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.

Well, it has been very informative but I think my time spent on this topic has come to an end. I still think Ayre is being deceptive by using the term "zero feedback," but unless we get some more information on their amplifier design I'll never know for sure. Ayre never responded to my email asking them to clarify and I did not expect they would.

I sure don't expect Hansen to jump in at this point and clear it up even though you can be sure he is watching this thread (I'm suprised he answered Keis' question at all even though it didn't tell us anything), and Ar_t evidently knows something that he can't or doesn't wish to share about the design. I understand that.

In any case, thanks for the history lesson Ar_t. I know more about amplifier design and the business of bringing them to market now than I did a few days ago so I suppose it was time well spent.

Ar_t you won't find the H2O at a dealership, nor the eAR. Being they are rare, the odds they both are in the same room with your amp, and a Rowland, sounds like the stuff of fiction. Who, and how, did this shootout come about?

Let's settle this. Send your amps to California for review. I will pay shipping both ways. What have you got to lose?

BTW, The Gallo is not a planar, neither is the Meadowlark, nor German Physics... etc. etc. Like I said, do a search.

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.

agree, Herman, time to exit this thread.

Ar_t has been very helpful in revealing the dark secrets of amp design. I don't know if this "So why do you feel threatened when I tell the dark secrets of the world of amp design." was directed at me of Muralman1? IFFF it was directed at me, I'll say that I am not threatened in the very least. Au contraire, I stand to gain a lot more knowing the info shared in the thread. Your having 20 years of product design doesn't diminish my capabilities one bit. In fact, we can talk at the same level, which might be enjoyable.

Anyway, what should have been learnt from this thread is that manuf will do the bare minimum to disclose aspects of their design. Even good/very good manuf held in high(er) esteem by consumers. There is no standards committee in this audio consumer market that'll keep them honest. The only people who can do this is, us, the consumer. This will happen ONLY if we consumers are educated enough to ask them pointed questions that'll give us an idea of what the manuf might have done inside the product we are about to spend a ton of cash on. Like Ar_t said, if someone is putting down $3K on audio gear, expect some serious questions to be asked! Not unreasonable.
Also, don't simply eat hook, line & sinker what the manuf has to say about his product. Ask some serious questions. Try to understand their implementation.
By keeping manuf-consumer loop closed, both parties will benefit - we will supply feedback about their products, keep them honest & let them know where their performance is sub-par. Hopefully this will not fall on deaf ears & they'll make products that we are seeking using the best possible methods to implement them. You want audio to be around, we'd better help each other. No other way out. (you do this at your place of work with your suppliers, correct? why is audio any different?)