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Integrato Ibrido Luxman LV104



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Incorporated in 1925, marketing their first tube radio in 1928, and introducing one of the best audio power transformers (the OY series) in 1958, LUX is not only one of the oldest names in HiFi - more importantly, it has been in the tube amplifier business before most of the current celebrities were a distant glimmer in their father's eye. Although only by special appointment, Luxman still produces tube gear, notably the SQ 38S integrated amp, the latest incarnation of a design that started life in 1964. Luxman is also notable for having tubes specially designed and manufactured for it's amps.

In 1984 Luxman stunned everyone by introducing a mass produced tube-MOSFET hybrid integrated amplifer, into a completely solid state dominated world of mainstream audio - the LV-103 [1st one was the LV-104?]. It was then followed with a tube hybrid CD player, the D-105. This unique line of components persisted in Luxman's lineup until 1992 and finished with the hard to find LV-107u. In 1986 Luxman gave it's already existing LV-105 model a full overhaul and re-introduced it as the LV-105u. It is widely accepted that the design really came into it's own with the untroduction of the u-postfixed amps, the LV-105u being the flagship until the LV-107u was introduced.

A unique amplifer design fitted with all the features that were typical of the times. Rated at 80WPC into 8 ohms, with low impedance compatibility. A full featured amp with 7+2 inputs: phono, tuner, CD, tape 1 and 2, AV 1 and 2. AV2 has two sets of inputs, rear and front, selectable by front panel switch. In addition, the 'processor in' jacks can be used as an extra 'direct' input. AV inputs also have a video component (AV 1 being a record capable device), with an extra video out for a monitor. A processor out and in connection on the back separates the pre and power sections and can be used in several ways.

This amplifier has one more prominent feature: an extremely low noise phono section, 90dB minimum for MM and 77dB minimum for MC. The usual tone controls are included, which are normally defeated, and switch on by a switch on the front panel. They have a relatively small +-5dB adjustment range, which is never the less much more usefull than the traditional and often too severe +-10dB or more. A loudness control, mono mode selector, separate record out selector, processor in/out and CD direct switches are also included. Two speaker pairs can be used (4-16 ohms single pair, 8-16 both pairs).
The most striking feature are of course the tubes, visible through a window on the front panel. The amp has a preheat mode that essentially keeps the whole circuit in standby to avoid a long startup time. Build quality is the typical high of the times, these amps were actually made in the same production facilities used by other well known names, such as Harman Kardon, NAD, Proton, and others.

The reviews of this amp have an astounding range - from the wildly exuberant to the 'avoid at all costs'. [...] It is truly surprising that an amp that was in production for 9 years and out of it for as many, has so many falsehoods and misconceptions about it floating in the audio circles. Past experience has shown that most such controversial units' expressed faults tend to be an expression of people thinking it's so darn near perfect, so why not make it completely perfect - the problem being, everyone's idea of perfection is different. If there is one fault to the concept, it's that Luxman never expanded this design into a fully differential hybrid amp, that would make even Nelson Pass proud - of course, it would have cost 2-3x the original MSRP then... Here are the common foibles:

1) "The LV 105 consists of a MOSFET power amp and a tube preamp" - not true. The whole series (LV-103, 105, 103u, 105u, and the rare 107u) are based on a high gain hybrid power amp with a passive front end. For some reason the idea floating around is that a passive front end was invented recently by people building tube amps based on 40+ year old Dynacos and Marantzes in their garages... In the case of the Luxman, the only active part of the 'preamp' is the solid state phono section and record out buffer.

2) "Only half of the dual triode is used" - only if you don't recognise a differential amplifier. This one keeps popping up since the original LV-103 - get the service manual and have a look! The amplifier is a FET - BJT - Triode - MOSFET hybrid, essentially incorporating every electronic amplification technique known to man. It has a total of 3 and a half stages, all differential except the MOSFET output. It's a JFET - BJT differential cascode with current mirror termination, followed by a dual triode differential stage with active load (BJT current source), and finally followed by a complementary power MOSFET output stage. The tube, a 6FQ7 (or 6CG7), is a dual medium mu driver triode capable of a couple Watts as a push-pull amp. The output are originally Toshiba second generation power MOSFETs, which were upgraded to third generation in the 107u and also in this particular unit - more below.

3) "The preamp is mediocre because it can't drive low impedance loads" - nonsense, it can hardly be true because there is no preamp, see (1). The tone controls are active and they use a common audio IC (NE5532 clone). The tone button by default routes the signal completely past them, including the IC. The passive section is very well done and introduces negligible noise - most competing amps using this concept lost about 12-16dB in the signal to noise ratio. Since there is no buffer, the amp will not drive a low imput impedance power amps through it's processor out jacks without loss of volume, except when the input is set to phono, as the phono section has a low impedance output. It will however impecably drive its own power amp of course!

4) "The processor in/out are not true pre-out/main-in connections" - true to a point - they separate the 'passive preamp' and power amp section in front of the volume control, rather than after it, as would be the common case. However, this setup has some advantages - it makes the 'procesor in' jacks another 'direct' input, bypassing a lot of cable length. All it takes to make this a true 'main-in' is to turn the volume all the way up. The 'processor out' jacks also make it possible to use the excellent phono section alone, as a phono preamp, by permanently selecting the 'phono' on the input selector. An interesting combination to use is the LV 105u in conjunction with a line level preamp. Given a good line amp, this system will be unsurpassed for the money. I know a person who has a setup like this in order to use the LV-105u's superb phono section, without loss of the power amp - he transfers LPs to CDs for a living.

5) "It is possible to modify this amp to get more power output" - Ideas about modifications have been floating around ever since the series made it's debut, some sound, some not. One was to replace the output MOSFETs with BJTs, and while possible, it is not at all simple requiring quite extensive modification, the result would only be different rather than better (whatever that is, this amp is already very good). A complete misconception is that any modification along these lines will get one more output power - this has no foundation in the truth. There is plenty of power, courtesy of a huge transformer and 16400uF of capacitors per channel, just for the power output - driver and phono have separate power supplies. The driver has a good +-20V extra output swing over the output - it will easily overcome the several V of Vgs for the MOSFETs! The idea of insufficient power probably comes from the LV-105u having an unusually but acurately graded volume selector - -10dB (psychoacustical half of maximum volume) is not at the half position, but rather about 2/3 of the range of the volume control, which may make one think it's not nearly as powerful as it's advertized.

6) "The preheat switch keeps the tube heaters on" - not true. It actually keeps the whole amplifier circuit on, just the speaker relay is off and the input is muted. The amp takes about 1 minute to warm up to functioning level (the internal circuitry waits until the output DC offset drops to under 50mV) but it really stabilizes completely after about 20 minutes or so, more if the ambient is cold. It will sound a bit odd for the first half to one hour. Therefore the 'preheat' function. The drawback of using it is that you use up tube life and generate a lot of heat, the advantage, the filaments are subjected to less shock from power on and off cycles.

Il modello LV 103




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