JVC JM-S7

October   1 9 7 5 october 1975
1 9 7 7 1977

The other rare V-Fet amplifier... Japan-only, unfortunately.

The JM-S7 uses 4 pairs of NEC Vertical Fet devices (2SK70A / 2SJ20A), thermally-stable FET inputs, 450VA trafo, 2x 22,000µF main caps, temp-stable componentry and superlative build quality.

The large heatsink suggests a Class-A design, and with a lavish 200mA bias current it means it is ! A little hidden engineer's dream novelty is the bias adjustment itself : a DIN-type socket hidden under the little cover plate around the power/speaker buttons allows for easier bias adjustment while the amp is standing upward; not a luxury with top-mounted circuit boards.
[Thank you Oscar !].

According to Shu, major japanese V-FET collector, "The sound of JM-S7 is very good. Its very clear as other V-FET amps and massive as a N7B, but little bit milder (gentle) than Sony's TA-N7B."

The JM-S7 cost 230,000¥ in 1975 and remained exceedingly rare. It still is - TA-N7Bs are abundant in comparison.
The chassis was reused for a 300B tube amp which remained at the protoyping stage in '76.


A real S7 here.

JVC JM-S7, image 1 JVC JM-S7, image 2 JVC JM-S7, image 3
JVC JM-S7 specifications
Title Value
Circuit : DC construction,
all stages direct coupled
pure complementary parallel push-pull OCL
Power output : 2x 110W (1Khz / 8 Ohm / 0,1% THD)
2x 147W (1Khz / 4 Ohm / 0,1% THD)
2x 100W (20Hz...20Khz / 8 Ohm / 0,1% THD)
2x 135W (20Hz...20Khz / 4 Ohm / 0,1% THD)
THD : 0,03% at 1Khz for 100W output
0,02% at 1Khz for 50W output
0,03% at 1Khz for 1W output
IMD : < 0,10% (100W, 8 Ohm)
< 0,05% (1W, 8 Ohm)
Power bandwidth : 6Hz...50Khz (-3dB output, 0,1% THD, both channels on)
Frequency response : 7Hz...80Khz (+0 / -1dB, 1W output, 8 Ohm)
Damping factor : > 80 (1Khz / 1W / 8 Ohm)
> 40 (DC...20Khz / 1W / 8 Ohm)
S/N ratio : > 101dB (input short-circuited)
Input : 1V / >47kOhm
Output : 4...16 Ohm (System 1 or 2)
8...16 Ohm (System 1 & 2)
Componentry : 8 V-FETs
44 transistors
39 diodes
2 ICs
PC : 230W
AC outlet : 1x non switched (300W max.)
Dimensions : 49 x 18 x 24cm
Weight : 20kg.
List price : 230,000¥ (1975...1977)
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