云外天
积分:7468 级别:论坛总版主 头衔: 来自:辽宁铁岭 | | | | [转帖]Hybrid JFET/Tube MC/MM Phono Preamp
The EB-1195/221 is a high quality, two-stage tube phono preamplifier with approx. 63 dB gain on the MC input and 44 dB gain on the MM input. The circuit is using three tubes and two single or one dual, low-noise JFET per channel, and is working without feedback.
The MC input stage is a low-noise, hybrid circuit made up of a dual (or two matched) JFET and a 6922 double triode. The two JFETs and the two halves of the double triode are connected in cascode. The current in the input stage is determined by the JFET source resistor R4, and is set to approx. 10 mA. The reference voltage for the triodes is developed across a 20V Zener diode. The voltage drop across V1 is the maximum permitted for the tube: 90V. The stage has to be supplied from +210V, which can be derived from the main 260V supply through a 3.3k/4.5W resistor (supplied with the KIT), or from a second, regulated supply of 210V. The gain of the MC input stage is close to 50 dB and the equivalent input noise is 120 nV.
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