Accuphase class-A stereo power amplifiers have a long
and distinguished history, since the P-260 launched in
1979, we have continued to develop them up until today.
The new A-75 is the latest class-A stereo power amplifier.
It is the succession model of A-70 which is the mainstay
of Accuphase since 2014.
A-75 achieved the further low noise performance and
super high damping factor that are in the class of its own,
with inheriting the ultimate technology features of the A-
250, the flagship class-A monophonic power amplifier of
Accuphase.
Please appreciate the alluring sound of A-75 which will
be an object of aspiration for the audiophiles.
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The size of A-75 is as same as the former model A-70.
The digital power meter shows the output power without
any effects of speaker impedance.
The LED bar graph shows the output voltage level.
2 pairs per channel of large speaker terminals are
equipped.
They are useful for bi-wired connection with loud
speakers.
2
To make the LED bar graph for output voltage level easy
to see, the size and numbers of LED elements in the bar
graph meter are enlarged.
**No. of LEDs: A-70 / 32 pcs -> A-75 / 38 pcs
“Auto-range function” is newly provided with the range
selection of digital power meter.
Decimal point of the displayed value is automatically
shifted in “Auto-range function” mode.
3
Strong power supply with a massive high-efficiency
toroidal transformer and two large 100000μF special
made filtering capacitors are installed.
The capacitance of capacitor is reinforced compared to
the former model.
**A-70: 82000μF
4
The continuous average output power(rated output
power) is 60W into 8Ω load.
However, its actual maximum output power is bigger,
saying 131W into 8Ω and 547W into 1Ω load.
**Output power is as same as A-70.
5
The performance highlights of A-75 are “Ultra low noise”
and “Super high Damping Factor”.
The A-75 features the latest instrumentation amplifier
topology. It consists of a complete balanced input
amplifier block and a power amplifier block.
The balance input amplifier block is related to the noise
performance and the power amplifier block is related to
the Damping Factor.
6
The former model A-70 has the excellent noise
performance.
However A-75 achieves even 23% lower output noise
voltage than A-70.
A-75 guarantees,
SN ratio: 122dB @Maximum-gain
7
The output noise is also reduced by the fully discrete
configuration amplifier which any ICs are not installed on
the signal paths.
8
A-75 has the guaranteed 1000 of Damping Factor.
It is 25% higher than the former model A-70.
The actual value is in excess of 2000.
**Damping Factor:
A index of speaker driving ability.
Higher Damping Factor amplifier has higher speaker
driving ability.
D.F. = 8Ω / Output-impedance
9
The output impedance is decreased by 10 parallel push-
pull final stage arrangement of MOS-FETs.
A-75 features the new power MOS-FET device which is
heavy-duty and has the large rated current characteristic.
**Current capacity of power MOS-FET
A-70’s MOS-FET: 10A
A-75’s MOS-FET: 33A
A-75’s MOS-FET
10
Remote Sensing is the technique to lower the output
impedance of amplifier by the negative feedback with
signal sensing from nearby the speaker terminals.
Balanced Remote Sensing is the technique to make the
output impedance even lower by both the signal sensing
and the GND sensing, that is the negative feedback of
GND level.
Not only Damping Factor, but also Total Harmonic
Distortion and Intermodulation Distortion are all improved
by the Balanced Remote Sensing.
11
Mechanical relays are the common components for
speaker protection but the super high Damping Factor is
achieved by the lower impedance component.
As the contact resistance of mechanical relay is higher
than people think, Accuphase has chosen the MOS-FET
switch instead of conventional mechanical relays for
speaker protection.
Thanks to this MOS-FET switch, the Damping Factor,
reliability and sound quality are all improved.
A-75 employs carefully-selected very low impedance
components such as the large speaker terminals, the
heavy-gauge edgewise coil and so on.
Making signal paths thick and short also helps attaining
the low impedance.
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