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작성일 : 05-01-11 19:07
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[막가표 발판 시리즈(2) 2A3/45] differentila amp의 이해
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글쓴이 :
막대기
 조회 : 1,613
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Easiest to illustrate with an example. Let's take two pentodes which are mismatched:
gm1 = 4mA/V
gm2 = 8mA/V
Let's say that each tube passes 100mA for a total of 200mA.
Now, with a bypassed cathode, in PP operation, suppose our driver stage puts out +1V to T1, -1V to T2
I1 will go from 100mA to 104mA
I2 will go from 100ma to 92mA
Net current is 196mA, previously 200mA
[incidentally, why do people speak of the need to get drive voltages perfectly matched in conventional PP amps - if we'd given T1 2v, and T2 half that, all would have been well. Tubes are never as well matched as the drive voltages allegedly should be]
Now let's see what happens with a 200mA CCS in the cathode. The CCS will change the voltage across it to keep the net current at 200mA; that's all it knows how to do. In this case, it turns out that it will have to drop a third of a volt, which both tubes see at the cathode:
Vgk1 = +1V + 0.333333V = 1.333333 volt
Vgk2 = -1V + 0.333333V = 0.666666 volt
I1 goes from 100mA to 100 + (4ma/V * 1.33333) = 105.3333
I2 goes from 100mA to 100 + (8ma/V * -0.6666) = 94.6666
Net current - 200mA, voila.
Even with horrendously mismatched drive, for example, input1 +1V, input2 -2V, the ccs decides to assert an extra volt on the cathodes, so :
Vgk1 is (+1 =+1) = 2V
Vgk2 is (-2 + 1) = -1V
and balance is restored (remember Gm1 is half Gm2).
With triodes, the changing anode voltages and effect of (dynamic) internal resistance make the picture a lot more complex, but presumably, none mentioned any of these to the CCS.
Btw, Gary, I just love the subversiveness of that amp, the fact that you're getting great sounds from PP, pentodes, feedback and a ton of sand. Your cascoded CCSs are definitely going to be making an appearance in my big PP amp project; thanks for sharing your research so generously.
지멋대로 해석항 결론
1. 차등 앰푸는 2개의 SE amp가 push pull 하는 것 -- PP앰푸와 다르다
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2. 차동회로는 피피도란스의 전류 언바란스를 없게하는 방법 --PP amp 에서 항상 문제인 fine detail 이 유지된다함 -- 만들어보아야 알죠?
3. 문제는 PP 출력단 common cathod 에 100ma 넘는 CCS without silicon -- fhxjtm, Mozzi,를 비롯한 많은 꼼방고수에게 현상금(술? 밥?) 걸고 만들어 보시기 원함 -- 세계의 꼼방으로 도약할 기회
일본애들은 실리콘 소자로 만든 회로는 무지막지하게 많음
질문 금지 -- 저도 모름
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