I have spent many hours reducing noise in my phono pre. I use a 12au7 for the first stage as it is supposed to be low in microphonics.
My amp is now quiet but I know I could reduce noise much further if I opted for a jfet. Would anyone recommend this?
My amp is now quiet but I know I could reduce noise much further if I opted for a jfet. Would anyone recommend this?
Why not split the difference and use a cascode input stage, jFET on the bottom, tube on the top? I use an NTE458/E88CC combo, but the Toshiba 2SK147 is a popular choice. Very, very quiet.
I used a 200V regulated supply. There are a lot of other options. Allen Wright has some good examples at his Vacuum State site and in his Preamp Cookbook. I've done things rather differently, but Allen's approach has the considerable virtue of being documented.
Excellent. I'll go to allens site and do some research. After all, thats part of the fun of DIY 🙂.
Thanks.
Thanks.
SY said:
SY,
Do you have the actual schematic?
I saw one from 'borbelyaudio' published in Costruire Hi-Fi some times
ago.
I built that preamp back in the early 1980s, so the schematic doesn't exist in digital form. I'll see if I can sketch something up. Basically, it's single-ended, the tube has a 180V rail, 45k plate resistor, a 6.9V reference sent to the grid, no resistor between the cathode and the FET drain, and a small source resistor (100 ohm). FETs were selected in-circuit (a lot of tedious plugging in and out).
AW's use of the FET/tube in CC differential is a better approach, I think.
AW's use of the FET/tube in CC differential is a better approach, I think.
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