Page 122 - Hi-Fi_News_-_December_2020 video

VINTAGE HI-FI

Yamaha C-2a/M-2

With VFETs costing top dollar and facing stiff competition from other semiconductors,
the late ’70s saw Yamaha unveil a new pre/power amp duo. How does it sound today?
Review: Adam Smith Lab: Paul Miller

t’s always intriguing to see how a
company reacts to the realisation
that a technology it has championed
Iis reaching its sell-by date. This was
the situation faced by Yamaha in the late
1970s. Since the middle of that decade, its
top-end products had made use of Jun-ichi
Nishizawa’s Static Induction Transistor –
more commonly known as the VFET – to
great effect. This led to the development
of designs such as the B-1 and B-2 power

amplifiers, and C-1 preamplifier, all of
which are still held in high regard.
SWITCH IN TIME
The problem was that only Yamaha and
Sony ever leveraged this technology
extensively, companies such as JVC and
Sansui merely dabbling before moving on. ABOVE: As the ’80s
As the end of the ’70s approached, Yamaha beckoned, silver fascias gave
had to deal with the fact that its amps way to black ones and colourful LEDs took
were becoming relatively expensive to the place of analogue power meters
manufacture and proving troublesome in
the hands of unwary service personnel. the top Japanese manufacturers had now according to the company, improved
There was a further issue too, which was embraced this improved technology. linearity and distortion at low signal levels.
that advances in silicon technology meant Come 1979, interest in Yamaha’s In addition, their ultrasonic bandwidth
that the MOSFET was not only becoming mighty B-1 and B-2 VFET power amplifi er promised improved linearity in the
more reliable but cheaper and easier to models was fading. ‘VFET’ was no longer ‘lower frequency’ audio band.
make. New iterations of these transistors the big buzzword, having been replaced
boasting increasingly high switching by ‘high f T’. These new MOSFETs boasted GLAM METAL
frequencies made their use as audio an impressive 80MHz switching with Power was provided to this output
output devices an obvious step, and all of dissipation up to 150W. So it was that stage via a large toroidal transformer
these formed the and a hefty discrete power supply. This
basis of Yamaha’s utilised 44,000μF of capacitance and
two new range- two regulated voltage supplies for each
topping power amplification stage. Meanwhile, the input

amplifiers – the M-4 amplifiers were also FET-based and saw a

and the 200W-per- dual-stage topology used, the aim here
channel M-2 tested being high stability and low distortion.
here [see PM’s Lab Apart from the two large electrolytics
Report, p127]. in the PSU, all other capacitors were either
In the case of the Mylar or polystyrene. Meanwhile, the amp’s
M-2’s output stage, internal earthing bar was pure copper,
Yamaha made use giving an ultra-low impedance connection
of three parallel- that promised ‘reduced intermodulation
connected Toshiba distortion, improved separation and
2SC2461 n-channel absolutely stable operation’.
devices and three
2SA1051 p-channel LEFT: Inside the C-2a can be seen the chunky
types. The use of mains transformer, selector switches located
three pairs of power near the input sockets to minimise signal path
devices offered, length, and the sealed control potentiometers

122 | www.hifi news.co.uk | DECEMBER 2020