Sound Quality Vs. Measurements

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The Quad 405 would hardly be described as a high slew rate amplifier . It's rather special use of feed-forward and feedback was said to make it imume to problems caused by the output filtering of CD players to the extent some removed the filters . It was said the Quad wasn't in the least bit troubled if doing so . I know Quad did use a far bit of bandwidth limiting , does anyone here believe feed forward would eliminate some slewing problems ? Some argue around that whilst not saying it categorically .
 
We measured the Quad at 35V/us.
However, the most interesting point made here (to me), is the mention of Keith Johnson, and his design philosophy. Just yesterday, I told my new tech (19 years old) that if there is someone I fear will beat me in the audio design race, it is Keith Johnson. He is DRIVEN, like I am, to make the best audio possible. Most either do it to make a living, or just for fun. I have known Keith (distantly) for more than 40 years. He is VERY competitive with me, a little too much for comfort, sometimes.
 
but it would probably not get him any further sales, and MIGHT cause harm, especially if you get a reviewer who, for some reason, takes a dislike for the product.
I was thinking just that.

Charles Hansen is like that with TAS, at the moment.
interesting, that's why I don't take reviews too seriously.
 
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I don't think that Keith is afraid of a component review, but it would probably not get him any further sales, and MIGHT cause harm, especially if you get a reviewer who, for some reason, takes a dislike for the product. Charles Hansen is like that with TAS, at the moment.

Spectral's systems approach flies in the face of a lot of audiophiles who want to play with mixing and matching, and generates resentment. I know a few who are quite negative about Keith and Spectral as a result, although even they have to acknowledge that he's made great recordings.

It is nice, though, to see Keith having been otherwise recognized, and presumably well-off after the sale of Pacific Microsonics to Microsoft. He was quite paranoid about his ideas being stolen back when I met him, through an acquaintance, circa 1979. I may have even put a bug in his ear then about settling time, or when I discussed it he may have merely been coy. I hasten to add that my application of it, of the settling behavior in general rather than just the speed/accuracy, to audio, was purely speculative then --- I wasn't doing audio other than incidentally. I made the distinction between data acquisition apps where one just had to be sure of the signal just before and during digitization, and what I presumed was true of audio, where the details of "getting there" were also of importance, in the sense that we may hear them.

Brad
 
funny you should mention Keith Johnson, I found about Spectral only recently. haven't listened to their amps but my gut tells me there must be something special about them.

Yeah - their astronomical price. :D :D :D Just kidding, although their prices are, shall we say, steep?

concerning settling time it would make all the sense in the world. but there's one thing that negates that (again I have to agree with Mr. Curl wrt that aspect): oversampling filters in most DACs seem to do way more harm with their pre- and post-ringing. some filter types minimize those artifacts but still you can't eliminate them completely. my DAC is based on the WM8742 and it has user-selectable filters (5 of them). I was curious to look at the output of the DAC on a scope with square waves and none of the 5 filters looked nice in this respect. yes, I know, what one actually sees there is a band-limited square wave that can't possibly look any other way once it's band-limited. but what should be noted is that (correct me if I'm wrong) I think settling time-related artifacts in an amp are generally much less severe.

Well, it's not like you HAVE to use them, you know. You can buy real time DACs, which use 8 parallel DACs and have no oversampling and no digital brickwall filters. I won one, not at all very expensive, but sounds way better than most CD players I have heard.
 
We measured the Quad at 35V/us.
However, the most interesting point made here (to me), is the mention of Keith Johnson, and his design philosophy. Just yesterday, I told my new tech (19 years old) that if there is someone I fear will beat me in the audio design race, it is Keith Johnson. He is DRIVEN, like I am, to make the best audio possible. Most either do it to make a living, or just for fun. I have known Keith (distantly) for more than 40 years. He is VERY competitive with me, a little too much for comfort, sometimes.

Well, if I am anything to go by, I have heard one of yours and one of his, both power amps, and by chance, both driven from the same source, at the time a darn expensive Luxman preamp, I forget the model designation. I know I got a headache when I heard the price. :D

Frankly John, I'd be hard pushed to declare a winner. I think those were two takes on the same theme, each with its strengths and small shortcomings, at least the way I heard them in that particular system (not mine, but one I do know rather well).

I didn't have to choose, so I was spared the soul stretching making of a choice between two products I both liked.

My point is, I don't think it's about either of you being better than the other, you are simply two men with a personally clear cut take on what you want, and you go for it. I find this to be of crucial value, I've seen and heard far too many designs with which it was not at all clear what the designer actually wanted. Indecisive, so to speak.

You know what I mean - some sound subdued, others sound bold and forthcoming, some sound like they don't give a hoot about music, others are almost begging for more, some try not to offend, other try to sound full of energy and forthcoming, etc. It's that somewhat vague feeling you get in your gut when listening critically (meaning only listening and doing nothing else besides except sipping good coffee and puffing a good cigar), one which you can't put into simple words because true quality products can NEVER be described in a few words.

So, I agree that Keith Johnson is in your league and is therefore true competition, but I don't think you need to worry just yet. On the other hand, aren't James Bongiorno (Ampzilla 2000, unfortunately haven't even seen it) and Dan d'Agostino also your true competition as well? Can you name just one field of human economic activity where there is no competition?

I have never met in person any of these folks, but I have corresponded with James Bongiorno for some time a few years back, and I can tell you that just like you, he is a man with a very strong opinion and a clear cut outlook on things audio - which, just like with you, includes some looks at some of the "new fangled" ideas of today. :D :D :D Heck, I even got a via-Internet interview from James, something that not many have managed to do, as far as I know.:p

I have to say this - he has NEVER ONCE left me without a complete and timely answer to any question I had. Why should he? He knows that I will never know what he knows about the subject, by the time I get to his level, he'll be light years ahead of me. Of course, out of respect, I tried very hard not to ask anything regarding his current models, or things which need a book to be explained. But I am grateful for his time and goodwill.
 
you have no idea how fascinating this is to me.
if there is any audio brand I'd buy before listening it's Spectral. IDK, maybe some subliminal marketing techniques are having an effect on me but...
talking about fetishism LOL

Spectral is very, very serious stuff, no doubt about it.

Even after hearing just one of their products,a power amp, that much is quite obvious.
 
And despite the high prices, how many other audio power amps can you use intentionally as an AM radio transmitter?

You got me there, Brad.

Although I have no idea what would I want an AM trasmitter for. :D Intentionally or not. :D

Out here, you go to jail if you own an unregistered transmitter of any significant power, and if you don't have proper permits from the local equivalent of FCC. Not hard to get, but you have to get them.
 
dvv said:
Well, it's not like you HAVE to use them, you know. You can buy real time DACs, which use 8 parallel DACs and have no oversampling and no digital brickwall filters. I won one, not at all very expensive, but sounds way better than most CD players I have heard.
The anti-aliasing filter at the record end will add ringing to a square wave, so you will see it at the DAC end whatever you do.

If, on the other hand, you are using a 'digital square wave' then you have to remember that this will never happen in real life because it would never make it through the anti-aliasing filter so it is hardly a fair test.
 
Keith Johnson uses some quite strange language, and concepts to describe what he's after, but the end goal is squarely where I come from:

The faster the transient-settling time in a system, the more easily you can reach in and pick out tiny details in an otherwise very big sound. For some reason - and I don't know exactly why - the staging usually appears wider when the speed and the settling is better. That seems to give a bigger perceptual window to reach in and hear fine detail. In other words, if the stage is small, then everything sounds cluttered in a small space.
The other factor you get with speed is lightness. The music can have a tremendous amount of high frequency energy, and yet you don't feel assaulted by the energy. It can be very bright, yet not at all harsh or hard to listen to - exactly the way a live instrument is. If you tried to reproduce a trumpet at a live volume, you couldn't stand to be in the room with the loudspeaker unless you get the speed issues right. With high-speed circuits, the harshness goes away and the bloated character is gone. It sounds lighter.
That's precisely what I look for, except the notion of "speedy" circuits makes me go, ehhh? Except, if you translate that to low distortion results; too much distortion = "heaviness", blahhness of sound ...

Frank
 
Keith Johnson uses some quite strange language, and concepts to describe what he's after, but the end goal is squarely where I come from:

That's precisely what I look for, except the notion of "speedy" circuits makes me go, ehhh? Except, if you translate that to low distortion results; too much distortion = "heaviness", blahhness of sound ...

Frank

With all respect, Frank, but I don't find anything strage in what Keith said, I think I understand excatly what he's saying. And obviously, I agree with him, at least in good part.

I also believe in wide bandwidth, which is probably obvious from the fact that I pay much attention to what Harman/Kardon does, and the late Bernard Kardon was THE wide bandwidth proponent.

What is missing from Keith's comment is how was this wide bandwidth achieved. Was is through inhrenetly wide bandwidth design, with an open loop full power bandwidth of say 100 kHz, then aided by relatively low global NFB of say 20-26 dB, a mix of more modest open loop bandwidth and more global NFB, or the traditional way, with lots of global NFB?

Harking back to the German LAS amp I posted some time ago, it's open loop bandwidth is just 4 kHz or so, the rest is about 49 dB of global NFB to make it hit the 1 MHz point, after which it was christened "Mega 1". No matter the fact that this particular model manages to pull this stunt off very succesfully and to sound good in the end, this is an exception rather than the rule.

On the other side of the scale, we have Matti Otala's 25/50W into 8/4 Ohms amp from 1978 (I think? Not sure about the year), which had an open loop bandwidth of 100 kHz and used only 20 dB of gobal NFB to get it to the same 1 MHz point. My own H/K 680 integrated, their top model in 1999, goes down the same route, as its 12 dB of global NFB allows it to hit 300 kHz (less bandwidth, true, but also less global NFB with less overall THD than Otala's model).

It's a question one always has to ask oneself when faced with a very wide bandwidth amp.
 
The anti-aliasing filter at the record end will add ringing to a square wave, so you will see it at the DAC end whatever you do.

If, on the other hand, you are using a 'digital square wave' then you have to remember that this will never happen in real life because it would never make it through the anti-aliasing filter so it is hardly a fair test.

Frankly, I never bothered to test the outboard DAC. Never felt the need to do it because right out of the box, as is, it provided me with very high quality sound, even if its output stage is a lowly AD 847 op amp.

In other restepcts, I find it has been done by the book - separate power supplies, from the rectifiers onward power regulated power supplies (using 7815/7915 3 point regulators and some good quality Sanyo capacitors of no small value, 3,300 uF each I think), etc.

In esence, it manages to convey a feeling of freedom of the music, so to speak, an unforced quality where it almost literally flows. I expect my hearing has adjusted to it over the years, and I have become hard to please CD player wise, ever since then. It does what it does with flying colours, I think.

I bought it on line (my first ever) from a crew from Australia, and I believe it's the best spent audio money I ever did. $250 has sure bought me one hell of a lot of audio quality. Or so I feel.

Because I feel that way, frankly, I have left all the arguing, testing and figure bashing to others less fortunate.
 
I found this an interesting read on slew rates .

DF96 might not agree about distortion due to feedback at the end of the discussion ?

Slew Rate etc.

Last night I went to a BBC recording of Beethoven , Britten , Mahler ( arr Britten ) and Poulenc the Gloria last night . The Beethoven was more like 78's or the 1944 German recordings I posted . Stunningly beautiful . Not lacking in treble , just endlessly soft . It will be interesting to hear the recordings . The Poulenc was in surround sound almost as the choir was very large . Spaced pair on strings ( about 8 feet above the conductors head ) , 4 ribbons ( ? ) for the choir . About 8 fill in mics .

Very interesting that John has measured the Quad 405 in the past , I was a little surprised how fast it was . My friend has one . I must do the without CD output filter test if satisfied no tweeter destroying nasties are coming out . It is an inverting amp , the friend who owns it refuses to try it in correct phase .
 
It beats me ! I did notice in some set ups it sounds boomy if in wrong phase .

If anyone reads the Slew PDF I would be interested if anyone supports using Complimentary Feedback Pairs for the LTP input . The writer of the PDF uses a single input CmfbP if my memory is correct . The design I like is 90% the original Hitachi amp , 10 % me . I like the fact it gives 100 W and near op amp distortion at 50 kHz with only 7 transistor devices ( Hitachi , mine 10 ) . The pair I probably will use are 2SA1085 and 2N2504 . I recently tried a cascode VAS . It was no better and no worse .That is important as suitable transistors are now rare . 2 x 2SD756 + 2 x 2sB716 replaced by 2 x BC550C+ 2 x MPSA 42 + 2 x MPSA 92 . If was fantastically stable .
 
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