Page 127 - Hi-Fi_News_-_December_2020 video

LAB
REPORT

YAMAHA C-2A/M-2 (Vintage)
As our inside shot illustrates [see p125], the M-2 is both densely
packed and dominated by a huge power supply, the latter
conferring a substantial 2x290W/8ohm and 2x490W/4ohm
output that’s comfortably in excess of its 240W/8ohm rating.

There’s headroom too, sufficient to support 342W, 635W and
655W into 8, 4 and 2ohm loads under dynamic conditions

while current-limiting/protection restricts the figure to just
35W/1ohm [see Graph 1, below]. Even in the 1970s, and despite
the compact layout, Yamaha’s trademark low-noise amplifi cation

was reflected in the M-2’s 96dB, and the C-2a’s 97dB, A-wtd S/N
ratio(s) (re. 0dBW and 0dBV, respectively). Distortion was very
low indeed too, just 0.0002-0.001% across the 20Hz-20kHz
audioband at 0dBW [see Graph 2, below], increasing with power
to 0.0004%/10W, 0.0017%/100W and 0.0023% at the rated
ABOVE: There’s no shortage of inputs on the C-2a while the M-2 [below] has two sets 240W/8ohm (all at 1kHz). The C-2a preamp’s distortion varies
of speaker outputs. The C-2a’s leftmost RCAs are for Phono 1 capacitance loading with gain rather than level, falling as low as 0.0005%/1kHz at full
plugs, and the M-2 offers variable input sensitivity plus AC and DC coupled inputs gain (+22.5dB), 0.0009% at +12dB gain, 0.007% at +6dB gain
and 0.027% at 0dB (unity) gain – all measured at the same 0dBV
preamp output. Incidentally, the C-2a’s maximum output is a
Finally, swapping in my Naim In the case of the C-2a, the high 18.5V (unbalanced).

Supernait amplifier with the C-2a panels act as heatsinks for the Frequency responses are very flat and extended, the C-2a

and M-2 in turn revealed that, as transistors inside, so do not be reaching out to within ±0.3dB from 7Hz-100kHz (the subsonic

rewarding as they both are, the real tempted to drill any ventilation filter acts below 20Hz to –6.7dB/10Hz and –20dB/5Hz) and the
M-2 from 1Hz/0dB to 100kHz/–1.3dB via its DC-coupled inputs.
star of the show is the C-2a preamp. holes to help with cooling (as has The output impedance(s) are respectably flat at 0.05ohm from

It turned out that the M-2 was been done on our review sample!). 20Hz-20kHz via the M-2 (rising to 0.22ohm/100kHz) and 175
responsible for that slight veil across As long as the heatsink compound ohm from 200Hz-100kHz via the C-2a (rising to 390ohm/25Hz).
the midband, the C-2a sounding as between transistors and panels is DC offsets are low and stereo separation >60dB midband. PM
open and insightful as anyone could in good order there should be no
wish for. The trouble is, when used issue. It does dry out, becoming less
with a different partner, the C-2a effective with age, so replacement
can feel a little lost without the as part of a service is sensible.

magnificent grip, control and impact Internally, neither unit contains
of its stablemate, the M-2. any semiconductors that can’t be
replaced with new ones, with the
BUYING SECONDHAND exception of the 2SK-101 dual-
The real enemy of the M-2 and C-2a FET module in the phono stage of
is heat. Both amps run very warm the C-2a. However, suitable single
and this can shorten the life of major replacements are available for this.
components. Blanket capacitor The bigger issue is that the
replacement is unnecessary, but function selector switches and rotary ABOVE: Dynamic power output vs. distortion up to 1%
some of the semiconductor devices controls are unique to the C-2a and THD into 8ohm (black trace), 4ohm (red), 2ohm (cyan)
can fail if they overheat. The best are fully sealed. Consequently, as and 1ohm (green) speaker loads. Max current is 18.1A
step to ensure longevity is to not they age and grow noisy, there is no
stack these amps, and allow plenty way to spray switch-cleaner inside.
of ventilation around them. Also, If you’re buying a unit secondhand,
make sure that the idle current and make sure that these controls work
DC offset of both units are correctly correctly and, if you own one, give
adjusted as per the service manuals. all the controls a run from end to
end with the power off every now
and again to wipe the contacts.
HI-FI NEWS VERDICT

Abandoning VFET technology
was a big step for Yamaha in the ABOVE: Distortion versus extended frequency from
5Hz-40kHz (black, 0dBV preamp; red, 0dBW power)
1970s, but the C-2a and M-2
show that the company never
lost its touch when it came to HI-FI NEWS SPECIFICATIONS
building premium pre/power Power output (<1% THD, 8/4ohm) 290W / 490W
amps. The M-2 is powerful,
Dynamic power (<1% THD, 8/4/2/1ohm) 342W / 635W / 655W / 35W
dynamic and fun while the C-2a
Output imp. (20Hz–20kHz/100kHz) 0.050–0.053ohm / 175ohm
is crisp, insightful and joyously
detailed. Together they make a Freq. resp. (20Hz–20kHz/100kHz, 0dBV) +0dB to –0.0dB/–0.3dB (C-2a)
formidable combination and one Freq. resp. (20Hz–20kHz/100kHz, 0dBW) +0dB to –0.1dB/–1.3dB (M-2)
that the vintage hi-fi enthusiast
A-wtd S/N ratio (re. 0dBV/0dBW) 96.7dB (C-2a) / 95.5dB (M-2)
would do well to seek out.
Dist. (20Hz-20kHz, 0dBV Pre/0dBW Pow.) 0.0001–0.002%/0.0002–0.001%
Sound Quality: 86% Power consumption (Idle/rated output) 95W / 825W (31W, C-2a)
ABOVE: Original brochure for Yamaha’s 0 - - - - - - - - 100 Dimensions (WHD) / Weight 435x183x362mm / 21kg
‘Natural Sound’ C-2a preamplifi er

DECEMBER 2020 | www.hifi news.co.uk | 127