hmmm I leave for a day and everybody is talking about caps.
No WAY am I starting a thread on that topic! Learned my lesson.
So new rule, if you must post off topic then you have to have either resist/resistor/resistance somewhere in the post.
EG - I would offer little resistance to Diana Krall...
No WAY am I starting a thread on that topic! Learned my lesson.
So new rule, if you must post off topic then you have to have either resist/resistor/resistance somewhere in the post.
EG - I would offer little resistance to Diana Krall...
Sonically, they rank somewhere between polystyrene and polycarbonate in my book, and below polypropylene and teflon. The less than optimal dielectric absorption K of approximately 4 (worse than mylar) to me significantly compromises any potential sonic advantages of mica's low loss characteristics. Of course, YMMV, but that has been my general experience with these capacitor types. I agree that micas tend to be very rugged parts.
When I design a tube circuit, I select resistor power ratings when practicable on the assumption that a tube may go short, and that I want the affected resistors to live if that happens, so I resultingly typically overrate them by a factor of 4 times the expected dissipation or better if I can fit the part.
I have used a few cement type caps in some speaker xovers but, aside from their electrical & sonic characteristics, seldom got a good feeling about their structural integrity, especially for the 10Watt and larger types. In my last speaker design, I tried Mills wirewound resistors and immediately noticed a very significant sonic improvement as opposed to the metal oxide types I was previously using.
That sounds consistent with what I've experienced regarding mechanical stability of parts in general. However, correct me if I'm wrong, but silver micas have limited applicability as wideband signal coupling capacitors. When I tried a 600V dipped mica in a phono eq circuit for the 75 & 318 uS eq portion, it appeared to noticeably add a sort of 'sugary' euphonic coloration as well as some graininess as compared to 630Vdc polypropylene film and foil. (the bulk of the phono eq slope is handled by an air/teflon copper foil capacitor that I constructed myself, incidentally). Of course this particular application consisted of a large but essentially constant DC voltage across the capacitor with a small (a couple volts average) AC signal superimposed upon it, so mica may perform better relatively speaking with a much larger AC signal relative to the DC signal - I haven't tried one in that application, largely since my OTL amp is DC coupled and uses no feedback stability compensation. I also go to considerable lengths to isolate and acoustically dampen my low and line level audio circuitry (which I've designed and constructed, incidentally) from ambient vibration which may affect my relative perception here.
thoriated said:
Don't underestimate silvered mica caps; they are more robust, more stable under heat than other types: and I use them as interstage couplers and snubbers, the advantage they can take the heat directly on tube sockets in a position where polystyrene would fail.
I used to live in an area where tamb = 35°C. The equipment internals with +50°C rise totalling 85°C can cause reliability problems for polystyrene.
Sonically I haven't detected any differences between polycarb or SM types.
richy
Re: Coming to a Conclusion
Amen.
I'm going to wait until the end of several weeks of break-in before starting measurement of the amp with redesigned output devices' current control.
jlsem said:You'll never hear the differences in the sound of a resistor (or capacitor for that matter) until the end of several weeks of break-in, so the whole exercise is pointless.
Amen.
I'm going to wait until the end of several weeks of break-in before starting measurement of the amp with redesigned output devices' current control.
badly burned out EL34
Here is the pic of the tube (aka as voltage controlled nonlinear resistor) I promised to post. Look a the stain on the anode and the now silky see-through getter...
That one also sent the mains tranny to heaven... of that rare Hiwatt 50W guitar top...
- Klaus
Here is the pic of the tube (aka as voltage controlled nonlinear resistor) I promised to post. Look a the stain on the anode and the now silky see-through getter...
That one also sent the mains tranny to heaven... of that rare Hiwatt 50W guitar top...
- Klaus
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