Nakamichi 610

Commentary

A preamplifier developed to be the best preamplifier for sound recording.

The input stage of the equalizer amplifier section uses a triple transistor circuit to improve the SN ratio and expand the dynamic range. In addition, the driver stage of the current drive system realizes low distortion factor.
In addition, high-quality parts such as metal film resistors and capacitors with excellent temperature characteristics are used to reduce RIAA deviation.

The microphone input is also taken into consideration, and a microphone amplifier is provided for each of the four channels of two stereo systems.
The microphone amplifier section has a sensitivity of 0.2 mV at 1k Ω 0 dB. It is equipped with 15 dB and 30 dB attenuators, and uses a unique circuit design to prevent S/N deterioration.
The dynamic margin of + 46 dB at the attenuator of 0 dB is sufficient.

It also has a dedicated monitor amplifier for headphones.
Differential input pure complimentary service OTL system is adopted for the circuit system, and headphones from 8 Ω to 200 Ω can be driven with enough space.

As a result of thorough unitization, interference between circuits and deterioration of sound quality due to conventional cord wiring is reduced.

A toroidal transformer with less leakage flux is used for the power supply part.
Uses a 2-stage voltage selector switch of 100 ~ 120V/220 ~ 240 V.

It is equipped with a master volume that can control all five input levels.
A metal film resistor with an interlocking error of ± 0.5 dB is used dB.

Equipped with a memory marker that can be used for fade-in / fade-out.

19 channels can be connected : 5 channels (2 stereo microphones and 1 blend microphone), 4 channels (2 phono stereo, 6 channels (deck stereo Route 3), 2 channels (1 tuner), 2 channels (1 tuner), 2 channels (1 aux), 2 channels (1 aux), and 2 channels (2 stereo sources and 2 blend microphones).
This allows you to mix five microphones, mix three microphones with one phono, mix two tape decks with a blend microphone, record from two tape decks, and switch playback using fade in / out of two phono.

Three tape decks can be connected to the tape circuit, allowing simultaneous recording of three tapes, dubbing between each other, mixing with other input sources, and mixing editing between tapes.
Either one can be selected with the tape monitor switch (1/2/3), and the recording input of the during monitoring deck is automatically cut off to prevent oscillation due to wraparound.

Eight different test tones, including pink noise, can be output and used for measurement, adjustment, and testing.
For example, you can adjust the reference level required for Dolby, etc., adjust the level matching when dubbing or copying with two decks, measure the numerical characteristics of Shuuu, and adjust the bias of the tape deck.

Equipped with a peak level meter.
This level meter is logarithmically compressed by two separate logarithmic amplifiers so that there is no indication error. The circuit has a very fast rise time of 120 msec. and a slow release time of 2 sec.

Equipped with a phase check and phase inversion function, it can be switched to opposite phase with one touch.

By using the Remote Control Unit RM-610 (sold separately), it is possible to switch between Route 3 speakers with one power amplifier, or switch between three power amplifiers.

There was a built-in rack sold separately. This rack was designed for the 600 series and you can mount a 600B cassette deck or a 620 power amplifier with the 610.
A wood cabinet for the 600 series was also sold as an optional item sold separately.

Model Rating

Type	Control amplifier
Input Sensitivity / Impedance	Mic : 0.2mV/1k Ω (attenuator : 15 dB, 30 dB) Phono : 1mV/200 Ω, 50k Ω, 100k Ω switching Aux, Tuner : 75mv/25k Ω Tape PB : 230mV/75k Ω Tape monitor : 316mV/75k Ω
Maximum input level	Mic : 1 v (+ 74 db, attenuator : 30 db) Phono:250mV(+48dB) Aux, Tuner, Tape PB : 50 v
Reference output level (0 dB) / output impedance / Load impedance	Monitor out : 1V/100 Ω / 1k Ω or more Line out : 316mV/600 Ω / 1k Ω or more Rec out : 316mV/2.2k Ω / 50k Ω or more Headset : 40mW/8 Ω / 8 Ω ~ 200 Ω
Maximum output level (clipping level)	Monitor out : 5V/1k Ω Line out : 5V/10k Ω Rec out : 5V/50k Ω Headphone : 300mW/8 ohm
Frequency characteristic	Mic : 30 Hz to 100 kHz + 0 to 1.5 dB Phono (RIAA deviation) : 30 Hz to 15 kHz ± 0.3 dB Aux, Tuner : 20 Hz to 100 kHz + 0 to 1.5 dB Tape PB : 10 Hz to 50 kHz ± 0.3 dB Monitor out : 5 Hz to 150 kHz + 0 to 1.5 dB
S/N ratio (IHF-A) (reference level) / input conversion ratio	Mic : 53 dB or more (0 dB) / -127dB 65 dB or More (Attenuator 15 dB) Phono : 80 dB or more (1 mV) / -140dB 90 dB or More (3 mV) Aux, Tuner, Tape PB : 85 dB or more (Vol max) 93 dB or More (Vol min, Input Open)
Residual noise level (Line out, IFF-A)	Headphone (8 Ω) : 4 μ V or less Line out/Rec out : 7 μ V or less (Vol max) 15 μ V or Less (Vol-30dB)
Distortion factor (Vol -20dB, Level vol max Line out2V)	Mic : 0.01% or less (f = 10 kHz or less) Phono : 0.005% or less (f = 10 kHz or less) 0.002% or Less (f = 1 kHz) Aux, Tuner, Tape PB : 0.005% or less
Test Tone
Oscillation frequency	1k, 3.16k, 4.16k, 10k, 11k, 13.16k, 14.16 kHz (by combination of switches) Pink Noise
Oscillator distortion factor	1 kHz to 14.16 kHz, 0.2% or less
Pink Noise	50 Hz to 15 kHz ± 2 dB (1/3 octave filter)
<level meter>
Indication range	-40dB to + 10 dB
Indication error	-20dB + 10 dB : ± 1 dB -40dB to -20dB : ± 2 dB
Frequency characteristic	50 Hz to 20 kHz + 0 -1dB (-30dB to + 10 dB)
<General>
Semiconductor used	FET : 2 Transistor : 134 units Diode : 27 units Zener diode : 5 pcs IC : 2
AC outlet	Switched : 2 systems (350 VA)
Pwer	AC100V ~ 120V/220V ~ 240 V, 50Hz/60Hz
Power consumption	Up to 20 VA
External dimensions	Width 400x Height 170x Depth 237 mm
Weight	Approx. 7 kg
Sold Separately	Dedicated Remote Control Unit RM-610 (¥ 18,000) 600 Series Embedded Rack SYSTEM-ONE (¥ 25,000) Wood Cabinet for 600 Series (¥ 11,000)