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In Reply to: RE: Any reason I have not seen a fixed bias phono stage??? posted by TomWh on December 09, 2014 at 08:03:04
The issue probably has to do with the need to provide an extremely clean DC voltage. A manufacturer would be hard pressed to justify the cost of the additional PS compared to a simple cathode bypass cap. For DIY, it's possible to do, but then a coupling cap has to be inserted to protect the cartridge. You might consider the 5755 for the first stage. It's a zero bias triode, so it doesn't require either a bypass cap (the cathode is grounded) or a coupling cap. I haven't heard this tube yet, but it's the next thing I want to try for a phono pre.
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Buy Chinese. Bury freedom.
Follow Ups:
Interstages like low rp tubes but thanks for the idea. Maybe a non interstage phono in the future. The great thing about doing this as a hobby is we can go so far out of the box. I do not have to sell it to anyone, just enjoy the sound that on the albums.
Thanks Tom
"Interstages like low rp tubes but thanks for the idea."
A little "sand" will allow you to have your cake and eat it too. The ZVN0545A enhancement mode MOSFET exhibits tiny capacitances. Even WIMPY high R P /low gm types, like the 12AX7, easily drive the little FET. DC couple (a complete "no brainer") ZVN0545A source followers to the wimpy triodes and your interstage trafos will be fed by a low impedance source.
Eli D.
Absolutely
Also the ZVN0545A has no effect on the sonics being a unity gain part.
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