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ZMA -- Class A??? (Read 4828 times)
Archie
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ZMA -- Class A???
10/20/16 at 17:32:04
 
I stumbled on a DIY Forum where they were discussing what Steve wrote about his design of the ZMA.  In general, they thrashed it!  They weren't evaluating the sound, just some of the design claims.  I don't have nearly enough knowledge to evaluate their assertions and I don't even know how relevant any of them they are.  What's the difference if an amp is Class A or Class AB?

One thing these guys suggested was the the big caps will possibly get cooked being so close to the output tubes.  Things do get hot up there but I've never felt that the caps get more than warm.  Could this be a valid concern and something that we might want to head off?

After 2 1/2 years with my ZMA, I am nothing but pleased and I'm not out hunting for trouble but can anyone comment?

Here's the link to the forum:  http://www.diyaudio.com/forums/tubes-valves/252999-40w-class-pp-kt66.html
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Lonely Raven
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Re: ZMA -- Class A???
Reply #1 - 10/20/16 at 20:28:20
 
Steve does tend to have a bit of marketing flourish, and is well known for it. I know some people simply wont take him or his products seriously because of it, and some flat out *hate* him saying he's pedaling snake oil because his descriptions are a bit out there, or numbers are rounded up or whatever.

I have asked him about the wattage of the ZMA since I was pretty sure you couldn't do class A 40watts, and have gotten different answers depending on what he feels like divulging and his mood. I get the feeling that this is just a case of rounding to the nearest 10 so people are less dismissive of the amp.

I see these guys at the link also taking his marketing a bit too literally. Steve knows the laws of physics quite well, and when he says the regulator tube has no heat, he's speaking relatively; dropping resistors do get hot, and compared to other tubes the regulator tubes really don't get hot...so from the point of view of generating enough heat to effect *anything* on the amp, yeah, I get what he's saying. †

I'm betting if these solder slingers actually saw what he was doing, saw a schematic or poked around in a ZMA with a probe they'd probably nod knowingly, wax on about how they'd do things differently, and maybe even offer some comments on how "pedestrian" his work is (believe me, I've heard this before from otherwise very knowledgeable EEs and amp builders alike). The fact is Steve tends to do things outside the norm, and most amp builders are just doing the same things, the same ways, with the same circuits since the 1940s straight from the military manuals. Part of what I love about Steve's work is he does a lot of "what if I did....". He's willing to experiment and fail, try things that most don't, and probably some things he shouldn't. LOL

I figure Steve's probably bending some numbers here and there to make things look more attractive to the guys who judge everything on specs...the "math guys" who don't even give gear a listen unless it looks good on paper. (shrug) I've learned to listen and trust my ears. I really don't care that my ZMA is probably 33watts rather than 40watts, though even I've rolled my eyes at some of his flourishes, it really just reminds me of how passionate he is about all this. Besides, I'd say he's a bit more successful than those solder slingers in the forums; the proof is in the puddin'.

Lastly, as for the caps, I don't think there is a worry at all. It's silly speculation, and the caps would probably wear out from use (power cycling) long before the heat of the power tubes does anything to them...hell, the big caps appear to be wrapped in a heat shrink plastic of some sort...if that stuff hasn't melted by the heat of the tubes, I can't imagine how the heat is shortening the life of the caps!! †Also, my ZMA has the big red caps which were Milspec NOS parts intended for use in a nuclear power plant....I'm pretty sure they are up to the task of handling a little heat from the power tubes! †::)
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« Last Edit: 10/20/16 at 20:29:16 by Lonely Raven »  
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Archie
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Re: ZMA -- Class A???
Reply #2 - 10/21/16 at 01:12:29
 
LR,

I kind of figured a lot of what you said.  I'd be curious to hear what those guys would have to say if any actually heard Steve's amps.

It's easy enough to make a heat shield for the caps if needed.  Any idea of the heat specs for either the black or red caps?  I'm guessing the outer jacket never hits 100 degrees F on mine.
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stone_of_tone
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Re: ZMA -- Class A???
Reply #3 - 10/21/16 at 01:54:04
 
Two years and nine months on mine. It never gets old to say: "you will need to pry my ZMA from my cold dead hands."

It took me 37 years to arrive at this great Amp. The audio fools can pontificate all they want to. I and I bet Steve just chuckles.

Good call out Archie and insight LR.

Steve, thank you for your ART.
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« Last Edit: 10/21/16 at 01:58:00 by stone_of_tone »  

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Re: ZMA -- Class A???
Reply #4 - 10/21/16 at 03:17:36
 
components offer explosive dynamics, purity of tone, neutrality, finesse, emotional realism and stable sound stage projection. Our engineers are established leaders in their respective fields of high-end audio expertise. Our range of activities covers the development of high performance vacuum triode power tubes, the design of sonically outstanding tube preamps, triode tube power amplifiers

is something you've not encountered before, it is unique in the world. It easily outperforms conventional line stages and any passive or transformer volume control on account of its patented direct-coupled output which allows for greater transparency while also preventing coloration

A huge power supply provides plenty of current storage to handle peak demands of your music. It can be switched on the fly from triode mode (Class A) at 60 watts per channel, to ultralinear mode (Class AB) at 120 watts per channel. This lets you enjoy the greatest possible minute details of your more delicate music, or ask for much more power when you want to turn it up a few notches.

From a listening perspective these amplifiers provide a fast tight bass, warm fluid mids, super smooth highs. Very three dimesional, holographic. Excellent depth of field, but refined. The special current feedback circuit design allows the amplifier to "listen to the room" via feedback from the speakers acting as microphones (using the law of reciprocity). The room speaker amplifier interaction provides a sense of remarkable ambience that is realistic and non fatiguing. The transformer output impedance allows the signal to follow the impedance curve of the loudspeaker, allowing a consistent voltage to be delivered to the loudspeaker at very low frequencies, a superb low end response!

So above I took some of what other brands print about their products and it doesn't seem much different than what Decware describes other than maybe more detail about what the Decware designs will provide.

I was never a tube amp person till I needed to replace a failing ss unit. I looked and read about many amps from large manufacturers to small ones and chose the ZMA One thing I can say is the physics of heated air is that is rises so will the caps melt? I doubt it and you do have  lifetime warranty so I don't Decware would design an amp that will require caps being replaced. Did those forum people have that problem on their ZMA or just speculating?

If you are pleased with your ZMA own it, love it and stop reading the junk and driving yourself nuts since you must have bought for a reason other than some other amp.

Trust your ears.


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Archie
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Re: ZMA -- Class A???
Reply #5 - 10/21/16 at 16:29:34
 
Jeff,

You examples help put some perspective on things.  I guess I was looking for a reality check as well as information on what the "Class" designations mean.  Also, I'm interested in heading off any problems that may only come with time.  (The disconnects between those forum critics and our experience with our Decware gear reminds me of dealing with my ex-wife!   Grin )
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Archie
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Re: ZMA -- Class A???
Reply #6 - 10/24/16 at 01:28:10
 
To follow up and "close the circle" on the cap heating question that I raised, my big caps (red) get only slightly warm to the touch even after having the amp on all day. †Granted, I've been running 6P3S-E output tubes which are smaller in diameter than KT-66s. †The tubes still get plenty hot though. †I seriously doubt that the capacitors will cook and degrade.
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« Last Edit: 10/24/16 at 01:30:03 by Archie »  
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Lon
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Re: ZMA -- Class A???
Reply #7 - 10/24/16 at 01:39:36
 
I doubt it too. You enjoying the tubes Archie?
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Archie
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Re: ZMA -- Class A???
Reply #8 - 10/24/16 at 17:19:11
 
I'm really liking them -- I have 3 quads.  Every once in a while I put my cryo'd Gold Lion KT-66s back in but I inevitably take them back out soon after.  For me it's more of an intangible and may have as much to do with my Ortofon Kontrapunkt b MC cartridge which some claim is more analytical than lush sounding.  The 6P3S-Es might take the edge off?
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Re: ZMA -- Class A???
Reply #9 - 10/24/16 at 17:23:04
 
Thanks for sharing. I like them too. The truth of the matter is that I have three sets of tubes I've been popping in and out this year and with the flexibility of the Torii Mk III I can make either of them really sing in the amp and I can live with any of them. (TAD KT66, JJ 6CA7, and these). All great sound-makers!
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Archie
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Re: ZMA -- Class A???
Reply #10 - 10/24/16 at 17:58:43
 
I'm looking forward to trying the JJ 6CA7s and the Hazen Grid modification.  I've been spending money like crazy recently on vinyl and another cartridge (Ortofon Cadenza Blue -- a good deal came up) so they will have to wait a bit.
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Lonely Raven
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Re: ZMA -- Class A???
Reply #11 - 10/24/16 at 21:54:35
 
Quote:
I'm looking forward to trying the JJ 6CA7s and the Hazen Grid modification. †I've been spending money like crazy recently on vinyl and another cartridge (Ortofon Cadenza Blue -- a good deal came up) so they will have to wait a bit.


I might even try those myself, when I have the funds. I still need to send Lon his 6P3S-E back. I could use both the JJ and the 6P3S-E in my guitar amps, so even if they don't get use in the ZMA, they are still useful to me. †:)

I'm trying out a '40s vintage set of 807 tubes in the ZMA right now. going to give them a few more hours to burn in, then compare Lon's 6P3S-E, and my old (stock) KT66 one late night (especially now that the house is so quiet with no pets and no girlfriend)

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« Last Edit: 10/24/16 at 21:56:07 by Lonely Raven »  
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Lonely Raven
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Re: ZMA -- Class A???
Reply #12 - 10/24/16 at 21:59:44
 
Quote:
It's easy enough to make a heat shield for the caps if needed.  Any idea of the heat specs for either the black or red caps?  I'm guessing the outer jacket never hits 100 degrees F on mine.


I'd have to double check, but I think you're right. When I first got my PS Audio P-10 Power Regenerator, I picked up a decent IR thermometer (the kind you point at a spot and it reads the heat reflection). I was checking the temps of the power transformers because the temp actually went down a few degrees with the cleaner power from the P10!! But I recall reading off my caps, and they were about 96F-97F

I think I know where the thermometer is, so I could double check when I get home later this week. I'm curious myself now.
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Denizen
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Re: ZMA -- Class A???
Reply #13 - 10/25/16 at 18:15:25
 
Why, yes Virginia, there is such a thing as class-a push-pull amplifiers. You can find an excellent description here http://www.aikenamps.com/index.php/the-last-word-on-class-a
research also sez 2 kt66 tubes operating in push-pull ultra-linear can produce 50 watts. All electrical failures are mechanical in nature,so can the caps fail, of course, but that doesn't mean they are going to fail from the meager amount of heat coming from an OA3. And as far as class is concerned, Steve has it in spades, those guys over at diy, not so much.
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Re: ZMA -- Class A???
Reply #14 - 10/25/16 at 19:30:49
 

Aiken knows his stuff...I've had a few of his guitar amps, and still have one of his Marshall clone 4X12 cabinets in RED.

Where do you see the part about KT66 being 50 watts though?
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stone_of_tone
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Re: ZMA -- Class A???
Reply #15 - 10/26/16 at 16:05:17
 
Good question LR? .....where does he see the part about KT66 being..... .

Anyway, to further comment on your well put response LR, " I've learned to listen and trust my ears. I really don't care that my ZMA is probably 33watts rather than 40watts (38 watts)." †

Ditto for me too and if it crosses into AB when I push her....don't care either. The ZMA is the best Amp I have heard (in 40 years/got into Audio when I was 13) when I push her to compression and incomparable under it.

Jeff1, great points too. You did your homework and chose the ZMA. I would love to hear your Legacy Sigs with it.

PS~reading the Aiken paper ...last word in class A.......confirms how important the phase splitter tubes are! The Telefunken E88CC/6922's are expensive....but a damn well worth it upgrade to your ZMA, IMHO. A pair of these in the PSplit's....really lets your Input tubes shine! For me it is: Mullard E188CC's and Ediswan's. † ......Tungsrams too.
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« Last Edit: 10/26/16 at 16:42:28 by stone_of_tone »  

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Archie
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Re: ZMA -- Class A???
Reply #16 - 10/26/16 at 17:04:01
 
Great article.  Cleared up many questions but raised a few too.  The talk about ultra-linear output was confusing.  I thought Steve's amps used "ultra-linear transformers" but does he also "local negative feedback" as the article mentions?

Stone, good point on the phase splitter tubes although as the article mentions, the Class of an amplifier doesn't change during operation.

Now I'm feeling a bit like "a little information can be a dangerous thing!"
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Re: ZMA -- Class A???
Reply #17 - 10/26/16 at 17:13:00
 
One time when I encountered someone giving me some grief about Decware amps I showed them this review. They knew Tone Audio and this had them scratching their heads and looking into Decware with a different eye.

http://www.tonepublications.com/review/decware-zen-mystery-amp/
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Re: ZMA -- Class A???
Reply #18 - 10/26/16 at 18:08:00
 
Whatever the case may be Archie involving the phase splitter tubes. When I put other tube sets in ~ changing only this one variable....the other's take away from the sonic signature of my Mullard & Ediswan input tubes. Though highly subjective, the difference is more than subtle.

Converse, of that....I hate the Telefunken E88CC's as input tubes.
As Splitter's, absolutely sublime and are an upgrade to my ZMA.

If in Class change you're referring to my going into AB mention....maybe it does with Steve's design?
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« Last Edit: 10/26/16 at 18:13:56 by stone_of_tone »  

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Re: ZMA -- Class A???
Reply #19 - 10/26/16 at 21:20:21
 
I like and have used Lon's approach a few times with a few ''audiophiles'' and after reading Jeff's review of the ZMA asking if they could come over an listen to our little system. All have been impressed by Decware and how it gets OUT of the way of the music and you just get DRAWN in. Magic boxes by the Zen Master. Happy listening, Chris.
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Re: ZMA -- Class A???
Reply #20 - 10/26/16 at 22:28:10
 
You're right. Mr. Aiken does know his stuff and so does Mr. Deckert. What I do find interesting is that you're quite willing to except the assessment of a few individuals based on what? Steve actually employs people to make his company work, he sources parts here in the U.S.A when he can.
He may spend 100's of hours and thousands of dollars to bring an amplifier to market. Over the years he has sold thousands of amplifiers all over the world and has almost as many satisfied customers, so what have those people over at DIY brought to the table.

As to where I get my information on the KT66 tube, I can't tell you it's top secret, all I can say is you should never search the internet for KT66 tube datasheets and you should never, ever go to this site where you'll find a schematic for a 50W kt66 based amplifier http://www.r-type.org/articles/art-085.htm or go to leben hi-fi stereo where they offer a 40W KT66 based amplifier (class unknown) the 50W is Class A/B but you should'nt go there.
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Re: ZMA -- Class A???
Reply #21 - 10/27/16 at 06:27:10
 
Hi Archie,

Sorry I didnít see this thread sooner! To the difference between Class A or Class AB is well written in the article Denizen posted written by Randall Aiken.

As Lonely Raven illuminates there are long time Decware bashers, it goes with the territory. Itís not uncommon for ďexpertsĒ on DIY forums to puff up their egos by bashing the real deal, which is the guys who have successfully built and shipped over 6000 amplifiers in the past 20 years with a lifetime warranty, all still in service.  

The big caps will not deteriorate from excessive heat from the output tubes, thatís the kind of thing that happens to DIY amplifiers that are not well engineered.  

Iím pleased to hear youíre still enjoying your ZMA after 2 1/2 years. Should be starting to get warmed up and sounding pretty good by now Wink

Lonely Raven,

If you look at a data sheet for the KT66 (http://www.r-type.org/pdfs/kt66.pdf) you will see in Push-Pull Pentode connection typical operation is 30 watts for the pair of tubes. If you look at the same operation with fixed bias instead of a cathode resistor, your power increases to 50 watts. Thatís in class AB1 operation. If you were to employee an ultra-linear output stage the power would increase significantly further. The ZMA is both fixed bias and ultra-linear.

You have asked about the wattage of the ZMA from time to time and if you got different answers it would have been the context of the question, not what I feel like divulging or my mood. Probably looks that way on my face when asked though, because Iím trying to decide how simple or complex to make the answer. For example, a simple answer would be 38/40 watts. A more truthful answer would be that it depends on the voltage at the wall outlet and itís effect on the B+ voltage of the amplifier as well as the bias supply. All of this will determine what the tubes bias up at relative to the available plate voltage which effects power. That is to say nothing about the gain of both the input tubes and output tubes. For example, the input tube may have a gain anywhere between 25 and 35. The output tubes also test with a gain figure anywhere between 15 and 30 when measured at 400V and -48v bias.

Happen to have a set of 25 input tubes and 15 output tubes and youíre going to get less than 38 watts. Put in a set of 35 input tubes and 25 output tubes and your going to have over 38 watts. This is of course measured into a dummy resistor not a complex impedance like a loudspeaker. Since dummy resistors make no sound, no audiophiles to date have used them for speakers so the power ratings are largely misleading. I know that into a loudspeaker most of our amplifiers actually put out significantly more power instead of less.  Öthe more complex answer.

Regarding class A operation I am guilty of being one who thinks that if an amplifier is biased close enough to class A that it maintains class A operation through the first several watts it is basically a class A amplifier to anyone who listens to it since 95% of an amplifierís playback resides in the first few watts.  However if I were marketing to engineers who already know it all, I would call it class AB1 and spare them the boredom
of an explanation.

Nevertheless to squelch this newly adopted rumor that a ZMA is 33 watts, I have taken the time to make a video of how we measure the power output.  It will be a helpful video for ZMA ownerís so it was no problem to make.
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Re: ZMA -- Class A???
Reply #22 - 10/27/16 at 06:28:14
 
Here is a link to the ZMA Testing Video:

https://decware.wistia.com/medias/clex9z20t4

Happy listening Smiley

Steve
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Re: ZMA -- Class A???
Reply #23 - 10/27/16 at 16:54:14
 
Steve, thanks for weighing in and clearing up the confusion -- that I started!  :P  

Can you comment on how Ultra Linear Output Stage feedback relates to "No negative feedback?"  The article referenced by Denizen mentions that feedback is used for ULOS but I'm guessing it's not the same or of a different order of magnitude?  And is the ULOS used in the ZMA the same as that of your amps with the UFO transformers or is a different concept altogether?

I realize that the proof is in the sound but somehow I'd like to be less confused when reading the add copy when comparing the various Decware amps.
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Re: ZMA -- Class A???
Reply #24 - 10/27/16 at 19:17:56
 
Hi Archie,

Ultra-Linear operation is accomplished when a portion of the voltage feeding the transformer is returned via a 40% tap back to the screen grid of the output tube.†This is kind of like half way in-between a triode and a pentode who's characteristic plate curves are parabolic in shape and far from linear. A triode plate current line is concave upward, while a tetrode or pentode current line is concave downward. †By hooking the screen grid to a 40% tap the plate current lines become straight and far more linear. †This improved linearity greatly reduces distortion as we saw in my video to 0.6%

The low impedance tap on the transformer when connected to the screen grid will have a voltage that is in phase with the plate voltage and a fixed fraction of it. For this reason many claim that Ultra-Linear operation is nothing more than local feedback in the output stage. As usual it is not that simple. Beyond the usual current/voltage feedback conditions between linear circuit elements there is also power feedback that happens when plate circuit power is supplied to a non-linear screen grid load and consequently the situation is more involved.

For example, when feedback is connected to a separate electrode (screen grid) within a tube it will introduce a new curvature into the existing tube plate curves. This is contrary to typical negative feedback which operates on the basis that feedback voltage and signal voltage are applied to the same place (a common element) so that the two voltages are additive which will always tend to improve linearity. However, with feedback going to separate electrodes a reverse curvature may be introduced to cancel existing non-linearity.

"Negative Feedback" as it's commonly known to audiophiles means taking the output and sending a portion of it back to the input AKA global feedback. Anything other than small if not tiny amounts of this will subjectively ruin the sound despite having lower THD and lower output impedance. That is because it smears the timing of low level ambient ques in the music causing the dimensionality and sound stage depth to collapse.

The ZMA uses no global feedback of any kind. Local feedback isn't usually a problem because there are no timing issues being caused by the transfer function of the amplifier, but as I pointed out, the  feedback of ultra-linear is not the same thing as the standard definition of local feedback.

The UFO transformers are primarily defined by their wide bandwidth and flat response, not type. †So far all of our UFO transformers are single-ended except the TORII JR which is Ultra-linear. †So far there are no plans to make the ZMA's ultra-linear transformer's any differently than we do now because we like the sound and performance. †The old saying - if it ain't broke, don't fix it.

I have to wonder if it's the ad copy that's confusing or the "expert analysis" of the ad copy that's confusing everyone? †I'll probably revisit the push pull amp pages and remove or change copy that can be spun as snake oil because it irritates the living crap out me that people do that.

Steve

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Re: ZMA -- Class A???
Reply #25 - 10/28/16 at 01:51:25
 
Steve, thank you for taking the time to answer my questions.  Fortunately, I've just taken your "ad copy" at it's word and I run a ZMC1, ZP3, CSP3, ZMA into HR1s and couldn't be happier!

One other minor thing I've wondered about, since you don't specifically say, is if the ZMA preserves the even ordered harmonics like your SET, Torii and Torii Jr amps?
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Re: ZMA -- Class A???
Reply #26 - 10/28/16 at 13:34:23
 
So there you have it Archie. As I eluded to in my reply #15 and again in reply #18.....crossing into AB (or AB1)......with peak power of 114 watts (when tubes are new and well matched out of the gate)......is pretty damn cool.

Most of my listening and I bet yours....stay's in Class A @ "the first several watts", Steve mentions in the 4th paragraph to Lonely Raven in Reply #21, with 3.8% THD, even order harmonic's.

With even order, our ear brain connection won't notice THD until at or above the 3.8 % (give or take, I think it is more like 3.2 to 3.5%).

Good, further question you ask about THD at peak 114 watts? I'm sure it rises, and does it pull up the odd order subdued peaks or stay even and compression is evident?

Well, to the ear, some compression is evident....but oh so sounding good where I don't need to back off the volume like I would with Solid State.

To further elaborate this point: Tube Amps too, with negative feedback I don't like either at any point on the volume knob. Especially when you push them.....they, like solid state can't do what the ZMA can do.....at all points on the volume knob. I recently sold my two Preamps too....the ZMA is so damn good and seasoned in now. Pre's sold: CSP3 and Audio Research LS-17 SE.
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« Last Edit: 10/28/16 at 17:04:36 by stone_of_tone »  

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Archie
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Re: ZMA -- Class A???
Reply #27 - 10/28/16 at 17:06:14
 
I find that I listen more in the range of "meters just starting to move" more and more.  So, I might be pushing the Class A into AB.  I can't help myself -- it's just so darned good!   Cheesy
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Re: ZMA -- Class A???
Reply #28 - 10/28/16 at 17:16:01
 
Oh yeah! My ZMA is dancin' a little bit right now.....to Steely Dan Gaucho....Glamour Profession has never been enjoyed better!

Sure, my System plays all of my Audiophile recordings with aplomb. True test of a System: Can it play 75 to 85% of your CD Collection....at the best.......... . Mine does.

.....just rolled into the title track ~ Gaucho.....goose bumps man....a natural ZMA High!
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« Last Edit: 10/28/16 at 17:20:20 by stone_of_tone »  

Sony as Transport
Illuminati D-60
Audio Alchemy DTI-Pro
Audio Magic Mystic Reference I2S
Audio Alchemy DDE 3.0
Kimber Select 1030
Zen Select #76
Kimber Select 3033
Polk Audio LS-90
Tri-config/TipToes & Vibropods underneath Speakers
360 degree Rm Treats
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Re: ZMA -- Class A???
Reply #29 - 10/28/16 at 20:13:38
 
Quote:
One other minor thing I've wondered about, since you don't specifically say, is if the ZMA preserves the even ordered harmonics like your SET, Torii and Torii Jr amps?


Yes, if you watch the video, I show you the harmonics of the ZMA in real time and they are dominated by even orders.

Steve
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Re: ZMA -- Class A???
Reply #30 - 10/28/16 at 21:34:49
 
I just got the chance to watch the video and what a great video!  Thanks.  Now I"ll be checking all my tubes for balance with the meters.

It helps explain why I get such kick ass sound/volume out of a 40 watt amp.   Cool
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