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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: RE: Dynaco PAS3 schematic posted by sony6060 on October 12, 2021 at 16:33:59:
Well, you just changed your claim from .01 to .02uF to higher values.
The Z that determines bass cut-off is the parallel sum of the input Z of the driven component and the output Z of the driver. But assuming a net Z of 470K ohms, you would want about 0.2uF, to achieve a cut-off at about 2 Hz. Yes, that's fine. But most "modern" tube amplifiers present more like a 100K ohms input Z and that is further reduced when you take into account the shunt resistance at the output of the driver. But even assuming 100K, then you need 1.0uF, for a 2 Hz cut-off. Anyway, we are comparing actual observations, and you claimed that you commonly have seen .01 to .02uF. All I am saying is THOSE values are way way lower than anything I have ever seen in working on preamplifiers and phono stages, not that my experience is vast. You mentioned Dynaco, and I dredged up the schematic of the most iconic Dyna preamplifier, the PAS3; the schematic shows an output C of 1.5uF. On my own, because you piqued my curiosity, I also looked at the Marantz 7C, another paragon. The coupler is 1.0uF. I don't doubt that there may be some much older designs, where the expectation would be for driving 470K ohms, you might see lower values, and I guess if bass cut-off was not such a big issue in those olden days, then you could use .02uF with 470K ohms, for a -3db point of 20Hz. I have never taken apart an early 1950s design. (The 7C and PAS3 are probably already late 50s/early 60s.) Anyway, I am just chatting here, trying to learn.
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- RE: Dynaco PAS3 schematic - Lew 10:02:47 10/13/21 (0)
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