Audio Database

PMA-700Z
Commentary

A pre-main amplifier developed in pursuit of the concept of Simple is Best.

An integrated amplifier usually consists of a pre-stage amplifier section such as an equalizer amplifier, an intermediate control section such as a tone control amplifier, and a final stage amplifier section such as a power amplifier.
In the direct-coupling method adopted in the PMA 700 z, the intermediate control section can be disconnected from the main circuit when it is not necessary, and a unique gain switch is provided to avoid unnecessary saturation. When the Toudin Feet and two filter switches are turned off, the signal from the equalizer amplifier and other function inputs only passes through active circuits with good transmission characteristics, such as emitter-follower stages and, if necessary, a + 10 dB booster amplifier, or through a nonreactive attenuator, and is connected to the power amplifier section with flat frequency characteristics in the range from 10 Hz to 150 kHz. This allows for less coloring and less playback sound.

The power amplifier section uses a 2-stage Darlington pure complimentary service direct-coupled 2-power supply OCL circuit.
DC stability and balance are required for all stages of OCL circuit and complimentary service circuit. However, PMA-700Z uses two differential amplifiers in the driver section to increase DC control capability and obtain stability. In addition, all stages of OCL improve low-frequency characteristics. Especially, output impedance is less than 0.16 Ω from ultra-low frequency to 10 kHz.
The Darlington transistor of the last stage configuration has a margin in the last stage by making it a discrete configuration, and switching distortion and crossover distortion are suppressed by ensuring the relativity of the complimentary service stage by carefully selecting the parts.

The power supply section uses a high-efficiency power transformer and a non-inductive high-ripple capacitor.

The tone control circuit uses an emitter follower for the first stage, a low-noise FET for the second stage, and a grounded collector amplified output for the third stage. The control characteristics are obtained by the tone control NF circuit which returns from the third stage to the second stage.
Bass and Treble can be adjusted with precise 2-dB step spacing using 11-contact rotary switch.

The tone control section is equipped with a turnover switch and a tone defeat switch.
The turnover switch allows you to select two high and low turnover frequencies, the Defeat switch flattens between 20 Hz and 20 kHz, the Tone Defeat switch jumps to the tone amplifier, and the first stage emitter-follower output is directly input to the next filter switch. The tone amplifier is designed with no basic gain, so there is no change in level when the tone jumps.

A Butterworth type filter circuit is used for both rumble and scratch noise.
This circuit also has no gain in the passband, so there is no level problem even if the circuit jumps when the filter switch is turned off.

In addition to the conventional muting switch, a 3-stage switching type gain switch and a unique level setting with a booster amplifier are adopted.
There are three gain positions : + 10 dB, 0 dB and -10dB. At + 10 dB, a booster amplifier with a gain of 10 dB is used. This state corresponds to the level of conventional thinking. When using an average cartridge, the standard PMA-700Z is used with a gain of 0 dB and a volume of around -10dB. A gain of -10dB is useful when using a sensitive cartridge.
The muting switch can reduce the volume by 20 dB based on a gain of 0 dB.

The equalizer amplifier improves the allowable input level and reduces the noise level.
Excellent RIAA deviation is a deviation with feedback from the final stage of the emitter-follower, which is less sensitive to selected high-precision parts and subsequent circuits.
In addition, the Phono2 input is equipped with a grounded base type low-noise pre-amplifier for MC cartridge, so that switching between MC and MM is possible.

The input circuit has a volume that can be adjusted when the rated output of the connected device is large to suppress distortion in the first stage amplifier.
This volume has the maximum standard input sensitivity.

An emitter-follower circuit is used for the recording output to avoid the effect of tape deck connection on sound quality.
Also, a DIN connector is attached to the Tape terminal.

The protection circuit is equipped with a final-stage transistor protection circuit and a speaker protection circuit.

Equipped with functions such as a null balance switch, a mode switch for selecting Rev/Stereo/L + R/L/R, a speaker selector switch, a dubbing switch, and a monitor switch.

Equipped with a loudness control.

Built-in pre-out and main-in terminals allow the pre-amplifier and power amplifier sections to be used independently.

Model Rating
Type Pre-main amplifier
Power Amplifier Unit
Circuit system Pure complimentary service all-stage direct connection 2 power supply OCL circuit
Rated Output (THD 0.05%)
Single-ch drive :

Both channel drive :
100W/100W (4 Ω)
80W/80W (8 Ω)
85W + 85W (4 Ω)
70W + 70W (8 Ω)
Total harmonic distortion factor 0.05% or Less (Sine Wave at Rated Output)
Cross modulation distortion factor
(60Hz:7kHz=4:1)
0.1% or Less (Sine Wave at Rated Output)
0.05% or Less (Sine Wave at 80 mW Equivalent Amplitude Output)
Power Band With 8 Hz ~ 30 kHz (THD 0.1%)
Frequency characteristic 8 Hz to 150 kHz ± 0.5 dB
Input sensitivity 1Vrms
Input impedance 80k Ω ± 20% (20 Hz to 20 kHz)
Output impedance 0.16 Ω or Less (10 kHz or Less, Pure Resistance)
Residual noise 0.5 mV or less
Preamplifier Section
Maximum power output 14.2 Vpeak or more
Rated output 1 Vrms (10 kHz, THD 0.05% or less)
Total harmonic distortion factor 0.02% or Less (Rated Output)
0.05% or Less (at 1 kHz, 10 Vpeak)
Input Sensitivity / Impedance Phono1 : 3.2mVrms/50k Ω ± 10%
Phono2 MM : 3.2mVrms/30k Ω ± 10%
Phono2 mc : 0.32mVrms/150 Ω ± 10%
Aux1, Tape1 : 320mVrms/50k Ω ± 10% (Level adj max)
Aux2, Tuner, Tape2 : 320mVrms/100k Ω ± 10%
Rec/PB1, 2 : 500mVrms/50k Ω ± 10%
Maximum allowable input Phono1, 2 (MM) : 100 mVrms or more (1 kHz)
Phono2 (MC) : 10 mVrms or more (1 kHz)
Tone Control Section Frequency Characteristics
Tone defeat:

Tone filter:
7 Hz ~ 300 kHz + 0 -1dB
10 Hz to 150 kHz ± 0.5 dB
15 Hz ~ 60 kHz + 0 -1dB
20 Hz to 20 kHz ± 0.5 dB
Tone control fold point Bass : 320 Hz, 640 Hz
Treble : 1.6 kHz, 3.2 kHz
Tone Control Variable Range 100 Hz ± 10 dB, 2 dB step
20 kHz ± 10 dB, 2 dB step
Filter characteristic Low : 40 Hz, 18dB/oct., Butterworth Type
High : 9 kHz, 18dB/oct., Butterworth
Loudness control characteristic Low frequency : 100 Hz, + 6.5 dB
High frequency : 10 kHz, + 6 dB
Muting -20dB (compared to the level at Gain SW, 0 dB)
<General>
RIAA deviation 20 Hz to 20 kHz ± 0.3 dB
Signal-to-noise ratio (IHF-A network
Input short)
Phono1 : 62 dB or more (78 dB or more - listed in separate catalog)
Phono2 mm : 62 dB or more (78 dB or more - listed in separate catalog)
Phono2 mc : 52 dB or more (65 dB or more - listed in separate catalog)
Tuner, Aux, Tape : 76 dB or more
Channel separation
(Phono-Speaker)
40 dB or More (20 kHz)
70 dB or More (300 Hz or Less)
Attached terminal Pre amp output : 1Vrms/E ・ F ・ OUT
Main amp input:1Vrms/Hi-IMP
Headphone port : Compatible with 8 Ω stereo headphones
AC outlet Switched : 2 systems, 250W
Unswitched : 1 line, 150W
Pwer 100 VAC, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law) 185W
External dimensions Width 430x Height 140x Depth 350 mm
Weight 12.5kg