A question about "class A" amplifiers. (1 Viewer)

[Manuel Delaflor]

I just bought a used amplifier, it is a Technics SU-X302 and appears to be old since I couldnt find any info on the Net.

Anyway, I know is not a superduper amplifier, still, it says on the front that it is Class A Amplifier (actually it says "new Class A"). What exactly does that mean?

It was really cheap (I think), I paid only 60 bucks for it, and I will couple it with a set of Paradigm Atoms for my bedroom listening...

 

[Jagan Seshadri]

Simple explanation: Class 'A' amps run hot but have low distortion.
Class 'A' power amplifiers mean that the output transistors are consuming power all of the time, regardless of the signal going to the speakers, kind of like a car engine using up fuel in idle...regardless of whether you're stopped or not.
Since current is always flowing through the output transistors even when there is no input, class 'A' amplifiers run hot but often have lower levels of distortion than other classes of amplifiers.
BUT "New Class A", according to Panasonic is where the:

bias of amplifier output step is controlled by a microprocessor and switching hysteresis is resolved to reduce switching distortion

which actually is a modification to the Class 'B' topology... So yours is not a true Class 'A' amplifier.
*Sigh* marketing hits again.
TRIVIA:
Class 'B','AB','D', and recently 'T' are all used in audio, each having benefits and drawbacks. The ultimate ideal is to have zero distortion and 100% power efficiency at the same time, and these different topologies try to come close to that ideal.
While not recognized in the technical community, some amplifiers topologies have been marketed as "classes": Class 'G' (Hitachi), Class 'H' (Soundcraftsmen), Class
'H+' (Technics), Class 'V' (Linn).
There are other classes not used in audio, but in radio, such as Class 'C' and Class 'E' amplifiers.
Read more in the online glossary
-JNS

 

[Manuel Delaflor]

Jagan, thanks for your answer, very informative...

 

[Manuel Delaflor]

Mark, thanks for your answer, its sad to find out that this amplifier is not a true Class A.. still, it is always warm and it has a huge heat dissipator and a cooler working at all times, also, it doesn't need to warm up before starting to sound good...
I don't know if any of these means anything but anyway... for the price....

 

[Stephen Matthew]

that is a pretty solid amp actually for the money... ive had one of those for years that i have used for playing around with and it has performed flawlessly. you got a good deal if it is in decent shape. my only gripe is that the stupid power button on mine is screwed up but nothing serious

 

[Manuel Delaflor]

Hey Stephen, good to read someone with first hand experience! Tell me something, I hope you can remember any specifications for this amplifier?

Thanks

 

[Manuel Delaflor]

I just found this info regarding "new class A" amplifiers from Technics, it is very likely just marketing stuff, but anyway...

Anyone else have experience with similar series of Technics amplifiers?

Here it goes:

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"To turn the concept of Silence Technology into audible reality, Technics engineers performed extensive research and development. Improvements were made on the basis of the three main factors that influence sound quality. First, circuit technology featuring original Technics innovations. Second, the key parts that go into an amplifier's circuitry. And third, amplifier construction. Only when all three of these attain a balance, can you expect true improvement in the sound of reproduced music. Instead of trying to make hit products, we take advantage of one of Technics strengths - original parts development and production of true progress in sound quality at a fundamental level. In the A-Series Amplifiers, significant improvements in all three factors come together to bring you closer than ever to the goal of Silence Technology.

Original Innovations in Circuit Technology

Super Linearity and Super Sound Quality - MOS Class AA

The best device for use in an amplifier's output stage is the MOS-FET (metal oxide semi-conductor field effect transistor). In contrast to the common bi-polar transistor which is a current amplification device, the MOS-FET uses input voltage to amplify output current, much like a vacuum tube. This gives the MOS-FET outstanding transfer characteristics particularly in terms of linearity, as confirmed by its audibly superior sound quality.

Technics MOS Class AA takes maximum advantage of MOS-FET linearity in its Class A voltage control amp, while using bi-polar transistors for the current drive amp, since the MOS-FET is not the optimum for such large current applications. The two amp circuits are linked by a Special Class AA Bridge Connection, creating a new kind of power amp stage. This epoch making MOS Class AA Circuit reaches its full potential by employing newly developed Technics original MOS-FET devices. This virtually ideal amp offers outstanding sound quality that is superior to that of conventional high-priced Class A amps, and is endowed with powerful speaker drive capability, all at a remarkably reasonable price.

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High Performance New MASTER Series Electrolytic Capacitor

The capacitor is another device with a definite influence on sound quality. It helps filter the rectified power supply current to provide a smooth DC current for audio signal amplification. As the capacitor handles large currents (the same number of amperes that drive the speakers) its performance is closely linked with sound quality. Capacitor vibration can easily spoil that quality.

The MASTER Series capacitors feature an improved electrolyte and aluminium foil construction for maximum performance. The latest version of these aluminium electrolytic capacitors feature an important development in their internal construction. Capacitors of this type employ separators between the aluminium foil cathode and anode. These separators provide structural strength and they keep the electrolyte in uniform contact with the aluminium foil. After a thorough review of possible separator materials, we selected Japanese "TA-KE" (ta-keh) bamboo.

This contributes to outstanding vibration damping characteristics and improved conductivity in the New MASTER Series electrolytic capacitors. The result is more dynamic, lifelike sound that brings out the delicate nuances of musical expression.

Selection of each of the materials used in this capacitor required persistent and repeated listening tests. It was only when the combination of materials was exactly right that we decided that this was truly the optimum capacitor for audio applications.

Advanced Virtual Battery Eliminates Power supply Noise and Achieves Low Impedance

Technics developed Virtual Battery Operation to effectively reduce noise from the power supply circuit. By taking advantage of MOS-FET characteristics this new concept provides performance rivalling that of a battery, the ideal audio power supply thereby assuring exceptional sound quality.

Conventional power supply noise passes through the reference voltage generator circuit, and bi-polar transistor, manifesting itself in the output. Virtual Battery Operation uses the reference voltage generator circuit to charge a capacitor which serves as a battery. The capacitor voltage is applied to the MOS-FET gate, preventing noise contamination. This eliminates power supply influence, supplying battery quality power for rich, deep bass, and clear middles and highs. By adding a monitor and control amp to this Advanced Version, voltage is stabilized regardless of current fluctuations. This achieves low impedance operation, thereby helping assure low-range solidity, mid-high-range clarity, and sharp imaging.

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Battery Drive Power Supply Keeps AC Noise out of the Signal Path

In a typical amp, the AC power supply is a major source of noise entering the audio signal path. This is particularly a problem in a control amp which handles very small signal levels as low as ten-thousandth of those of the power amp. The SU-C1000M2 control amp solves this problem by employing a battery drive power supply.

This completely separates the AC power supply from the audio signal path, minimizing switching noise and noise pickup between components. This assures more faithful reproduction of delicate signals such as hall reverberation - so you can hear every detail of a solo piano or violin. And even in the AC mode, the R-core transformer minimizes leakage flux, assuring power supply stability with remarkably low noise.

A special NiCd battery pack provides about 15 hours of continuous operation. Battery recharging begins automatically whenever power is switched off. In case long continuous use does exhaust the battery, the amp switches automatically to conventional rectified AC operation accompanied by simultaneous battery recharging. After about ten hours, when full charging is complete battery drive then resumes.

R-Core Transformer - Effective Protection Against Magnetic Flux Leakage

Conventional amps normally use an EI or Toroidal transformer. The square cross-section of both types of core prevents even coil winding. This concentrates flux in parts of the coil, reducing efficiency and leading to flux leakage.

Technics engineers addressed this problem with the R-Core Transformer. As the name implies, this has its coil wound on an R-shaped core of iron, an arrangement that is extremely efficient, and also effective in reducing flux leakage. The resultis a clean audio performance with minimized harshness at the high-end.

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Anti-Vibration Structural Developments

Technics Hybrid Diecast Panel Suppresses Vibrations While Offering a Sophisticated Appearance

The front panel of a new A-series amps also serves as a base for mounting various parts. This front panel helps to protect parts from internal and external vibrations to maintain high sound quality. Technics, Hybrid Diecast Panel boasts better vibration damping properties than regular aluminium panels, and incorporates a newly highly rigid, high-precision material. The result is a finish look and feel of true quality.

THCB (Technics Hybrid Construction Base) Vibration-Damping Construction SupportsCircuit Components

The pre-amp section, which handles small signals, is susceptible to both internal and external vibrations. These vibrations can adversely affect sound more than most people imagine. As a solution to this problem, Technics developed a special vibration-damping base called the THCB. Its unique shock -suppressing capability is achieved by combining two materials with contrasting properties: Visco-elastic hard rubber - proven over years of use in Technics turntables - and sheet steel.

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