Stereo Power Amplifier GM70PA

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Encountering a clear sound


Drive low efficiency speakers without difficulty

Margin output

Adopts a direct-heat triode GM70, which is slightly larger than 845 (Pp = 100W) (Pp = 125W) and has a low impedance, and realizes an output of 30W + 30W (4Ω load) and 20W + 20W (8Ω load). Drive the low efficiency speakers that are


Normal,DualMono,Bridge mode switching

It can be used as a stereo amplifier in "NormalMode".
We add one more and drive high region and low region with "DualMonoMode" and can use as bi-amp.
In "BridgeMode", it is possible to double the output by 1.5.
* DualMono and BridgeMode are valid for Lch / XLR input.


A method of driving with this machine with one speaker each on the left and right with a speaker that has a HIGH / LOW terminal



Using this machine one by one for each of the left and right, and driving with about twice the output compared to when using one


Key technology is no NFB

A negative feedback circuit was invented in 1927, and the performance of the amplifier steadily improved. However, looking at it from a miniature level, the negative feedback circuit (servo control) returns underexposed signals back to the "+" and returns underexposed signals back to the original. This vibration and Odd's different words will cause cross-modulation and become different from the original sound.
In order to prevent this oscillation, it is necessary to perform ideal servo control or use non-feedback as a linearity (linearity) for components, such as, amplifier elements and capacitors.


Two stage configuration to insure low distortion rates

You cannot avoid distortion when you are using an amplifying element. A countermeasure is choosing to use a device with good linearity or reducing the number of devices being used.
For the first stage of the two-stage configuration, we use the highly reliable, linearity vacuum tube C3g developed by Deutsche Telekom for triode connection. It consists of the high-linearity amplifying tube 2 spheres of the first stage tube C3g and the output tube 212E. This suppresses the harmonic distortion and the intermodulation distortion for a brief moment while returning non-return.
C3g is a second-hand good, but we are securing a large amount of inventory at CS Port, so we do not have to worry about maintenance.

Outstanding noise processing technology

Rectifiers and contacts used for general power supply are sources of noise. Since these noises are sharp noise of rising, they occur over a band of 50Hz to several hundred MHz, causing intermodulation and entering the audio band to make the sound muddy. A large amount of noise is generated even at the switching power supply, and the same phenomenon occurs. Based on years of switching power supply design, CS Port suppresses / cuts unnecessary noise by its noise processing technology and achieves clear sound.

Intermodulation distortion is worse than harmonic distortion

Harmonic distortion is when a signal passes through an element and generates an integer multiple signal, which can be heard comfortably to humans.
Among these distortions, intermodulation distortion is a huge concern.
This is because it generates uncorrelated signals that are not in the original signal, resulting in an unpleasant sound. For example, when a signal of 1kHz and a signal of 1.1kHz pass through a rectifier or an amplifying element, a respective sum signal and a difference signal are generated. 100Hz and 2.1kHz were not found in the original signal. Since the audio signal is a collection of frequencies, some frequencies cause intermodulation, which invade audio signal. This creates a loss of the three-dimensional sound effect. Again, components with good linearity are less likely to cause cross-modulation.

Pearl material suitable for high-end


Large output transformer for extra

Employs a large output transformer developed independently for the GM70PA. Drive from a minute signal to a large signal in a wide band with a multilayer sandwich winding. The combination of low winding resistance and drive capability of this unit realizes a large damping factor of 5 or more as a non-feedback amplifier, and firmly drives the low range of the speaker.

RCA unbalanced input and true balanced input

True balanced transmission can only be done with a transformer. GM70PA adopts RCA unbalanced input and XLR balanced input connector. It has a balance winding, and a high performance transformer of original design using a super permalloy core faithfully transmits even a minute signal from the low region to the high region.
※ RCA unbalanced input and XLR balanced input are used only one or the other. (Cannot be used simultaneously)


Use of a full-fledged oil condenser

The official name is oil paper condenser. Paper is the best insulation material because it has a low dielectric constant and low dielectric loss. Oil paper is impregnated with insulating oil on the paper. Moreover, the conductor is aluminum foil, which is a big difference from the one using a general vapor deposition film. It is reliable and suitable for audio applications, but it is not widely used nowadays because it is large and expensive. In the world of sounds, it is said to be a "golden material" that produces clear, rich midrange sounds.

Switching power supply + analog power supply

The high-grade power supply that was able to be achieved only by the development of the audio grade low noise switching power supply. Insert an analog power supply with high-speed response in the latter stage, and carefully make the 1000 V high-voltage power supply stable.

Product Summary

Stereo Power Amplifier GM70PA

Type GM70PA
Method Input transformer Built-in class A Vacuum tube stereo power amplifier
Constitution Input trans - C3g 3 tube - FET driver - GM70 tube - Output trans
  • Normal,DualMonoMode ......30W+30W
    (Load impedance 4Ω THD:5%)
  • Normal,DualMonoMode ......20W+20W
    (Load impedance 8Ω THD:5%)
  • BridgeMode......60W
    (Load impedance 8Ω THD:5%)
  • BridgeMode......40W
    (Load impedance 4Ω THD:5%)
Frequency 20-30kHz -2dB/10W
Total harmonic distortion THD
  • Normal,DualMonoMode......0.7% / 10W 0.2% / 1W 1kHz
  • BridgeMode......0.5% / 10W 0.1% / 1W
NFB None
S/N ratio 90dB/1W(20-20kHz)
Cross talk 40dB/1W(20-20kHz)
Input sensitivity
  • Normal,DualMonoMode......1V / 30W 4Ω 1V / 20W 8Ω
  • BridgeMode ......1V / 60W 8Ω 1V / 40W 4Ω
Input RCA / XLR Each 1
Impedance 2.5kΩ 1kHz
Mode switching By rear rotary switch ※DualMono,BridgeMode input to Lch XLR
Volume None
Dumping factor DF
  • Normal,DualMonoMode......2.8(4Ω) 5.6(8Ω)
Power supply AC100 / 120 / 200 / 240V 50,60Hz
Power consumption 400W
Size 470W×430D×201H Knob,SP terminal not included
Weight 27kg
Finish Silver alumite
Warranty period 5 years (excluding consumables) registration is required


  • Please do not touch the vacuum tube as it will get hot and it will burn.
  • Since the input impedance of this unit is 2.5 kΩ, drive it with a device with an output impedance of 500 Ω or less.
  • The specifications, design, design and price may be changed without notice.

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