are not single ended.

    Stasis is not pure class A if you use the above definition, which most do.

    My Pass Aleph 30 is pure class A as it is single ended. Simply put the conductors are on 100% all the time.

    Research single ended and it will explain. There are opinions on the subject and many feel pure Class A sounds better than a push/pull configuration. But there are lots of variables and lot's of "hybrid" designs (for lack of a better word) that sound great.

    H9

    Post edited by heiney9 on
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30 | EE Avant Pre | EE Mini Max Plus DAC | MIT Shotgun S3 | MIT Z P/C's | updated SDA 1C| SQ Box Touch/Welbourne Labs P/S- Tubes add soul!
  • motorstereomotorstereo Posts: 1,297
    ^^^^^Thanks for the clarification but I'll take their word for it
    m7jt9rgukwal.png

  • mhardy6647mhardy6647 Posts: 22,990
    edited April 28
    heiney9 wrote: »
    I had a pair of Monarchy sm70 monoblocks that were class A. Ran hot as a firecracker, weren't my cup of tea sonically and required putting a grease fitting on the power meter. I did the happy the dance the day they left a few months ago.

    Pure class A is considered "single ended". The Monarchy's are not single ended.

    Stasis is not pure class A if you use the above definition, which most do.

    My Pass Aleph 30 is pure class A as it is single ended. Simply put the conductors are on 100% all the time.

    Research single ended and it will explain. There are opinions on the subject and many feel pure Class A sounds better than a push/pull configuration. But there are lots of variables and lot's of "hybrid" designs (for lack of a better word) that sound great.

    H9

    Well, no -- not exactly. It is perfectly possible to bias a push-pull amplifier to operate in Class A (both sets of devices "on" and conducting for the full cycle). This is incredibly inefficient (which is why the aforementioned Yamaha CA-800 runs so hot in Class A bias!). BUT there are push-pull amps (tube or solid state) that operate in Class A. Very inefficient, but can sound very good.

    The takeway is this: single-ended (SE) vs. PP (push-pull) doesn't give enough information to "answer the question" -- i.e., "Is the amp operating in Class A, Class B, or Class AB?".

    NOW, that being said, all single ended amplifiers are operating in Class A -- they have to, by definition. This is true no matter how many output devices there are in the single-ended amp. E.g., it is also perfectly possible to make a 'single ended parallel' amplifier stage with two output devices (or even more!) operated in parallel -- but the class of operation will still be Class A.

    Hope this is helpful!
  • heiney9heiney9 Posts: 24,112
    edited April 28
    ^^^^^Thanks for the clarification but I'll take their word for it
    m7jt9rgukwal.png

    It's market speak. Beleive what you want, but I've heard them, my brother had a pair and I've examined them and they don't fit the definition of pure class A.

    There are lots of buzz words and you can twist the phrase "pure class A" anyway you want.

    To most pure class A = single ended. The Monarchy's are not single ended and they even use an op-amp at the output stage.

    I'm out of this one because it's a very misunderstood concept because of the marketing guru's mucking it all up.

    Get your learn on if you are truly interested.........then you'll see what I mean.

    H9

    P.s I thought they sounded wonderful, even with an op-amp in the output.

    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30 | EE Avant Pre | EE Mini Max Plus DAC | MIT Shotgun S3 | MIT Z P/C's | updated SDA 1C| SQ Box Touch/Welbourne Labs P/S- Tubes add soul!
  • mhardy6647mhardy6647 Posts: 22,990
    edited April 28
    Again, all single ended amplifiers operate in Class A but that in no way implies that a push-pull amplifier cannot be operated in Class A. For very practical reasons (heat and power consumption being the major reasons), most push-pull audio amplifiers operate in Class AB. Class B is the most electrically efficient, but suffers from some anti-high-fidelity distortion issues (see below). Class AB is a compromise that permits reasonably
    efficient operation and reasonably acceptable distortion behavior for "hifi".

    The problem with any fixed bias operating point that switches the active devices (tubes or transistors) off for any part of the waveform is a rather unpleasant form of nonlinearity referred to as crossover distortion. In pure Class B, the crossover distortion occurs at exactly zero volts (the "crossover point" from negative to positive) of the signal waveform, and will be at its worse. Class AB bias points, which allow some overlap of activity between the "push" and "pull" output devices, can decrease the crossover distortion, as can negative feedback.

    Class A push-pull amplifiers have the harmonic distortion behavior of all push-pull amplifiers (i.e., cancellation of even harmonic distortion products) but they will lack crossover distortion.

    Nelson Pass' "F5" is an example of a Class A push-pull hifi amplifier; you can build one yourself.

    https://www.audioxpress.com/article/you-can-diy-the-f5-power-amplifier
    http://www.firstwatt.com/

    It's not related to amplifier operation "class", but there is a profound difference in the distortion spectra of single-ended vs. push-pull amplifiers. That's a different topic entirely, but the difference between single-ended and push-pull probably has far more real audible impact in a good hifi amplifier than does Class A vs. AB bias (in a push pull amplifier).

    The problem with marketing hyperbole comes in with a plethora of "pseudo-Class A" amplifier bias schemes that are claimed to give the best of both worlds. My advice, FWIW, view such claims skeptically but use the ears to evaluate the results (rather than reading ad copy, magazine reviews, or internet pontification -- like mine! ;) ).
  • mhardy6647mhardy6647 Posts: 22,990
    Oh, while I am on the soap box :)
    Op amps.

    1) It is perfectly possible (indeed, very common) to operate an operational amplifier (op amp) single ended/Class A. Modern audio equipment is chock full of them.

    Remember that any unbalanced audio stage (e.g., a line level preamp that uses "RCA" plugs and jacks for interconnection) is single-ended/Class A.

    2) The knock against op amps is generally directed at inexpensive integrated circuit (IC) 'chip' op amps. It is perfectly possible to make op amps with discrete components. Indeed, it's perfectly possible to make discrete, vacuum tube op amps. They were very common in the days of analog computers, e.g.

    Here are two examples of high quality, discrete op amps designed for audio use.
    https://www.bursonaudio.com/products/supreme-sound-opamp-v5/
    https://sparkoslabs.com/discrete-op-amps/
  • mhardy6647mhardy6647 Posts: 22,990
    edited April 28
    Here's a Heathkit analog computer. That row of vacuum tube modules at the top across the back is a phalanx of discrete, vacuum tube op amps. I count fifteen.


    15947088165_bd40b4f045_b.jpgHeathkit analog computer by Mark Hardy, on Flickr

    As an aside, I actually had one of these Heathkit computers! Wish I still did -- it was very big, very heavy, and rather difficult to 'program' it to do useful things. :)

  • DoneandGoneDoneandGone Posts: 52
    There’s a pair of SM 70 Pros up for sale here in BC for $1,200 CAD. Are they worth a look (listen)? Are they sonically not that good motorstereo?
    Audio Room
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    Kef XQ1 bookshelves
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    Homemade sound absorption
    Lots of blocks for weight and a red single listening chair
  • motorstereomotorstereo Posts: 1,297
    My impressions are at first listen I thought they sounded very nice but after living with them for a while I began to think differently. They run hot (130-140 F) so that means they're cold weather amps. They also will drive up your electric bill if you leave them on all day like I used to. We all hear differently and you just may like their sound. Mine sounded their best on a pair smooth sounding ads 1530's and I didn't care for them on a pair of more revealing khorns where I thought they were harsh sounding. The khorns were the speakers I wanted to pair them with and unfortunately they just didn't have synergy to my ears.
  • DoneandGoneDoneandGone Posts: 52
    Interesting observations, thanks. They are now sold, but the guy did say there was a intermittent problem with one of the power switches. Running so hot, turning on/off frequently because of the overheating explains that issue now. Cheers
    Audio Room
    PS Audio Perfectwave DAC MK2, Bridge 1 streaming perfectly now B)
    Marantz PM-8005 integrated
    Foundation Research LC2
    Kef XQ1 bookshelves
    Dual Goldenear Forcefield 3 Subs
    PS Audio receptacle
    3 PS Audio Noise Harvesters
    PS Audio power, interconnects and speaker cables
    Homemade sound absorption
    Lots of blocks for weight and a red single listening chair
  • mhardy6647mhardy6647 Posts: 22,990
    True Class A amplifiers will always, always, run hot -- the output devices are always dissipating full power, all the time, even at idle (zero signal).

    If you can't cook on top of it (whether vacuum tube or solid state), it's probably not really Class A! ;)




  • motorstereomotorstereo Posts: 1,297
    edited April 29
    Yes they sure do run hot. I had a Yamaha R9 receiver that had a class A switch and it would run luke warm until that switch was engaged. It also would instantly start drawing more current according the power conditioner I had it plugged into. I never could hear a difference in the sound though.
  • BlueFoxBlueFox Posts: 12,050
    After I got my amps 4-5 years ago for final three weeks in July, I went crazy when I got the electric bill, since I have to run the AC when I play the stereo. I immediately had solar installed, and while it doesn't quite cover the summer electric bill, it is manageable now.
    Bud - Silicon Valley

    Lumin X1
    Sony XA-5400ES SACD
    Pass XP-22 pre, X600.5 amps
    Magico S5 MKII Mcast Rose speakers, SPOD spikes

    Shunyata Triton v3/Typhon QR on preamp, Denali 2000 (2) on amps
    Shunyata Sigma XLR analog ICs, Sigma speaker cables
    Shunyata Sigma HC (2), Sigma Analog, Sigma Digital, Z Anaconda (3) power cables

    Mapleshade Samson V.3 four shelf solid maple rack, Micropoint brass footers
    Three 20 amp circuits.
  • BetaBeta Posts: 263
    aknvt2gh03xh.jpg

    I believe I fall into this camp. CAD-805RS Monoblocks. Yes. They put out a lot of heat.
  • DoneandGoneDoneandGone Posts: 52
    Beta, is the heat from your amps bowing the shelf above? I'm sure it has nothing to do with 150lb+ of PS Audio equipment
    Audio Room
    PS Audio Perfectwave DAC MK2, Bridge 1 streaming perfectly now B)
    Marantz PM-8005 integrated
    Foundation Research LC2
    Kef XQ1 bookshelves
    Dual Goldenear Forcefield 3 Subs
    PS Audio receptacle
    3 PS Audio Noise Harvesters
    PS Audio power, interconnects and speaker cables
    Homemade sound absorption
    Lots of blocks for weight and a red single listening chair
  • BetaBeta Posts: 263
    edited April 29
    Beta, is the heat from your amps bowing the shelf above? I'm sure it has nothing to do with 150lb+ of PS Audio equipment

    That photograph makes the shelf look like it's sagging. It's not. It's straight. Out of curiosity, I just placed a level on it. It's dead even.
  • DoneandGoneDoneandGone Posts: 52
    Haha, visual distortion due to poor optics of your portable electronic image capturing device?
    Out of interest, does the Powerbase influence the P20? if nothing else, it looks super cool.
    Audio Room
    PS Audio Perfectwave DAC MK2, Bridge 1 streaming perfectly now B)
    Marantz PM-8005 integrated
    Foundation Research LC2
    Kef XQ1 bookshelves
    Dual Goldenear Forcefield 3 Subs
    PS Audio receptacle
    3 PS Audio Noise Harvesters
    PS Audio power, interconnects and speaker cables
    Homemade sound absorption
    Lots of blocks for weight and a red single listening chair
  • jayman_1975jayman_1975 Posts: 676
    I own 2. PS audio 200c and 200cx. They run smokin hot and sound amazing.
    Onkyo TX NR 5008 modified by The Upgrade Company
    Oppo BDP 93 modified by The Upgrade Company
    Arcam CD37
    Monitor Audio Gold GS 60
    Revolver Audio Music 5 towers.(surround)
    Vandersteen V2W
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