Part of the re-launch of Luxman : post-Alpine and built by AZDEN. Or : the last period of actual worldwide visibility and proper sales - even if with much smaller lineups and shrinking distribution.
The C-7 initially was the "small" one yet the C-5 and C-3 were later on added to make the C-7 the (high-class) middle of the road, sporting new directions added to proven but renewed circuits.
Circuits-wise, the famed Duo-ß which had preceded the Alpine takeover was surviving it, in enhanced form.
OD ßeta, or Optimized Dual ßeta, does away with the DC Servo loop to not treat low frequencies independently from the rest of the range. This however works with CSSC...
CSSC, or Complementary Single Stagger Circuit, comes from radio-frequency engineering (back to basics :) with a second-stage current transfer circuit to increase the cutoff frequency, thus allowing the first stage to reach wide range for the amp through phase reversal alone - without phase compensation.
The result is not only high bandwidth but very high slew rate as well.
Next is a High Inertia Power Supply which, through custom high-capacity, well-regulated transformer and layout, allows exceptional open-loop characteristics, drastically minimizing delay between input and power-supply output.
The internal layout is like that of a C-10 : bar the attenuator and depth notwithstanding they even look exactly alike !
Said Precision Level attenuator remains invisible but nevertheless is a 4-gang version of the one used in the Sony TA-E1 (the ALPS RK50), also used in the C-9 and C-9II.
The rest is like any 1987-1994 Lux component : five-point FRP (Fiber Reinforced Plastics) composite base, mechanically decoupled & low-impedance power-supply shielded sub-enclosure, ultra select parts and a backlit front logo which "enhances beauty".
This 1994/95 new direction brought a simplification : the C-7 is a line preamplifier - no phono stage inside. You have to either buy an external E-03 or go the integrated route with the L-507s for vinyl sonic pleasures.
Like all components since 1987, the massive extruded fronts were all made at Luxman's with a high-precision CNC machine customed in... true Luxman tradition.
Later upgraded as C-7i, then as C-7f.
The 7 and the 7i both have a wood enclosure and a rounded bottom flap ; the 2000/2001 7f was only made in "custom" mode (wood enclosure replaced by metal, flat bottom flap, less champgne-ish overall anodizing) and had a "Signature" added next to its model engraving, with (or without) a "Version Up" sticker added on the back...
Put differently, that's FOUR possible versions for one preamp -
Lux is Luxman is complexman.
The C-7 was built by AZDEN, the C-7i and C-7f had a LUX T-Tag.
That "LUX" tag had appeared once before, just before the Alpine sale. And after the 7 / 7i, indeed, Luxman changed hands again and preamps got to be made by Goto D.S...
A real C-7 here, a real C-7i here and a C-7f (Ver. Up) here.