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stuxter
Senior Member Joined: 26 Mar 2008 Status: Offline Points: 140 |
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3 eggs - 0 eggs =3 eggs
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Somebody will argue it isn't |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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stuxter
Senior Member Joined: 26 Mar 2008 Status: Offline Points: 140 |
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Yeah.. and i think i know who that somebody is
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Courtesy Headwize 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."
Edited by Graham Slee - 29 Jun 2008 at 8:37am |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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dvv
Regular Joined: 12 Jan 2008 Location: Belgrade, Serbi Status: Offline Points: 95 |
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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.
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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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 |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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dvv
Regular Joined: 12 Jan 2008 Location: Belgrade, Serbi Status: Offline Points: 95 |
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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.
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