http://www.audionote.co.uk/articles/art_audio_hell.shtml

The old method: comparison by reference

We should begin by examining the method in current favour: The usual procedure is to use one or more favoured recordings and, playing slices of them on two different systems (or the same system alternating two components, which amounts to the same thing); and then deciding which system (or component) you like better, or which one more closely matches your belief about some internalized reference, or which one “tells you more” about the music on the recording. It won’t work! … not event if you use a dozen recordings of presumed pedigree … not even if you compare the stage size frequency range, transient response, tonal correctness, instrument placement, clarity of test, etc. – not even if you compare your memory of your emotional response with one system to that of another – it makes little difference. The practical result will be the same: What you will learn is which system (or component) more closely matches your prejudice about the way a given recording ought to sound. And since neither the recordings nor the components we use are accurate to begin with, then this method cannot tell us which system is more accurate! It is methodological treason to evaluate something for accuracy against a reference with tools which are inaccurate – not least of which is our memory of acoustical data. Therefore, it is very likely to the point of certainty that a positive response to a system using this method is the result of a pleasing complementarity between recording, playback system, experience, memory, and expectation; all of which is very unlikely to be duplicated due to the extraordinarily wide variation which exists in recording method and manufacture. (Ask yourself, when you come across a component or system which plays many of your “reference” recordings well, if it also plays all your recordings well. The answer is probably “no;” and the explanation we usually offer puts the blame on the other recordings, not the playback system. And, no, we’re not going to argue that all recordings are good; but that all recordings are much better than you have let yourself believe).

Recognising that many will consider these statements as audiophile heresy; we urge you to keep in mind our mutual objective: to prevent boredom and frustration, and to keep our interest in upgrading our playback system enjoyable and on track. To this end it becomes necessary that we lay aside our need to have verified in our methodology beliefs about the way our recordings and playback systems ought to sound. As we shall see, marriage to such beliefs practically guarantees us passage to AUDIO HELL. It is our contention that, while nothing in the recording or playback chain is accurate, accuracy is the only worthwhile objective; for when playback is as accurate as possible, the chances for maximum recovery of the recorded program is greatest; and when we have as much of that recording to hand – or to ear – then we have the greatest chance for an intimate experience with the recorded performance. It only remains to describe a methodology which improves that likelihood. (This follows shortly).

Listeners claiming an inside track by virtue of having attended the recording session are really responding to other, perhaps unconscious, clues when they report significant similarities between recording session and playback. As previously asserted, no-one can possibly know in any meaningful way what is on the master tape or the resulting software, even if they auditioned the playback through the engineer’s “reference” monitoring system. Anyone who thinks that there exists some “reference” playback system that sounds just like the live event simply isn’t paying attention; or at best doesn’t understand how magic works. After all, if it weren’t for the power of suggestion, hi-fi would have been denounced decades ago as a fraud. Remember those experiments put on by various hi-fi promoters in the fifties in which most of the audience “thought” they were listening to a live performance until the drawing of the curtain revealed the Wizard up to his usual tricks. The truth is the audience “thought” no such thing; they merely went along for the ride without giving what they were hearing any critical thought at all. It is the nature of our psychology to believe what we see and to “hear” what we expect to hear. Only cynics and paranoids point out fallibility when everyone else is having a good time.

Another relevant misunderstanding involves the correct function of “monitoring equipment”. The purpose of such equipment is to get an idea of how whatever is being recorded will play back on a known system and then to make adjustments in recording procedure. It should never be understood by either the recording producer or the buyer that the monitoring system is either definitive or accurate, even though the engineer makes all sorts of placement and equipment decisions based on what their monitoring playback reveals. They have to use something, after all; and the best recording companies go to great lengths to make use of monitoring equipment that tells them as much as possible about what they are doing. But no matter what monitoring components are used, they can never be the last word on the subject; and it is entirely possible to achieve more realistic results with a totally different playback system, for example, a more accurate one. Notice “more accurate,” not “accurate.” It bears repeating that there is no such thing as an accurate system, nor an accurate component, nor an accurate recording. Yet as axiomatic as any audiophile believes these assertions to be, they are instantly forgotten the moment we begin a critical audition.

The proposed method: Comparison by contrast.

When auditioning only two playback systems using the usual method, we will have at least a 50% chance of choosing the one which is more accurate. However, evaluations of single components willy-nilly test the entire playback chain; therefore efforts to choose the more accurate component are compounded by the likelihood that we will be equally uncertain as to the accuracy of each of the system’s associated components if for no other reason than that they were chosen by a method which only guarantees prejudice. How can we have any confidence that having chosen one component by such a method that its presence in the system won’t mislead us when evaluating other components in the playback chain, present or future?

The way to sort out which system or component is more accurate is to invert the test. Instead of comparing a handful of recordings – presumed to be definitive – on two different systems to determine which one coincides with our present feeling about the way that music ought to sound, play a larger number of recordings of vastly different styles and recording technique on two different systems to hear which system reveals more differences between the recordings. This is a procedure which anyone with ears can make use of, but requires letting go of some of our favoured practices and prejudices.

In more detail, it would go something like this: Line up about two dozen recordings of different kinds of music – pop vocal, orchestral, jazz, chamber music, folk, rock, opera, piano – music you like, but recordings of which you are unfamiliar. (It is very important to avoid your favourite “test” recordings, presuming that they will tell you what you need to know about some performance parameter or other, because doing so will likely only serve to confirm or deny an expectation based on prior “performances” you have heard on other systems or components. More later.) First with one system and then the other, play through complete numbers from all of these in one sitting. (The two systems may be entirely different or have only one variable such as cables, amplifier, or speaker).

The more accurate system is the one which reproduces more differences – more contrast between the various program sources.

To suggest a simplified example, imagine a 1940’s wind-up phonograph playing recordings of Al Jolson singing “Swanee” and The Philadelphia Orchestra playing Beethoven. The playback from these recordings will sound more alike than LP versions of these very recordings played back through a reasonably good modern audio system. Correct? What we’re after is a playback system which maximizes those differences. Some orchestral recordings, for example, will present stages beyond the confines of the speaker borders, others tend to gather between the speakers; some will seem to articulate instruments in space; others present them in a mass as if perceived from a balcony; some will present the winds recessed deep into the orchestra; others up front; some will overwhelm us with a bass drum of tremendous power; others barely distinguish between the character of timpani and bass drum. In respect to our critical evaluation process, it is of absolutely no consequence that these differences may have resulted from performing style or recording methodology and manufacture, or that they may have completely misrepresented the actual live event. Therefore, when comparing two speaker systems, it would be a mistake to assume that the one which always presents a gigantic stage well beyond the confines of the speakers, for example, is more accurate. You might like – even prefer – what the system does to staging, but the other speaker, because it is realizing differences between recordings, is very likely more accurate; and in respect to all the other variables from recording to recording, may turn out to be more revealing of the performance.

Some pop vocal recordings present us with resonant voices, others dry; some as part of the instrumental texture, others envelope us leaving the accompanying instruments and vocals well in the background; some are nasal, some gravelly, some metallic, others warm. The “Comparison by Reference” method would have us respond positively to that playback system, together with the associated “reference” recording, that achieves a pre-conceived notion of how the vocal is presented and how it sounds in relation to the instruments in regard to such parameters as relative size, shape, level, weight, definition, et al. Over time, we find ourselves preferring a particular presentation of pop vocal (or orchestral balance, or rock thwack, or jazz intimacy, or piano percussiveness – you name it) and infer a correctness when approximated by certain recordings. We then compound our mistake by raising these recordings to reference status (pace Prof. Johnson), and then seek this “correct” presentation from every system we later evaluate; and if it isn’t there, we are likely to dismiss that system as incorrect. The problem is that since neither recording nor playback system was accurate to begin with, the expectation that later systems should comply is dangerous. In fact, if their presentations are consistently similar, then they must be inaccurate by definition simply because either by default or intention no two recordings are exactly similar. And while there are other important criteria which any satisfactory audio component or system must satisfy – absence of fatigue being one of the most essential – very little is not subsumed by the new method of comparison offered here.

من اینو یکم بسطش میدم

قبل از شروع نصب و راه اندازی یک سیستم صوتی :

قبل از هر تغييري در اتصالات و وصل و قطع كابل ها بهتره دستگاه ها كامل خاموش باشند .

قبل از هر چیزی دستگاه ها باید از نظر سلامت چک شود و دستگاه دست دوم یا قدیمی ممکنه ایراد داشته باشه که به عنوان مثال یه امپلی فایر باید از نظر گراند لوپ داخلی یا نشت خازن روی مسیر سیگنال یا ولتاژ dc خروجی چک شود. برای چک کردن بعد از چك كردن ولتاژ ها و بعد از نصب صحیح همه دستگاه ها، ببینید روی بلندگو چه صدایی میشنوید.

برای تست دستگاه ها باید به یک پريز و یک گراند مشترک وصل باشد و تو سیستم هر دستگاه فقط از یک مسیر به گراند وصل باشد و اگر یک کابل (چه Interconnect چه کابل دیجیتال)  گراند دو دستگاه را به هم وصل کند باید یکی از ان دستگاه ها موقع اتصال به برق فقط به فاز و نول برق وصل شود و گراند برق آن دستگاه به گراند پریز وصل نشود.

جالب اينكه حتي همه اتصالات اينتركانكت ها و كابل هاي برق رو از نظر گراند لوپ چك كرده باشید ولي بعد يه مدت (مثلا ۲۰۰ ساعت) ميبينيد سيستم پيوسته كار كرده صدا بد شده و مجبوريد

كل سيستم رو خاموش كنيد

اتصالات رو جدا كنيد

سيستم هارو روشن كنيد برای ۳ دقیقه

سيستم ها رو خاموش كنيد

كابل هارو وصل كنيد و يه شروع دوباره داشته باشيد.

بهتره يه sweep فركانسي از ٢٠ هرتز اهسته تا ٢٠ كيلوهرتز با كاهش دامنه تو افزايش فركانس به سيستم بديم براي دي مگنتايز.

دليل اين مساله هم ميتونه گراند لوپ داخل دستگاه ها باشه و هم دو كانال بودن چون ما دستگاه هامون استريو هست نه مونو و هر دستگاه استريو گراند هر دو كانالش به هم وصله.
در هر حال توصيه من اينه :
كل اتصالات و مسير انتقال سيگنال رو سينگل (غير بالانس RCA( استفاده كنيد البته دستگاه هایی هستن که بالانس طراحی شدن و احتمالا با بالانس بهتر میشن. هر دو حالت رو چک کنید.
تمامي لوپ هاي گراند رو حذف كنيد.
هر ٢٠٠ ساعت شايدم كمتر يكبار ببينيد قطع و وصل همه كابل ها طبق چيزي كه گفتم صدا رو سرحال مياره يا نه ، اگر صدا بهتر شد هر چند وقت اين كار رو بكنيد.

در هر حال هر دستگاه نباید از دو مسیر به گراند وصل شود. خود گراند ساختمون بهتره کیفیت خوبی داشته باشه و نباید سیم کشی بد ساختمان باعث خرابی گراند بشه. اگر در خانه شما همش لامپ ها موقع روشن شدن میسوزن احتمالا مشکل سیم کشی بد دارید. ولتاژ بين گراند و نول در حالت ايده ال بايد صفر باشد .

ولتاژ AC برق شهر در مناطق مختلف ممكنه تا ١٠ ولت فرق كنه مثلا ٢٣٠ ولت تا ٢٢٠ ولت و حتي در ساعات شبانه روز هم من ديدم تا ٥ ولت تفاوت داشته. مثلا ساعت ٤ صبح ٢٣٠ ولت و ساعت ١١ شب ٢٢٧ ولت.
ولتاژ DC بين فاز و نول هم تو چند ساختمون مختلف تست كردم ١٥ ميلي ولت بود .
ولتاژ AC بين گراند و نول هم تو ساعات مختلف شبانه روز ممكنه فرق كنه و عددش تو واحد ما بين ١/١٥ در ساعات ٤ صبح تا ٢ ولت در ساعات پيك مثل ١٠ شب تغيير ميكرد.
براي از بين بردن ولتاژ DC بين فاز و نول بايد از ترانس ايزوله ١ به ١ استفاده كنيم كه بهتره بالاي 5kw باشه و براي كاهش اختلاف ولتاژ بين نول و گراند بايد سيم كشي با كابل ضخيم مستقيم از كنتور بياد بصورت شيلد كامل و گراند هم اختصاصي تو حياط درست كنيم.

Checking for Earth ground on your receptacles is quite easy. All you need is an AC line tester like the one pictured below. You can purchase one of these AC line testers for about $10 at most home improvement stores, hardware stores, and electronics stores. They not only tell you if your receptacle is properly grounded, they also tell you if the AC line and load wires are properly phased or reversed. Just plug it into a receptacle and and read the LEDs. Easy peasy.

https://www.mojo-audio.com/blog/audiophile-grounding/

http://www.ecmweb.com/content/diagnosing-power-problems-receptacle

نویز و هام در سیستمهای صوتی (بخش سوم)

مورد بعدی برای وصل کابل های برق حتما پولاریتی برق هر دستگاه رو ببینید تو کدوم حالت درسته و همه دستگاه ها رو بعد از تشخیص پولاریتی درست به هم وصل کنید.

دو نكته مهمه يكي اينكه حتما با ولتمتر دقیق اندازه گيري بشه چون دقت فازمتر ديجيتالي كمه و دوم اينكه حتما دستگاه روشن باشه.

پولاریتی برق دستگاه

بعد از نصب همه دستگاه ها اگر روی بلندگو وقتی سورس شما موزیک پخش نمیکنه (حالت STOP) و با چسبوندن گوشتون به بلندگو فقط و فقط نویز سفید یا پینک نویز میشنوید که اون نویز با تغییر ولوم افزایش و کاهش داره میشه گفت کل سیستم سالم هست. صدای نویز سفید یا پینگ نویز تو اینترنت هست و میتونید بشنوید و مثل صدای ششششش هست. یه حالت ملایم داره که همه فرکانسها رو دربر میگیره و این نویز سفيد يا پينك هرچقدر بیشتر باشه نشونه بدي نيست چون دستگاه هایی که فیدبک منفی کمتری دارند این نوع نویز رو میشنویم. هر دو کانال باید نویزشون یه اندازه باشه.

در این حالت اگر وقتی همه دستگاه ها روشنه و یک دستگاه رو اون وسط خاموش کنید و از برق بکشید اگر هنگام جدا کردن کابل برق اون دستگاه (چه وقتی کابل های سیگنال بهش وصل هست یا وصل نیست در هر کدوم از دو حالت) نویزی روی بلندگو نیاد یعنی اون دستگاهها در داخل گراند لوپ یا مشکل داخلی ندارند.

هر ایجاد نویزی موقع خاموش روشن کردن یا جداکردن کابل برق دستگاه خاموش (چه زمانی که همه اینترکانکت ها بهش وصله چه زمانی که کابلی بهش وصل نیست) نشونه مشکل در سیستم هست.

این نویز هایی که میگم (غیر از وایت نویز یا پینک نویز) طوریه ممکنه شنونده مجبور باشه گوشش رو به بلندگو نزدیک کنه و حتی مقدار کم نویز هم باعث کاهش داینامیک میشه.

اگر نویز حالت BUZZ یا HUM داره سیستم شما مشکل داره و حداقل یکی از دستگاه ها داره خرابکاری میکنه.

اگر نویز BUZZ یا HUM با تغییر ولوم زیاد و کم میشه نشون میده که یکی از اجزاش مثل خازن در مسیر سیگنال خرابه و اگر با تغییر ولوم زیاد و کم نشه مشکل از منبع تغذیه هست که در هر دو حالت دستگاه باید بره سرویس و حالت دوم یکم بدتره.

به هيچ وجه حتي اگر اين نوع نويز كم باشه اون دستگاه رو نگه نداريد و حتما بفرستيد سرويس بشه . سيستم هاي با فيدبك منفي كم و بلندگوي حساسيت بالا خيلي بهتر اين ايرادات رو نشون ميدن .

نکته اساسی اینجاست نمیشه با قطع کردن اتصال یک دستگاه (منظورم اینترکانکت های متصل به اون دستگاه هست) بفهمیم ایراد از اون دستگاه هست یا نه مگر اینکه اون دستگاه رو بطور کامل از برق و گراند و همه اتصالات جدا کنیم و ببریم یه گوشه بزاریم و یه دستگاه دیگه جاش بیاریم.

هر دستگاهی وقتی روشنه خروجیش نباید ولتاژ dc داشته باشه و از این نظر لامپی ها بخاطر داشتن ترانس خروجي خیالمون ازشون راحته که ولتاژ خروجی dc نمیدن که بزنه بلندگو یا دستگاه بعدی رو خراب کنه. حتما این مورد رو با ولتمتر دیجیتال براي خروجي همه دستگاه ها چک کنید.

لامپ دستگاه ها هم بايد حتما چك بشه كه سالم باشند .

حتما وضعیت نویز رو با شنیدن بلندگو دقیق چک کنید چون درسته خود نویز موقع شنیدن موسیقی شنیده نمیشه اما عملا باعث کمپرشن داینامیک صدا میشه که تاثيرش روي صدا خیلی بد هست.

https://bottlehead.com/smf/index.php?topic=3364.0

This being a DIY electronics forum we see a lot of posts about hum or noise. And quite often I see someone chasing a problem by looking into aspects of the setup that would not create the particular kind of noise heard. So to make this noise troubleshooting process more efficient I propose a set of definitions of various kinds of noise and some suggestions as to where to look to reduce them.

Hum – this has become a catch-all phrase. Basically there are two kinds of hum, 60Hz hum and 120Hz hum (or 50hz and 100Hz in countries with 50Hz AC). Obviously one sounds an octave deeper than the other, but there are other characteristics to the sound that make them fairly easy to distinguish.

60Hz hum is a softer, more rounded sound. It is usually caused by magnetic coupling, i.e., something is picking up the radiated magnetic field of a power transformer or choke. Tubes and cables are common points of coupling. Distance is your friend here, though moving the cable or piece of gear that is picking up the hum around without adding distance from the transformer can help too. Cables that are radially symmetric like coax and high quality shielded twisted pair are better at rejecting this noise. Mounting inductors so that they are electrically isolated from the chassis can reduce eddy currents in the chassis that can add hum as well. This is done in all Bottlehead kits. Speaking of transformers, occasionally the hum is actually a mechanical vibration of the power transformer transmitted directly through the air rather than through the speakers. Tightening the transformer mounting screws can help and in more extreme cases some type of vibration damping may be necessary.

120Hz hum usually has a distinct buzzy content to it. This the buzzy content of the hum is electrostatic in nature rather than magnetic and is usually due to the power supply rectifiers’ spikes not being properly shunted to ground. Thus 120Hz buzz is often associated with ground loops or lifted grounds, and is probably the most common issue. The best way to troubleshoot this is to disconnect any input cables and short the inputs of the device in question, to see if the buzz remains or if it is actually coming from the cable or equipment ahead of the gear. If the buzz remains, you may have a ground loop with other equipment. A “cheater plug”, that converts a three prong power plug into a two prong plug, can be used to see if the problem goes away when the device is separated from the safety ground of the other gear. While this is not considered the safest method of operation and should probably not be left in this condition, it can help to establish if you have a ground loop that needs to be dealt with. The third and perhaps most common problem is that there is a cold solder joint or loose connection in the gear. Going over all of the solder joints with an iron to reflow them is a simple and most often very effective method of resolving buzzing issues. For some reason many builders are reticent to do this, to the point where they will spend several days asking for other suggestions on the forum before trying it. I have no explanation as to psychology of this, it seems about the easiest thing one could do to eliminate a problem without spending a lot of time tracing and measuring things.

Another rare occurrence that can cause 120Hz hum is a filter capacitor installed backwards. This can also cause a lot worse problems than hum as the capacitor shorts out or vents its guts all over your amp, and should be fixed before the device is powered up again.

Hiss or rushing sound – this is an entirely different phenomenon, due to self noise generated in a tube or in a SS device like a regulator. It is most often associated with preamp circuits that are amplifying very small signals. If it is due to a tube (this would be the most likely case in our kits) the solution is usually to simply replace the tube with one that is more quiet. Typically the more exotic high priced variants of a given tube are expensive because they tend to be more quiet in circuit than less expensive variants. If the rushing sound is from a regulator it may be that the regulator needs to be bypassed or that a SS component in the regulator has failed.

Crackling – this is perhaps one of the more unnerving sounds. It is usually due to an intermittent connection. That connection might be at a tube/socket interface, in which case inserting and removing the tube a few times may cure it. It may be a worn jack, in which case it is usually prudent to replace the jack. It may be a bad solder joint somewhere in the circuit, in which case the solution once again is to reheat the solder joints in the device in order to reflow any bad connections. It may also be in the cable ahead of the gear in question. Try a different cable and see if the problem goes away.

Popping – if there is a single popping sound sometime during or after warm up it may be a tube arcing over slightly as it comes up to voltage and the tube my need to be replaced. If the pop occurs exactly as the power switch is cycled on or off the solution is simply to have any equipment downstream of the device turned off when the power switch is cycled. If the popping is in a steady pattern it may be a failing capacitor which is charging to a certain potential at which point it discharges abruptly and then repeats this cycle. A capacitor in this state needs to be replaced. Tubes can do this cyclic popping as well. If it is mild it may go away as the tube heats up and its internal structure expands.

در انتها موزيك رو با چند اهنگ خوب پخش كنيد و جاي مثبت منفي كابل هر دو بلندگو رو عوض كنيد ببينيد تو كدوم حالت صدا بهتره كه به اين ميگن تشخيص فاز درست اكوستيكي. پولاريتي سيگنال چون ممكنه تو يكي از دستگاه ها عوض شده باشه اين تست بسيار بسيار لازمه و قبل از شروع اب بندي اين كار رو انجام بديد و هر دستگاه جديدي هم جايگزين ميكنيد حتما اين تست رو انجام بديد كه فاز درست مشخص بشه.

صحت فاز سیگنال