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작성일 : 04-09-16 10:27
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[파라피드300B/SE] ultrapath cap 간략 경과보고.
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글쓴이 :
새잡이
 조회 : 1,420
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선오디오 회로를 보시면 아시겠지만... 원래 린올슨 아미티에 관심이 있었지만 제작하지 않는한 상용품은 없으므로 구하기가 불가능하고 그래도 조금이라도 비슷한 회로 구조를 찾아보았는데 그나마 선오디오가 인터스테이지를 사용해 위상 분할을 하는 비슷한 구조의 제품이라 구매를 해봤었읍니다. 물론 아미티와 관도 다르고 회로도 다르기 떄문에 소리야 비슷한 점이 있겠냐 만은 그네들이 주장하는 트랜스를 이용한 위상 분할 의 소리는 경험해 볼 수 있었고 상대적으로 사운드도 기존의 300비 앰프 에 비해 충분히 좋다고 할 만한 소리를 내주고 있었지요.... 그러나 늘 아미티에 목이 말라 있었는데 일단 몇가지 옵션을 생각할 수 있었읍니다. 입력트랜스와 인터 스테이지를 구해서 아미티처럼 개조를 하는 방법이 있었지만...이는 늘 게인문제로 찜찜하였고... 출력단 쪽의 캐소드 접속을 아미티 처럼 ultrapath접속을 시도해 보는 것이었지요. 캡 값이야 아미티와 비슷하게 가면되니까 캡 값 결정에 고민할 필요도 없고...
그래서 결국 어제 솔렌 47uf 를 구해 아미티 처럼 아웃풋의 센터 텝에서 캐소드 저항 위로 ul cap을 달아봤읍니다...
대략적인 사운드 변화가 있는데 캡을 이제 막 단거라 평가하긴 이르지만...
1) 앰프 게인이 좀 증가한 것 같고, 그에 따라 험도 약간 증가하는 것 같습니다. 한 3-6db정도 같은데...
2) 사운드의 변화는 솔렌 캡에 따른 솔렌 특유의 음색적 변화도 있지만 저역쪽의 변화가 눈에 띠네요. 파라피드 앰프 처럼 제동력과 스피드가 향상됩니다. 단단하다고 표현들을 많이 하구요. 47uf의 고용량을 달아서인지 이전보다 저역량이 적어졌다고 말하기는 힘들고 대신 이전이 좀 풍성하고 흐린 느낌이면 좀더 깔끔하고 분명해진 통제력을 느낄 수 있읍니다.
3) 무대감이 입체적이과 좌우로 많이 펼쳐진 변화를 보여주구요.
4) low level resolution이라고 할까요.... 일단 소음량에서도 전대역이 고르게 잘 나와줍니다. 볼륨을 많이 줄이면 이전에는소리가 답답하고 중고역만 들을 수 있었지만 변경 후에는 소리가 답답하지 않고 저역을 포함하여 전대역이 고루 들립니다.
단점은 ... 험이 좀 늘어났다는 점이고 (이는 b+의 리플이 출력관에서 증폭되서라는데) 대용량의 고압 캡이 없어서 결국 솔렌을 쓸 수 밖에 없었는데 솔렌이 조금 소리가 높은 중역대가 강한(억센) 편이라 음색상에 조금 맘에 안든다는 점입니다. 번인을 좀 시키니 (몇 시간 정도 ) 소리가 좀더 편안해지고 안정화되고 유연해지는 것에 희망을 걸어봅니다.
선오디오 내부를 보니...... 첨 받을때는 꺠끗하던 것이 초짜가 배선하고 납땜을 해서인지 어수선 하네요....
ultrapath의 사운드와 parafeed사운드가 상당히 유사한 점이 많은 것에 놀랐읍니다...
찾아 보니 UP와 parafeed에 관한 글이 있어 올립니다. 저는 무신 뜻인지 모르겠는데.... 모찌님 설명 부탁드려도 될까요?
I think you may be confusing the "UP cap" with the "UP topology", and parafeed just adds to the mix. Neither of your approaches is needed in xxx's case because he started from a parafeed topology. I will try to explain although my success rate hasn't been too good the last couple times...;-)
The UP "topology" works by ensuring the shortest path for the signal from the plate of the tube (AC source) to the cathode of the tube (AC ground). If there were no DC involved, we could get away with plate -> OPT -> cathode and have a very clean, simple circuit. However, we need DC to "power" the tube (AC generator) and that's where the UP capacitor comes in. You need the cap to pass AC signals while blocking DC - that's all. Otherwise the DC would flow through the AC return path and not through the tube. That is the key principle - UP cap is only needed to block DC while allowing AC to pass 'mostly' unmolested (although we know caps always distort AC).
With a conventional SE topology the only feasible location for the UP cap is between the top of the OPT and the cathode. This position allows the AC to go from plate thru OPT to cathode, and blocks the DC from jumping from the top of the OPT to DC ground. This is consistent with the UP theory. Conventional PP UP amps work the same way.
Now consider parafeed. Parafeed already has a DC blocking cap to prevent the DC from passing thru the OPT and straight to DC ground. The ONLY change needed to convert parafeed to UP-parafeed is to take the ground side of the OPT and connect it to the cathode (AC ground) instead of DC ground. No additional caps are needed and the location of the cap (B+ leg or ground leg of the OPT) doesn't matter "electrically". Based on the above, xxx can put the P&O caps in either leg of the OPT and still have a UP circuit as long as he keeps the return leg of the OPT connected to the cathode. No extra caps are needed.
Now for the real-world caveats...;-) We know that converting any circuit to ultrapath has several side-effects that must be dealt with:
1. The UP topology (in theory) eliminates the need for the cathode bypass cap since the AC return path no longer passes through the cathode resistor. However, this is only true if the UP cap is large enough to shunt all AC through it - thus you need a larger cap than usual for parafeed. I think we took xxx's 45's from 3.3uf up to 20uf? I am running 70uf in my conventional 2A3 OPT circuit and it sounds great. Jack E. recommends UP caps as big as 100uf for some circuits.
2. The cathode bypass cap also acts as a low impedance shunt to DC ground for any heater to filament noise - thus you may not be able to eliminate it when ultrapathing indirectly heated triodes (6SN7s, etc). I found this to be true when I tried ultrapathing my IT coupled 6SN7 stage. It hummed like a bee no matter how big the UP cap because I had no low impedance path to DC ground! There are other solutions to this problem - battery powered heaters or fixed bias come to mind. I just put in a 220uf cathode bypass cap and the buzz went away - it didn't change the sound of the UP circuit at all.
3. Despite opinion to the contrary, all tube output stages have capacitors in the AC return path - you can't power the tubes without them. The beauty of parafeed and ultrapath is they both take the power supply caps (big honkin' 'lytics) out of the AC return and allow us to select high quality caps for the AC return. Parafeed makes it easier since there are tons of reasonably priced, good sounding 3uf to 8uf caps out there.
[BTW, I would say the minimum VDC rating for a parafeed or UP cap is B+, plus the max positive AC voltage swing, plus 20%. For example: 350V B+, add +150V signal swing, add 20% = 600VDC!)]
Unfortunately for UP aficionados, the selection of good sounding 70uf/600VDC caps is limited (and expensive). Just imagine trying to find 70uf/1000V.
4. In std parafeed circuits when the B+ energizes it puts a transient through the OPT to DC ground. This causes the turn on pop and magnetizes the OPT for some period of time. Converting to UP-parafeed places the cathode resistor in series with the OPT during the DC turn on transient and reduces the pop and (I am guessing) the magnetization effect. yyy has a theory that placing the parafeed cap in the B+ leg of the parafeed OPT will eliminate or minimize the pop - I suspect it doesn't matter but would like to test it empirically to find out.
5. Since the UP caps must be fairly large and high voltage, the selection is limited. I'm finding that most applications need a high quality small (.1uf to .47uf) bypass cap to restore the top end and transient snap. In my UP linestage I'm running 28uf of paper & foil in oil caps with a .22 p&o bypass. On the 2A3's I'm running a 70uf polypro & oil with a .1uf teflon cap. Auricaps and Hovlands have been suggested by other ultrapath fans, but I haven't tried them yet.
I probably missed something, but I hope it helps. Just remember two things - the UP topology is the key, not the UP cap. And contrary to popular opinion the AC return caps are in the signal path, like it or not, so we need parafeed or UP to optimize that path. End of sermon. ;-)
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