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Romy the Cat
Boston, MA
Posts 10,160
Joined on 05-28-2004
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Post #:
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308
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Post ID:
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26082
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Reply to:
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26077
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Alex,
I cannot answer your questions objectively. It was over 15
years ago when I was working with this phonostage and since I built the last
version, I did not make any experiments with it. I do feel the design is
spectacular, and I am lucky enough to use possibly the best imaginable step-up
transformer, which in my view highlights the advantages of this phonostage.
However, I would not deny that any further modification might even improve what
it does - I just did not do it. The output capacitors is a big subject, and
certainly "better" capacitors might produce better results. The
conversation as to which output capacitor is better is a big subject, and
people have their own opinions. A long time ago I found peace with electrocube
950 and I did not revise my view on it, but it was over 25 years ago. I very
much presume that over the last 25 years there are better capacitors. I do warn
you that it is not just about quality of capacitors but also application of
capacitors. For example, the same capacitor which acts as a coupling capacitor
between two stages and driving directly heated single ended triode might not be
such a wonderful thing. As it is famous, when we drive powerful single ended
triode with a powerful current source we take advantage to the preceding stage
current to drive the triode into class 1B operation. We are taking advantage
that direct heated triodes can work with grid current and it gives an
additional oomph to drive complicated loads (base reflects design).
The classic example would be Lamm ML3, where 4 parallel powerful drivers
are driving GM70. Everybody praises how wonderful it is as it can drive
something like Wilsons and indeed GM70 is wonderful to work on the negative
side. There is a problem however with this thinking. If the amplifier like ML3
has a coupling capacitors between the stages, and Lamm does use electrocube
950s, then in the time when driver stage pushing amplifier in plate currents
the polarity of the capacitor changes. It means each time when driving voltage
higher than bias volutage, the tubes can handle it but the capacitors
repolarize in real time. From my perspective, I would rather prefer to have
crappy capacitor which would be positively or negatively biased than to have
capacitors which repolarize in real time, particularly during loud
passages.
So, to answer more or less methodologically/objectively what
kind of output capacitors should be used in this phonostage, we certainly
cannot think abstractly but we need to conduct experiments and make empiric
judgements about the results. I disagree with rowuk that capacitors might not
lead to separation of musical instruments. Anything can lead to anything. The
key is to find methadologically proper approach to evaluate it and reflect how
this change in the sound can lead you to improve your personal listening
objectives. Pretty much if I were to commission myself a task to question the
quality of my output capacitor, it would probably take a couple of weeks of
experiments to do it more or less convincingly against my own self-criticism.
With all the craziness around me right now I cannot pull it off, so I probably
will wait until kids go to college. 
Alex, please if you do some experiments and you come to some
kind of conclusions, please post them.
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
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