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发表于 2014-2-8 12:57
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试节译:
《静寂之声》The Sound of Silence 第一版
低噪胆管的挑选
....
三极胆管比五极胆管噪声低。但是,若将五极胆管接成三极放大,五极胆管要比三极胆管噪音低。可以将三极胆管并联,双三极管,例如PCC88家族的胆管,可以把噪声电压降到1.42 NV / rtHz,这值绝可以媲美用优秀FET和BJTs晶体管做的MM唱放输入级。此外,这类三极胆管比EF280F/EF810F等类型晶体管更容易买得到。
然而,如果仅用单只三极胆管做MM唱的第一级放大,允其量,噪声电压最好可做到2.01NV / rtHz,这还比不上FET或BJT,更不用说用在MC唱放第一级放大!…即使用升压变压器,用单只三极胆管做MC唱放第一级放大,其性能也不如FET和BJTs晶体管做的MC唱放。
Selection of Low-Noise Valves
The triodes are less noisy than the pentodes, but, configured as triodes in many cases the pentodes are much better than the triodes. This small disadvantage of the triodes can easily be surmounted by paralleling the two triodes of a dual-triode like the ones of the PCC88 family, bringing noise voltage down to 1.42 nV/rtHz in B1. This value is absolutely comparable with the values of very good FETs and BJTs for MM phono amp input stages. In addition, on the market these triodes are easier to get than e.g. the EF280F/EF810F types.
Nevertheless, if we put in place only one triode as a 1st stage of a low noise am- plifier for MM cartridge amplification even a noise voltage density of 2.01 nV/rtHz doesn’t beat the respective ones from a FET or from a BJT, to say nothing of MC am- plification! As will be shown in one of the next sections even a transformer doesn’t help to improve the valve’s performance compared with the one of FETs/BJTs. |
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