YAMAHA C-70

Commentary

Control amplifier equipped with pure current dam and new linear transfer.

All unit amplifiers of the C-70 are of DC or DC servo configuration, A-class system by new linear transfer, and pure current dam are mounted.
The circuit configuration consists of an MC/MM independent equalizer amplifier, a 0 dB buffer amplifier, a volume amplifier and an inverting amplifier.

All unit amplifiers are equipped with pure current dams except for the tone control and headphone amplifier.
In the Pure Current Dam, the non-linear component flowing in the power supply line is cut off at several Hz by a semiconductor inductance and a large-capacity electrolytic capacitor which are connected in series with the power supply. Thus, only the DC component flows in the power supply line, and each unit amplifier is cut off from the power supply in terms of AC. In addition, since the change of the current in the ground line is also suppressed, the effect of having an independent power supply is obtained.

A new linear transfer circuit is mounted on the output stage of each unit amplifier except for the buffer amplifier and headphone amplifier.
This circuit operates so that the voltage drop caused by the emitter resistance of the bias circuit is always constant, and the power supply supplies the same undistorted current as the output signal, thereby eliminating the effect of current distortion caused by the gm curve of the element, which cannot be avoided by the conventional pure A bias circuit.

Real-time equalizer is used in the equalizer section.
This circuit is an NF-CR type circuit using two RIAA elements, which enables ideal equalization in terms of frequency characteristics and time.
In addition, the built-in 5 Hz, -12dB/oct servo eliminates the problem that the cone of the woofer swings due to low-frequency Lungs in actual use, and suppresses the generation of distortion caused by such ultra-low-frequency noise.

The C-70 EQ does not take the form of inserting an MC head amplifier. It is equipped with an EQ amplifier exclusively for MC to reduce transmission loss. The MC EQ is a low-noise bipolar transistor complimentary service, and the MM EQ is a low-noise FET complimentary service. Combined with pure current dams and new linear transfers, the C-70 EQ has excellent characteristics.

The C-70 uses a newly developed arithmetic volume control.
This is different from the conventional volume in principle and effect. The volume is placed between the input and output of the inverting amplifier and the gain of the amplifier is changed according to the position of the 2nd terminal of the volume. This eliminates any degradation in the high-frequency characteristics when the volume is reduced due to the capacity of the volume itself. In addition, the S/N ratio when the volume is reduced is improved.

The tone control section of the C-70 employs parametric tone control through servo operation, and the three control parameters of center frequency (fo), frequency bandwidth (Q), and boost / cut amount (Level) can be independently controlled.

Both positive and negative output terminals are mounted.

Equipped with a disk direct switch.
When this switch is ON, you can pass the input selector, mode selector, parametric tone control, and high filter, and simply output the output from the equalizer amplifier to the pre-out.

The input selector adopts a logic control method, and the operability is improved by using a plunger switch.
Highly reliable gold-clad relays are used in the disk direct and muting switches. These two switches have built-in memory and can be restored to the previous operating state when the power is turned on.

It uses high-quality parts such as electrolytic capacitors in plastic cases, especially high-precision RIAA elements, non-magnetic gold plated pin jacks, and polarized oxygen-free copper power cords.

Equipped with subsonic filter and high filter.

Equipped with a Direct Phono terminal that is directly connected from the input terminal to each MC/MM equalizer.

It has a special amplifier for headphones.

Equipped with a Rec Out Selector that can be selected independently of the source from which the recording source is played back.

Equipped with a mode selector, it is possible to switch between stereo and monaural.

Equipped with AC outlet.

Model Rating

Type	Control amplifier
Amplifier Unit
Input Sensitivity / Impedance	Phono MC : 100 μ V/100 Ω Phono MM : 2.5mV/47 Ω, 100 Ω / 100 pF, 220 pF, 330 pF Aux, Tape, Tuner : 150mV/47k Ω
Maximum allowable input	Phono MC(1kHz):13mV Phono MC(20kHz):100mV Phono MM(1kHz):300mV
Output Voltage / Impedance	Rec out : 150mV/470 Ω Pre-out : 1.5V/47 Ω
Maximum power output	Pre out : 10 v (20 Hz to 20 kHz, 0.01%)
Headphone Output / Impedance	4.7 V (100 Ω), 0.55 V (8 Ω) / 68 Ω (1 kHz, THD0.01%)
Frequency characteristic	Aux, Tape, Tuner : 5 hz to 100 khz + 0 to 0.5 db
Total harmonic distortion rate (20 Hz to 20 kHz)	Phono MC-Rec out:0.001%(3V) Phono MM-Rec out:0.001%(3V) Aux, Tape, Tuner (Tone off) : 0.001% (5 v)
Cross modulation distortion factor	Aux, Tape, Tuner (Tone off) : 0.002% (5 v)
Signal-to-noise ratio	IHF-A-Network (Input Short) Phono MC : 76 dB (100 μ V) Phono MM:88dB(2.5mV) Aux, Tape, Tuner (Tone off) : 105 dB New IHF Phono MC:80dB Phono MM:82dB Aux, Tape, Tuner : 104 dB
Input Equivalent Noise (IHF-A-Network)	Phono MC:-156dBV Phono MM:-140dBV
Residual Noise (IHF-A-Network)	1.8 μ V
Channel separation (1 kHz, Vol. -30dB)	Phono MM : 80 dB (short) Phono MC : 70 dB (short) Aux, Tape, Tuner : 70 dB (5.1k Ω)
Parametric Tone Control	Low Frequency : 31.5 Hz to 800 Hz High : 800 Hz to 20 kHz Level Low, High : ± 12 dB Bandwidth Low, High : Q 0.3 to 3.0
Filter characteristic	Subsonic Filter : 15 Hz, -12dB/oct. High Filter : 10 kHz, -12dB/oct.
Audio Muting	-20dB
Tracking error	2dB
Semiconductor used	Transistor : 158 units IC : 15 FET : 14 LED : 9 pcs Diode : 79 pcs
AC outlet	Switched : 1 system, 500 Wmax Unswitched : 2 lines, 500 Wmax total
Pwer	100 VAC, 50Hz/60Hz
Power consumption	50W
External dimensions	Width 435x Height 96.5x Depth 369 mm
Weight	7.5kg