Historical look at amps

I think that your cut and paste may be mistaken. Either that, or I did not explain it fully.

Voltage feedback.......the "normal" kind. As you increase the gain, the bandwidth DOES drop. The product remains constant, but that is not the same. Conversely, as you lower the gain, the bandwidth increases.

One of the reasons firms like Comlinear came up with "current-feedback" is that (within reason) you can change the gain and NOT affect the bandwidth.

OK.......more damning inside info!!!!!

Any one here have preamp based on the Burr-Brown PGA2310?? Anyone???

Ever stop to think how they get such a large range of attenuation, all the way down from......I dunno.......-90 or more.....all the way up to a gain of.......30 dB or so. A lot of range, right. How do they do that? It must be some sort of miracle, because competing digital potentiometers have ranges less than half as much. Right?

Wrong! Here is what they do:

It uses some sort of digital pot, just like the others, to give a narrow range of adjustment. (I forget what....I measured it one day.) But at a certain point, as you slowly bring the level up or down, they suddenly switch the gain on the internal op-amp. Easy to do by changing the resistors in the feedback path.

OK.......what does this have to what the subject at hand?

If you measure the noise on the output, you will see that it jumps when they switch the resistors in the feedback loop.

And the bandwidth changes too! The -3 dB point changes. It changes so radically that at full gain, the response at 20 kHz is down quite a bit. I forget what, but it was quite a lot. It may have been -2 dB. Don't quote me, because I did not write it down. if you want to know the exact number, ask me and I will measure it.

As for my amps, would you rather that I lie and say that they are the greatest ever? Would that make you want to rush out and buy one? I bet it wouldn't. But if you did, and it sounded bright next to your SS amp, you might be mad. Look, as far as I know, no one who is posting in this thread has design experience comparable to me. So why do you feel threatened when I tell the dark secrets of the world of amp design. I would think that frank and open discussion would be welcome. When you are asking someone to fork over $3k or more on something that they are gong to put in their sound room, and stare at it for (hopefully) years to come, is trying to pull the wool over their eyes going to make them want to keep it?? I would rather be upfront about the strengths and weaknesses of my products. Much better than hyping them to death, getting a handful of quick sales, only to see them here in the "used amps for sale" section 6 months later. That kind of advertising does not make for a long-lived business.

But the truth is, most listeners "think" that a "digital" amp, with the same - 3 dB as a conventional SS amp, will "sound" bright.

Oh......I almost forgot........this is important......sorry.....but:

The guys who think that they sound bright all have cone transducer speakers. The ones who don't think that it sounds bright.........drum roll........have planar speakers! Sorry, I forgot to mention that. Probably because I had already sold amps to everyone that I could who owned planar speakers, and now I am trying to sell to the rest of the world. And they have cone loudspeakers. Now I have headaches.

Calm down, Vince.......it was an honest omission.

In fact, I recently sent out an evaluation unit. The guy spoke very highly of it. He liked it better than the "Brand N" amp that he was a dealer for. I knew that it was a winner because he and his girl friend were able to listen to it for hours on end. Then he complained about the binding posts. And said that I might want to "tone down" the HF a little, as he felt that most people with a cone speaker system would find it a bit bright. He said it, not me. Remember, he liked it.

Oh......btw......I do know how mine stack up against Rowland, Ear, and H2O. Wanna guess how??????? I'll give you a hint: guess which one they bought. Frankly, I'm not sure why. Maybe they wanted something that looked almost as cool as the Rowland, but less expensive. Or they did not want to have to fight trying to get big fat speaker cables up inside some crazy looking triangular gizmo with Speakon connectors.

Seriously, I only saw one model Ayre amp. Can't even remember the model number. Heard several of them, in more than one location. They were the hot ticket to go with a certain Thiel speaker, that badly needed "taming". Last time I saw Charlie Hansen, he was at Avalon. If I knew more, I would say so. The only reason that I know as much as I do, they did silk screen the schematic on the inside of the lid.

OK.....tweeter level and amp brightness......as promised.

A buddy who designs speakers calls me one day, fretting over what level to set the tweeter on his latest product. If he used the one made by a mutual friend, it was one setting. If he used one of the "East Coast Big Boys", he had to set it 0.25 dB different. He asked for my advice.

My advice was: "Well, who is the target user? Since we all share dealers together, it may be a safe bet that they will have our CD player, and an amp/preamp combo by "our buddy". I would set it up to sound right with it."

"Yeah, but......if I do, it won't sound right on the other one."

"Who cares? None of your customers can afford that stuff."

"Yeah, but......if I send it to Stereophile, and they do a review on it, you know what kind of amp they are going to hook up to it."

"You're screwed, bub. You lose either way."

I know some of you are going; "A quarter of a dB. One quarter of a dB makes that much difference? C'mon, bub, you're pulling our leg."

Nope, 0.25 dB is a LARGE difference. You figure that level change on this speaker is from around 5 kHz to 20 kHz. Two octaves. Definitely the difference between "just right" and "too bright/too dark".

Back to amps........you-know-who frets about 0.2, maybe 0.3 dB, on his "digital" amps. From around 10 kHz to 20 kHz. One octave. Yes, not as wide a range, but I can assure you that much level difference in an octave is audible.

Just like the 0.25 dB over one octave in an RIAA network. In absolute numbers, taken at one point, not much. Added all together, over one or two octaves, a lot of energy.

OK.....more food for thought on amp design.

EVERY amp designer that I know will tell you, if they are honest, that if there is "too much" going on in the HF region (like overshoot in a cascode stage, very easy to do), that the bass will sound wrong. Getting the bass "right" on a conventional SS amp is not as easy as you might think. A lot of things can creep in that cause too much HF energy. Everything from circuit topology to power transformer and filter cap selection.

The worst sounding amp that I ever made had some fancy caps, intended for SMPS. Low ESR, low ESL, put several in parallel to lower those numbers even more.

Absolutely no bass at all. None. Zero. Nada. Useless for anything other than PA use.

Put in some regular ol' filter caps, only one per rail. Product ready to ship. Go figure.

I am not being difficult. I have a long-standing feud with someone that does exactly what I am commenting on. It will just be a matter of time that he finds this through Google, and the feud will spill over to here. So, while it may be beneficial to you, it may give him fodder to slander me even further by using my posts here as ammo.

Trust me.......ok.

Ok.......my company is Analog Research-Technology. We used to have an entire line of electronics, way back when. Way back when we had dealers. The migration to HT put them all out of business, so we went even more underground than usual.

With the recent introduction of the new "self-oscillating" Class D amps (digital amps to some of you............), I decided to gear up and start making 5-channel amps for the HT crowd. Somehow, I have a hard time getting excited about that market, and since we were amazed at how good they sounded, we became sidetracked and made some stereo versions.

One of my customers mentioned here that he has one of amps......well, actually, he has a 5-channel one also......and next thing that you know, my phone is ringing, wanting info, etc. If it were not for that, you never would have heard of me.

Is that help any???

Or do you want:

I live in Texas. I eat really hot peppers and curry. I have a '73 'Cuda hidden away in the garage. I don't drive it much because gas costs too damn much, it rides hard as hell, and I am too damn old to get excited about trying to operate a 4-speed with a clutch that is even stiffer than the suspension.

Or.......

I don't like the sound of feedback. I guess that you have already figured that out. I tend to build stuff that is full of discrete circuitry. Trying to find ways to add all that extra stuff onto a Class D amp module was a minor challenge. The next ones will have even more discrete circuitry. (Hint: it is either power supply, or input stages.)

Anything else that you may care to ask?

The Ayre amps use local feedback, sometimes called degeneration, and no loop feedback.

The Stasis amps had no feedback from the speaker output to the signal input, but instead had feedback loops applied to "building blocks".

The new generation of so-called "digital" amps (the self-oscillating varieties) do have overall feedback loops from the output to the modulator. Some sense current, some voltage, some both.

How do you figure it has to do with stabilising?? Stabilising what?

And which way do you use for marketing, and which for precision? By precision, do you mean THD numbers of 0.00001%? Seems to me that is done for marketing, as the amps in the mid-70s using that approach sounded rotten.

Some of us design it so that it sounds best to us. Whether others agree or like it is another matter. ("Some" being most every amp designer that I know.)

I don't know of any designer that looks to feedback as a solution to bias stabilisation in a SS amp. Lowering noise, distortion and output impedance, yes. Increasing bandwidth and input impedance, ditto.

Maybe the guys who design tube gear do, but I don't hang around with any.

But since this was supposed to be about a "historical look at amps", and feedback...........let me ramble on some about the stuff that I have done.

Mid 80s.......overall feedback, but much less than usual. Maybe 10-20 dB.

Late 80s.....no loop feedback in the voltage gain stage, loop feedback for the outputs. (Similar to Stasis.)

Mid 90s.......no loop feedback anywhere.

Early 00s........"digital" amps. Tons of loop feedback.

Looks like we have come full circle.

Someone asked me a question via e-mail that is probably too technical for everyone here, but.......

As I was formulating my response (it was about current-feedback vs voltage-feedback), some thoughts came to me that might help to clear up this "zero feedback" subject.

Let's put semantics aside. Whether "current-feedback" is really current feedback, or a special condition of voltage feedback is not the issue. I said "Hell, let's call it a bean bag amp.......anything, but we need to have an agreed upon term to call this type of amp."

The crux: "current-feedback" amps have a bandwidth that remains constant, regardless of gain. Traditional feedback amps do not: as the gain increases, their bandwidth goes down. There has to be a way to define this type of amp. It may not qualify as a unique situation, but it is very different in marked ways from typical amps.

And this leads to the "zero feedback" concept, as used by Ayre.

Amps without loop feedback.........any loop feedback.........have a distinctive sound. It is unmistakable. If you hear one side by side any other amp, you will understand immediately what I mean.

The issue here seems to be concern that Ayre is the one playing fast and loose with buzzwords, created just for marketing measures. I disagree. I believe that is others who are guilty of it, and perhaps Ayre is being cast in with them.

Here are some examples of ways to fudge "zero feedback" when it really isn't anything close.

Rowland, Threhold/Forte, and others (me, at one time) used an output stage that used a feedback loop around it, but had no connection to the input. So, overall feedback free? Yes. Zero feedback free? No way.

(If you compared one of our amps with the zero feedback output stage to the one with a local loop, you would have no difficulty hearing the distinct sound of zero feedback. I modded every one that I could track down, and every single owner liked the modded version. Despite higher THD and output Z.)

Ok......let's take the analogy one step further...............to say...........a Boulder amp.

Most use two separate gain cells, each one has a feedback loop around it. No feedback from one to the other. Now, overall loop feedback free, but definitely not feedback free!

Ok.....let's go the Eagle (Electron Kinetics).............

An integrator input, driving a transresistance stage. Feedback loop around from the output to the transresistance stage, but the integrator is outside the feedback loop. Again, overall feedback free, but nowhere near zero feedback.

Ok, here is one:

Someone builds an integated amp, with a typical amp that has a feedback loop around the amp stage, but a separate buffer for the preamp section. You could stretch the point that it is overall feedback free. No feedback from output back to input........just like the Eagle. I hardly think that anyone would believe that it would qualify as a feedback free design.

But that sounds exactly what Maxim is doing!

Here is an excerpt from the Maxim data sheet, and it does not sound like zero feedback to me.

"Since these devices operate without negative feedback, there is no loop gain to transform the input impedance upward, as in closed-loop buffers."

Ok.........sounds like no feedback from output to input. No loop feedback design.

They go on to make the same claim that there is no feedback to decrease output Z. OK, still sounds like no loop feedback.

But get this!

"The MAX4200–MAX4205 include local feedback around the buffer’s class-AB output stage to ensure low output impedance and reduce gain sensitivity to load variations."

Ah-ha! Caught in the act!

Well, the datasheet goes on to talk about the advantages of not being "closed loop". I agree with their assertions. But they openly claim that it has local feedback. What do we call it? Ok......no overall loop feedback, but they admit it has a local feedback loop.

So, as C. Hansen pointed out in his e-mail response, there is no agreed upon dictionary definition of what constitutes a feedback free design. Hell, engineers can not even agree upon what to call circuits that do have feedback. (There was a heated exchange on one of the DIY nerd forums months ago on the current- vs. voltage-feedback terminology.) How can we expect you guys to be able to sort out who is making bold statements about their gear, and who is just making b*** s*** about their gear?

Well, the only way to know who is telling the truth is to listen. I have not heard an Ayre design in around 10 years. But I can attest that it was definitely free of any loop feedback. I seriously doubt that stance has changed.

Ok.......so how can we tell, you ask?

To me, the front-back soundstage is the first clue. Designs without any loop feedback have much more separation here. Feedback tends to have the effect of compressing things from front to rear. The other things that I notice is that the bass "seems" to be more lifelike. Maybe not have the punch feedback amps have, but bass notes seem to be more lifelike, and each one stands out individually from the others. Heavy feedback amps may have serious "crunch factor" but to my ears, the bass notes tend to all sound the same.

Who likes which one, and why, means nowt to me. Just be assured that there are distinct differences between so-called "zero feedback" amps, and all other amps that do employ ANY type of loop feedback. What may sound like marketing hype, double talk, or just plain crapola could well be. Except in the case of Ayre. Their claims are an accurate reflection of their products.

Well, enough if that. I would rather exchange thoughts on why "digital" amps have to be more rolled off so that prospective customers won't kvetch that they sound bright. But, if you guys want to talk about other amp topics, I will do so as time permits. (I know that tomorrow is out, maybe evening.)

Ayre does not use any loop feedback. You don't have to ask them............

As for the sound of amps without global feedback: yes.

The amps we made in the mid-90s (where I got rid of the feedback loop in the output stage) really opened things up. It did sound much more lifelike, although it did lack that certain "punch" that is needed to make a product marketable to a wider market. Fortunately, we were able to find the small segment of the market that wanted something else in their amps.

As for the "closed-in" sound. Yes, that seems to be a direct function of lood feedback. I am not going to try to claim that I know why, but I know that is is true for conventional amps. I can verfiy this by taking the average amps, and lowering the loop gain. This can easily be done by placing a resistor from the collector to the base in the VAS (voltage amplification stage). Yes, the same place that you will find a Miller compensation cap. As the loop gain is lowered, the soundstage opens up, things become more lifelike.

And the bottom end and impact drops off............

(Modding amps this way lead to me to think "Why am I working on the other guy's stuff, and trying to fix the obvious problems? I can do better from scratch." So, I did. 20 years later I wonder what the hell I was thinking.)

BTW........I know from my discussions from those 2 guys who design C-J gear, that they spend a lot of time carefully changing loop gain, to where things just fall into place. Too much, or too little, things don't sound the way they like.

Now.......the obvious question:

Class D had lots of feedback. Yep. Bottom end and punch, right? Yep.

Closed in soundstage?

Nope. Don't ask. I will be the first to admit I have no clue why.

I registered as a manufacturer, and I initially thought that would have been sufficient. On my profile, there is no such indication, so any advice on how to better identify my connection would be welcome.

As Ross Perot would say: "I'm all ears."

Only problem with the first 2 suggestions........

I know of some people (on other forums) that make countless useless posts, only so that they can get their name in front of as many people as possible. Again.

I would rather not appear to be one of them.

Not many people are familiar with my company. We keep a low profile.

I think the best approach would be some sort of indicator for commercial posters. Maybe someone who knows the powers that be can suggest that. I do not want to e source ofd confusion, any more than you guys need any.

Do you guys have any idea how hard it is to NOT use any (local) feedback, anywhere?

Thought so.........

I know you aren't trying to argue. But it does get frustrating to us technical types when it seems like we speak, but no one listens. I know........maybe we don't put it in terms the layman can grasp. But all too often the layman's response comes across to us as it is us who is the one that "no capisce".

OK.......let us look at some very elementary building blocks, and you will understand what I mean. I hope.

Almost all SS amps use emitter-follower outputs. Even ones that use what is called a "complementary feedback pair", like Rowland and Threshold/Forte used in the 80s, still have an emitter follower at its core.

The emitter follower, but its very nature, has 100% local, degenerative feedback. Simple as that. Followers are all over the place in a typical amp. Even ones with ICs, use lots of them. A very handy building block. Sometimes it used to amplify current (output stage), sometimes to isolate stages or even just to shift voltage levels. So, any circuit with one in it anywhere has feedback.

Obviously.......it is local, not loop. That is the point that the guy from Ayre was trying to make.

Another example:

Take a single 1 transistor circuit......make an amplifier with it. Well, to do so, you need to stick a resistor in the emitter leg in order to bias it on. Guess what........more local feedback.

You say that you don't want feedback there.......ok......here are your options:

Take the resistor out. Connect the emitter to ground. Great, now you have something that won't bias on in a linear manner. You have what is called a Class C amp. Great for RF, useless for audio.

Bypass the resistor with a capacitor. Fine, except that it won't look like 0 ohms at all (or really any) frequency. So, there will always be a small amount of local feedback.

Come up with some bias scheme that allows the emitter to be at ground wrt AC, but not DC. You need 2 supplies......and what eventually ends up is you take the easy way out and make a differential amplifier. Ok......great.....now you have done away with the local feedback, but to make something functional, you have to apply loop feedback if want it to incorporate it into an amp design. Or apply local degeneration to make it work without overall loop feedback.

Now.....if you really want to get confused.......get a couple of amp designers with very different views and ask them if they prefer voltage feedback or current feedback. One guy will claim that current feedback is a made up term, that what the other guy calls current feedback is really voltage feedback. No, the other will claim that current feedback does exist, and that it is something that is used in conjunction with a certain topology that is characterised by bandwidth that does not change with gain......etc., blah, blah........enough squabbling to drive even me mad.

In that case, I would have to side with the layman and tell both of them to shut up. But I would not suggest that either try to run for political office. If they ran against each other, we would have to find some way to void the election, since one would have to win.

(Amps using "current feedback" have been made. Analog Devices has a paper called the "Alexander Amplifier". You can find it on their site. Rowland made an amp using that scheme.......Model 8(?), maybe. I made a CD player that had a current feedback circuit inside. The dealers hated it, and I almost lost all of them.....a story for some other day.)

But back to the original subject.......historical look at amps. You would need to include "current feedback" types to have a complete perspective. Another subject of discussion could be bandwidth........how much does an amp really need, and does it help? Some amps......Spectral........have tons of bandwidth.......and some will say that they sound bright as a result.

(BTW.....if you do build amps with overall loop feedback, the more bandwidth, the better. It just gets very hard to increase it beyond a certain point. No sure how Spectral does what they do, except the designer is a sharp dude.)

I bring this part up because I have found that Class D amps, with the same bandwidth as a typical SS amp, will sound bright to almost all listeners. You have to lower the bandwidth to make it "sound" the same. Honestly, I am not sure why. On one hand it is interesting, the other frustrating as hell for an amp designer.

The next rung??? Don't know that I would characterise it that way. I would say it is just another branch on the tree, and trust me, I have climbed all over it.

OK.....at this point someone scratches their head and goes "Doesn't this guy make digital amps now? Did he abandon "zero feedback?"

Yes, and no.

Making "digital" as a way to segue into the HT market. "Zero feedback" designs are not going to go far there. At least not for amps. Small, light, efficient, powerful, lots of "oomph"; Class D is the way to go.

As for anything else that we make.......still has "zero feedback" inside. In fact, a lot of "zero feedback" thinking in the auxillary parts of the "digital" amps.

One thing that has been missing so far is the role of transisor evolution in all of this. Most of it is way too technical, but there are a few major developments in transistor design that have led us to where are. And a few side branches, like MOSFETS. Not only do they allow for kilowatt Class D amps, but different processes led to amps like the Acoustat line (and others) which found favor with electrostat owners. The Trans Nova series comes to mind.

Yes, the intrinsic emitter resistance does constitute local feedback, but I was trying not to get too technical.

Ok, speaking of emitters and such, the development of "ring emitter" transistors lead to a radical change in transistor design. Back when I started getting serious about amp design, you had 2 choices: RCA and Motorola. RCA (for whatever reason) did not make high-power PNP devices. Motorola did. With those, we had amps like the SWTP "Tiger" series. A bit unstable, but probably the first step towards modern amp design. Even then, the transistors were made with diffused processes, and were not the most rugged in the world. Eventually, they learned how to make epitaxial processes, and things started to take off. Some firms, Bedini as example, stuck to using only NPN devices in the outputs.(The RCA approach.) But most everyone else went to complementary devices. However, out of that grew the 0.000001% THD wars, and the resultant bad sound.

(Looking back......in hindsight......there may not be a convincing reason to use complementary devices in closed loop amps. Remember, the little 20 watt Bedini did sound good.)

I suspect that the guys who came up with the ring-emitter concept were probably used to designing RF transistors. Sanken, Toshiba, and Fujitsu all had strong contenders. Linear, fairly rugged, and perhaps most important: low capacitance. This allowed designers to push the bandwidth higher, as we were all concerned with TIM, SID, and a host of other "new" mechanisms that we were becoming convinced explained why our amps all sounded like doo-doo. Somewhere, things had gone horribly wrong.

To me, the thing that really got my attention was not only the linearity and low capacitance, but the new packing concept. WOW! You can bolt the transistor to the heat sink, on the inside, bend the leads 90 degrees, and hook it right to the PCB! No more drilling hole through the heat sinks, using nasty sockets, steel cases with screws going through them to make electrical contact, etc.

But let me pause and give praise to the guy who may have been the first to "think outside of the box", when it came to using ring-emitters, and in an entirely different manner.

John Iverson.

Not only did he incorporate the new transistors, mounted in a different manner, but he came up with an usual input stage, followed by an even more unusual gain stage. I had not seen anything like it before. He refined the gain stage somewhat in the later versions of the Eagle amps.

OK......what was so great about it?

Some will argue, but transistors are basically current controlled devices. (Yes, you have to create a voltage to have current......not the point here.) If you think as the input/control signal as a current, and design with current linearity, not necessarily voltage linearity, as the parameter to optimise, you come up with ideas that have not been used before.

At least not in audio power amplifiers. I suspect John may have worked on some military/government electronics somewhere in his career. Regardless, guys who thought like him gave us things like folded cascodes, and other techniques that increased both linearity and bandwidth.

The more linear it is to start with, the better it will sound if you use feedback to lower it. Likewise with bandwidth: the higher you can get it, the more stable an amp should be.

So, a lot of factors came along that made it easier to build amps that were inherently more linear than the junk we designed in the 70s. Some of us decided that designing by specs was even more meaningless than the rest of the crowd, and we got rid of all the loop feedback. But none of it would have possible 25-30 years ago. The semiconductors did not exist, we had our head(s) screwed on backwards, and it took some cock-eyed ideas (which may have been invalid!) to get them oriented back in the right direction.

Actually......now that I think about it......Audio Research was on the leading edge in SS design with the notoriously unreliable D-100. It used a "zero-feedback" output stage....what was it...mid 70s?......long before anyone else thought of that concept. (The problem was mostly a heat sink issue. The amp could have been reliable with about 2, maybe 4, times the heat sink surface area.) The input stage may have been bad.........I don't know, the modules were potted, but the output stage concept was a good one. I know..........I have used it the last 10+ years. With decent transistors on much larger heat sinks.

OK.....that ought to be enough to digest for a while. I appreciate the encouraging e-mails. Thanks.

Vince......don't start again, ok?? I have too much research on this subject to be off my rocker. Remember, I have building stuff commercially for around 20 years. I am not some young upstart just getting his feet wet. We all know that Henry's amps sound just wonderful on your Apogees. Great. We are happy for you. I doubt that you have dragged a half dozen or so amps, of varying topologies, to as many different systems as we have. Trends emerge........

Well, I can not speak for C. Hansen. I do not know his motivations. I can only surmise that his inclusion of the Maxim part was to show that there really isn't any dictionary accepted definition.

As for how I know.........

At one time, they had the schematic silk-screened on the inside of the lid. I listened to it. Confirmed what needed to be confirmed. Besides, you see someone at CES or RMAF......you talk; you know someone who used to work there; you seem to have a lot of dealers in common; lots of ways that stuff gets around. None of us design in a vacuum, and secrets have a way of not staying secret. I had a dealer in Chicago once call me and 'fess up that he may have been the one who gave Mark Brasfield the idea for a transimpedance amp as an I/V stage. After he heard mine, and I 'splained how it worked. I dunno.......maybe Mark came up with the same idea on his own, just 6 moths later.

Is that both clear and evasive enough? I'm thinking of running for office! Actually, I am fixin' to head out into the hot Texas sun, and bake what little is left of my brain. If I don't return, you will know why. Just look for my dry, withered body..........

Listening to all those bright Class D amps has made me bonkers to start with. It's a joke.......you're supposed to laugh, ok. It won't kill you. Try it.

Maybe when I return tonight, I can relate a story about a buddy in the speaker business, who had a hard time deciding on the tweeter level on his new creation. Seems that he had to change it 0.25 dB depending on what brand of SS amp he listened to it on. And this was before Class D! Wonder how is faring now........I'll have to send him one and drive him over the edge! (Yeah, another attempt at humour.)

I did not say that I heard them at a dealer.

I sent them to guys who had aleady brought one of those models in to audition. And sent them back, unsatisfied. There are a few times when I found someone who actually owned one of those brands. There is a big difference when doing a serious side-by-side comparison, as opposed to a "shootout", where there has to be a winner and a loser.

Actually, you may recall, I didn't buy their explanation why they preferred ours over the others. Some guys get carried away exaggerating minor warts. The guys that I placed the most faith in their reasoning was the ones that said they all sounded very close, but chose ours for other reasons. Features........ease of use and interfacing.......looks, whatever. As grateful as I am when someone thinks ours sounds better, I tend to dismiss their enthusiasm when it overflows with superlatives.

I know the Gallo isn't planar. Strangest looking thing I have ever seen.

No, I am not doing a Google search, because I know the truth. I have to.......I build this stuff.

Honestly, I do not see why you seem so defensive. I have not maligned Henry's, or anyone else's, efforts on this genre of amps. I may have a different opinion wrt their pros and cons. They may be among the best we have to work with at present, but I seriously expect that we will have many other options in the near future. And you can rest assured that I will be just as honest and forthcoming about them, at that time.