Give me ultimate proof...
Printed From: Graham Slee Hifi System Components
Category: Headphone Audio
Forum Name: High Fidelity Headphone User
Forum Description: Technical Q&A, hints and tips
URL: https://www.hifisystemcomponents.com/forum/forum_posts.asp?TID=158
Printed Date: 27 Mar 2026 at 12:15am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: Give me ultimate proof...
Posted By: Graham Slee
Subject: Give me ultimate proof...
Date Posted: 12 May 2008 at 6:38pm
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@dvv, or anybody else professing a knowledge, this is my challenge: Give me ultimate proof beyond all doubt that; 1] there is such a thing as damping factor (I never heard about it in broadcast audio!) 2] and therefore prove the case that headphone amp output impedance must be some fraction of headphone impedance. I will expect a proper mathematical argument that is not subjective in any way. I have thrown down the gauntlet. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Replies:
Posted By: Graham Slee
Date Posted: 13 May 2008 at 8:29am
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Ah well, 14 hours have passed by so I guess there must be other pressing issues affecting the technical minds of this community, so I'll start us off... What is the impedance of the load? Is it pure resistance? If it were pure resistance then there would be no need for this imaginary thing called damping factor? If it is not pure resistance then how do we express the load's impedance? If we don't know the thing that isn't pure resistance how do we express this other thing? Maybe we don't know what this other thing is? What does the mathematician call something that is an unknown, or something that in itself is unsolvable? An example of an unknown or unsolvable number is the square root of minus eleven! Try working that out! It is however, a number. So how does the mathematician account for numbers like that? Imaginary numbers! Have you ever seen the notation j in a mathematical formula? Therefore, if the load isn't pure resistance, and this other part of the impedance is not known we call it j. And so the load resistance can be expressed as jx Ohms. (x being the real part) Somebody willing to take it from here? ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Guests
Date Posted: 13 May 2008 at 9:31am
It's a lorra, lorra years since I took GCE "O" Level maths and physics  so I'll leave this to others  .
Meanwhile I will continue my search for a pesticide that I can legally use to control red ants in customers lawns. Strange that nothing is cleared for such use!
Graham, you have your concerns with the good ole EU, but they are are making my job a misery too
 Adrian.
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Posted By: Dave Millier
Date Posted: 13 May 2008 at 9:59am
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Graham
Are you mis-representing imaginary numbers and complex mathematics on purpose to suit your thesis? I'm sure you know perfectly well that the square root of -1 (i) is *defined* in mathematics and there is nothing dodgy about complex maths.
As to how this related to "damping factor", I haven't a clue.
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Graham Slee wrote:Posted By: Graham Slee
Date Posted: 13 May 2008 at 3:38pm
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Read it again David, "square root of minus 11" Damping factor is expressed as load impedance over output impedance, Zload/Zout. Assuming Z = resistance, we are given glib results based on nominal loudspeaker impedance. But the loudspeaker is far from a constant Z, more like jZ, and inside the audible spectrum. Therefore damping factor is one of those terms invented by hi-fi, which serves no purpose other than showing off. It was probably conceived to explain to the average man how output impedance compares with load impedance, but it hasn't worked, going on the number of inquiries I get about cartridge matching and matching one piece of equipment to another. The result is most people think that the higher damping factor can stop the mechanical forces of a loudspeaker dead. Not the case in my observations. And if it can't do it for a speaker it can't do it for anything. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 13 May 2008 at 3:47pm
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PS. My error, I was educated using j instead of i (perhaps j was too Jehovan?... )  ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Dave Millier
Date Posted: 13 May 2008 at 5:21pm
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I'm afraid "load impedence" and "output impedence" are as much of a mystery to me as damping factor as I know nothing about electronics!
But I take your point about loudspeaker impedence. I've seen graphs from the old days of Hifi Choice when they cared about such things that showed loudspeaker impedence going all over the place. One reason for claiming that power amps needed 50amps of peak current output I seem remember - why was the NAD 3020 better than 200W behemoths? Current delivery. Or so they said. Must have been right then ;-)
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Posted By: Graham Slee
Date Posted: 14 May 2008 at 8:52am
So right that people reach for their cheque books, spending £15,000 in one go I'm told. Yes the man with the beard - he probably had spectacles and a false nose too, but my friend didn't notice... Tell me Dave, what is the time period used to determine the peak current? I'd be very interested to know. I think I've got some math somewhere to work that out - something like dX/dY... "If you go down to Willow Farm........... " ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: stuxter
Date Posted: 14 May 2008 at 9:23am
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........."to look for butterflies, flutterbyes, gutterflies Open your eyes, it's full of surprise, everyone lies" |
Posted By: Graham Slee
Date Posted: 14 May 2008 at 6:15pm
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...."like the fox on the rocks" (the cinema [Roxy] or TV news [Fox/Pathe...]) ...."and the musical box" (the radio) ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: stuxter
Date Posted: 14 May 2008 at 9:09pm
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Touch`e Mr Slee
you know the old saying....
"As Sure As Eggs Is Eggs"
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Posted By: dvv
Date Posted: 14 May 2008 at 10:53pm
Blimey, I just noticed this thread ... 
Graham, since you asked the question, we can argue and argue, but the simple fact is that if I use my Sennheiser HD595, or my Sony 270, or my Grado cans on a headphone amp which has an output impedance of approximately 1 Ohm, the bass above all sounds tighter and better defined than when I use the same cans on amps with an IEC recommended outpit impedance of 120 Ohms.
If I use my AD826AN based headphone amp which has current boosting transistors, namely a BC 546B driving an MJ15030 and a BC 556B driving an MJ15031, AND which has an LF411 based DC Servo circuit, I get an overall clearer sound.
I believe, or if you prefer I choose to believe that this is no freak accident, no great stroke of luck, and no God's little finger pointing at me, but rather the fact that I do possess a reasonable damping factor of 15:1 into 30 Ohm cans, and the fact that there are no nasty capacitors to muck around with frequency and phase response.
Now, you can choose to consider all this pure drivel and hence disregard it altogether, or you may choose to investigate. If you do choose to investigate, then by all means do try a balance knob as well, you could find it well worth the effort and the extra expense. And if you want to hog it, try a L+R switch as well, it's a wee little thing, but it does so much.
In a few days, I'll be turning 55 and I no longer have much of a stomach for theorizing, I turn more and more towards hard practice - implement it and see what you get, you'll do the maths later. As if anybody gives a damn about maths, which can become far too abstract far too fast, the customers are especially keen on the maths.
Speaking of maths, have you ever in your life experienced the mathematical rule that a minus multiplied by another minus will produce a plus? I haven't, and in hard fact, it is my experience that if anyone does someone one wrong, he will be paid back by a far greater wrong sometime, somewhere, somehow. Quite the opposite of math, don't you think?
Not being belligerent here, simply avoiding what I feel is an essentially useless argument, in which you will hit me with a lot of formulas, and I will slug you by constantly saying "Been there, done that, it sucks". No future in it.
Case in point - I just got back from a demo. I DEMONSTRATED to a hard core tube fellow what a simple, text book unity gain buffer based on an AD826AN can do for his beloved tube sound; he took it like a man.  A very nice fellow, actually, or I wouldn't be wasting my time. Tubes and op amps? How pervrese can you be? Next to me, Marquis de Sade is still in the kindergarten.  ------------- True audio lives on the fringes of the industry. |
Posted By: Graham Slee
Date Posted: 17 Jun 2008 at 2:21am
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The trouble with the AD826 is that it cannot drive the capacitive load of even the tiniest driver transistor. It can do 186pF on a 7.5V peak excursion, anything heavier than that and it will bandwidth limit which means heavy input filtering or a spike in the HF response which the much slower transistors won't like, unless you opt for ultra high distortion by excluding them from the NFB loop like I see one of my competitors does (and with a different op-amp). The suggested output transistors (or anything similar) would not give sufficient Hfe for the small current demands of headphones for the 546/556 to be operated at low enough current to keep their input (base-emitter) capacitance down, and values between 1nF and 10nF can be expected - more that the 826's 186pF. This is partly why we stopped using it in headphone circuits. It is however good in some of our phono stages because the EQ network slugs the peak. I recently repented from my anti-spice model stance and I learned quite a bit about what I'd calculated on paper in a new light. Somehow we get more high fidelity the further we distance ourselves from hi-fi. Maybe one day folk will realise...? However, the MJE15032's would make a very good 20W amp for loudspeakers given a good discrete voltage amp and pre-drivers. I think we'll be working on that next. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 17 Jun 2008 at 2:29am
You mean X=X as not in X=Y which many would have it in HI-FI-FO-FUM... ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: stuxter
Date Posted: 17 Jun 2008 at 8:03am
3 eggs - 0 eggs =3 eggs 
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Posted By: Graham Slee
Date Posted: 17 Jun 2008 at 10:07am
Somebody will argue it isn't  ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: stuxter
Date Posted: 17 Jun 2008 at 10:48am
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Yeah.. and i think i know who that somebody is
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Posted By: Graham Slee
Date Posted: 29 Jun 2008 at 8:36am
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Courtesy Headwize http://www.headwize.com/faqs.htm#amp - http://www.headwize.com/faqs.htm#amp"Is an amplifier's damping factor important to headphone performance?
However, even if the theory were correct for loudspeakers, its applicability to headphones is suspect. John Woodgate, a contributor to The Loudspeaker and Headphone Handbook (1988), had the following to say about the effect of damping factor on headphone performance:
However, the source impedance affects the *frequency response* of a loudspeaker because the motional impedance varies with frequency, and thus so does the voltage drop across the source impedance. This means that the source impedance (including the cable) should be less than about one-twentieth (not one two-hundredth or less!) of the rated impedance of the loudspeaker, to give a *worst-possible change* in frequency response from true voltage-drive of 0.5 dB. The motional impedance of headphone transducers varies very little (or should vary very little - someone can always do it wrong!) with frequency, so the source impedance can be high with no ill effect. The IEC 61938 international standard specifies that headphones should be driven by a 120 ohm source - regardless of the impedance of the headphones themselves. If the headphones were designed to this standard, then an amplifier's high output impedance should have little effect on the sound of the headphones. In general, headphones with a flat impedance curve over the audio range will not be affected by high output impedance. For example, in May 1995, Stereo Review published a review of the Grado SR125 headphones. The impedance curve of the SR125s, which have a nominal impedance of 32 ohms, varied from 31 to 36 ohms over the entire 20Hz to 20kHz spectrum. Not all headphones may be as well behaved as the Grados, but neither do they usually have the roller-coaster impedance runs of a loudspeaker. Tube amplifiers (with their high output impedances), it should be noted, have very low damping factors."
------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: dvv
Date Posted: 02 Jul 2008 at 9:35pm
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Graham, just because somebody in office feels something is like whatever, I don't necessarily have to agree with him. Nor does the fact that he is in office make him automatically right, a simple fact of life far too many bureaucrats naturally forget very quickly.
Personally, I define the damping factor as the difference between the output impedance of a device and the work load it has to drive. I do believe that is the text book definition, but I could be wrong.
As for its real life effects, things are not quite so simple. It may or may not be real, or even exist, depending on who you ask. If you should by chance ask me, I'd tell you that I don't know for a fact that it actually exists, but my ears tell me there is a simple threshold of a difference, approximately 15:1 or so, which if present appears to provide somewhat more clarity overall and definitily a tighter and better controlled bass.
But I would also surely point out that this is a general rule only, because it is not at all unimportant HOW that damping factor was achieved. You and I know, but for the sake of those who are not in this business, a high damping factor may be obtained by desiging a very high quality stage which is very linear before any negative feedback is applied and consequently needs very little NFB, or it can be designed in 15 minutes, in which case it is likely to require quite a lot of negative feedback, which will also reduce the output impedance in the process, providing for a crazy damping factor (someting like 2,000:1; yes, I have seen that claim as well).
As for AD826, well, I have been telling you that such a high quality op amp DOES need current boosting trannies a bit over what you used. To linearize the output stage even before feedback, I use a small signal driver, typically MPSA 06/56 (they are all but indestructable), driving larger brother MJE 15030/15031. BAT85 diodes do the polarizing work damn well.
That's when I use op amps, usually because of space constraints. When I have thing all going my way, I stick to discrete designs. I realize this is not very convenient for you for reasons of available space, or budget for that matter, but I cannot resist the results if some care is taken. Such as, for example, an open loop bandwidth of over 250 kHz; practically speaking, I don't really need any feedback, although I do use it in moderate amounts, typically 15...18 dB (5:1 ... 8:1). This usually allows me to achieve a 10V rms output at around 2 MHz. Then I go the opposite direction, I start curtailing the bandwidth, HOWEVER not by simply inserting bootstrap capacitors, but by limiting each stage. In the end, I usually park at around 600 kHz with NFB, which when I throw in an input capacitor to reduce this to 400 kHz.
400 kHz was not a randomly chosen figure; if my -3dB point is there, my phase shift at 20 kHz, arguably the top of our hearing bandwidth, should be less than 2 degrees, i.e. below the arguable threshold of hearing. That's the advantage of discrete, you can get there with careful design and very little overall feedback, and in the end, it doesn't cost all that much more than using a quality op amp with current boosters. Though as ever, one can go overboard ...
I wrote all this figuring if you are going to exchange my ideas on using medium power trannies in headphone amps for more of your beer, you might as well know the whole story, it could save you some time.
 Oh, by the way, don't use MJE 15030/15031 for a 20W/8 Ohms amp, do take a look at Toshiba's 2SA1942/2SC5200, now THOSE are just the babies for you. At 20W/8 Ohms, they will take you to 1 MHz easy in a SEPP circuit. I know this is what you crave.
And I did warn you that external power supplies were nothing but trouble way back in '03, remember? I'm sad to say I was right more than I ever dreamed I would be. Time for a wholesome design, with internal classic PSU, internally switchable 115-230 VAC. ------------- True audio lives on the fringes of the industry. |
Posted By: Graham Slee
Date Posted: 04 Jul 2008 at 4:02am
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My dear dvv, Me thinks we here at GSPAudio are about to overturn the tables in the temple... As soon as we can, we'll send you samples - I doubt you will be able to convince your eyes ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: dvv
Date Posted: 04 Jul 2008 at 7:38pm
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Mr G,
You know that over the years, I have had nothing but faith in GPS Audio. Which is why we argue, but if you look back, I do believe most of those arguments resulted in a bit more clarity for both of our visions. This is something that I find to be very satisfying indeed, and I daresay, I am rather proud of it.
But there's no denying each one of us still holds his own fort. This is, in my view, also very good, individuality is a boon if it's not taken to its extreme.
As for my eyes, never mind them, do something for my ears if you will.
As for GSP Audio, I have a nagging feeling it is ready to go heavyweight boxing, perhaps with a slight nudge from friends. I told you you had it in you years ago, but as always, it takes time for the realization to mature and sink in, trust me, I fared no different or better myself. It took me 2 (two) YEARS to produce an unconditionally stable power amplifier with just 6 dB of NFB. 2 years to get it down from 14 dB! "Unconditional" being 2 Ohms in parallel with 2.2 uF.
BTW, I will be away in Greece July 18 - August 8. All booked, all ready to go. ------------- True audio lives on the fringes of the industry. |
Posted By: Graham Slee
Date Posted: 06 Jul 2008 at 7:33am
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"As for GSP Audio, I have a nagging feeling it is ready to go heavyweight..." There is nowhere else left to go. If you read some of the other forums, public opinion is that everybody else can do just as well. However, in saying that, few have ever experienced our products. The forums tend to seal the fate of all who fail to innovate. Innovation has to be what it means. It is no good doing anything conventional anymore, and even if you did, the politician always profits by his doctrine. The end stays the same: the required result is the utmost in customer satisfaction. Team innovation with customer satisfaction and the right prices in a slowing market, with the knowledge that the customer is getting something hand-built in England, and it may just succeed? That's what most people who find us expect, and we need to give that to them. So far we have but like I said, the forum mentality is capable of breaking the nerve of our potential new customers. So, in a way we have to offer "magic spells" on top of what we already do. However, these innovations, although they may appear as "magic", are in fact good solid engineering innovations grounded in reality. I am basically building on existing foundations that have supported a growth of near on 40% per annum for some time now. We have our critics: all say similar things - that I am "old-hat" in some ways, but all admit that this "old-hat" sounds spectacularly good, and some of these comments actually get published. That tells me I am sufficiently unconventional to get noticed, but still well grounded in proper engineering. I quite like being there. The problem with modern design is that it's boring: always the same - eternal rehashes of the same convention - a bit like going to church every Sunday expecting eternal life... The great thing about "old-hat" is the innovative spirit it had. And all these new terms like Damping Factor were invented in some ill-meaning minds to kill that spirit. Well, it's still alive in me. And that's why we have our differences (though we remain great friends!) Look back at the innovations in the tube days! Where did they all go? Not one tube amp these days features one - they've all been brought in-line with current thinking! It's only nostalgia now that makes them novelty - it's the only selling feature they have - people convince their ears that the sound is right even though most valve gear sounds totally alien to people like me who remember how really fluid they actually were. But if you use "old-hat" innovations of the valve days with solid-state it's remarkable how valve like the results sound - and ain't that what people have been saying about our products all the time? That's my point and why I sail a different ship on its different course. The "experts" will always argue what I do can't sound as good as it actually does - their ears cannot convince their eyes - it's they that have the problem. How else can anybody explain that 40% annual growth? I guess that now I've got this reputation I could start to take the easy option and milk the cash cow, but that would be to betray my customers. So instead I tread the hard road, but the results are what I seek and I seek till I find. Prove all things. Hold fast that which is good.  ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: dvv
Date Posted: 07 Jul 2008 at 9:12pm
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Over the last year or so, by sheer chance I have come across a great deal of vintage devices of all sorts. They may well be "old hat", but let me tell you, fire up that Amcron DC300 power amp, and you will be not surprised, but flabbergasted. I guarantee it. But don't try to take it apart - that's a process some 5-6 hours long, because it's made quite literally like a tank.
Looks aside, it sounds like no modern power amp I have had the good luck to hear in the last 5 years at least. Including the Levinsons and Krells.
Graham, you said it - modern audio is not based on solid engineering, but on sheer marketing muscle. We "old hats" know that all too well, I'm afraid. Our problem is getting through to the kids of today, who are truly the MP3 generation.
Anyway, I can't wait to see what you have come up with. ------------- True audio lives on the fringes of the industry. |
Posted By: Graham Slee
Date Posted: 08 Jul 2008 at 1:27am
Oh, just 4 years research trying to pin-point exactly what European RoHS did to the sound... Typical - Politicians change the laws of the universe without knowing jack-sh1t about them. Egged on by the hyper rich green wellie brigade, and their Baldrick minded supporters. Anybody else would have keeled over and given up the ghost - in fact I should be pushing-up daisies by now... Let's see: 4 years, mostly spent finding out exactly what went wrong. That's about 80 hours a week. And let's say I should charge out my time at 50 quid a hour? so 52 x 80 x 50 = £208,000.00 Or quite near half a million dollars! Not bad for a miners son? And what's the secret? Sorry, there's a price to pay for all that research. How's about a cool million? That's in GBP by the way Hint of bitterness in my words? Dead right there is! ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: elektrikgypsy
Date Posted: 16 Jul 2008 at 9:22pm
| Can't help with damping theory, I'm afraid, but uniting a comment from Graham on another thread about trying things out for yourself and listening to the results, i can personally attest to the 3020 current / speaker thing. Yonks ago i wanted to check some second hand LS3/5a speakers that had come into a shop that day. There was a Quad pre knocking about, but nothing really similar to my system that we could put it through. On a whim (both rock musicians, you see; no sense of decorum or audiophile sensibilities) we stuck it in the back of a 3020e, turned the volume to max, and controlled it from the Quad volume pot. I sense what you're thinking, but i have to tell you, it rocked!! I've never heard those speakers come alive quite like that - they're very hard to drive. Needless to say I bought them, and still love them (though these days powered with a little more finesse by a Crimson pre-power. Mind you, if i could lay my hands on that 'friend' who nicked my 3020e....). |
Posted By: elektrikgypsy
Date Posted: 17 Jul 2008 at 12:57am
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Oops - posted that without noticing there were another couple of pages of comments... However, while I'm here... ;-) Amcron! Patron saint of SPL! Gawd bless you sir! Hallowed to the back of the auditorium... And as for the MP3 kids of today - well, yes, but... one of the biggest growth areas in music is vinyl. And it's not all old buffers - the young guys get it, and some of them are getting turned on to how good the latest turntables are - well, current vinyl replay tech generally - and how damn good it can sound. I have a couple of thousand LPs here, and am doing my own spot of evangelising with certain success. But the thing is, so many people are mobile, or moving from flat to flat all the time, and that requires portable or mobile solutions. MP3 is a flippin godsend - I can fit my entire CD collection on one shirt pocket drive. We all know it's not up to vinyl. Fine. We just want it to sound the very best it can, nonetheless. Compressed digital audio is here to stay - let's really enjoy it. I don't stop being aware of the sound when i step away from my home and my vinyl. I want the highest possible quality for home and away. Yes, I'm already impressed enough with my Solo that I'm hoping to buy a voyager for road use. And if you could perfect a small but perfectly formed DAC that could sneak the musical info on the mp3s in my Macbook onto nicer audio rep equipment than that found inside it, well, I'd follow that other chap's lead and experiment with some respectable active speakers to go with the decent headphones. Hifi on the move. Because wherever i am, it's about the music! |
Posted By: dvv
Date Posted: 07 Aug 2008 at 9:36pm
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I too am mobile. This morning, I woke up on the Kassandra peninsula near Thessaloniki, Greece, and tonight, I'll sleep in my own bed in Belgrade, Serbia. A matter of 8 hours' drive, no big deal. I must have been the only silly git with Grado headphones listening to a Philips portable CD ("Discman") at the pool of the hotel, everybody else was plugged into some MP3 device. I readily agree they are far more practical, but I find their sound to be lacking quality which my current portable player does afford me. And with a charger always with me, batteries are no problem, standard AA fare. Now, even I would have thought myself a weirdo, if two kids from Slovakia had not asked for a test drive of the setup; they ended up commenting that their MP3 devices were nowhere near that level of sound quality. No idea what they had, but I was pleasantly surprised, I must admit. Perhaps I just provided some deliverance for two (audio) souls? Surely the MP3 devices are far more practical insomuch that they are readily portable, small and handy - but in my personal view, the quality compromise is unacceptable. No pain, no gain. Re: AMCRON. All I can say is oodles of power with an uncommonly wholesome sound, built to last forever and a day. Very convincing and very honest - it does what it does and doesn't even pretend to do what it doesn't do. I love that kind of approach in general. ------------- True audio lives on the fringes of the industry. |