진공관 TV 보신 분도 계실 줄 알지만.. 과거 거의 대부분의 전자제품은 진공관이었습니다..



그리고 거의 대부분의 진공관제품은 도태가 되었지요...



그런데 유독 오디오에서만 진공관이 없어지질 않습니다..

오히려 Tube sound 라고 해서 마니아 층이 더 많아지는 추세지요..

특히 전자음악이나 녹음스튜디오에서는 비록 불편하지만 Tube Sound가 더 좋은 소리를 내는 것을 우리는 쉽게 접할 수 있습니다..

물론 대세는 TR로 대변되는 반도체지만요..



오디오는 객관적으로 봐야 합니다.... 현상이 있다면 분명 이유가 존재하거든요..





반도체와 진공관의 장단점을 비교적 객관적이고 세밀하게 비교해 논 문헌이 있어서.. 소개를 할까 합니다..







Vacuum Tubes and Transistors Compared



Adapted from IEEE & Eric Barbour



Vacuum Tubes: Advantages



1. Superior sound quality.

2. Highly linear without negative feedback, especially small-signal types.

3. Smooth clipping is widely considered more musical than transistors.

4. Tolerant of large overloads and voltage spikes.

5. Characteristics highly independent of temperature, greatly simplifying biasing.

6. Wider dynamic range than transistors circuits, due to higher operating voltages and overload tolerance.

7. Device capacitances vary only slightly with signal voltages (Miller effect).

8. Capacitive coupling can be done with small, high-quality film capacitors, due to inherently high-impedances of tube ciruits.

9. Circuit designs tend to be simpler than transistorized equivalents, which are greatly complicated by the need to linearize intrinsically non-linear transistors.

10. Operation is usually in Class A or Class AB, minimizing crossover notch distortion.

11. Output transformer in power amp protects speaker from DC voltage due to malfunction and protects tubes from shorts and blunts back-emf spikes from speaker.

12. Tubes can be relatively easily replaced by user.



Vacuum Tubes: Disadvantages



1. Bulky, hence less suitable for portable products. Milbert mobile tube equipment is portable and battery powered. It's not particularly small but not particularly bulky: the TC crossovers put tubes in the dashboard, and the BaM-235ab is a 60watt shoebox sized amp that delivers the best sound you've ever heard.

2. Higher operating voltages generally required.

3. High power consumption; needs heater supply that generates waste heat and yields lower efficiency, notably for small-signal circuits.

4. Glass tubes are fragile, compared to metal transistors.

5. Sometimes more prone to microphonics than transistors, depending upon circuit and device. (Does not apply to patented Milbert BaM-235ab, impervious to audible microphonics.)

6. Cathode electron-emitting materials are used up in operation. (Does not apply to patented Milbert BaM-235ab, which has operating currents (and thus, operating lifetimes) two orders of magnitude below conventional tube designs (milliamps, not hundreds of milliamps, of bias current).

7. High-impedance devices that need impedance matching transformer for low-impedance loads, like speakers; however, the magnetic cushion provided by an output transformer prevents the output tubes from blowing up. In dramatic contrast to transistorized amps, the Milbert BaM-235ab will never blow up, even if you play it at full power into a directly shorted or completely open output! This advantage is difficult to overstate, especially in car audio where transistorized-amp faults are common but servicing is inconvenient.

8. Sometimes higher cost than equivalently powered transistors.



Transistors: Advantages



1. Usually lower cost and smaller than tubes, especially in small-signal circuits.

2. Can be combined in the millions on one cheap die to make an integrated circuit, whereas tubes are limited to at most three functional units per glass bulb.

3. Lower power consumption, less waste heat, and high efficiency than equivalent tubes, especially in small-signal circuits.

4. Can operate on lower-voltage supplies for greater safety, lower costs, tighter clearances.

5. Matching transformers not required for low-impedance loads.

6. Usually more physical ruggedness than tubes (depends upon construction).



Transistors: Disadvantages



1. Tendency toward higher distortion than equivalent tubed circuits.

2. Complex circuits and considerable negative feedback required for low distortion.

3. Sharp clipping, in a manner widely considered non-musical, due to considerable negative feedback commonly used. Does not gracefully roll-off or gently compress; instead, cuts off sharply, suddenly and abruptly with extremely hard edge.

4. Device capacitances tend to vary wildly with applied voltages (Miller effect).

5. Large unit-to-unit manufacturing tolerances and unreliable variations in key parameters, such as gain and threshold voltage.

6. Stored-charge effects add signal delay, which complicates high-frequency and feedback design.

7. Device parameters vary considerably with temperature, complicating biasing and increasing likelihood of thermal runaway, hotspots and unreproducible behavior.

8. Cooling is less efficient than with tubes, because lower operating temperature is required for reliability. Tubes prefer hot; transistors do not. Massive, expensive and unwieldy heat sinks are always required for power transistors, yet they are not always effective (power output transistors still blow up; whereas, tubes fade down gracefully over time with warning and usually without catatrophic results).

9. Power MOSFETs have high input capacitances that vary with voltage, complicating driver circuitry.

10. Class B totem-pole circuits are common, which cause severe crossover distortion, or else necessitate huge amounts of negative feedback to correct. This "measures well" for steady-state signals, but it completely "sucks the life out of" dynamic and transient signals such as music.

11. Less tolerant of overloads and voltage spikes than tubes. Except for their robust and forgiving heater filaments, it is very difficult, bordering on impossible, to blow out a tube with overvoltage; whereas, most transistors can be destroyed with as little as six volts, and every transistor can be destroyed by some voltage. Tubes are much harder to "zap."

12. Nearly all transistor power amps have directly-coupled outputs that can damage speakers, even with active protection.

13. Capacitive coupling usually requires high-value electrolytic capacitors, which give audibly and measurably inferior performance at audio frequency extremes.

14. Greater tendency to pick up radio frequency interference and self-oscillate to the point of self-destruction, due to rectification by low-voltage diode junctions or slew-rate effects.

15. Maintenance more difficult; devices are not easily replaced by user.

16. Biasing more difficult, as temperature effects and device variations complicate circuitry and degrade performance.

17. Older transistors and ICs often become unavailable after only 20 years, and sometimes much less, making replacement difficult or impossible. Tubes have a staying power, proven over many decades.

18. Hardly scientific or objective, but whereas transistors operate on an invisibly microscopic, quantum scale, tubes exist and operate on an intuitive, human scale. You can see the heaters light up, you can sometimes see a glowing plasma, and you can feel and hear the warmth. Everything about tubes exists in a more human realm than hard, cold transistors. Measure away, but it's the sound that matters.







어렴풋이 생각했던 것보다는 좀 자세히 들여다 보니까... 상식과는 많이 다르지요??

이것을 아주 간단하게 정리하면..



진공관은 오디오적인 효과는 참 좋다. 하지만 현대기기의 필수조건인 작고 효율적으로 만들기는 힘이 든다. (휴대성이 거의 불가능)



반대로.. TR은 진공관의 단점을 거의 완벽하게 커버를 하지만.. 진공관의 장점까지 다 갖기는 힘들다는 것이지요..



물론 회로의 발전으로 이런 반도체의 단점은 많이 좋아졌지만... 소자가 가지고 있는 기본적인 성향까지 바꿀 수는 없어서 반도체회로는 진공관에 비해서 아주 복잡할 수 밖에 없습니다. 진공관회로는 소자의 특성 때문에 복잡하게 만들 필요가 없고요..



또 실제로 숙련된 음악가들이나 녹음 엔지니어들이 Tube sound를 선호하는 이유는 Tube sound가 TR에 비해서 더 많은 헤드룸을 확보할 수 있기에 일반적인 상식과는 달리 더 높은 다이나믹레인지를 구현할 수 있다는 것이고 게다가 오버로딩이 될 때 나타나는 하모닉스의 패턴도 tube Sound가 더 자연스럽게 귀에 와 닿는다는 것입니다..