2005 V-FET PAGES

Sony TA-4650 Integrated amplifier

(vertical field effect transistor)

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The late seventies TA4650 , TA5650 and TA8650 are amongst the best integrated amplifiers ever built. They all use an output device that was developed by Junichi Nishizawa at Tohoku University. These devices are physically larger than the later MOSFETs and became known as Vertical Field Effect Transistors due to their unusual construction.

Junichi Nishizawa vfets

 They have often been described as "solid state valves" and share many strengths of a triode valve. They are extremely linear devices and because of their size can dissipate heat efficiently. The linearity meant that these amplifiers are highly musical and needed a minimum of negative feedback. Their construction minimizes any build up of electrical charge this enables a higher rate of switching. In a VFET the gate and source electrodes are separated by a thick layer of silicon dioxide and this helps keep input capacitance to a minimum.

 It is then no surprise that these amplifiers display the best of both worlds. The sonic performance of a valve amp, space, sweetness tied to the greater reliability of a transistor.

 These amplifiers are now rapidly approaching 30 years old. This increasing age is not deterring a very loyal band of owners. Even when compared against the best of current designs these amplifiers are simply outstanding. They are superbly engineered and the output devices have been well protected. The TA4650 subject of this article has been taking centre stage in my system for over 12 months. It looks fantastic, runs cool even on steamy South East Queensland evenings. It drives all speakers with great ease.

Sony TA 4650 (30W per channel)

Here is my mint TA-4650. Cool running and super sweet.

Matched to the right speakers those 2 V-FETS per channel are very hard to beat

I highly recommend the small "living Audio" Ce-4a with these

PURE MAGIC

This amp also has the optional wooden side cheeks (a traditional Japanese symbol of quality)

Most of the internal caps have been replaced with green or brown NICHICON-MUSE

Dimensions 460mm wide, 168mm high, 323mm deep.

 Mass unpacked = 12.4kg

Power Amplifier,

 power output  30W + 30W (8 ohm)

 power bandwidth 5Hz- 70KHz

 harmonic distortion < 0.05% at 1W output

 input sensitivity 1V for rated output

 frequency response 2Hz- 100KHz

Preamplifier

5 inputs (2 phono, tuner 2 aux) two tape

 tone controls bass and treble

 both +/- 10dB with various turnover points

 filters both 6dB/ octave attenuation high filter at 6KHz, low filter at 35Hz.

 I love the basic exterior design of these V-FET amplifiers. The preamplifier controls are all grouped together within a slim rectangular section. Its neat and you automatically think of the separate sections of a block diagram. Powering up there is a brief delay before the speakers switch in.