![\"\"](\"http:\/\/phonogalerie.com\/fr\/images\/Elberg-MD12mk2.gif\")
<\/a><\/p>\nPrix : 1495\u20ac TTC<\/strong><\/p>\n Le pr\u00e9-amplifictateur ELBERG MD12 MK2 comprend un inverseur pour toutes les gravures, verticales ou lat\u00e9rales, et un autre pour choisir entre les cellules, qu’elles soient \u00e0 aimant mobile, ou \u00e0 bobines mobiles. L’entr\u00e9e pour les cellules \u00e0 bobines mobiles offre un choix de trois imp\u00e9dances de charge : 50, 100 et 200 ohms. L’ancien ELBERG MD12 n’est plus disponible.<\/strong><\/p>\n Note \u00e0 propos des pr\u00e9-amplificateurs pour disques :<\/p>\n Tous les ing\u00e9nieurs du son et les collectionneurs s\u00e9rieux connaissent la difficult\u00e9 de jouer les 78 tours et les premiers vinyles dans les meilleures conditions. En effet, l’\u00e9qualisation RIAA ordinaire d’une entr\u00e9e \u00ab\u00a0phono\u00a0\u00bb telle qu’on la trouve sur les amplificateurs courants ne correspond pas \u00e0 l’\u00e9qualisation du disque original.<\/strong><\/p>\n Particuli\u00e8rement les 78 tours pr\u00e9sentent une multitude d’\u00e9qualisations qui d\u00e9pendent de leur \u00e2ge et de leur marque. Il peut \u00e9galement y avoir des diff\u00e9rences sonores pour deux disques d’un m\u00eame label qui d\u00e9pendent de l’ing\u00e9nieur du son qui a effectu\u00e9 la prise.<\/p>\n Parce que cela n’existait pas, j’ai cr\u00e9\u00e9 un pr\u00e9-ampli multi-courbes pour les 78 tours et les vinyles, le ELBERG M12 MK2, en association avec B. Elberg, ELT – Danemark. Elberg est tr\u00e8s connu et appr\u00e9ci\u00e9 au Danemark pour ses l\u00e9gendaires tables de mixage professionnelles \u00ab\u00a0ELBERG SERIES 15\u00a0\u00bb. La Maison de la radio danoise compte parmi ses clients. Ce pr\u00e9-ampli particulier est construit selon des normes professionnelles, mais il est indispensable pour le collectionneur simplement soucieux d’\u00e9couter ses disques dans les meilleures conditions :<\/p>\n Beaucoup de choses ont \u00e9t\u00e9 perfectionn\u00e9es depuis la premi\u00e8re s\u00e9rie : rapport signal\/bruit, pr\u00e9cision des courbes de r\u00e9ponses. L’\u00e9lectronique a \u00e9t\u00e9 enti\u00e8rement refaite pour un meilleur rendu et une qualit\u00e9 irr\u00e9prochable.<\/p>\n A propos des pr\u00e9-amplificateurs <\/strong><\/p>\n Du temps des disques 78t, l’enregistrement \u00e9tait limit\u00e9 en fr\u00e9quences. D’autre part, les fr\u00e9quences graves demandaient une amplitude du sillon incompatible avec la surface du disque. On se contentait alors d’une plage de 150 \u00e0 3000Hz. Entre 1925 et 1956, chaque compagnie de disque a mis au point une courbe de pr\u00e9-accentuation qui renforce les aigus et att\u00e9nue les graves lors de l’enregistrement. Une courbe inverse est appliqu\u00e9e \u00e0 la sortie de la platine pour \u00e9couter le disque.<\/p>\n Comme il devenait commercialement ing\u00e9rable de changer les r\u00e9glages du pr\u00e9-ampli en fonction du label de disque, l’association des \u00e9diteurs phonographiques am\u00e9ricains (Recording Industry Association of America – RIAA) a mis au point un standard pour cette courbe en 1956 en se basant sur le format utilis\u00e9 par RCA et Victor depuis 1953.<\/p>\n La cellule phono d\u00e9livre un signal de tr\u00e8s bas niveau: 3mV pour les mod\u00e8les \u00e0 aimant mobile, 0,3mV pour ceux \u00e0 bobine mobile. Il faut donc augmenter le niveau pour l’amener aux 0,6V usuels d’une entr\u00e9e ligne. Cette augmentation de niveau est assur\u00e9e soit par un pr\u00e9-amplificateur, soit par l’entr\u00e9e bas niveau d’un ampli courant du commerce. Lorsqu’on joue des disques sur un tel ampli, il faut brancher la platine sur l’entr\u00e9e \u00ab\u00a0phono\u00a0\u00bb, parfois aussi appel\u00e9e entr\u00e9e \u00e9qualis\u00e9e RIAA, ou CCIR. La courbe d’\u00e9qualisation RIAA, pr\u00e9vue pour les vinyles apr\u00e8s 1956 uniquement<\/strong> abaisse d’une part le niveau des sons graves de 500 \u00e0 50 Hz, de 6 dB par octave \u00e0 500 Hz, \u00e0 17 dB \u00e0 50Hz; d’autre part il augmente le niveau des aigus de 2120Hz \u00e0 10kHz, de 6dB par octave \u00e0 2120Hz \u00e0 13,7 dB \u00e0 10 kHz. Les fr\u00e9quences de 500 et 2120Hz sont dites fr\u00e9quences palier. La fr\u00e9quence palier est celle \u00e0 partir de laquelle le son est chang\u00e9 de \u00b13 dB.<\/p>\n Ce syst\u00e8me fonctionne bien pour les 45 tours et les 33 tours apr\u00e8s 1956. mais pour les disques plus anciens (de 1888 \u00e0 … 1960 pour certaines compagnies !), cette courbe n’est pas la bonne.<\/p>\n (English version)<\/p>\n The cutting equalizations on all 78 RPMs and LPs before 1955 have been very different, and specially, the 78 RPM curves are very different from the RIAA eq curve. Because of that it is not possible to use The RIAA input on your amplifier, if you want a good quality when playing 78 RPMs.<\/p>\n I want to thank Roger Wilmut for basic information about reproduction of 78 RPMs and allowing me to use his eq settings.For better understanding of the problems of reproduction of records, read the following articles (with a few edits from my hand), with kind permission, taken from Roger Wilmuts home page: \u00ab\u00a0Reproduction of 78rpm records<\/a>\u00a0\u00bb<\/p>\n EQUALIZATION OF GRAMOPHONE RECORDS<\/strong><\/p>\n The simplest form of disk-cutter consists of a amplifier, similar to that used to drive a loudspeaker, connected to a cutting-head having a stylus connected to a coil, which is placed in the field from a strong magnet (or, more usually in later designs, a magnet within a coil). When the signal is applied to the coil, the stylus moves and engraves a groove in the blank disk. (There is of course a lot more to it than that, but we are considering only the basics here.)<\/p>\n However, because the cutter head’s movements translate the amplitude swings of the original signal into velocity – the rate at which the stylus moves during its swings – low-frequency signals would be recorded with a much larger swing than high-frequency signals of the same original amplitude. In order to keep the movements of the groove much the same at all frequencies (given equal level signals) it is necessary to use a circuit to introduce – in the theoretical situation – a 6 dB\/octave cut as the frequency decreases – i.e., halve the frequency and you halve the voltage.<\/p>\n In the reverse situation, that of a reproduction head, the principal is that of a wire moved in a magnetic field – it is the rate of cutting ‘lines of force’ that matters. The cutter head works exactly in reverse, like a simple motor, where increased voltage means increased speed. Therefore the constant amplitude groove theoretically achieved produces a signal where the bass is low and the treble high: so a 6 dB\/octave cut with increasing frequency would be called for.<\/p>\n In the real world, losses in the head with increased frequency complicate the issue. Early cutter heads were highly inefficient, and so, while the bass cut described above was used, the treble tailed away, resulting in equal groove modulations (movements) up to mid frequencies, but decreasing above that.<\/p>\n To compensate for this, the playback characteristic boosted the bass below 200 Hz but left it flat above that – effectively providing a 6 dB\/octave boost to the higher frequencies (and the surface noise). With the later improvements in cutters, it was possible to pack more treble onto the records, and so new equalizations provided for a 6 dB\/octave cut above a turnover frequency which varied between 3.4 and about 6 kHz depending on the system. This meant that the surface noise became less obtrusive. It was also common to flatten out the bass at the very lowest frequencies to reduce the boost of rumble from the turntable.<\/p>\n Similar techniques were applied to microgroove records, and the final standard, RIAA provides for a bass boost below 500.5 Hz and a treble cut above the lower frequency of 2,2125 kHz – the latter reflecting the considerably increased amount of treble which can be cut onto an LP.<\/p>\n It can therefore be seen that playing a 78 with RIAA equalization – all that is available to many people – produces far less top than is correct – particularly for the earliest electrical, where the result is akin to turning the treble control right down. (Turning it right up gives an improvement, but doesn’t touch the important mid-range.)<\/p>\n Use of the correct curves when reproducing 78s produces a startling improvement in the quality (although admittedly the surface noise can become a problem); many of these recordings are much higher quality than you might suppose. At the time the format disappeared the recommended stylus size was 60\u00b5 (0.0025″) conical tip. This would be satisfactory for records made in the final few years, but for the great majority of the time since the beginning of 78s in 1896 the grooves were wider than the ‘standard’, with the result that a 60\u00b5 stylus skates about in the bottom of the groove, seriously increasing the surface noise.<\/p>\n The basic stylus is conical, with a spherical tip; the included angle of the cone is 60 degrees. Most modern styli are elliptical: i.e. they look the same from the front, but from the side they have a much narrower angle. This enables them to track movements in the groove more easily (as the groove moves from side to side it effectively narrows – not across its direct width but across the diameter of the conical tip, at an angle to the direction of travel: consequently a spherical tip will ride up in the groove).<\/p>\n The illustrations below could apply equally to a spherical tip and an elliptical tip seen from the front: in practice I would always recommend elliptical.<\/p>\n Serious mastering engineers and collectors often have a collection of styli sizes, conical truncated as well as elliptical truncated. A good starting point could be:<\/p>\n A good address for buying cartridges and styli, as well as retipping of styli, is<\/p>\n Expert Stylus Company SPEEDS<\/strong><\/p>\n By no means all 78s were actually recorded at 78 rpm. Even in the late 1920s English Columbia was still using 80 rpm, and prior to about 1921 speeds were widely variable. Some of the audio tracks included in the Music hall section of this site were transferred at speeds as low as 74 rpm, and I have come across records where the speed was as low as 68 or as high as 84 rpm.<\/p>\n To make matters worse, relatively few records state the speed (and when they do it’s not always accurate). If the work is a classical piece such as an opera aria, it is possible to check the correct pitch against a score or a modern recording: but as occasionally singers would transpose, this isn’t completely reliable. My best recommendation is to gradually reduce the speed of a record until it starts to sound sluggish, and then increase it slightly (in my experience the ear is much more sensitive to low speeds than high speeds). I’m afraid it’s all rather rule of thumb; and the narrow bandwidth of old records doesn’t make it any easier.<\/p>\n As to a turntable capable of coping with these speeds that is yet another problem. I don’t know of any normally available turntable which has more than a tiny variation (usually 2 or 3 %), which is nowhere near enough); but electronically controlled turntables may be modifiable. You need a speed range of 72 to 82 to cover most records.<\/p>\n For further information. see Roger Wilmuts Web site:<\/p>\n http:\/\/www.rfwilmut.clara.net\/repro78\/repro.html<\/a><\/p>\n On this site, you will find a lot of information about 78 rpm and a lot of links.<\/p>\n HOW TO USE THE PREAMPLIFIER<\/strong><\/p>\n\n
\nL’affichage \u00e0 diodes est tr\u00e8s simple.<\/li>\n<\/p>\n
\nSTYLUS TRACKING<\/strong><\/p>\nA modern record groove should be a neat 90 degrees, with the stylus making contact at only two points part-way up the groove wall, thus avoiding any debris in the bottom of the groove. (Some modern microgroove styli have a flat section at the contact point, giving a wider area of contact which reduces wear: however it can also increase noise from worn or damaged groove walls and I would be dubious about its use for 78s).<\/p>\nHowever older 78s were cut to be used with steel needles, on the assumption that the needle would wear down to fit the groove in the first few seconds: when this wider groove is tracked with a 2.5 thou stylus the result is ‘bottoming’ as can be seen here.<\/p>\nHere the combination of a larger basic size: 70\u00b5 (0.0028″) works on the majority of records, although larger sizes may be helpful with very old records – and the truncated tip (which is spherical down to the contact points but truncated below) result in vastly better tracking. Like LPs, Records in good condition, will be better reproduced If the stylus is elliptical. This brings a considerable improvement in distortion and will be with reduced surface noise and greater analysis. With records in poor condition, you often will have a better reproduction with conical styli.<\/p>\n\n\n
\n Records from<\/td>\n Conical truncated<\/td>\n Eliptical truncated<\/td>\n<\/tr>\n \n Before 1920:<\/td>\n 100\u00b5 (0.0040″)<\/td>\n 100\u00b5 x 30\u00b5 (0.0040″ x 0.0012″)<\/td>\n<\/tr>\n \n 1920 – 1939:<\/td>\n 90\u00b5 (0.0035″)<\/td>\n 90\u00b5 x 30\u00b5 (0.0035″ x 0.0012″)<\/td>\n<\/tr>\n \n 1939 – :<\/td>\n 70\u00b5 (0.0028″)<\/td>\n 70\u00b5 x 25\u00b5 (0.0028″ x 0.0009″)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
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\nSurrey KT21 \u00ab\u00a0QD – England
\nTel: +44 01372 276604<\/p>\n<\/a><\/p>\n